From 8815105bf2462787885214a12af927d484226f21 Mon Sep 17 00:00:00 2001
From: Torsten Grote <t@grobox.de>
Date: Thu, 30 Jul 2020 16:40:23 -0300
Subject: Split out common code into multiplatform Kotlin library

---
 .gitignore                                         |   1 +
 .gitlab-ci.yml                                     |   1 +
 .idea/gradle.xml                                   |   1 +
 anastasis-ui/build.gradle                          |   2 +-
 build.gradle                                       |   4 -
 cashier/.gitlab-ci.yml                             |   1 +
 cashier/build.gradle                               |   2 +-
 .../main/java/net/taler/cashier/MainViewModel.kt   |  16 +-
 merchant-lib/.gitlab-ci.yml                        |   1 +
 merchant-lib/build.gradle                          |   2 +-
 .../main/java/net/taler/merchantlib/Response.kt    |   3 +-
 .../java/net/taler/merchantlib/MerchantApiTest.kt  |   1 +
 merchant-terminal/.gitlab-ci.yml                   |   1 +
 settings.gradle                                    |   3 +
 taler-kotlin-android/.gitignore                    |   1 +
 taler-kotlin-android/.gitlab-ci.yml                |  12 +
 taler-kotlin-android/build.gradle                  |  78 ++++++
 taler-kotlin-android/consumer-rules.pro            |   0
 taler-kotlin-android/proguard-rules.pro            |  21 ++
 taler-kotlin-android/src/main/AndroidManifest.xml  |  24 ++
 .../src/main/java/net/taler/common/AmountMixin.kt  |  51 ++++
 .../src/main/java/net/taler/common/AndroidUtils.kt | 123 ++++++++
 .../main/java/net/taler/common/ByteArrayUtils.kt   |  53 ++++
 .../main/java/net/taler/common/CombinedLiveData.kt |  51 ++++
 .../main/java/net/taler/common/ContractTerms.kt    |  91 ++++++
 .../src/main/java/net/taler/common/Event.kt        |  51 ++++
 .../src/main/java/net/taler/common/NfcManager.kt   | 234 ++++++++++++++++
 .../main/java/net/taler/common/QrCodeManager.kt    |  42 +++
 .../src/main/java/net/taler/common/SignedAmount.kt |  40 +++
 .../src/main/java/net/taler/common/TalerUtils.kt   |  57 ++++
 .../main/res/drawable/selectable_background.xml    |  21 ++
 .../src/main/res/values-night/colors.xml           |   5 +
 .../src/main/res/values/colors.xml                 |  24 ++
 .../src/main/res/values/strings.xml                |  21 ++
 .../java/net/taler/common/ContractTermsTest.kt     |  74 +++++
 taler-kotlin-common/.gitlab-ci.yml                 |   6 +-
 taler-kotlin-common/build.gradle                   | 130 +++++----
 taler-kotlin-common/consumer-rules.pro             |   0
 taler-kotlin-common/proguard-rules.pro             |  21 --
 .../commonMain/kotlin/net/taler/common/Amount.kt   | 198 +++++++++++++
 .../src/commonMain/kotlin/net/taler/common/Time.kt |  81 ++++++
 .../commonMain/kotlin/net/taler/common/Version.kt  |  70 +++++
 .../kotlin/net/taler/common/AmountTest.kt          | 234 ++++++++++++++++
 .../kotlin/net/taler/common/TestUtils.kt           |  26 ++
 .../kotlin/net/taler/common/VersionTest.kt         |  65 +++++
 .../src/jsMain/kotlin/net/taler/common/Time.kt     |  23 ++
 .../src/jvmMain/kotlin/net/taler/common/Time.kt    |  21 ++
 taler-kotlin-common/src/main/AndroidManifest.xml   |  24 --
 .../src/main/java/net/taler/common/Amount.kt       | 246 ----------------
 .../src/main/java/net/taler/common/AndroidUtils.kt | 123 --------
 .../main/java/net/taler/common/ByteArrayUtils.kt   |  53 ----
 .../main/java/net/taler/common/CombinedLiveData.kt |  51 ----
 .../main/java/net/taler/common/ContractTerms.kt    |  91 ------
 .../src/main/java/net/taler/common/Event.kt        |  51 ----
 .../src/main/java/net/taler/common/NfcManager.kt   | 234 ----------------
 .../main/java/net/taler/common/QrCodeManager.kt    |  42 ---
 .../src/main/java/net/taler/common/SignedAmount.kt |  40 ---
 .../src/main/java/net/taler/common/TalerUtils.kt   |  58 ----
 .../src/main/java/net/taler/common/Version.kt      |  70 -----
 .../main/res/drawable/selectable_background.xml    |  21 --
 .../src/main/res/values-night/colors.xml           |   5 -
 taler-kotlin-common/src/main/res/values/colors.xml |  24 --
 .../src/main/res/values/strings.xml                |  21 --
 .../src/nativeMain/kotlin/net/taler/common/Time.kt |  23 ++
 .../src/test/java/net/taler/common/AmountTest.kt   | 311 ---------------------
 .../src/test/java/net/taler/common/VersionTest.kt  |  65 -----
 wallet/.gitlab-ci.yml                              |   1 +
 wallet/build.gradle                                |  10 +-
 .../main/java/net/taler/wallet/MainViewModel.kt    |   5 +
 .../net/taler/wallet/exchanges/ExchangeFees.kt     |  53 +---
 .../net/taler/wallet/payment/PaymentResponses.kt   |  13 +-
 71 files changed, 1924 insertions(+), 1699 deletions(-)
 create mode 100644 taler-kotlin-android/.gitignore
 create mode 100644 taler-kotlin-android/.gitlab-ci.yml
 create mode 100644 taler-kotlin-android/build.gradle
 create mode 100644 taler-kotlin-android/consumer-rules.pro
 create mode 100644 taler-kotlin-android/proguard-rules.pro
 create mode 100644 taler-kotlin-android/src/main/AndroidManifest.xml
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/AmountMixin.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/AndroidUtils.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/ByteArrayUtils.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/CombinedLiveData.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/ContractTerms.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/Event.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/NfcManager.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/QrCodeManager.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/SignedAmount.kt
 create mode 100644 taler-kotlin-android/src/main/java/net/taler/common/TalerUtils.kt
 create mode 100644 taler-kotlin-android/src/main/res/drawable/selectable_background.xml
 create mode 100644 taler-kotlin-android/src/main/res/values-night/colors.xml
 create mode 100644 taler-kotlin-android/src/main/res/values/colors.xml
 create mode 100644 taler-kotlin-android/src/main/res/values/strings.xml
 create mode 100644 taler-kotlin-android/src/test/java/net/taler/common/ContractTermsTest.kt
 delete mode 100644 taler-kotlin-common/consumer-rules.pro
 delete mode 100644 taler-kotlin-common/proguard-rules.pro
 create mode 100644 taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Amount.kt
 create mode 100644 taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Time.kt
 create mode 100644 taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Version.kt
 create mode 100644 taler-kotlin-common/src/commonTest/kotlin/net/taler/common/AmountTest.kt
 create mode 100644 taler-kotlin-common/src/commonTest/kotlin/net/taler/common/TestUtils.kt
 create mode 100644 taler-kotlin-common/src/commonTest/kotlin/net/taler/common/VersionTest.kt
 create mode 100644 taler-kotlin-common/src/jsMain/kotlin/net/taler/common/Time.kt
 create mode 100644 taler-kotlin-common/src/jvmMain/kotlin/net/taler/common/Time.kt
 delete mode 100644 taler-kotlin-common/src/main/AndroidManifest.xml
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/Amount.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/AndroidUtils.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/ByteArrayUtils.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/CombinedLiveData.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/ContractTerms.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/Event.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/NfcManager.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/QrCodeManager.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/SignedAmount.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/TalerUtils.kt
 delete mode 100644 taler-kotlin-common/src/main/java/net/taler/common/Version.kt
 delete mode 100644 taler-kotlin-common/src/main/res/drawable/selectable_background.xml
 delete mode 100644 taler-kotlin-common/src/main/res/values-night/colors.xml
 delete mode 100644 taler-kotlin-common/src/main/res/values/colors.xml
 delete mode 100644 taler-kotlin-common/src/main/res/values/strings.xml
 create mode 100644 taler-kotlin-common/src/nativeMain/kotlin/net/taler/common/Time.kt
 delete mode 100644 taler-kotlin-common/src/test/java/net/taler/common/AmountTest.kt
 delete mode 100644 taler-kotlin-common/src/test/java/net/taler/common/VersionTest.kt

diff --git a/.gitignore b/.gitignore
index 7e4952a..caf9ce6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 *.iml
 .gradle
 /local.properties
+/.idea/artifacts
 /.idea/caches
 /.idea/libraries
 /.idea/misc.xml
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 48f1aec..6dc4426 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -14,6 +14,7 @@ include:
   - local: 'merchant-lib/.gitlab-ci.yml'
   - local: 'merchant-terminal/.gitlab-ci.yml'
   - local: 'taler-kotlin-common/.gitlab-ci.yml'
+  - local: 'taler-kotlin-android/.gitlab-ci.yml'
   - local: 'wallet/.gitlab-ci.yml'
 
 after_script:
diff --git a/.idea/gradle.xml b/.idea/gradle.xml
index 581abbf..01ed15f 100644
--- a/.idea/gradle.xml
+++ b/.idea/gradle.xml
@@ -14,6 +14,7 @@
             <option value="$PROJECT_DIR$/cashier" />
             <option value="$PROJECT_DIR$/merchant-lib" />
             <option value="$PROJECT_DIR$/merchant-terminal" />
+            <option value="$PROJECT_DIR$/taler-kotlin-android" />
             <option value="$PROJECT_DIR$/taler-kotlin-common" />
             <option value="$PROJECT_DIR$/wallet" />
           </set>
diff --git a/anastasis-ui/build.gradle b/anastasis-ui/build.gradle
index 0391c7c..ff0eec5 100644
--- a/anastasis-ui/build.gradle
+++ b/anastasis-ui/build.gradle
@@ -51,7 +51,7 @@ android {
 }
 
 dependencies {
-    implementation project(":taler-kotlin-common")
+    implementation project(":taler-kotlin-android")
 
     implementation 'com.google.android.material:material:1.2.0-beta01'
     implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
diff --git a/build.gradle b/build.gradle
index 76f687e..442d232 100644
--- a/build.gradle
+++ b/build.gradle
@@ -24,7 +24,3 @@ allprojects {
         maven { url 'https://jitpack.io' }
     }
 }
-
-task clean(type: Delete) {
-    delete rootProject.buildDir
-}
diff --git a/cashier/.gitlab-ci.yml b/cashier/.gitlab-ci.yml
index 6a7baed..6b73dee 100644
--- a/cashier/.gitlab-ci.yml
+++ b/cashier/.gitlab-ci.yml
@@ -6,6 +6,7 @@ cashier_test:
     changes:
       - cashier/**/*
       - taler-kotlin-common/**/*
+      - taler-kotlin-android/**/*
       - build.gradle
   script: ./gradlew :cashier:check :cashier:assembleRelease
   artifacts:
diff --git a/cashier/build.gradle b/cashier/build.gradle
index 0d06c60..641a039 100644
--- a/cashier/build.gradle
+++ b/cashier/build.gradle
@@ -54,7 +54,7 @@ android {
 }
 
 dependencies {
-    implementation project(":taler-kotlin-common")
+    implementation project(":taler-kotlin-android")
     implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
     implementation 'androidx.security:security-crypto:1.0.0-rc02'
     implementation 'com.google.android.material:material:1.1.0'
diff --git a/cashier/src/main/java/net/taler/cashier/MainViewModel.kt b/cashier/src/main/java/net/taler/cashier/MainViewModel.kt
index c8d9a3b..a4fd35e 100644
--- a/cashier/src/main/java/net/taler/cashier/MainViewModel.kt
+++ b/cashier/src/main/java/net/taler/cashier/MainViewModel.kt
@@ -40,6 +40,7 @@ import net.taler.common.isOnline
 
 private val TAG = MainViewModel::class.java.simpleName
 
+private const val VERSION_BANK = "0:0:0"
 private const val PREF_NAME = "net.taler.cashier.prefs"
 private const val PREF_KEY_BANK_URL = "bankUrl"
 private const val PREF_KEY_USERNAME = "username"
@@ -86,20 +87,21 @@ class MainViewModel(private val app: Application) : AndroidViewModel(app) {
     fun checkAndSaveConfig(config: Config) {
         mConfigResult.value = null
         viewModelScope.launch(Dispatchers.IO) {
-            val url = "${config.bankUrl}/accounts/${config.username}/balance"
+            val url = "${config.bankUrl}/config"
             Log.d(TAG, "Checking config: $url")
             val result = when (val response = makeJsonGetRequest(url, config)) {
                 is HttpJsonResult.Success -> {
-                    val balance = response.json.getString("balance")
+                    val version = response.json.getString("version")
+                    // TODO check if version is compatible
+                    val currency = response.json.getString("currency")
                     try {
-                        val amount = SignedAmount.fromJSONString(balance)
-                        mCurrency.postValue(amount.amount.currency)
-                        prefs.edit().putString(PREF_KEY_CURRENCY, amount.amount.currency).apply()
+                        mCurrency.postValue(currency)
+                        prefs.edit().putString(PREF_KEY_CURRENCY, currency).apply()
                         // save config
                         saveConfig(config)
                         ConfigResult.Success
-                    } catch (e: AmountParserException) {
-                        ConfigResult.Error(false, "Invalid Amount: $balance")
+                    } catch (e: Exception) {
+                        ConfigResult.Error(false, "Invalid Config: ${response.json}")
                     }
                 }
                 is HttpJsonResult.Error -> {
diff --git a/merchant-lib/.gitlab-ci.yml b/merchant-lib/.gitlab-ci.yml
index 62a7516..8f7c7c2 100644
--- a/merchant-lib/.gitlab-ci.yml
+++ b/merchant-lib/.gitlab-ci.yml
@@ -2,6 +2,7 @@ merchant_lib_test:
   stage: test
   only:
     changes:
+      - taler-kotlin-common/**/*
       - merchant-lib/**/*
       - build.gradle
   script: ./gradlew :merchant-lib:check
diff --git a/merchant-lib/build.gradle b/merchant-lib/build.gradle
index 128f4c1..33e8379 100644
--- a/merchant-lib/build.gradle
+++ b/merchant-lib/build.gradle
@@ -45,7 +45,7 @@ android {
 }
 
 dependencies {
-    api project(":taler-kotlin-common")
+    api project(":taler-kotlin-android")
 
     implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
 
diff --git a/merchant-lib/src/main/java/net/taler/merchantlib/Response.kt b/merchant-lib/src/main/java/net/taler/merchantlib/Response.kt
index 9aefa5f..65a12a9 100644
--- a/merchant-lib/src/main/java/net/taler/merchantlib/Response.kt
+++ b/merchant-lib/src/main/java/net/taler/merchantlib/Response.kt
@@ -16,7 +16,6 @@
 
 package net.taler.merchantlib
 
-import android.util.Log
 import io.ktor.client.call.receive
 import io.ktor.client.features.ClientRequestException
 import io.ktor.client.features.ResponseException
@@ -32,7 +31,7 @@ class Response<out T> private constructor(
             return try {
                 success(request())
             } catch (e: Throwable) {
-                Log.e("merchant-lib", "Error", e)
+                println(e)
                 failure(e)
             }
         }
diff --git a/merchant-lib/src/test/java/net/taler/merchantlib/MerchantApiTest.kt b/merchant-lib/src/test/java/net/taler/merchantlib/MerchantApiTest.kt
index ea5a12a..deed81e 100644
--- a/merchant-lib/src/test/java/net/taler/merchantlib/MerchantApiTest.kt
+++ b/merchant-lib/src/test/java/net/taler/merchantlib/MerchantApiTest.kt
@@ -113,6 +113,7 @@ class MerchantApiTest {
         val unpaidResponse = CheckPaymentResponse.Unpaid(false, "http://taler.net/foo")
         httpClient.giveJsonResponse("http://example.net/instances/testInstance/private/orders/$orderId") {
             """{
+                "order_status": "unpaid",
                 "paid": ${unpaidResponse.paid},
                 "taler_pay_uri": "${unpaidResponse.talerPayUri}"
             }""".trimIndent()
diff --git a/merchant-terminal/.gitlab-ci.yml b/merchant-terminal/.gitlab-ci.yml
index 74ac21f..d159902 100644
--- a/merchant-terminal/.gitlab-ci.yml
+++ b/merchant-terminal/.gitlab-ci.yml
@@ -5,6 +5,7 @@ merchant_test:
       - merchant-terminal/**/*
       - merchant-lib/**/*
       - taler-kotlin-common/**/*
+      - taler-kotlin-android/**/*
       - build.gradle
   script: ./gradlew :merchant-terminal:check :merchant-terminal:assembleRelease
   artifacts:
diff --git a/settings.gradle b/settings.gradle
index 14d898d..6175852 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -1,4 +1,7 @@
 include ':cashier', ':merchant-terminal', ':wallet'
 include ':taler-kotlin-common'
+include ':taler-kotlin-android'
 include ':merchant-lib'
 include ':anastasis-ui'
+
+enableFeaturePreview('GRADLE_METADATA')
diff --git a/taler-kotlin-android/.gitignore b/taler-kotlin-android/.gitignore
new file mode 100644
index 0000000..796b96d
--- /dev/null
+++ b/taler-kotlin-android/.gitignore
@@ -0,0 +1 @@
+/build
diff --git a/taler-kotlin-android/.gitlab-ci.yml b/taler-kotlin-android/.gitlab-ci.yml
new file mode 100644
index 0000000..bb5af21
--- /dev/null
+++ b/taler-kotlin-android/.gitlab-ci.yml
@@ -0,0 +1,12 @@
+taler_kotlin_android_test:
+  stage: test
+  only:
+    changes:
+      - taler-kotlin-android/**/*
+      - taler-kotlin-common/**/*
+      - build.gradle
+  script: ./gradlew :taler-kotlin-android:check
+  artifacts:
+    paths:
+      - taler-kotlin-android/build/reports/lint-results.html
+    expire_in: 1 week
diff --git a/taler-kotlin-android/build.gradle b/taler-kotlin-android/build.gradle
new file mode 100644
index 0000000..d6d6003
--- /dev/null
+++ b/taler-kotlin-android/build.gradle
@@ -0,0 +1,78 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+plugins {
+    id 'com.android.library'
+    id 'kotlin-android'
+    id 'kotlin-android-extensions'
+    id 'kotlinx-serialization'
+}
+
+android {
+    compileSdkVersion 29
+    //noinspection GradleDependency
+    buildToolsVersion "$build_tools_version"
+
+    defaultConfig {
+        minSdkVersion 24
+        targetSdkVersion 29
+        versionCode 1
+        versionName "0.1"
+
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+        consumerProguardFiles 'consumer-rules.pro'
+    }
+
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+        }
+    }
+
+    packagingOptions {
+        exclude("META-INF/*.kotlin_module")
+    }
+
+}
+
+dependencies {
+    api project(":taler-kotlin-common")
+
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation 'androidx.appcompat:appcompat:1.1.0'
+    implementation 'androidx.core:core-ktx:1.3.0'
+
+    // Navigation
+    implementation "androidx.navigation:navigation-ui-ktx:$nav_version"
+    implementation "androidx.navigation:navigation-fragment-ktx:$nav_version"
+
+    // ViewModel and LiveData
+    def lifecycle_version = "2.2.0"
+    implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
+
+    // QR codes
+    implementation 'com.google.zxing:core:3.4.0'  // needs minSdkVersion 24+
+
+    // JSON parsing and serialization
+    api "org.jetbrains.kotlinx:kotlinx-serialization-runtime:0.20.0"
+    implementation "com.fasterxml.jackson.module:jackson-module-kotlin:2.10.2"
+
+    lintChecks 'com.github.thirdegg:lint-rules:0.0.4-alpha'
+
+    testImplementation 'junit:junit:4.13'
+    testImplementation 'org.json:json:20190722'
+}
diff --git a/taler-kotlin-android/consumer-rules.pro b/taler-kotlin-android/consumer-rules.pro
new file mode 100644
index 0000000..e69de29
diff --git a/taler-kotlin-android/proguard-rules.pro b/taler-kotlin-android/proguard-rules.pro
new file mode 100644
index 0000000..f1b4245
--- /dev/null
+++ b/taler-kotlin-android/proguard-rules.pro
@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile
diff --git a/taler-kotlin-android/src/main/AndroidManifest.xml b/taler-kotlin-android/src/main/AndroidManifest.xml
new file mode 100644
index 0000000..902ddc1
--- /dev/null
+++ b/taler-kotlin-android/src/main/AndroidManifest.xml
@@ -0,0 +1,24 @@
+<!--
+  ~ This file is part of GNU Taler
+  ~ (C) 2020 Taler Systems S.A.
+  ~
+  ~ GNU Taler is free software; you can redistribute it and/or modify it under the
+  ~ terms of the GNU General Public License as published by the Free Software
+  ~ Foundation; either version 3, or (at your option) any later version.
+  ~
+  ~ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+  ~ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  ~ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License along with
+  ~ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+  -->
+
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="net.taler.common">
+
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+    <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.NFC" />
+
+</manifest>
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/AmountMixin.kt b/taler-kotlin-android/src/main/java/net/taler/common/AmountMixin.kt
new file mode 100644
index 0000000..f9b1330
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/AmountMixin.kt
@@ -0,0 +1,51 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import com.fasterxml.jackson.core.JsonGenerator
+import com.fasterxml.jackson.core.JsonParser
+import com.fasterxml.jackson.databind.DeserializationContext
+import com.fasterxml.jackson.databind.JsonMappingException
+import com.fasterxml.jackson.databind.SerializerProvider
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize
+import com.fasterxml.jackson.databind.annotation.JsonSerialize
+import com.fasterxml.jackson.databind.deser.std.StdDeserializer
+import com.fasterxml.jackson.databind.ser.std.StdSerializer
+
+/**
+ * Used to support Jackson serialization along with KotlinX.
+ */
+@JsonSerialize(using = AmountSerializer::class)
+@JsonDeserialize(using = AmountDeserializer::class)
+abstract class AmountMixin
+
+class AmountSerializer : StdSerializer<Amount>(Amount::class.java) {
+    override fun serialize(value: Amount, gen: JsonGenerator, provider: SerializerProvider) {
+        gen.writeString(value.toJSONString())
+    }
+}
+
+class AmountDeserializer : StdDeserializer<Amount>(Amount::class.java) {
+    override fun deserialize(p: JsonParser, ctxt: DeserializationContext): Amount {
+        val node = p.codec.readValue(p, String::class.java)
+        try {
+            return Amount.fromJSONString(node)
+        } catch (e: AmountParserException) {
+            throw JsonMappingException(p, "Error parsing Amount", e)
+        }
+    }
+}
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/AndroidUtils.kt b/taler-kotlin-android/src/main/java/net/taler/common/AndroidUtils.kt
new file mode 100644
index 0000000..b46f306
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/AndroidUtils.kt
@@ -0,0 +1,123 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import android.content.Context
+import android.content.Context.CONNECTIVITY_SERVICE
+import android.content.Intent
+import android.content.pm.PackageManager.MATCH_DEFAULT_ONLY
+import android.net.ConnectivityManager
+import android.net.NetworkCapabilities.NET_CAPABILITY_INTERNET
+import android.os.Build.VERSION.SDK_INT
+import android.os.Looper
+import android.text.format.DateUtils.DAY_IN_MILLIS
+import android.text.format.DateUtils.FORMAT_ABBREV_ALL
+import android.text.format.DateUtils.FORMAT_ABBREV_MONTH
+import android.text.format.DateUtils.FORMAT_ABBREV_RELATIVE
+import android.text.format.DateUtils.FORMAT_NO_YEAR
+import android.text.format.DateUtils.FORMAT_SHOW_DATE
+import android.text.format.DateUtils.FORMAT_SHOW_TIME
+import android.text.format.DateUtils.FORMAT_SHOW_YEAR
+import android.text.format.DateUtils.MINUTE_IN_MILLIS
+import android.text.format.DateUtils.formatDateTime
+import android.text.format.DateUtils.getRelativeTimeSpanString
+import android.view.View
+import android.view.View.INVISIBLE
+import android.view.View.VISIBLE
+import android.view.inputmethod.InputMethodManager
+import androidx.core.content.ContextCompat.getSystemService
+import androidx.fragment.app.Fragment
+import androidx.navigation.NavDirections
+import androidx.navigation.fragment.findNavController
+
+fun View.fadeIn(endAction: () -> Unit = {}) {
+    if (visibility == VISIBLE && alpha == 1f) return
+    alpha = 0f
+    visibility = VISIBLE
+    animate().alpha(1f).withEndAction {
+        if (context != null) endAction.invoke()
+    }.start()
+}
+
+fun View.fadeOut(endAction: () -> Unit = {}) {
+    if (visibility == INVISIBLE) return
+    animate().alpha(0f).withEndAction {
+        if (context == null) return@withEndAction
+        visibility = INVISIBLE
+        alpha = 1f
+        endAction.invoke()
+    }.start()
+}
+
+fun View.hideKeyboard() {
+    getSystemService(context, InputMethodManager::class.java)
+        ?.hideSoftInputFromWindow(windowToken, 0)
+}
+
+fun assertUiThread() {
+    check(Looper.getMainLooper().thread == Thread.currentThread())
+}
+
+/**
+ * Use this with 'when' expressions when you need it to handle all possibilities/branches.
+ */
+val <T> T.exhaustive: T
+    get() = this
+
+fun Context.isOnline(): Boolean {
+    val cm = getSystemService(CONNECTIVITY_SERVICE) as ConnectivityManager
+    return if (SDK_INT < 29) {
+        @Suppress("DEPRECATION")
+        cm.activeNetworkInfo?.isConnected == true
+    } else {
+        val capabilities = cm.getNetworkCapabilities(cm.activeNetwork) ?: return false
+        capabilities.hasCapability(NET_CAPABILITY_INTERNET)
+    }
+}
+
+fun Intent.isSafe(context: Context): Boolean {
+    return context.packageManager.queryIntentActivities(this, MATCH_DEFAULT_ONLY).isNotEmpty()
+}
+
+fun Fragment.navigate(directions: NavDirections) = findNavController().navigate(directions)
+
+fun Long.toRelativeTime(context: Context): CharSequence {
+    val now = System.currentTimeMillis()
+    return if (now - this > DAY_IN_MILLIS * 2) {
+        val flags = FORMAT_SHOW_TIME or FORMAT_SHOW_DATE or FORMAT_ABBREV_MONTH or FORMAT_NO_YEAR
+        formatDateTime(context, this, flags)
+    } else getRelativeTimeSpanString(this, now, MINUTE_IN_MILLIS, FORMAT_ABBREV_RELATIVE)
+}
+
+fun Long.toAbsoluteTime(context: Context): CharSequence {
+    val flags = FORMAT_SHOW_TIME or FORMAT_SHOW_DATE or FORMAT_SHOW_YEAR
+    return formatDateTime(context, this, flags)
+}
+
+fun Long.toShortDate(context: Context): CharSequence {
+    val flags = FORMAT_SHOW_DATE or FORMAT_SHOW_YEAR or FORMAT_ABBREV_ALL
+    return formatDateTime(context, this, flags)
+}
+
+fun Version.getIncompatibleStringOrNull(context: Context, otherVersion: String): String? {
+    val other = Version.parse(otherVersion) ?: return context.getString(R.string.version_invalid)
+    val match = compare(other) ?: return context.getString(R.string.version_invalid)
+    if (match.compatible) return null
+    if (match.currentCmp < 0) return context.getString(R.string.version_too_old)
+    if (match.currentCmp > 0) return context.getString(R.string.version_too_new)
+    throw AssertionError("$this == $other")
+}
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/ByteArrayUtils.kt b/taler-kotlin-android/src/main/java/net/taler/common/ByteArrayUtils.kt
new file mode 100644
index 0000000..fba0d07
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/ByteArrayUtils.kt
@@ -0,0 +1,53 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+object ByteArrayUtils {
+
+    private const val HEX_CHARS = "0123456789ABCDEF"
+
+    fun hexStringToByteArray(data: String): ByteArray {
+        val result = ByteArray(data.length / 2)
+
+        for (i in data.indices step 2) {
+            val firstIndex = HEX_CHARS.indexOf(data[i])
+            val secondIndex = HEX_CHARS.indexOf(data[i + 1])
+
+            val octet = firstIndex.shl(4).or(secondIndex)
+            result[i.shr(1)] = octet.toByte()
+        }
+        return result
+    }
+
+
+    private val HEX_CHARS_ARRAY = HEX_CHARS.toCharArray()
+
+    @Suppress("unused")
+    fun toHex(byteArray: ByteArray): String {
+        val result = StringBuffer()
+
+        byteArray.forEach {
+            val octet = it.toInt()
+            val firstIndex = (octet and 0xF0).ushr(4)
+            val secondIndex = octet and 0x0F
+            result.append(HEX_CHARS_ARRAY[firstIndex])
+            result.append(HEX_CHARS_ARRAY[secondIndex])
+        }
+        return result.toString()
+    }
+
+}
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/CombinedLiveData.kt b/taler-kotlin-android/src/main/java/net/taler/common/CombinedLiveData.kt
new file mode 100644
index 0000000..4e7016b
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/CombinedLiveData.kt
@@ -0,0 +1,51 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MediatorLiveData
+import androidx.lifecycle.Observer
+
+class CombinedLiveData<T, K, S>(
+    source1: LiveData<T>,
+    source2: LiveData<K>,
+    private val combine: (data1: T?, data2: K?) -> S
+) : MediatorLiveData<S>() {
+
+    private var data1: T? = null
+    private var data2: K? = null
+
+    init {
+        super.addSource(source1) { t ->
+            data1 = t
+            value = combine(data1, data2)
+        }
+        super.addSource(source2) { k ->
+            data2 = k
+            value = combine(data1, data2)
+        }
+    }
+
+    override fun <S : Any?> addSource(source: LiveData<S>, onChanged: Observer<in S>) {
+        throw UnsupportedOperationException()
+    }
+
+    override fun <T : Any?> removeSource(toRemote: LiveData<T>) {
+        throw UnsupportedOperationException()
+    }
+
+}
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/ContractTerms.kt b/taler-kotlin-android/src/main/java/net/taler/common/ContractTerms.kt
new file mode 100644
index 0000000..0d5fe5b
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/ContractTerms.kt
@@ -0,0 +1,91 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import androidx.annotation.RequiresApi
+import com.fasterxml.jackson.annotation.JsonIgnore
+import com.fasterxml.jackson.annotation.JsonInclude
+import com.fasterxml.jackson.annotation.JsonInclude.Include.NON_EMPTY
+import com.fasterxml.jackson.annotation.JsonInclude.Include.NON_NULL
+import com.fasterxml.jackson.annotation.JsonProperty
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import net.taler.common.TalerUtils.getLocalizedString
+
+@Serializable
+data class ContractTerms(
+    val summary: String,
+    @SerialName("summary_i18n")
+    @get:JsonProperty("summary_i18n")
+    val summaryI18n: Map<String, String>? = null,
+    val amount: Amount,
+    @SerialName("fulfillment_url")
+    @get:JsonProperty("fulfillment_url")
+    val fulfillmentUrl: String,
+    val products: List<ContractProduct>
+)
+
+@JsonInclude(NON_NULL)
+abstract class Product {
+    @get:JsonProperty("product_id")
+    abstract val productId: String?
+    abstract val description: String
+
+    @get:JsonProperty("description_i18n")
+    abstract val descriptionI18n: Map<String, String>?
+    abstract val price: Amount
+
+    @get:JsonProperty("delivery_location")
+    abstract val location: String?
+    abstract val image: String?
+
+    @get:JsonIgnore
+    val localizedDescription: String
+        @RequiresApi(26)
+        get() = getLocalizedString(descriptionI18n, description)
+}
+
+@Serializable
+data class ContractProduct(
+    @SerialName("product_id")
+    override val productId: String? = null,
+    override val description: String,
+    @SerialName("description_i18n")
+    override val descriptionI18n: Map<String, String>? = null,
+    override val price: Amount,
+    @SerialName("delivery_location")
+    override val location: String? = null,
+    override val image: String? = null,
+    val quantity: Int
+) : Product() {
+    @get:JsonIgnore
+    val totalPrice: Amount by lazy {
+        price * quantity
+    }
+}
+
+data class ContractMerchant(
+    val name: String
+)
+
+@Serializable
+@JsonInclude(NON_EMPTY)
+class Timestamp(
+    @SerialName("t_ms")
+    @JsonProperty("t_ms")
+    val ms: Long
+)
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/Event.kt b/taler-kotlin-android/src/main/java/net/taler/common/Event.kt
new file mode 100644
index 0000000..779247f
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/Event.kt
@@ -0,0 +1,51 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.Observer
+import java.util.concurrent.atomic.AtomicBoolean
+
+/**
+ * Used as a wrapper for data that is exposed via a [LiveData] that represents an one-time event.
+ */
+open class Event<out T>(private val content: T) {
+
+    private val isConsumed = AtomicBoolean(false)
+
+    /**
+     * Returns the content and prevents its use again.
+     */
+    fun getIfNotConsumed(): T? {
+        return if (isConsumed.compareAndSet(false, true)) content else null
+    }
+
+}
+
+fun <T> T.toEvent() = Event(this)
+
+/**
+ * An [Observer] for [Event]s, simplifying the pattern of checking if the [Event]'s content has
+ * already been consumed.
+ *
+ * [onEvent] is *only* called if the [Event]'s contents has not been consumed.
+ */
+class EventObserver<T>(private val onEvent: (T) -> Unit) : Observer<Event<T>> {
+    override fun onChanged(event: Event<T>?) {
+        event?.getIfNotConsumed()?.let { onEvent(it) }
+    }
+}
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/NfcManager.kt b/taler-kotlin-android/src/main/java/net/taler/common/NfcManager.kt
new file mode 100644
index 0000000..11e1e1e
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/NfcManager.kt
@@ -0,0 +1,234 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import android.app.Activity
+import android.content.Context
+import android.nfc.NfcAdapter
+import android.nfc.NfcAdapter.FLAG_READER_NFC_A
+import android.nfc.NfcAdapter.FLAG_READER_SKIP_NDEF_CHECK
+import android.nfc.NfcAdapter.getDefaultAdapter
+import android.nfc.Tag
+import android.nfc.tech.IsoDep
+import android.util.Log
+import net.taler.common.ByteArrayUtils.hexStringToByteArray
+import org.json.JSONObject
+import java.io.ByteArrayOutputStream
+import java.net.URL
+import javax.net.ssl.HttpsURLConnection
+
+@Suppress("unused")
+private const val TALER_AID = "A0000002471001"
+
+class NfcManager : NfcAdapter.ReaderCallback {
+
+    companion object {
+        const val TAG = "taler-merchant"
+
+        /**
+         * Returns true if NFC is supported and false otherwise.
+         */
+        fun hasNfc(context: Context): Boolean {
+            return getNfcAdapter(context) != null
+        }
+
+        /**
+         * Enables NFC reader mode. Don't forget to call [stop] afterwards.
+         */
+        fun start(activity: Activity, nfcManager: NfcManager) {
+            getNfcAdapter(activity)?.enableReaderMode(activity, nfcManager, nfcManager.flags, null)
+        }
+
+        /**
+         * Disables NFC reader mode. Call after [start].
+         */
+        fun stop(activity: Activity) {
+            getNfcAdapter(activity)?.disableReaderMode(activity)
+        }
+
+        private fun getNfcAdapter(context: Context): NfcAdapter? {
+            return getDefaultAdapter(context)
+        }
+    }
+
+    private val flags = FLAG_READER_NFC_A or FLAG_READER_SKIP_NDEF_CHECK
+
+    private var tagString: String? = null
+    private var currentTag: IsoDep? = null
+
+    fun setTagString(tagString: String) {
+        this.tagString = tagString
+    }
+
+    override fun onTagDiscovered(tag: Tag?) {
+
+        Log.v(TAG, "tag discovered")
+
+        val isoDep = IsoDep.get(tag)
+        isoDep.connect()
+
+        currentTag = isoDep
+
+        isoDep.transceive(apduSelectFile())
+
+        val tagString: String? = tagString
+        if (tagString != null) {
+            isoDep.transceive(apduPutTalerData(1, tagString.toByteArray()))
+        }
+
+        // FIXME: use better pattern for sleeps in between requests
+        // -> start with fast polling, poll more slowly if no requests are coming
+
+        while (true) {
+            try {
+                val reqFrame = isoDep.transceive(apduGetData())
+                if (reqFrame.size < 2) {
+                    Log.v(TAG, "request frame too small")
+                    break
+                }
+                val req = ByteArray(reqFrame.size - 2)
+                if (req.isEmpty()) {
+                    continue
+                }
+                reqFrame.copyInto(req, 0, 0, reqFrame.size - 2)
+                val jsonReq = JSONObject(req.toString(Charsets.UTF_8))
+                val reqId = jsonReq.getInt("id")
+                Log.v(TAG, "got request $jsonReq")
+                val jsonInnerReq = jsonReq.getJSONObject("request")
+                val method = jsonInnerReq.getString("method")
+                val urlStr = jsonInnerReq.getString("url")
+                Log.v(TAG, "url '$urlStr'")
+                Log.v(TAG, "method '$method'")
+                val url = URL(urlStr)
+                val conn: HttpsURLConnection = url.openConnection() as HttpsURLConnection
+                conn.setRequestProperty("Accept", "application/json")
+                conn.connectTimeout = 5000
+                conn.doInput = true
+                when (method) {
+                    "get" -> {
+                        conn.requestMethod = "GET"
+                    }
+                    "postJson" -> {
+                        conn.requestMethod = "POST"
+                        conn.doOutput = true
+                        conn.setRequestProperty("Content-Type", "application/json; utf-8")
+                        val body = jsonInnerReq.getString("body")
+                        conn.outputStream.write(body.toByteArray(Charsets.UTF_8))
+                    }
+                    else -> {
+                        throw Exception("method not supported")
+                    }
+                }
+                Log.v(TAG, "connecting")
+                conn.connect()
+                Log.v(TAG, "connected")
+
+                val statusCode = conn.responseCode
+                val tunnelResp = JSONObject()
+                tunnelResp.put("id", reqId)
+                tunnelResp.put("status", conn.responseCode)
+
+                if (statusCode == 200) {
+                    val stream = conn.inputStream
+                    val httpResp = stream.buffered().readBytes()
+                    tunnelResp.put("responseJson", JSONObject(httpResp.toString(Charsets.UTF_8)))
+                }
+
+                Log.v(TAG, "sending: $tunnelResp")
+
+                isoDep.transceive(apduPutTalerData(2, tunnelResp.toString().toByteArray()))
+            } catch (e: Exception) {
+                Log.v(TAG, "exception during NFC loop: $e")
+                break
+            }
+        }
+
+        isoDep.close()
+    }
+
+    private fun writeApduLength(stream: ByteArrayOutputStream, size: Int) {
+        when {
+            size == 0 -> {
+                // No size field needed!
+            }
+            size <= 255 -> // One byte size field
+                stream.write(size)
+            size <= 65535 -> {
+                stream.write(0)
+                // FIXME: is this supposed to be little or big endian?
+                stream.write(size and 0xFF)
+                stream.write((size ushr 8) and 0xFF)
+            }
+            else -> throw Error("payload too big")
+        }
+    }
+
+    private fun apduSelectFile(): ByteArray {
+        return hexStringToByteArray("00A4040007A0000002471001")
+    }
+
+    private fun apduPutData(payload: ByteArray): ByteArray {
+        val stream = ByteArrayOutputStream()
+
+        // Class
+        stream.write(0x00)
+
+        // Instruction 0xDA = put data
+        stream.write(0xDA)
+
+        // Instruction parameters
+        // (proprietary encoding)
+        stream.write(0x01)
+        stream.write(0x00)
+
+        writeApduLength(stream, payload.size)
+
+        stream.write(payload)
+
+        return stream.toByteArray()
+    }
+
+    private fun apduPutTalerData(talerInst: Int, payload: ByteArray): ByteArray {
+        val realPayload = ByteArrayOutputStream()
+        realPayload.write(talerInst)
+        realPayload.write(payload)
+        return apduPutData(realPayload.toByteArray())
+    }
+
+    private fun apduGetData(): ByteArray {
+        val stream = ByteArrayOutputStream()
+
+        // Class
+        stream.write(0x00)
+
+        // Instruction 0xCA = get data
+        stream.write(0xCA)
+
+        // Instruction parameters
+        // (proprietary encoding)
+        stream.write(0x01)
+        stream.write(0x00)
+
+        // Max expected response size, two
+        // zero bytes denotes 65536
+        stream.write(0x0)
+        stream.write(0x0)
+
+        return stream.toByteArray()
+    }
+
+}
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/QrCodeManager.kt b/taler-kotlin-android/src/main/java/net/taler/common/QrCodeManager.kt
new file mode 100644
index 0000000..e2a9a55
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/QrCodeManager.kt
@@ -0,0 +1,42 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import android.graphics.Bitmap
+import android.graphics.Bitmap.Config.RGB_565
+import android.graphics.Color.BLACK
+import android.graphics.Color.WHITE
+import com.google.zxing.BarcodeFormat.QR_CODE
+import com.google.zxing.qrcode.QRCodeWriter
+
+object QrCodeManager {
+
+    fun makeQrCode(text: String, size: Int = 256): Bitmap {
+        val qrCodeWriter = QRCodeWriter()
+        val bitMatrix = qrCodeWriter.encode(text, QR_CODE, size, size)
+        val height = bitMatrix.height
+        val width = bitMatrix.width
+        val bmp = Bitmap.createBitmap(width, height, RGB_565)
+        for (x in 0 until width) {
+            for (y in 0 until height) {
+                bmp.setPixel(x, y, if (bitMatrix.get(x, y)) BLACK else WHITE)
+            }
+        }
+        return bmp
+    }
+
+}
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/SignedAmount.kt b/taler-kotlin-android/src/main/java/net/taler/common/SignedAmount.kt
new file mode 100644
index 0000000..03a0d6e
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/SignedAmount.kt
@@ -0,0 +1,40 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import android.annotation.SuppressLint
+
+data class SignedAmount(
+    val positive: Boolean,
+    val amount: Amount
+) {
+
+    companion object {
+        @Throws(AmountParserException::class)
+        @SuppressLint("CheckedExceptions")
+        fun fromJSONString(str: String): SignedAmount = when (str.substring(0, 1)) {
+            "-" -> SignedAmount(false, Amount.fromJSONString(str.substring(1)))
+            "+" -> SignedAmount(true, Amount.fromJSONString(str.substring(1)))
+            else -> SignedAmount(true, Amount.fromJSONString(str))
+        }
+    }
+
+    override fun toString(): String {
+        return if (positive) "$amount" else "-$amount"
+    }
+
+}
\ No newline at end of file
diff --git a/taler-kotlin-android/src/main/java/net/taler/common/TalerUtils.kt b/taler-kotlin-android/src/main/java/net/taler/common/TalerUtils.kt
new file mode 100644
index 0000000..bb2e78a
--- /dev/null
+++ b/taler-kotlin-android/src/main/java/net/taler/common/TalerUtils.kt
@@ -0,0 +1,57 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import androidx.annotation.RequiresApi
+import androidx.core.os.LocaleListCompat
+import java.util.Locale
+
+object TalerUtils {
+
+    @RequiresApi(26)
+    fun getLocalizedString(map: Map<String, String>?, default: String): String {
+        // just return the default, if it is the only element
+        if (map == null) return default
+        // create a priority list of language ranges from system locales
+        val locales = LocaleListCompat.getDefault()
+        val priorityList = ArrayList<Locale.LanguageRange>(locales.size())
+        for (i in 0 until locales.size()) {
+            priorityList.add(Locale.LanguageRange(locales[i].toLanguageTag()))
+        }
+        // create a list of locales available in the given map
+        val availableLocales = map.keys.mapNotNull {
+            if (it == "_") return@mapNotNull null
+            val list = it.split("_")
+            when (list.size) {
+                1 -> Locale(list[0])
+                2 -> Locale(list[0], list[1])
+                3 -> Locale(list[0], list[1], list[2])
+                else -> null
+            }
+        }
+        val match = Locale.lookup(priorityList, availableLocales)
+        return match?.toString()?.let { map[it] } ?: default
+    }
+
+}
+
+/**
+ * Returns the current time in milliseconds epoch rounded to nearest seconds.
+ */
+fun now(): Long {
+    return ((System.currentTimeMillis() + 500) / 1000) * 1000
+}
diff --git a/taler-kotlin-android/src/main/res/drawable/selectable_background.xml b/taler-kotlin-android/src/main/res/drawable/selectable_background.xml
new file mode 100644
index 0000000..3c383a8
--- /dev/null
+++ b/taler-kotlin-android/src/main/res/drawable/selectable_background.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ This file is part of GNU Taler
+  ~ (C) 2020 Taler Systems S.A.
+  ~
+  ~ GNU Taler is free software; you can redistribute it and/or modify it under the
+  ~ terms of the GNU General Public License as published by the Free Software
+  ~ Foundation; either version 3, or (at your option) any later version.
+  ~
+  ~ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+  ~ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  ~ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License along with
+  ~ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+  -->
+
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@color/selectedBackground" android:state_activated="true" />
+    <item android:drawable="@android:color/transparent" />
+</selector>
diff --git a/taler-kotlin-android/src/main/res/values-night/colors.xml b/taler-kotlin-android/src/main/res/values-night/colors.xml
new file mode 100644
index 0000000..10bdbb9
--- /dev/null
+++ b/taler-kotlin-android/src/main/res/values-night/colors.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="highlightedBackground">#2E2E2E</color>
+    <color name="selectedBackground">#363636</color>
+</resources>
diff --git a/taler-kotlin-android/src/main/res/values/colors.xml b/taler-kotlin-android/src/main/res/values/colors.xml
new file mode 100644
index 0000000..c916442
--- /dev/null
+++ b/taler-kotlin-android/src/main/res/values/colors.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ This file is part of GNU Taler
+  ~ (C) 2020 Taler Systems S.A.
+  ~
+  ~ GNU Taler is free software; you can redistribute it and/or modify it under the
+  ~ terms of the GNU General Public License as published by the Free Software
+  ~ Foundation; either version 3, or (at your option) any later version.
+  ~
+  ~ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+  ~ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  ~ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License along with
+  ~ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+  -->
+
+<resources>
+    <color name="highlightedBackground">#E4E4E4</color>
+    <color name="selectedBackground">#DADADA</color>
+
+    <color name="green">#388E3C</color>
+    <color name="red">#C62828</color>
+</resources>
diff --git a/taler-kotlin-android/src/main/res/values/strings.xml b/taler-kotlin-android/src/main/res/values/strings.xml
new file mode 100644
index 0000000..a5b1df1
--- /dev/null
+++ b/taler-kotlin-android/src/main/res/values/strings.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?><!--
+  ~ This file is part of GNU Taler
+  ~ (C) 2020 Taler Systems S.A.
+  ~
+  ~ GNU Taler is free software; you can redistribute it and/or modify it under the
+  ~ terms of the GNU General Public License as published by the Free Software
+  ~ Foundation; either version 3, or (at your option) any later version.
+  ~
+  ~ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+  ~ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  ~ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License along with
+  ~ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+  -->
+
+<resources>
+    <string name="version_invalid">Invalid version. Please try again later!</string>
+    <string name="version_too_old">App too old. Please upgrade!</string>
+    <string name="version_too_new">Service outdated. Please wait until it gets upgraded.</string>
+</resources>
diff --git a/taler-kotlin-android/src/test/java/net/taler/common/ContractTermsTest.kt b/taler-kotlin-android/src/test/java/net/taler/common/ContractTermsTest.kt
new file mode 100644
index 0000000..79a7598
--- /dev/null
+++ b/taler-kotlin-android/src/test/java/net/taler/common/ContractTermsTest.kt
@@ -0,0 +1,74 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import com.fasterxml.jackson.databind.DeserializationFeature
+import com.fasterxml.jackson.databind.ObjectMapper
+import com.fasterxml.jackson.module.kotlin.KotlinModule
+import com.fasterxml.jackson.module.kotlin.readValue
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class ContractTermsTest {
+
+    private val mapper = ObjectMapper()
+        .registerModule(KotlinModule())
+        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
+        .addMixIn(Amount::class.java, AmountMixin::class.java)
+
+    @Test
+    fun test() {
+        val json = """
+            {
+              "amount":"TESTKUDOS:0.5",
+              "extra":{
+                "article_name":"1._The_Free_Software_Definition"
+              },
+              "fulfillment_url":"https://shop.test.taler.net/essay/1._The_Free_Software_Definition",
+              "summary":"Essay: 1. The Free Software Definition",
+              "refund_deadline":{"t_ms":1596128414000},
+              "wire_transfer_deadline":{"t_ms":1596128564000},
+              "products":[],
+              "h_wire":"KV40K023N8EC1F5100TYNS23C4XN68Y1Z3PTJSWFGTMCNYD54KT4S791V2VQ91SZANN86VDAA369M4VEZ0KR6DN71EVRRZA71K681M0",
+              "wire_method":"x-taler-bank",
+              "order_id":"2020.212-01M9VKEAPF76C",
+              "timestamp":{"t_ms":1596128114000},
+              "pay_deadline":{"t_ms":"never"},
+              "max_wire_fee":"TESTKUDOS:1",
+              "max_fee":"TESTKUDOS:1",
+              "wire_fee_amortization":3,
+              "merchant_base_url":"https://backend.test.taler.net/instances/blog/",
+              "merchant":{"name":"Blog","instance":"blog"},
+              "exchanges":[
+                {
+                    "url":"https://exchange.test.taler.net/",
+                    "master_pub":"DY95EXAHQ2BKM2WK9YHZHYG1R7PPMMJPY14FNGP662DAKE35AKQG"
+                },
+                {
+                    "url":"https://exchange.test.taler.net/",
+                    "master_pub":"DY95EXAHQ2BKM2WK9YHZHYG1R7PPMMJPY14FNGP662DAKE35AKQG"}
+                ],
+                "auditors":[],
+                "merchant_pub":"8DR9NKSZY1CXFRE47NEYXM0K85C4ZGAYH7Y7VZ22GPNF0BRFNYNG",
+                "nonce":"FK8ZKJRV6VX6YFAG4CDSC6W0DWD084Q09DP81ANF30GRFQYM2KPG"
+              }
+        """.trimIndent()
+        val contractTerms: ContractTerms = mapper.readValue(json)
+        assertEquals("Essay: 1. The Free Software Definition", contractTerms.summary)
+    }
+
+}
diff --git a/taler-kotlin-common/.gitlab-ci.yml b/taler-kotlin-common/.gitlab-ci.yml
index 49d3e98..c241e31 100644
--- a/taler-kotlin-common/.gitlab-ci.yml
+++ b/taler-kotlin-common/.gitlab-ci.yml
@@ -4,8 +4,4 @@ taler_kotlin_common_test:
     changes:
       - taler-kotlin-common/**/*
       - build.gradle
-  script: ./gradlew :taler-kotlin-common:check
-  artifacts:
-    paths:
-      - taler-kotlin-common/build/reports/lint-results.html
-    expire_in: 1 week
+  script: ./gradlew :taler-kotlin-common:jvmTest
diff --git a/taler-kotlin-common/build.gradle b/taler-kotlin-common/build.gradle
index dd083b7..129881d 100644
--- a/taler-kotlin-common/build.gradle
+++ b/taler-kotlin-common/build.gradle
@@ -1,72 +1,82 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
 plugins {
-    id 'com.android.library'
-    id 'kotlin-android'
-    id 'kotlin-android-extensions'
+    id 'org.jetbrains.kotlin.multiplatform'
     id 'kotlinx-serialization'
 }
 
-android {
-    compileSdkVersion 29
-    //noinspection GradleDependency
-    buildToolsVersion "$build_tools_version"
+group 'net.taler'
+version '0.0.1'
 
-    defaultConfig {
-        minSdkVersion 24
-        targetSdkVersion 29
-        versionCode 1
-        versionName "0.1"
+apply plugin: 'maven-publish'
 
-        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
-        consumerProguardFiles 'consumer-rules.pro'
+kotlin {
+    jvm()
+    // This is for iPhone simulator
+    // Switch here to iosArm64 (or iosArm32) to build library for iPhone device
+    iosX64("ios") {
+        binaries {
+            framework()
+        }
     }
-
-    buildTypes {
-        release {
-            minifyEnabled false
-            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+    linuxX64("linux")
+    js {
+        browser {
+        }
+        nodejs {
+        }
+    }
+    sourceSets {
+        def serialization_version = "0.20.0"
+        commonMain {
+            dependencies {
+                implementation kotlin('stdlib-common')
+                implementation "org.jetbrains.kotlinx:kotlinx-serialization-runtime-common:$serialization_version"
+            }
+        }
+        commonTest {
+            dependencies {
+                implementation kotlin('test-common')
+                implementation kotlin('test-annotations-common')
+            }
+        }
+        jvmMain {
+            dependencies {
+                implementation kotlin('stdlib-jdk8')
+                implementation "org.jetbrains.kotlinx:kotlinx-serialization-runtime:$serialization_version"
+            }
+        }
+        jvmTest {
+            dependencies {
+                implementation kotlin('test')
+                implementation kotlin('test-junit')
+            }
+        }
+        jsMain {
+            dependencies {
+                implementation kotlin('stdlib-js')
+                implementation "org.jetbrains.kotlinx:kotlinx-serialization-runtime-js:$serialization_version"
+            }
+        }
+        jsTest {
+            dependencies {
+                implementation kotlin('test-js')
+            }
+        }
+        nativeMain {
+            dependsOn commonMain
+            dependencies {
+                implementation "org.jetbrains.kotlinx:kotlinx-serialization-runtime-native:$serialization_version"
+            }
+        }
+        nativeTest {
+            dependsOn commonTest
+        }
+        configure([targets.linux, targets.ios]) {
+            compilations.main.source(sourceSets.nativeMain)
+            compilations.test.source(sourceSets.nativeTest)
         }
     }
-
 }
 
-dependencies {
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    implementation 'androidx.appcompat:appcompat:1.1.0'
-    implementation 'androidx.core:core-ktx:1.3.0'
-
-    // Navigation
-    implementation "androidx.navigation:navigation-ui-ktx:$nav_version"
-    implementation "androidx.navigation:navigation-fragment-ktx:$nav_version"
-
-    // ViewModel and LiveData
-    def lifecycle_version = "2.2.0"
-    implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
-
-    // QR codes
-    implementation 'com.google.zxing:core:3.4.0'  // needs minSdkVersion 24+
-
-    // JSON parsing and serialization
-    api "org.jetbrains.kotlinx:kotlinx-serialization-runtime:0.20.0"
-    implementation "com.fasterxml.jackson.module:jackson-module-kotlin:2.10.2"
-
-    lintChecks 'com.github.thirdegg:lint-rules:0.0.4-alpha'
-
-    testImplementation 'junit:junit:4.13'
-    testImplementation 'org.json:json:20190722'
+configurations {
+    compileClasspath
 }
diff --git a/taler-kotlin-common/consumer-rules.pro b/taler-kotlin-common/consumer-rules.pro
deleted file mode 100644
index e69de29..0000000
diff --git a/taler-kotlin-common/proguard-rules.pro b/taler-kotlin-common/proguard-rules.pro
deleted file mode 100644
index f1b4245..0000000
--- a/taler-kotlin-common/proguard-rules.pro
+++ /dev/null
@@ -1,21 +0,0 @@
-# Add project specific ProGuard rules here.
-# You can control the set of applied configuration files using the
-# proguardFiles setting in build.gradle.
-#
-# For more details, see
-#   http://developer.android.com/guide/developing/tools/proguard.html
-
-# If your project uses WebView with JS, uncomment the following
-# and specify the fully qualified class name to the JavaScript interface
-# class:
-#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
-#   public *;
-#}
-
-# Uncomment this to preserve the line number information for
-# debugging stack traces.
-#-keepattributes SourceFile,LineNumberTable
-
-# If you keep the line number information, uncomment this to
-# hide the original source file name.
-#-renamesourcefileattribute SourceFile
diff --git a/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Amount.kt b/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Amount.kt
new file mode 100644
index 0000000..84d10c5
--- /dev/null
+++ b/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Amount.kt
@@ -0,0 +1,198 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlinx.serialization.Decoder
+import kotlinx.serialization.Encoder
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.Serializer
+import kotlin.math.floor
+import kotlin.math.pow
+import kotlin.math.roundToInt
+
+class AmountParserException(msg: String? = null, cause: Throwable? = null) : Exception(msg, cause)
+class AmountOverflowException(msg: String? = null, cause: Throwable? = null) : Exception(msg, cause)
+
+@Serializable(with = KotlinXAmountSerializer::class)
+data class Amount(
+    /**
+     * name of the currency using either a three-character ISO 4217 currency code,
+     * or a regional currency identifier starting with a "*" followed by at most 10 characters.
+     * ISO 4217 exponents in the name are not supported,
+     * although the "fraction" is corresponds to an ISO 4217 exponent of 6.
+     */
+    val currency: String,
+
+    /**
+     * The integer part may be at most 2^52.
+     * Note that "1" here would correspond to 1 EUR or 1 USD, depending on currency, not 1 cent.
+     */
+    val value: Long,
+
+    /**
+     * Unsigned 32 bit fractional value to be added to value representing
+     * an additional currency fraction, in units of one hundred millionth (1e-8)
+     * of the base currency value.  For example, a fraction
+     * of 50_000_000 would correspond to 50 cents.
+     */
+    val fraction: Int
+) : Comparable<Amount> {
+
+    companion object {
+
+        private const val FRACTIONAL_BASE: Int = 100000000 // 1e8
+
+        private val REGEX_CURRENCY = Regex("""^[-_*A-Za-z0-9]{1,12}$""")
+        val MAX_VALUE = 2.0.pow(52).toLong()
+        private const val MAX_FRACTION_LENGTH = 8
+        const val MAX_FRACTION = 99_999_999
+
+        fun zero(currency: String): Amount {
+            return Amount(checkCurrency(currency), 0, 0)
+        }
+
+        fun fromJSONString(str: String): Amount {
+            val split = str.split(":")
+            if (split.size != 2) throw AmountParserException("Invalid Amount Format")
+            return fromString(split[0], split[1])
+        }
+
+        fun fromString(currency: String, str: String): Amount {
+            // value
+            val valueSplit = str.split(".")
+            val value = checkValue(valueSplit[0].toLongOrNull())
+            // fraction
+            val fraction: Int = if (valueSplit.size > 1) {
+                val fractionStr = valueSplit[1]
+                if (fractionStr.length > MAX_FRACTION_LENGTH)
+                    throw AmountParserException("Fraction $fractionStr too long")
+                val fraction = "0.$fractionStr".toDoubleOrNull()
+                    ?.times(FRACTIONAL_BASE)
+                    ?.roundToInt()
+                checkFraction(fraction)
+            } else 0
+            return Amount(checkCurrency(currency), value, fraction)
+        }
+
+        fun min(currency: String): Amount = Amount(currency, 0, 1)
+        fun max(currency: String): Amount = Amount(currency, MAX_VALUE, MAX_FRACTION)
+
+
+        internal fun checkCurrency(currency: String): String {
+            if (!REGEX_CURRENCY.matches(currency))
+                throw AmountParserException("Invalid currency: $currency")
+            return currency
+        }
+
+        internal fun checkValue(value: Long?): Long {
+            if (value == null || value > MAX_VALUE)
+                throw AmountParserException("Value $value greater than $MAX_VALUE")
+            return value
+        }
+
+        internal fun checkFraction(fraction: Int?): Int {
+            if (fraction == null || fraction > MAX_FRACTION)
+                throw AmountParserException("Fraction $fraction greater than $MAX_FRACTION")
+            return fraction
+        }
+
+    }
+
+    val amountStr: String
+        get() = if (fraction == 0) "$value" else {
+            var f = fraction
+            var fractionStr = ""
+            while (f > 0) {
+                fractionStr += f / (FRACTIONAL_BASE / 10)
+                f = (f * 10) % FRACTIONAL_BASE
+            }
+            "$value.$fractionStr"
+        }
+
+    operator fun plus(other: Amount): Amount {
+        check(currency == other.currency) { "Can only subtract from same currency" }
+        val resultValue = value + other.value + floor((fraction + other.fraction).toDouble() / FRACTIONAL_BASE).toLong()
+        if (resultValue > MAX_VALUE)
+            throw AmountOverflowException()
+        val resultFraction = (fraction + other.fraction) % FRACTIONAL_BASE
+        return Amount(currency, resultValue, resultFraction)
+    }
+
+    operator fun times(factor: Int): Amount {
+        // TODO consider replacing with a faster implementation
+        if (factor == 0) return zero(currency)
+        var result = this
+        for (i in 1 until factor) result += this
+        return result
+    }
+
+    operator fun minus(other: Amount): Amount {
+        check(currency == other.currency) { "Can only subtract from same currency" }
+        var resultValue = value
+        var resultFraction = fraction
+        if (resultFraction < other.fraction) {
+            if (resultValue < 1L)
+                throw AmountOverflowException()
+            resultValue--
+            resultFraction += FRACTIONAL_BASE
+        }
+        check(resultFraction >= other.fraction)
+        resultFraction -= other.fraction
+        if (resultValue < other.value)
+            throw AmountOverflowException()
+        resultValue -= other.value
+        return Amount(currency, resultValue, resultFraction)
+    }
+
+    fun isZero(): Boolean {
+        return value == 0L && fraction == 0
+    }
+
+    fun toJSONString(): String {
+        return "$currency:$amountStr"
+    }
+
+    override fun toString(): String {
+        return "$amountStr $currency"
+    }
+
+    override fun compareTo(other: Amount): Int {
+        check(currency == other.currency) { "Can only compare amounts with the same currency" }
+        when {
+            value == other.value -> {
+                if (fraction < other.fraction) return -1
+                if (fraction > other.fraction) return 1
+                return 0
+            }
+            value < other.value -> return -1
+            else -> return 1
+        }
+    }
+
+}
+
+@Serializer(forClass = Amount::class)
+object KotlinXAmountSerializer: KSerializer<Amount> {
+    override fun serialize(encoder: Encoder, value: Amount) {
+        encoder.encodeString(value.toJSONString())
+    }
+
+    override fun deserialize(decoder: Decoder): Amount {
+        return Amount.fromJSONString(decoder.decodeString())
+    }
+}
diff --git a/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Time.kt b/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Time.kt
new file mode 100644
index 0000000..962e004
--- /dev/null
+++ b/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Time.kt
@@ -0,0 +1,81 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import net.taler.common.Duration.Companion.FOREVER
+import kotlin.math.max
+
+expect fun nowMillis(): Long
+
+@Serializable
+data class Timestamp(
+    @SerialName("t_ms")
+    val ms: Long
+) : Comparable<Timestamp> {
+
+    companion object {
+        const val NEVER: Long = -1  // TODO or UINT64_MAX?
+        fun now(): Timestamp = Timestamp(nowMillis())
+    }
+
+    /**
+     * Returns a copy of this [Timestamp] rounded to seconds.
+     */
+    fun truncateSeconds(): Timestamp {
+        if (ms == NEVER) return Timestamp(ms)
+        return Timestamp((ms / 1000L) * 1000L)
+    }
+
+    operator fun minus(other: Timestamp): Duration = when {
+        ms == NEVER -> Duration(FOREVER)
+        other.ms == NEVER -> throw Error("Invalid argument for timestamp comparision")
+        ms < other.ms -> Duration(0)
+        else -> Duration(ms - other.ms)
+    }
+
+    operator fun minus(other: Duration): Timestamp = when {
+        ms == NEVER -> this
+        other.ms == FOREVER -> Timestamp(0)
+        else -> Timestamp(max(0, ms - other.ms))
+    }
+
+    override fun compareTo(other: Timestamp): Int {
+        return if (ms == NEVER) {
+            if (other.ms == NEVER) 0
+            else 1
+        } else {
+            if (other.ms == NEVER) -1
+            else ms.compareTo(other.ms)
+        }
+    }
+
+}
+
+@Serializable
+data class Duration(
+    /**
+     * Duration in milliseconds.
+     */
+    @SerialName("d_ms")
+    val ms: Long
+) {
+    companion object {
+        const val FOREVER: Long = -1  // TODO or UINT64_MAX?
+    }
+}
diff --git a/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Version.kt b/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Version.kt
new file mode 100644
index 0000000..8774115
--- /dev/null
+++ b/taler-kotlin-common/src/commonMain/kotlin/net/taler/common/Version.kt
@@ -0,0 +1,70 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlin.math.sign
+
+/**
+ * Semantic versioning, but libtool-style.
+ * See https://www.gnu.org/software/libtool/manual/html_node/Libtool-versioning.html
+ */
+data class Version(
+    val current: Int,
+    val revision: Int,
+    val age: Int
+) {
+    companion object {
+        fun parse(v: String): Version? {
+            val elements = v.split(":")
+            if (elements.size != 3) return null
+            val (currentStr, revisionStr, ageStr) = elements
+            val current = currentStr.toIntOrNull()
+            val revision = revisionStr.toIntOrNull()
+            val age = ageStr.toIntOrNull()
+            if (current == null || revision == null || age == null) return null
+            return Version(current, revision, age)
+        }
+    }
+
+    /**
+     * Compare two libtool-style versions.
+     *
+     * Returns a [VersionMatchResult] or null if the given version was null.
+     */
+    fun compare(other: Version?): VersionMatchResult? {
+        if (other == null) return null
+        val compatible = current - age <= other.current &&
+                current >= other.current - other.age
+        val currentCmp = sign((current - other.current).toDouble()).toInt()
+        return VersionMatchResult(compatible, currentCmp)
+    }
+
+    /**
+     * Result of comparing two libtool versions.
+     */
+    data class VersionMatchResult(
+        /**
+         * Is the first version compatible with the second?
+         */
+        val compatible: Boolean,
+        /**
+         * Is the first version older (-1), newer (+1) or identical (0)?
+         */
+        val currentCmp: Int
+    )
+
+}
diff --git a/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/AmountTest.kt b/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/AmountTest.kt
new file mode 100644
index 0000000..e184307
--- /dev/null
+++ b/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/AmountTest.kt
@@ -0,0 +1,234 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlin.random.Random
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+import kotlin.test.fail
+
+class AmountTest {
+
+    companion object {
+        fun getRandomAmount() = getRandomAmount(getRandomString(1, Random.nextInt(1, 12)))
+        fun getRandomAmount(currency: String): Amount {
+            val value = Random.nextLong(0, Amount.MAX_VALUE)
+            val fraction = Random.nextInt(0, Amount.MAX_FRACTION)
+            return Amount(currency, value, fraction)
+        }
+    }
+
+    @Test
+    fun testFromJSONString() {
+        var str = "TESTKUDOS:23.42"
+        var amount = Amount.fromJSONString(str)
+        assertEquals(str, amount.toJSONString())
+        assertEquals("TESTKUDOS", amount.currency)
+        assertEquals(23, amount.value)
+        assertEquals((0.42 * 1e8).toInt(), amount.fraction)
+        assertEquals("23.42 TESTKUDOS", amount.toString())
+
+        str = "EUR:500000000.00000001"
+        amount = Amount.fromJSONString(str)
+        assertEquals(str, amount.toJSONString())
+        assertEquals("EUR", amount.currency)
+        assertEquals(500000000, amount.value)
+        assertEquals(1, amount.fraction)
+        assertEquals("500000000.00000001 EUR", amount.toString())
+
+        str = "EUR:1500000000.00000003"
+        amount = Amount.fromJSONString(str)
+        assertEquals(str, amount.toJSONString())
+        assertEquals("EUR", amount.currency)
+        assertEquals(1500000000, amount.value)
+        assertEquals(3, amount.fraction)
+        assertEquals("1500000000.00000003 EUR", amount.toString())
+    }
+
+    @Test
+    fun testFromJSONStringAcceptsMaxValuesRejectsAbove() {
+        val maxValue = 4503599627370496
+        val str = "TESTKUDOS123:$maxValue.99999999"
+        val amount = Amount.fromJSONString(str)
+        assertEquals(str, amount.toJSONString())
+        assertEquals("TESTKUDOS123", amount.currency)
+        assertEquals(maxValue, amount.value)
+        assertEquals("$maxValue.99999999 TESTKUDOS123", amount.toString())
+
+        // longer currency not accepted
+        assertThrows<AmountParserException>("longer currency was accepted") {
+            Amount.fromJSONString("TESTKUDOS1234:$maxValue.99999999")
+        }
+
+        // max value + 1 not accepted
+        assertThrows<AmountParserException>("max value + 1 was accepted") {
+            Amount.fromJSONString("TESTKUDOS123:${maxValue + 1}.99999999")
+        }
+
+        // max fraction + 1 not accepted
+        assertThrows<AmountParserException>("max fraction + 1 was accepted") {
+            Amount.fromJSONString("TESTKUDOS123:$maxValue.999999990")
+        }
+    }
+
+    @Test
+    fun testFromJSONStringRejections() {
+        assertThrows<AmountParserException> {
+            Amount.fromJSONString("TESTKUDOS:0,5")
+        }
+        assertThrows<AmountParserException> {
+            Amount.fromJSONString("+TESTKUDOS:0.5")
+        }
+        assertThrows<AmountParserException> {
+            Amount.fromJSONString("0.5")
+        }
+        assertThrows<AmountParserException> {
+            Amount.fromJSONString(":0.5")
+        }
+        assertThrows<AmountParserException> {
+            Amount.fromJSONString("EUR::0.5")
+        }
+        assertThrows<AmountParserException> {
+            Amount.fromJSONString("EUR:.5")
+        }
+    }
+
+    @Test
+    fun testAddition() {
+        assertEquals(
+            Amount.fromJSONString("EUR:2"),
+            Amount.fromJSONString("EUR:1") + Amount.fromJSONString("EUR:1")
+        )
+        assertEquals(
+            Amount.fromJSONString("EUR:3"),
+            Amount.fromJSONString("EUR:1.5") + Amount.fromJSONString("EUR:1.5")
+        )
+        assertEquals(
+            Amount.fromJSONString("EUR:500000000.00000002"),
+            Amount.fromJSONString("EUR:500000000.00000001") + Amount.fromJSONString("EUR:0.00000001")
+        )
+        assertThrows<AmountOverflowException>("addition didn't overflow") {
+            Amount.fromJSONString("EUR:4503599627370496.99999999") + Amount.fromJSONString("EUR:0.00000001")
+        }
+        assertThrows<AmountOverflowException>("addition didn't overflow") {
+            Amount.fromJSONString("EUR:4000000000000000") + Amount.fromJSONString("EUR:4000000000000000")
+        }
+    }
+
+    @Test
+    fun testTimes() {
+        assertEquals(
+            Amount.fromJSONString("EUR:2"),
+            Amount.fromJSONString("EUR:2") * 1
+        )
+        assertEquals(
+            Amount.fromJSONString("EUR:2"),
+            Amount.fromJSONString("EUR:1") * 2
+        )
+        assertEquals(
+            Amount.fromJSONString("EUR:4.5"),
+            Amount.fromJSONString("EUR:1.5") * 3
+        )
+        assertEquals(Amount.fromJSONString("EUR:0"), Amount.fromJSONString("EUR:1.11") * 0)
+        assertEquals(Amount.fromJSONString("EUR:1.11"), Amount.fromJSONString("EUR:1.11") * 1)
+        assertEquals(Amount.fromJSONString("EUR:2.22"), Amount.fromJSONString("EUR:1.11") * 2)
+        assertEquals(Amount.fromJSONString("EUR:3.33"), Amount.fromJSONString("EUR:1.11") * 3)
+        assertEquals(Amount.fromJSONString("EUR:4.44"), Amount.fromJSONString("EUR:1.11") * 4)
+        assertEquals(Amount.fromJSONString("EUR:5.55"), Amount.fromJSONString("EUR:1.11") * 5)
+        assertEquals(
+            Amount.fromJSONString("EUR:1500000000.00000003"),
+            Amount.fromJSONString("EUR:500000000.00000001") * 3
+        )
+        assertThrows<AmountOverflowException>("times didn't overflow") {
+            Amount.fromJSONString("EUR:4000000000000000") * 2
+        }
+    }
+
+    @Test
+    fun testSubtraction() {
+        assertEquals(
+            Amount.fromJSONString("EUR:0"),
+            Amount.fromJSONString("EUR:1") - Amount.fromJSONString("EUR:1")
+        )
+        assertEquals(
+            Amount.fromJSONString("EUR:1.5"),
+            Amount.fromJSONString("EUR:3") - Amount.fromJSONString("EUR:1.5")
+        )
+        assertEquals(
+            Amount.fromJSONString("EUR:500000000.00000001"),
+            Amount.fromJSONString("EUR:500000000.00000002") - Amount.fromJSONString("EUR:0.00000001")
+        )
+        assertThrows<AmountOverflowException>("subtraction didn't underflow") {
+            Amount.fromJSONString("EUR:23.42") - Amount.fromJSONString("EUR:42.23")
+        }
+        assertThrows<AmountOverflowException>("subtraction didn't underflow") {
+            Amount.fromJSONString("EUR:0.5") - Amount.fromJSONString("EUR:0.50000001")
+        }
+    }
+
+    @Test
+    fun testIsZero() {
+        assertTrue(Amount.zero("EUR").isZero())
+        assertTrue(Amount.fromJSONString("EUR:0").isZero())
+        assertTrue(Amount.fromJSONString("EUR:0.0").isZero())
+        assertTrue(Amount.fromJSONString("EUR:0.00000").isZero())
+        assertTrue((Amount.fromJSONString("EUR:1.001") - Amount.fromJSONString("EUR:1.001")).isZero())
+
+        assertFalse(Amount.fromJSONString("EUR:0.00000001").isZero())
+        assertFalse(Amount.fromJSONString("EUR:1.0").isZero())
+        assertFalse(Amount.fromJSONString("EUR:0001.0").isZero())
+    }
+
+    @Test
+    fun testComparision() {
+        assertTrue(Amount.fromJSONString("EUR:0") <= Amount.fromJSONString("EUR:0"))
+        assertTrue(Amount.fromJSONString("EUR:0") <= Amount.fromJSONString("EUR:0.00000001"))
+        assertTrue(Amount.fromJSONString("EUR:0") < Amount.fromJSONString("EUR:0.00000001"))
+        assertTrue(Amount.fromJSONString("EUR:0") < Amount.fromJSONString("EUR:1"))
+        assertEquals(Amount.fromJSONString("EUR:0"), Amount.fromJSONString("EUR:0"))
+        assertEquals(Amount.fromJSONString("EUR:42"), Amount.fromJSONString("EUR:42"))
+        assertEquals(
+            Amount.fromJSONString("EUR:42.00000001"),
+            Amount.fromJSONString("EUR:42.00000001")
+        )
+        assertTrue(Amount.fromJSONString("EUR:42.00000001") >= Amount.fromJSONString("EUR:42.00000001"))
+        assertTrue(Amount.fromJSONString("EUR:42.00000002") >= Amount.fromJSONString("EUR:42.00000001"))
+        assertTrue(Amount.fromJSONString("EUR:42.00000002") > Amount.fromJSONString("EUR:42.00000001"))
+        assertTrue(Amount.fromJSONString("EUR:0.00000002") > Amount.fromJSONString("EUR:0.00000001"))
+        assertTrue(Amount.fromJSONString("EUR:0.00000001") > Amount.fromJSONString("EUR:0"))
+        assertTrue(Amount.fromJSONString("EUR:2") > Amount.fromJSONString("EUR:1"))
+
+        assertThrows<IllegalStateException>("could compare amounts with different currencies") {
+            Amount.fromJSONString("EUR:0.5") < Amount.fromJSONString("USD:0.50000001")
+        }
+    }
+
+    private inline fun <reified T : Throwable> assertThrows(
+        msg: String? = null,
+        function: () -> Any
+    ) {
+        try {
+            function.invoke()
+            fail(msg)
+        } catch (e: Exception) {
+            assertTrue(e is T)
+        }
+    }
+
+}
diff --git a/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/TestUtils.kt b/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/TestUtils.kt
new file mode 100644
index 0000000..e3a6c17
--- /dev/null
+++ b/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/TestUtils.kt
@@ -0,0 +1,26 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlin.random.Random
+
+private val charPool: List<Char> = ('a'..'z') + ('A'..'Z') + ('0'..'9')
+fun getRandomString(minLength: Int = 1, maxLength: Int = Random.nextInt(0, 1337)) =
+    (minLength..maxLength)
+        .map { Random.nextInt(0, charPool.size) }
+        .map(charPool::get)
+        .joinToString("")
diff --git a/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/VersionTest.kt b/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/VersionTest.kt
new file mode 100644
index 0000000..f4f17ea
--- /dev/null
+++ b/taler-kotlin-common/src/commonTest/kotlin/net/taler/common/VersionTest.kt
@@ -0,0 +1,65 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+class VersionTest {
+
+    @Test
+    fun testParse() {
+        assertNull(Version.parse(""))
+        assertNull(Version.parse("foo"))
+        assertNull(Version.parse("foo:bar:foo"))
+        assertNull(Version.parse("0:0:0:"))
+        assertNull(Version.parse("0:0:"))
+        assertEquals(Version(0, 0, 0), Version.parse("0:0:0"))
+        assertEquals(Version(1, 2, 3), Version.parse("1:2:3"))
+        assertEquals(Version(1337, 42, 23), Version.parse("1337:42:23"))
+    }
+
+    @Test
+    fun testComparision() {
+        assertEquals(
+            Version.VersionMatchResult(true, 0),
+            Version.parse("0:0:0")!!.compare(Version.parse("0:0:0"))
+        )
+        assertEquals(
+            Version.VersionMatchResult(true, -1),
+            Version.parse("0:0:0")!!.compare(Version.parse("1:0:1"))
+        )
+        assertEquals(
+            Version.VersionMatchResult(true, -1),
+            Version.parse("0:0:0")!!.compare(Version.parse("1:5:1"))
+        )
+        assertEquals(
+            Version.VersionMatchResult(false, -1),
+            Version.parse("0:0:0")!!.compare(Version.parse("1:5:0"))
+        )
+        assertEquals(
+            Version.VersionMatchResult(false, 1),
+            Version.parse("1:0:0")!!.compare(Version.parse("0:5:0"))
+        )
+        assertEquals(
+            Version.VersionMatchResult(true, 0),
+            Version.parse("1:0:1")!!.compare(Version.parse("1:5:1"))
+        )
+    }
+
+}
diff --git a/taler-kotlin-common/src/jsMain/kotlin/net/taler/common/Time.kt b/taler-kotlin-common/src/jsMain/kotlin/net/taler/common/Time.kt
new file mode 100644
index 0000000..b114022
--- /dev/null
+++ b/taler-kotlin-common/src/jsMain/kotlin/net/taler/common/Time.kt
@@ -0,0 +1,23 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlin.js.Date
+
+actual fun nowMillis(): Long {
+    return Date().getMilliseconds().toLong()
+}
diff --git a/taler-kotlin-common/src/jvmMain/kotlin/net/taler/common/Time.kt b/taler-kotlin-common/src/jvmMain/kotlin/net/taler/common/Time.kt
new file mode 100644
index 0000000..6cd9040
--- /dev/null
+++ b/taler-kotlin-common/src/jvmMain/kotlin/net/taler/common/Time.kt
@@ -0,0 +1,21 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+actual fun nowMillis(): Long {
+    return System.currentTimeMillis()
+}
diff --git a/taler-kotlin-common/src/main/AndroidManifest.xml b/taler-kotlin-common/src/main/AndroidManifest.xml
deleted file mode 100644
index 902ddc1..0000000
--- a/taler-kotlin-common/src/main/AndroidManifest.xml
+++ /dev/null
@@ -1,24 +0,0 @@
-<!--
-  ~ This file is part of GNU Taler
-  ~ (C) 2020 Taler Systems S.A.
-  ~
-  ~ GNU Taler is free software; you can redistribute it and/or modify it under the
-  ~ terms of the GNU General Public License as published by the Free Software
-  ~ Foundation; either version 3, or (at your option) any later version.
-  ~
-  ~ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
-  ~ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
-  ~ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
-  ~
-  ~ You should have received a copy of the GNU General Public License along with
-  ~ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
-  -->
-
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="net.taler.common">
-
-    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
-    <uses-permission android:name="android.permission.INTERNET" />
-    <uses-permission android:name="android.permission.NFC" />
-
-</manifest>
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/Amount.kt b/taler-kotlin-common/src/main/java/net/taler/common/Amount.kt
deleted file mode 100644
index 992f93b..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/Amount.kt
+++ /dev/null
@@ -1,246 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import android.annotation.SuppressLint
-import com.fasterxml.jackson.core.JsonGenerator
-import com.fasterxml.jackson.core.JsonParser
-import com.fasterxml.jackson.databind.DeserializationContext
-import com.fasterxml.jackson.databind.JsonMappingException
-import com.fasterxml.jackson.databind.SerializerProvider
-import com.fasterxml.jackson.databind.annotation.JsonDeserialize
-import com.fasterxml.jackson.databind.annotation.JsonSerialize
-import com.fasterxml.jackson.databind.deser.std.StdDeserializer
-import com.fasterxml.jackson.databind.ser.std.StdSerializer
-import kotlinx.serialization.Decoder
-import kotlinx.serialization.Encoder
-import kotlinx.serialization.KSerializer
-import kotlinx.serialization.Serializable
-import kotlinx.serialization.Serializer
-import org.json.JSONObject
-import java.lang.Math.floorDiv
-import kotlin.math.pow
-import kotlin.math.roundToInt
-
-class AmountParserException(msg: String? = null, cause: Throwable? = null) : Exception(msg, cause)
-class AmountOverflowException(msg: String? = null, cause: Throwable? = null) : Exception(msg, cause)
-
-@Serializable(with = KotlinXAmountSerializer::class)
-@JsonSerialize(using = AmountSerializer::class)
-@JsonDeserialize(using = AmountDeserializer::class)
-data class Amount(
-    /**
-     * name of the currency using either a three-character ISO 4217 currency code,
-     * or a regional currency identifier starting with a "*" followed by at most 10 characters.
-     * ISO 4217 exponents in the name are not supported,
-     * although the "fraction" is corresponds to an ISO 4217 exponent of 6.
-     */
-    val currency: String,
-
-    /**
-     * The integer part may be at most 2^52.
-     * Note that "1" here would correspond to 1 EUR or 1 USD, depending on currency, not 1 cent.
-     */
-    val value: Long,
-
-    /**
-     * Unsigned 32 bit fractional value to be added to value representing
-     * an additional currency fraction, in units of one hundred millionth (1e-8)
-     * of the base currency value.  For example, a fraction
-     * of 50_000_000 would correspond to 50 cents.
-     */
-    val fraction: Int
-) : Comparable<Amount> {
-
-    companion object {
-
-        private const val FRACTIONAL_BASE: Int = 100000000 // 1e8
-
-        @Suppress("unused")
-        private val REGEX = Regex("""^[-_*A-Za-z0-9]{1,12}:([0-9]+)\.?([0-9]+)?$""")
-        private val REGEX_CURRENCY = Regex("""^[-_*A-Za-z0-9]{1,12}$""")
-        private val MAX_VALUE = 2.0.pow(52)
-        private const val MAX_FRACTION_LENGTH = 8
-        private const val MAX_FRACTION = 99_999_999
-
-        @Throws(AmountParserException::class)
-        @SuppressLint("CheckedExceptions")
-        fun zero(currency: String): Amount {
-            return Amount(checkCurrency(currency), 0, 0)
-        }
-
-        @Throws(AmountParserException::class)
-        @SuppressLint("CheckedExceptions")
-        fun fromJSONString(str: String): Amount {
-            val split = str.split(":")
-            if (split.size != 2) throw AmountParserException("Invalid Amount Format")
-            return fromString(split[0], split[1])
-        }
-
-        @Throws(AmountParserException::class)
-        @SuppressLint("CheckedExceptions")
-        fun fromString(currency: String, str: String): Amount {
-            // value
-            val valueSplit = str.split(".")
-            val value = checkValue(valueSplit[0].toLongOrNull())
-            // fraction
-            val fraction: Int = if (valueSplit.size > 1) {
-                val fractionStr = valueSplit[1]
-                if (fractionStr.length > MAX_FRACTION_LENGTH)
-                    throw AmountParserException("Fraction $fractionStr too long")
-                val fraction = "0.$fractionStr".toDoubleOrNull()
-                    ?.times(FRACTIONAL_BASE)
-                    ?.roundToInt()
-                checkFraction(fraction)
-            } else 0
-            return Amount(checkCurrency(currency), value, fraction)
-        }
-
-        @Throws(AmountParserException::class)
-        @SuppressLint("CheckedExceptions")
-        fun fromJsonObject(json: JSONObject): Amount {
-            val currency = checkCurrency(json.optString("currency"))
-            val value = checkValue(json.optString("value").toLongOrNull())
-            val fraction = checkFraction(json.optString("fraction").toIntOrNull())
-            return Amount(currency, value, fraction)
-        }
-
-        @Throws(AmountParserException::class)
-        private fun checkCurrency(currency: String): String {
-            if (!REGEX_CURRENCY.matches(currency))
-                throw AmountParserException("Invalid currency: $currency")
-            return currency
-        }
-
-        @Throws(AmountParserException::class)
-        private fun checkValue(value: Long?): Long {
-            if (value == null || value > MAX_VALUE)
-                throw AmountParserException("Value $value greater than $MAX_VALUE")
-            return value
-        }
-
-        @Throws(AmountParserException::class)
-        private fun checkFraction(fraction: Int?): Int {
-            if (fraction == null || fraction > MAX_FRACTION)
-                throw AmountParserException("Fraction $fraction greater than $MAX_FRACTION")
-            return fraction
-        }
-
-    }
-
-    val amountStr: String
-        get() = if (fraction == 0) "$value" else {
-            var f = fraction
-            var fractionStr = ""
-            while (f > 0) {
-                fractionStr += f / (FRACTIONAL_BASE / 10)
-                f = (f * 10) % FRACTIONAL_BASE
-            }
-            "$value.$fractionStr"
-        }
-
-    @Throws(AmountOverflowException::class)
-    operator fun plus(other: Amount): Amount {
-        check(currency == other.currency) { "Can only subtract from same currency" }
-        val resultValue = value + other.value + floorDiv(fraction + other.fraction, FRACTIONAL_BASE)
-        if (resultValue > MAX_VALUE)
-            throw AmountOverflowException()
-        val resultFraction = (fraction + other.fraction) % FRACTIONAL_BASE
-        return Amount(currency, resultValue, resultFraction)
-    }
-
-    @Throws(AmountOverflowException::class)
-    operator fun times(factor: Int): Amount {
-        if (factor == 0) return zero(currency)
-        var result = this
-        for (i in 1 until factor) result += this
-        return result
-    }
-
-    @Throws(AmountOverflowException::class)
-    operator fun minus(other: Amount): Amount {
-        check(currency == other.currency) { "Can only subtract from same currency" }
-        var resultValue = value
-        var resultFraction = fraction
-        if (resultFraction < other.fraction) {
-            if (resultValue < 1L)
-                throw AmountOverflowException()
-            resultValue--
-            resultFraction += FRACTIONAL_BASE
-        }
-        check(resultFraction >= other.fraction)
-        resultFraction -= other.fraction
-        if (resultValue < other.value)
-            throw AmountOverflowException()
-        resultValue -= other.value
-        return Amount(currency, resultValue, resultFraction)
-    }
-
-    fun isZero(): Boolean {
-        return value == 0L && fraction == 0
-    }
-
-    fun toJSONString(): String {
-        return "$currency:$amountStr"
-    }
-
-    override fun toString(): String {
-        return "$amountStr $currency"
-    }
-
-    override fun compareTo(other: Amount): Int {
-        check(currency == other.currency) { "Can only compare amounts with the same currency" }
-        when {
-            value == other.value -> {
-                if (fraction < other.fraction) return -1
-                if (fraction > other.fraction) return 1
-                return 0
-            }
-            value < other.value -> return -1
-            else -> return 1
-        }
-    }
-
-}
-
-@Serializer(forClass = Amount::class)
-object KotlinXAmountSerializer: KSerializer<Amount> {
-    override fun serialize(encoder: Encoder, value: Amount) {
-        encoder.encodeString(value.toJSONString())
-    }
-
-    override fun deserialize(decoder: Decoder): Amount {
-        return Amount.fromJSONString(decoder.decodeString())
-    }
-}
-
-class AmountSerializer : StdSerializer<Amount>(Amount::class.java) {
-    override fun serialize(value: Amount, gen: JsonGenerator, provider: SerializerProvider) {
-        gen.writeString(value.toJSONString())
-    }
-}
-
-class AmountDeserializer : StdDeserializer<Amount>(Amount::class.java) {
-    override fun deserialize(p: JsonParser, ctxt: DeserializationContext): Amount {
-        val node = p.codec.readValue(p, String::class.java)
-        try {
-            return Amount.fromJSONString(node)
-        } catch (e: AmountParserException) {
-            throw JsonMappingException(p, "Error parsing Amount", e)
-        }
-    }
-}
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/AndroidUtils.kt b/taler-kotlin-common/src/main/java/net/taler/common/AndroidUtils.kt
deleted file mode 100644
index b46f306..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/AndroidUtils.kt
+++ /dev/null
@@ -1,123 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import android.content.Context
-import android.content.Context.CONNECTIVITY_SERVICE
-import android.content.Intent
-import android.content.pm.PackageManager.MATCH_DEFAULT_ONLY
-import android.net.ConnectivityManager
-import android.net.NetworkCapabilities.NET_CAPABILITY_INTERNET
-import android.os.Build.VERSION.SDK_INT
-import android.os.Looper
-import android.text.format.DateUtils.DAY_IN_MILLIS
-import android.text.format.DateUtils.FORMAT_ABBREV_ALL
-import android.text.format.DateUtils.FORMAT_ABBREV_MONTH
-import android.text.format.DateUtils.FORMAT_ABBREV_RELATIVE
-import android.text.format.DateUtils.FORMAT_NO_YEAR
-import android.text.format.DateUtils.FORMAT_SHOW_DATE
-import android.text.format.DateUtils.FORMAT_SHOW_TIME
-import android.text.format.DateUtils.FORMAT_SHOW_YEAR
-import android.text.format.DateUtils.MINUTE_IN_MILLIS
-import android.text.format.DateUtils.formatDateTime
-import android.text.format.DateUtils.getRelativeTimeSpanString
-import android.view.View
-import android.view.View.INVISIBLE
-import android.view.View.VISIBLE
-import android.view.inputmethod.InputMethodManager
-import androidx.core.content.ContextCompat.getSystemService
-import androidx.fragment.app.Fragment
-import androidx.navigation.NavDirections
-import androidx.navigation.fragment.findNavController
-
-fun View.fadeIn(endAction: () -> Unit = {}) {
-    if (visibility == VISIBLE && alpha == 1f) return
-    alpha = 0f
-    visibility = VISIBLE
-    animate().alpha(1f).withEndAction {
-        if (context != null) endAction.invoke()
-    }.start()
-}
-
-fun View.fadeOut(endAction: () -> Unit = {}) {
-    if (visibility == INVISIBLE) return
-    animate().alpha(0f).withEndAction {
-        if (context == null) return@withEndAction
-        visibility = INVISIBLE
-        alpha = 1f
-        endAction.invoke()
-    }.start()
-}
-
-fun View.hideKeyboard() {
-    getSystemService(context, InputMethodManager::class.java)
-        ?.hideSoftInputFromWindow(windowToken, 0)
-}
-
-fun assertUiThread() {
-    check(Looper.getMainLooper().thread == Thread.currentThread())
-}
-
-/**
- * Use this with 'when' expressions when you need it to handle all possibilities/branches.
- */
-val <T> T.exhaustive: T
-    get() = this
-
-fun Context.isOnline(): Boolean {
-    val cm = getSystemService(CONNECTIVITY_SERVICE) as ConnectivityManager
-    return if (SDK_INT < 29) {
-        @Suppress("DEPRECATION")
-        cm.activeNetworkInfo?.isConnected == true
-    } else {
-        val capabilities = cm.getNetworkCapabilities(cm.activeNetwork) ?: return false
-        capabilities.hasCapability(NET_CAPABILITY_INTERNET)
-    }
-}
-
-fun Intent.isSafe(context: Context): Boolean {
-    return context.packageManager.queryIntentActivities(this, MATCH_DEFAULT_ONLY).isNotEmpty()
-}
-
-fun Fragment.navigate(directions: NavDirections) = findNavController().navigate(directions)
-
-fun Long.toRelativeTime(context: Context): CharSequence {
-    val now = System.currentTimeMillis()
-    return if (now - this > DAY_IN_MILLIS * 2) {
-        val flags = FORMAT_SHOW_TIME or FORMAT_SHOW_DATE or FORMAT_ABBREV_MONTH or FORMAT_NO_YEAR
-        formatDateTime(context, this, flags)
-    } else getRelativeTimeSpanString(this, now, MINUTE_IN_MILLIS, FORMAT_ABBREV_RELATIVE)
-}
-
-fun Long.toAbsoluteTime(context: Context): CharSequence {
-    val flags = FORMAT_SHOW_TIME or FORMAT_SHOW_DATE or FORMAT_SHOW_YEAR
-    return formatDateTime(context, this, flags)
-}
-
-fun Long.toShortDate(context: Context): CharSequence {
-    val flags = FORMAT_SHOW_DATE or FORMAT_SHOW_YEAR or FORMAT_ABBREV_ALL
-    return formatDateTime(context, this, flags)
-}
-
-fun Version.getIncompatibleStringOrNull(context: Context, otherVersion: String): String? {
-    val other = Version.parse(otherVersion) ?: return context.getString(R.string.version_invalid)
-    val match = compare(other) ?: return context.getString(R.string.version_invalid)
-    if (match.compatible) return null
-    if (match.currentCmp < 0) return context.getString(R.string.version_too_old)
-    if (match.currentCmp > 0) return context.getString(R.string.version_too_new)
-    throw AssertionError("$this == $other")
-}
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/ByteArrayUtils.kt b/taler-kotlin-common/src/main/java/net/taler/common/ByteArrayUtils.kt
deleted file mode 100644
index fba0d07..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/ByteArrayUtils.kt
+++ /dev/null
@@ -1,53 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-object ByteArrayUtils {
-
-    private const val HEX_CHARS = "0123456789ABCDEF"
-
-    fun hexStringToByteArray(data: String): ByteArray {
-        val result = ByteArray(data.length / 2)
-
-        for (i in data.indices step 2) {
-            val firstIndex = HEX_CHARS.indexOf(data[i])
-            val secondIndex = HEX_CHARS.indexOf(data[i + 1])
-
-            val octet = firstIndex.shl(4).or(secondIndex)
-            result[i.shr(1)] = octet.toByte()
-        }
-        return result
-    }
-
-
-    private val HEX_CHARS_ARRAY = HEX_CHARS.toCharArray()
-
-    @Suppress("unused")
-    fun toHex(byteArray: ByteArray): String {
-        val result = StringBuffer()
-
-        byteArray.forEach {
-            val octet = it.toInt()
-            val firstIndex = (octet and 0xF0).ushr(4)
-            val secondIndex = octet and 0x0F
-            result.append(HEX_CHARS_ARRAY[firstIndex])
-            result.append(HEX_CHARS_ARRAY[secondIndex])
-        }
-        return result.toString()
-    }
-
-}
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/CombinedLiveData.kt b/taler-kotlin-common/src/main/java/net/taler/common/CombinedLiveData.kt
deleted file mode 100644
index 4e7016b..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/CombinedLiveData.kt
+++ /dev/null
@@ -1,51 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import androidx.lifecycle.LiveData
-import androidx.lifecycle.MediatorLiveData
-import androidx.lifecycle.Observer
-
-class CombinedLiveData<T, K, S>(
-    source1: LiveData<T>,
-    source2: LiveData<K>,
-    private val combine: (data1: T?, data2: K?) -> S
-) : MediatorLiveData<S>() {
-
-    private var data1: T? = null
-    private var data2: K? = null
-
-    init {
-        super.addSource(source1) { t ->
-            data1 = t
-            value = combine(data1, data2)
-        }
-        super.addSource(source2) { k ->
-            data2 = k
-            value = combine(data1, data2)
-        }
-    }
-
-    override fun <S : Any?> addSource(source: LiveData<S>, onChanged: Observer<in S>) {
-        throw UnsupportedOperationException()
-    }
-
-    override fun <T : Any?> removeSource(toRemote: LiveData<T>) {
-        throw UnsupportedOperationException()
-    }
-
-}
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/ContractTerms.kt b/taler-kotlin-common/src/main/java/net/taler/common/ContractTerms.kt
deleted file mode 100644
index b891ef7..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/ContractTerms.kt
+++ /dev/null
@@ -1,91 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import androidx.annotation.RequiresApi
-import com.fasterxml.jackson.annotation.JsonIgnore
-import com.fasterxml.jackson.annotation.JsonIgnoreProperties
-import com.fasterxml.jackson.annotation.JsonInclude
-import com.fasterxml.jackson.annotation.JsonInclude.Include.NON_EMPTY
-import com.fasterxml.jackson.annotation.JsonInclude.Include.NON_NULL
-import com.fasterxml.jackson.annotation.JsonProperty
-import kotlinx.serialization.SerialName
-import kotlinx.serialization.Serializable
-import net.taler.common.TalerUtils.getLocalizedString
-
-@Serializable
-@JsonIgnoreProperties(ignoreUnknown = true)
-data class ContractTerms(
-    val summary: String,
-    @SerialName("summary_i18n")
-    val summaryI18n: Map<String, String>? = null,
-    val amount: Amount,
-    @SerialName("fulfillment_url")
-    val fulfillmentUrl: String,
-    val products: List<ContractProduct>
-)
-
-@JsonInclude(NON_NULL)
-abstract class Product {
-    @get:JsonProperty("product_id")
-    abstract val productId: String?
-    abstract val description: String
-
-    @get:JsonProperty("description_i18n")
-    abstract val descriptionI18n: Map<String, String>?
-    abstract val price: Amount
-
-    @get:JsonProperty("delivery_location")
-    abstract val location: String?
-    abstract val image: String?
-
-    @get:JsonIgnore
-    val localizedDescription: String
-        @RequiresApi(26)
-        get() = getLocalizedString(descriptionI18n, description)
-}
-
-@Serializable
-data class ContractProduct(
-    @SerialName("product_id")
-    override val productId: String? = null,
-    override val description: String,
-    @SerialName("description_i18n")
-    override val descriptionI18n: Map<String, String>? = null,
-    override val price: Amount,
-    @SerialName("delivery_location")
-    override val location: String? = null,
-    override val image: String? = null,
-    val quantity: Int
-) : Product() {
-    @get:JsonIgnore
-    val totalPrice: Amount by lazy {
-        price * quantity
-    }
-}
-
-data class ContractMerchant(
-    val name: String
-)
-
-@Serializable
-@JsonInclude(NON_EMPTY)
-class Timestamp(
-    @SerialName("t_ms")
-    @JsonProperty("t_ms")
-    val ms: Long
-)
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/Event.kt b/taler-kotlin-common/src/main/java/net/taler/common/Event.kt
deleted file mode 100644
index 779247f..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/Event.kt
+++ /dev/null
@@ -1,51 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import androidx.lifecycle.LiveData
-import androidx.lifecycle.Observer
-import java.util.concurrent.atomic.AtomicBoolean
-
-/**
- * Used as a wrapper for data that is exposed via a [LiveData] that represents an one-time event.
- */
-open class Event<out T>(private val content: T) {
-
-    private val isConsumed = AtomicBoolean(false)
-
-    /**
-     * Returns the content and prevents its use again.
-     */
-    fun getIfNotConsumed(): T? {
-        return if (isConsumed.compareAndSet(false, true)) content else null
-    }
-
-}
-
-fun <T> T.toEvent() = Event(this)
-
-/**
- * An [Observer] for [Event]s, simplifying the pattern of checking if the [Event]'s content has
- * already been consumed.
- *
- * [onEvent] is *only* called if the [Event]'s contents has not been consumed.
- */
-class EventObserver<T>(private val onEvent: (T) -> Unit) : Observer<Event<T>> {
-    override fun onChanged(event: Event<T>?) {
-        event?.getIfNotConsumed()?.let { onEvent(it) }
-    }
-}
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/NfcManager.kt b/taler-kotlin-common/src/main/java/net/taler/common/NfcManager.kt
deleted file mode 100644
index 11e1e1e..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/NfcManager.kt
+++ /dev/null
@@ -1,234 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import android.app.Activity
-import android.content.Context
-import android.nfc.NfcAdapter
-import android.nfc.NfcAdapter.FLAG_READER_NFC_A
-import android.nfc.NfcAdapter.FLAG_READER_SKIP_NDEF_CHECK
-import android.nfc.NfcAdapter.getDefaultAdapter
-import android.nfc.Tag
-import android.nfc.tech.IsoDep
-import android.util.Log
-import net.taler.common.ByteArrayUtils.hexStringToByteArray
-import org.json.JSONObject
-import java.io.ByteArrayOutputStream
-import java.net.URL
-import javax.net.ssl.HttpsURLConnection
-
-@Suppress("unused")
-private const val TALER_AID = "A0000002471001"
-
-class NfcManager : NfcAdapter.ReaderCallback {
-
-    companion object {
-        const val TAG = "taler-merchant"
-
-        /**
-         * Returns true if NFC is supported and false otherwise.
-         */
-        fun hasNfc(context: Context): Boolean {
-            return getNfcAdapter(context) != null
-        }
-
-        /**
-         * Enables NFC reader mode. Don't forget to call [stop] afterwards.
-         */
-        fun start(activity: Activity, nfcManager: NfcManager) {
-            getNfcAdapter(activity)?.enableReaderMode(activity, nfcManager, nfcManager.flags, null)
-        }
-
-        /**
-         * Disables NFC reader mode. Call after [start].
-         */
-        fun stop(activity: Activity) {
-            getNfcAdapter(activity)?.disableReaderMode(activity)
-        }
-
-        private fun getNfcAdapter(context: Context): NfcAdapter? {
-            return getDefaultAdapter(context)
-        }
-    }
-
-    private val flags = FLAG_READER_NFC_A or FLAG_READER_SKIP_NDEF_CHECK
-
-    private var tagString: String? = null
-    private var currentTag: IsoDep? = null
-
-    fun setTagString(tagString: String) {
-        this.tagString = tagString
-    }
-
-    override fun onTagDiscovered(tag: Tag?) {
-
-        Log.v(TAG, "tag discovered")
-
-        val isoDep = IsoDep.get(tag)
-        isoDep.connect()
-
-        currentTag = isoDep
-
-        isoDep.transceive(apduSelectFile())
-
-        val tagString: String? = tagString
-        if (tagString != null) {
-            isoDep.transceive(apduPutTalerData(1, tagString.toByteArray()))
-        }
-
-        // FIXME: use better pattern for sleeps in between requests
-        // -> start with fast polling, poll more slowly if no requests are coming
-
-        while (true) {
-            try {
-                val reqFrame = isoDep.transceive(apduGetData())
-                if (reqFrame.size < 2) {
-                    Log.v(TAG, "request frame too small")
-                    break
-                }
-                val req = ByteArray(reqFrame.size - 2)
-                if (req.isEmpty()) {
-                    continue
-                }
-                reqFrame.copyInto(req, 0, 0, reqFrame.size - 2)
-                val jsonReq = JSONObject(req.toString(Charsets.UTF_8))
-                val reqId = jsonReq.getInt("id")
-                Log.v(TAG, "got request $jsonReq")
-                val jsonInnerReq = jsonReq.getJSONObject("request")
-                val method = jsonInnerReq.getString("method")
-                val urlStr = jsonInnerReq.getString("url")
-                Log.v(TAG, "url '$urlStr'")
-                Log.v(TAG, "method '$method'")
-                val url = URL(urlStr)
-                val conn: HttpsURLConnection = url.openConnection() as HttpsURLConnection
-                conn.setRequestProperty("Accept", "application/json")
-                conn.connectTimeout = 5000
-                conn.doInput = true
-                when (method) {
-                    "get" -> {
-                        conn.requestMethod = "GET"
-                    }
-                    "postJson" -> {
-                        conn.requestMethod = "POST"
-                        conn.doOutput = true
-                        conn.setRequestProperty("Content-Type", "application/json; utf-8")
-                        val body = jsonInnerReq.getString("body")
-                        conn.outputStream.write(body.toByteArray(Charsets.UTF_8))
-                    }
-                    else -> {
-                        throw Exception("method not supported")
-                    }
-                }
-                Log.v(TAG, "connecting")
-                conn.connect()
-                Log.v(TAG, "connected")
-
-                val statusCode = conn.responseCode
-                val tunnelResp = JSONObject()
-                tunnelResp.put("id", reqId)
-                tunnelResp.put("status", conn.responseCode)
-
-                if (statusCode == 200) {
-                    val stream = conn.inputStream
-                    val httpResp = stream.buffered().readBytes()
-                    tunnelResp.put("responseJson", JSONObject(httpResp.toString(Charsets.UTF_8)))
-                }
-
-                Log.v(TAG, "sending: $tunnelResp")
-
-                isoDep.transceive(apduPutTalerData(2, tunnelResp.toString().toByteArray()))
-            } catch (e: Exception) {
-                Log.v(TAG, "exception during NFC loop: $e")
-                break
-            }
-        }
-
-        isoDep.close()
-    }
-
-    private fun writeApduLength(stream: ByteArrayOutputStream, size: Int) {
-        when {
-            size == 0 -> {
-                // No size field needed!
-            }
-            size <= 255 -> // One byte size field
-                stream.write(size)
-            size <= 65535 -> {
-                stream.write(0)
-                // FIXME: is this supposed to be little or big endian?
-                stream.write(size and 0xFF)
-                stream.write((size ushr 8) and 0xFF)
-            }
-            else -> throw Error("payload too big")
-        }
-    }
-
-    private fun apduSelectFile(): ByteArray {
-        return hexStringToByteArray("00A4040007A0000002471001")
-    }
-
-    private fun apduPutData(payload: ByteArray): ByteArray {
-        val stream = ByteArrayOutputStream()
-
-        // Class
-        stream.write(0x00)
-
-        // Instruction 0xDA = put data
-        stream.write(0xDA)
-
-        // Instruction parameters
-        // (proprietary encoding)
-        stream.write(0x01)
-        stream.write(0x00)
-
-        writeApduLength(stream, payload.size)
-
-        stream.write(payload)
-
-        return stream.toByteArray()
-    }
-
-    private fun apduPutTalerData(talerInst: Int, payload: ByteArray): ByteArray {
-        val realPayload = ByteArrayOutputStream()
-        realPayload.write(talerInst)
-        realPayload.write(payload)
-        return apduPutData(realPayload.toByteArray())
-    }
-
-    private fun apduGetData(): ByteArray {
-        val stream = ByteArrayOutputStream()
-
-        // Class
-        stream.write(0x00)
-
-        // Instruction 0xCA = get data
-        stream.write(0xCA)
-
-        // Instruction parameters
-        // (proprietary encoding)
-        stream.write(0x01)
-        stream.write(0x00)
-
-        // Max expected response size, two
-        // zero bytes denotes 65536
-        stream.write(0x0)
-        stream.write(0x0)
-
-        return stream.toByteArray()
-    }
-
-}
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/QrCodeManager.kt b/taler-kotlin-common/src/main/java/net/taler/common/QrCodeManager.kt
deleted file mode 100644
index e2a9a55..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/QrCodeManager.kt
+++ /dev/null
@@ -1,42 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import android.graphics.Bitmap
-import android.graphics.Bitmap.Config.RGB_565
-import android.graphics.Color.BLACK
-import android.graphics.Color.WHITE
-import com.google.zxing.BarcodeFormat.QR_CODE
-import com.google.zxing.qrcode.QRCodeWriter
-
-object QrCodeManager {
-
-    fun makeQrCode(text: String, size: Int = 256): Bitmap {
-        val qrCodeWriter = QRCodeWriter()
-        val bitMatrix = qrCodeWriter.encode(text, QR_CODE, size, size)
-        val height = bitMatrix.height
-        val width = bitMatrix.width
-        val bmp = Bitmap.createBitmap(width, height, RGB_565)
-        for (x in 0 until width) {
-            for (y in 0 until height) {
-                bmp.setPixel(x, y, if (bitMatrix.get(x, y)) BLACK else WHITE)
-            }
-        }
-        return bmp
-    }
-
-}
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/SignedAmount.kt b/taler-kotlin-common/src/main/java/net/taler/common/SignedAmount.kt
deleted file mode 100644
index 03a0d6e..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/SignedAmount.kt
+++ /dev/null
@@ -1,40 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import android.annotation.SuppressLint
-
-data class SignedAmount(
-    val positive: Boolean,
-    val amount: Amount
-) {
-
-    companion object {
-        @Throws(AmountParserException::class)
-        @SuppressLint("CheckedExceptions")
-        fun fromJSONString(str: String): SignedAmount = when (str.substring(0, 1)) {
-            "-" -> SignedAmount(false, Amount.fromJSONString(str.substring(1)))
-            "+" -> SignedAmount(true, Amount.fromJSONString(str.substring(1)))
-            else -> SignedAmount(true, Amount.fromJSONString(str))
-        }
-    }
-
-    override fun toString(): String {
-        return if (positive) "$amount" else "-$amount"
-    }
-
-}
\ No newline at end of file
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/TalerUtils.kt b/taler-kotlin-common/src/main/java/net/taler/common/TalerUtils.kt
deleted file mode 100644
index 444caa4..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/TalerUtils.kt
+++ /dev/null
@@ -1,58 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import androidx.annotation.RequiresApi
-import androidx.core.os.LocaleListCompat
-import java.util.*
-import kotlin.collections.ArrayList
-
-object TalerUtils {
-
-    @RequiresApi(26)
-    fun getLocalizedString(map: Map<String, String>?, default: String): String {
-        // just return the default, if it is the only element
-        if (map == null) return default
-        // create a priority list of language ranges from system locales
-        val locales = LocaleListCompat.getDefault()
-        val priorityList = ArrayList<Locale.LanguageRange>(locales.size())
-        for (i in 0 until locales.size()) {
-            priorityList.add(Locale.LanguageRange(locales[i].toLanguageTag()))
-        }
-        // create a list of locales available in the given map
-        val availableLocales = map.keys.mapNotNull {
-            if (it == "_") return@mapNotNull null
-            val list = it.split("_")
-            when (list.size) {
-                1 -> Locale(list[0])
-                2 -> Locale(list[0], list[1])
-                3 -> Locale(list[0], list[1], list[2])
-                else -> null
-            }
-        }
-        val match = Locale.lookup(priorityList, availableLocales)
-        return match?.toString()?.let { map[it] } ?: default
-    }
-
-}
-
-/**
- * Returns the current time in milliseconds epoch rounded to nearest seconds.
- */
-fun now(): Long {
-    return ((System.currentTimeMillis() + 500) / 1000) * 1000
-}
diff --git a/taler-kotlin-common/src/main/java/net/taler/common/Version.kt b/taler-kotlin-common/src/main/java/net/taler/common/Version.kt
deleted file mode 100644
index 8774115..0000000
--- a/taler-kotlin-common/src/main/java/net/taler/common/Version.kt
+++ /dev/null
@@ -1,70 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import kotlin.math.sign
-
-/**
- * Semantic versioning, but libtool-style.
- * See https://www.gnu.org/software/libtool/manual/html_node/Libtool-versioning.html
- */
-data class Version(
-    val current: Int,
-    val revision: Int,
-    val age: Int
-) {
-    companion object {
-        fun parse(v: String): Version? {
-            val elements = v.split(":")
-            if (elements.size != 3) return null
-            val (currentStr, revisionStr, ageStr) = elements
-            val current = currentStr.toIntOrNull()
-            val revision = revisionStr.toIntOrNull()
-            val age = ageStr.toIntOrNull()
-            if (current == null || revision == null || age == null) return null
-            return Version(current, revision, age)
-        }
-    }
-
-    /**
-     * Compare two libtool-style versions.
-     *
-     * Returns a [VersionMatchResult] or null if the given version was null.
-     */
-    fun compare(other: Version?): VersionMatchResult? {
-        if (other == null) return null
-        val compatible = current - age <= other.current &&
-                current >= other.current - other.age
-        val currentCmp = sign((current - other.current).toDouble()).toInt()
-        return VersionMatchResult(compatible, currentCmp)
-    }
-
-    /**
-     * Result of comparing two libtool versions.
-     */
-    data class VersionMatchResult(
-        /**
-         * Is the first version compatible with the second?
-         */
-        val compatible: Boolean,
-        /**
-         * Is the first version older (-1), newer (+1) or identical (0)?
-         */
-        val currentCmp: Int
-    )
-
-}
diff --git a/taler-kotlin-common/src/main/res/drawable/selectable_background.xml b/taler-kotlin-common/src/main/res/drawable/selectable_background.xml
deleted file mode 100644
index 3c383a8..0000000
--- a/taler-kotlin-common/src/main/res/drawable/selectable_background.xml
+++ /dev/null
@@ -1,21 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--
-  ~ This file is part of GNU Taler
-  ~ (C) 2020 Taler Systems S.A.
-  ~
-  ~ GNU Taler is free software; you can redistribute it and/or modify it under the
-  ~ terms of the GNU General Public License as published by the Free Software
-  ~ Foundation; either version 3, or (at your option) any later version.
-  ~
-  ~ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
-  ~ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
-  ~ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
-  ~
-  ~ You should have received a copy of the GNU General Public License along with
-  ~ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
-  -->
-
-<selector xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:drawable="@color/selectedBackground" android:state_activated="true" />
-    <item android:drawable="@android:color/transparent" />
-</selector>
diff --git a/taler-kotlin-common/src/main/res/values-night/colors.xml b/taler-kotlin-common/src/main/res/values-night/colors.xml
deleted file mode 100644
index 10bdbb9..0000000
--- a/taler-kotlin-common/src/main/res/values-night/colors.xml
+++ /dev/null
@@ -1,5 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<resources>
-    <color name="highlightedBackground">#2E2E2E</color>
-    <color name="selectedBackground">#363636</color>
-</resources>
diff --git a/taler-kotlin-common/src/main/res/values/colors.xml b/taler-kotlin-common/src/main/res/values/colors.xml
deleted file mode 100644
index c916442..0000000
--- a/taler-kotlin-common/src/main/res/values/colors.xml
+++ /dev/null
@@ -1,24 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--
-  ~ This file is part of GNU Taler
-  ~ (C) 2020 Taler Systems S.A.
-  ~
-  ~ GNU Taler is free software; you can redistribute it and/or modify it under the
-  ~ terms of the GNU General Public License as published by the Free Software
-  ~ Foundation; either version 3, or (at your option) any later version.
-  ~
-  ~ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
-  ~ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
-  ~ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
-  ~
-  ~ You should have received a copy of the GNU General Public License along with
-  ~ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
-  -->
-
-<resources>
-    <color name="highlightedBackground">#E4E4E4</color>
-    <color name="selectedBackground">#DADADA</color>
-
-    <color name="green">#388E3C</color>
-    <color name="red">#C62828</color>
-</resources>
diff --git a/taler-kotlin-common/src/main/res/values/strings.xml b/taler-kotlin-common/src/main/res/values/strings.xml
deleted file mode 100644
index a5b1df1..0000000
--- a/taler-kotlin-common/src/main/res/values/strings.xml
+++ /dev/null
@@ -1,21 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?><!--
-  ~ This file is part of GNU Taler
-  ~ (C) 2020 Taler Systems S.A.
-  ~
-  ~ GNU Taler is free software; you can redistribute it and/or modify it under the
-  ~ terms of the GNU General Public License as published by the Free Software
-  ~ Foundation; either version 3, or (at your option) any later version.
-  ~
-  ~ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
-  ~ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
-  ~ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
-  ~
-  ~ You should have received a copy of the GNU General Public License along with
-  ~ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
-  -->
-
-<resources>
-    <string name="version_invalid">Invalid version. Please try again later!</string>
-    <string name="version_too_old">App too old. Please upgrade!</string>
-    <string name="version_too_new">Service outdated. Please wait until it gets upgraded.</string>
-</resources>
diff --git a/taler-kotlin-common/src/nativeMain/kotlin/net/taler/common/Time.kt b/taler-kotlin-common/src/nativeMain/kotlin/net/taler/common/Time.kt
new file mode 100644
index 0000000..8a4091a
--- /dev/null
+++ b/taler-kotlin-common/src/nativeMain/kotlin/net/taler/common/Time.kt
@@ -0,0 +1,23 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2020 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.common
+
+import kotlin.system.getTimeMillis
+
+actual fun nowMillis(): Long {
+    return getTimeMillis()
+}
diff --git a/taler-kotlin-common/src/test/java/net/taler/common/AmountTest.kt b/taler-kotlin-common/src/test/java/net/taler/common/AmountTest.kt
deleted file mode 100644
index 97d9667..0000000
--- a/taler-kotlin-common/src/test/java/net/taler/common/AmountTest.kt
+++ /dev/null
@@ -1,311 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import com.fasterxml.jackson.databind.ObjectMapper
-import com.fasterxml.jackson.module.kotlin.KotlinModule
-import com.fasterxml.jackson.module.kotlin.readValue
-import org.json.JSONObject
-import org.junit.Assert.assertEquals
-import org.junit.Assert.assertFalse
-import org.junit.Assert.assertTrue
-import org.junit.Assert.fail
-import org.junit.Test
-
-class AmountTest {
-
-    @Test
-    fun `test fromJSONString() works`() {
-        var str = "TESTKUDOS:23.42"
-        var amount = Amount.fromJSONString(str)
-        assertEquals(str, amount.toJSONString())
-        assertEquals("TESTKUDOS", amount.currency)
-        assertEquals(23, amount.value)
-        assertEquals((0.42 * 1e8).toInt(), amount.fraction)
-        assertEquals("23.42 TESTKUDOS", amount.toString())
-
-        str = "EUR:500000000.00000001"
-        amount = Amount.fromJSONString(str)
-        assertEquals(str, amount.toJSONString())
-        assertEquals("EUR", amount.currency)
-        assertEquals(500000000, amount.value)
-        assertEquals(1, amount.fraction)
-        assertEquals("500000000.00000001 EUR", amount.toString())
-
-        str = "EUR:1500000000.00000003"
-        amount = Amount.fromJSONString(str)
-        assertEquals(str, amount.toJSONString())
-        assertEquals("EUR", amount.currency)
-        assertEquals(1500000000, amount.value)
-        assertEquals(3, amount.fraction)
-        assertEquals("1500000000.00000003 EUR", amount.toString())
-    }
-
-    @Test
-    fun `test fromJSONString() accepts max values, rejects above`() {
-        val maxValue = 4503599627370496
-        val str = "TESTKUDOS123:$maxValue.99999999"
-        val amount = Amount.fromJSONString(str)
-        assertEquals(str, amount.toJSONString())
-        assertEquals("TESTKUDOS123", amount.currency)
-        assertEquals(maxValue, amount.value)
-        assertEquals("$maxValue.99999999 TESTKUDOS123", amount.toString())
-
-        // longer currency not accepted
-        assertThrows<AmountParserException>("longer currency was accepted") {
-            Amount.fromJSONString("TESTKUDOS1234:$maxValue.99999999")
-        }
-
-        // max value + 1 not accepted
-        assertThrows<AmountParserException>("max value + 1 was accepted") {
-            Amount.fromJSONString("TESTKUDOS123:${maxValue + 1}.99999999")
-        }
-
-        // max fraction + 1 not accepted
-        assertThrows<AmountParserException>("max fraction + 1 was accepted") {
-            Amount.fromJSONString("TESTKUDOS123:$maxValue.999999990")
-        }
-    }
-
-    @Test
-    fun `test JSON deserialization()`() {
-        val mapper = ObjectMapper().registerModule(KotlinModule())
-        var str = "TESTKUDOS:23.42"
-        var amount: Amount = mapper.readValue("\"$str\"")
-        assertEquals(str, amount.toJSONString())
-        assertEquals("TESTKUDOS", amount.currency)
-        assertEquals(23, amount.value)
-        assertEquals((0.42 * 1e8).toInt(), amount.fraction)
-        assertEquals("23.42 TESTKUDOS", amount.toString())
-
-        str = "EUR:500000000.00000001"
-        amount = mapper.readValue("\"$str\"")
-        assertEquals(str, amount.toJSONString())
-        assertEquals("EUR", amount.currency)
-        assertEquals(500000000, amount.value)
-        assertEquals(1, amount.fraction)
-        assertEquals("500000000.00000001 EUR", amount.toString())
-
-        str = "EUR:1500000000.00000003"
-        amount = mapper.readValue("\"$str\"")
-        assertEquals(str, amount.toJSONString())
-        assertEquals("EUR", amount.currency)
-        assertEquals(1500000000, amount.value)
-        assertEquals(3, amount.fraction)
-        assertEquals("1500000000.00000003 EUR", amount.toString())
-    }
-
-    @Test
-    fun `test fromJSONString() rejections`() {
-        assertThrows<AmountParserException> {
-            Amount.fromJSONString("TESTKUDOS:0,5")
-        }
-        assertThrows<AmountParserException> {
-            Amount.fromJSONString("+TESTKUDOS:0.5")
-        }
-        assertThrows<AmountParserException> {
-            Amount.fromJSONString("0.5")
-        }
-        assertThrows<AmountParserException> {
-            Amount.fromJSONString(":0.5")
-        }
-        assertThrows<AmountParserException> {
-            Amount.fromJSONString("EUR::0.5")
-        }
-        assertThrows<AmountParserException> {
-            Amount.fromJSONString("EUR:.5")
-        }
-    }
-
-    @Test
-    fun `test fromJsonObject() works`() {
-        val map = mapOf(
-            "currency" to "TESTKUDOS",
-            "value" to "23",
-            "fraction" to "42000000"
-        )
-
-        val amount = Amount.fromJsonObject(JSONObject(map))
-        assertEquals("TESTKUDOS:23.42", amount.toJSONString())
-        assertEquals("TESTKUDOS", amount.currency)
-        assertEquals(23, amount.value)
-        assertEquals(42000000, amount.fraction)
-        assertEquals("23.42 TESTKUDOS", amount.toString())
-    }
-
-    @Test
-    fun `test fromJsonObject() accepts max values, rejects above`() {
-        val maxValue = 4503599627370496
-        val maxFraction = 99999999
-        var map = mapOf(
-            "currency" to "TESTKUDOS123",
-            "value" to "$maxValue",
-            "fraction" to "$maxFraction"
-        )
-
-        val amount = Amount.fromJsonObject(JSONObject(map))
-        assertEquals("TESTKUDOS123:$maxValue.$maxFraction", amount.toJSONString())
-        assertEquals("TESTKUDOS123", amount.currency)
-        assertEquals(maxValue, amount.value)
-        assertEquals(maxFraction, amount.fraction)
-        assertEquals("$maxValue.$maxFraction TESTKUDOS123", amount.toString())
-
-        // longer currency not accepted
-        assertThrows<AmountParserException>("longer currency was accepted") {
-            map = mapOf(
-                "currency" to "TESTKUDOS1234",
-                "value" to "$maxValue",
-                "fraction" to "$maxFraction"
-            )
-            Amount.fromJsonObject(JSONObject(map))
-        }
-
-        // max value + 1 not accepted
-        assertThrows<AmountParserException>("max value + 1 was accepted") {
-            map = mapOf(
-                "currency" to "TESTKUDOS123",
-                "value" to "${maxValue + 1}",
-                "fraction" to "$maxFraction"
-            )
-            Amount.fromJsonObject(JSONObject(map))
-        }
-
-        // max fraction + 1 not accepted
-        assertThrows<AmountParserException>("max fraction + 1 was accepted") {
-            map = mapOf(
-                "currency" to "TESTKUDOS123",
-                "value" to "$maxValue",
-                "fraction" to "${maxFraction + 1}"
-            )
-            Amount.fromJsonObject(JSONObject(map))
-        }
-    }
-
-    @Test
-    fun `test addition`() {
-        assertEquals(
-            Amount.fromJSONString("EUR:2"),
-            Amount.fromJSONString("EUR:1") + Amount.fromJSONString("EUR:1")
-        )
-        assertEquals(
-            Amount.fromJSONString("EUR:3"),
-            Amount.fromJSONString("EUR:1.5") + Amount.fromJSONString("EUR:1.5")
-        )
-        assertEquals(
-            Amount.fromJSONString("EUR:500000000.00000002"),
-            Amount.fromJSONString("EUR:500000000.00000001") + Amount.fromJSONString("EUR:0.00000001")
-        )
-        assertThrows<AmountOverflowException>("addition didn't overflow") {
-            Amount.fromJSONString("EUR:4503599627370496.99999999") + Amount.fromJSONString("EUR:0.00000001")
-        }
-        assertThrows<AmountOverflowException>("addition didn't overflow") {
-            Amount.fromJSONString("EUR:4000000000000000") + Amount.fromJSONString("EUR:4000000000000000")
-        }
-    }
-
-    @Test
-    fun `test times`() {
-        assertEquals(
-            Amount.fromJSONString("EUR:2"),
-            Amount.fromJSONString("EUR:2") * 1
-        )
-        assertEquals(
-            Amount.fromJSONString("EUR:2"),
-            Amount.fromJSONString("EUR:1") * 2
-        )
-        assertEquals(
-            Amount.fromJSONString("EUR:4.5"),
-            Amount.fromJSONString("EUR:1.5") * 3
-        )
-        assertEquals(
-            Amount.fromJSONString("EUR:1500000000.00000003"),
-            Amount.fromJSONString("EUR:500000000.00000001") * 3
-        )
-        assertThrows<AmountOverflowException>("times didn't overflow") {
-            Amount.fromJSONString("EUR:4000000000000000") * 2
-        }
-    }
-
-    @Test
-    fun `test subtraction`() {
-        assertEquals(
-            Amount.fromJSONString("EUR:0"),
-            Amount.fromJSONString("EUR:1") - Amount.fromJSONString("EUR:1")
-        )
-        assertEquals(
-            Amount.fromJSONString("EUR:1.5"),
-            Amount.fromJSONString("EUR:3") - Amount.fromJSONString("EUR:1.5")
-        )
-        assertEquals(
-            Amount.fromJSONString("EUR:500000000.00000001"),
-            Amount.fromJSONString("EUR:500000000.00000002") - Amount.fromJSONString("EUR:0.00000001")
-        )
-        assertThrows<AmountOverflowException>("subtraction didn't underflow") {
-            Amount.fromJSONString("EUR:23.42") - Amount.fromJSONString("EUR:42.23")
-        }
-        assertThrows<AmountOverflowException>("subtraction didn't underflow") {
-            Amount.fromJSONString("EUR:0.5") - Amount.fromJSONString("EUR:0.50000001")
-        }
-    }
-
-    @Test
-    fun `test isZero()`() {
-        assertTrue(Amount.zero("EUR").isZero())
-        assertTrue(Amount.fromJSONString("EUR:0").isZero())
-        assertTrue(Amount.fromJSONString("EUR:0.0").isZero())
-        assertTrue(Amount.fromJSONString("EUR:0.00000").isZero())
-        assertTrue((Amount.fromJSONString("EUR:1.001") - Amount.fromJSONString("EUR:1.001")).isZero())
-
-        assertFalse(Amount.fromJSONString("EUR:0.00000001").isZero())
-        assertFalse(Amount.fromJSONString("EUR:1.0").isZero())
-        assertFalse(Amount.fromJSONString("EUR:0001.0").isZero())
-    }
-
-    @Test
-    fun `test comparision`() {
-        assertTrue(Amount.fromJSONString("EUR:0") <= Amount.fromJSONString("EUR:0"))
-        assertTrue(Amount.fromJSONString("EUR:0") <= Amount.fromJSONString("EUR:0.00000001"))
-        assertTrue(Amount.fromJSONString("EUR:0") < Amount.fromJSONString("EUR:0.00000001"))
-        assertTrue(Amount.fromJSONString("EUR:0") < Amount.fromJSONString("EUR:1"))
-        assertTrue(Amount.fromJSONString("EUR:0") == Amount.fromJSONString("EUR:0"))
-        assertTrue(Amount.fromJSONString("EUR:42") == Amount.fromJSONString("EUR:42"))
-        assertTrue(Amount.fromJSONString("EUR:42.00000001") == Amount.fromJSONString("EUR:42.00000001"))
-        assertTrue(Amount.fromJSONString("EUR:42.00000001") >= Amount.fromJSONString("EUR:42.00000001"))
-        assertTrue(Amount.fromJSONString("EUR:42.00000002") >= Amount.fromJSONString("EUR:42.00000001"))
-        assertTrue(Amount.fromJSONString("EUR:42.00000002") > Amount.fromJSONString("EUR:42.00000001"))
-        assertTrue(Amount.fromJSONString("EUR:0.00000002") > Amount.fromJSONString("EUR:0.00000001"))
-        assertTrue(Amount.fromJSONString("EUR:0.00000001") > Amount.fromJSONString("EUR:0"))
-        assertTrue(Amount.fromJSONString("EUR:2") > Amount.fromJSONString("EUR:1"))
-
-        assertThrows<IllegalStateException>("could compare amounts with different currencies") {
-            Amount.fromJSONString("EUR:0.5") < Amount.fromJSONString("USD:0.50000001")
-        }
-    }
-
-    private inline fun <reified T : Throwable> assertThrows(
-        msg: String? = null,
-        function: () -> Any
-    ) {
-        try {
-            function.invoke()
-            fail(msg)
-        } catch (e: Exception) {
-            assertTrue(e is T)
-        }
-    }
-
-}
diff --git a/taler-kotlin-common/src/test/java/net/taler/common/VersionTest.kt b/taler-kotlin-common/src/test/java/net/taler/common/VersionTest.kt
deleted file mode 100644
index 70f30eb..0000000
--- a/taler-kotlin-common/src/test/java/net/taler/common/VersionTest.kt
+++ /dev/null
@@ -1,65 +0,0 @@
-/*
- * This file is part of GNU Taler
- * (C) 2020 Taler Systems S.A.
- *
- * GNU Taler is free software; you can redistribute it and/or modify it under the
- * terms of the GNU General Public License as published by the Free Software
- * Foundation; either version 3, or (at your option) any later version.
- *
- * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
- * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
- * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with
- * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
- */
-
-package net.taler.common
-
-import org.junit.Assert.assertEquals
-import org.junit.Assert.assertNull
-import org.junit.Test
-
-class VersionTest {
-
-    @Test
-    fun testParse() {
-        assertNull(Version.parse(""))
-        assertNull(Version.parse("foo"))
-        assertNull(Version.parse("foo:bar:foo"))
-        assertNull(Version.parse("0:0:0:"))
-        assertNull(Version.parse("0:0:"))
-        assertEquals(Version(0, 0, 0), Version.parse("0:0:0"))
-        assertEquals(Version(1, 2, 3), Version.parse("1:2:3"))
-        assertEquals(Version(1337, 42, 23), Version.parse("1337:42:23"))
-    }
-
-    @Test
-    fun testComparision() {
-        assertEquals(
-            Version.VersionMatchResult(true, 0),
-            Version.parse("0:0:0")!!.compare(Version.parse("0:0:0"))
-        )
-        assertEquals(
-            Version.VersionMatchResult(true, -1),
-            Version.parse("0:0:0")!!.compare(Version.parse("1:0:1"))
-        )
-        assertEquals(
-            Version.VersionMatchResult(true, -1),
-            Version.parse("0:0:0")!!.compare(Version.parse("1:5:1"))
-        )
-        assertEquals(
-            Version.VersionMatchResult(false, -1),
-            Version.parse("0:0:0")!!.compare(Version.parse("1:5:0"))
-        )
-        assertEquals(
-            Version.VersionMatchResult(false, 1),
-            Version.parse("1:0:0")!!.compare(Version.parse("0:5:0"))
-        )
-        assertEquals(
-            Version.VersionMatchResult(true, 0),
-            Version.parse("1:0:1")!!.compare(Version.parse("1:5:1"))
-        )
-    }
-
-}
diff --git a/wallet/.gitlab-ci.yml b/wallet/.gitlab-ci.yml
index 56768f7..c417aa9 100644
--- a/wallet/.gitlab-ci.yml
+++ b/wallet/.gitlab-ci.yml
@@ -4,6 +4,7 @@ wallet_test:
     changes:
       - wallet/**/*
       - taler-kotlin-common/**/*
+      - taler-kotlin-android/**/*
       - build.gradle
   script: ./gradlew :wallet:check :wallet:assembleRelease
   artifacts:
diff --git a/wallet/build.gradle b/wallet/build.gradle
index 8cca8dc..1761018 100644
--- a/wallet/build.gradle
+++ b/wallet/build.gradle
@@ -23,7 +23,7 @@ plugins {
     id "de.undercouch.download"
 }
 
-def walletCoreVersion = "v0.7.1-dev.14"
+def walletCoreVersion = "v0.7.1-dev.16"
 
 static def versionCodeEpoch() {
     return (new Date().getTime() / 1000).toInteger()
@@ -47,7 +47,7 @@ android {
         minSdkVersion 24
         targetSdkVersion 29
         versionCode 6
-        versionName "0.7.1.dev.14"
+        versionName "0.7.1.dev.16"
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
         buildConfigField "String", "WALLET_CORE_VERSION", "\"$walletCoreVersion\""
     }
@@ -83,6 +83,10 @@ android {
         jvmTarget = "1.8"
     }
 
+    packagingOptions {
+        exclude("META-INF/*.kotlin_module")
+    }
+
     lintOptions {
         abortOnError true
         ignoreWarnings false
@@ -93,7 +97,7 @@ android {
 }
 
 dependencies {
-    implementation project(":taler-kotlin-common")
+    implementation project(":taler-kotlin-android")
     implementation project(":anastasis-ui")
     implementation 'net.taler:akono:0.1'
 
diff --git a/wallet/src/main/java/net/taler/wallet/MainViewModel.kt b/wallet/src/main/java/net/taler/wallet/MainViewModel.kt
index 3d725d0..ffa2dea 100644
--- a/wallet/src/main/java/net/taler/wallet/MainViewModel.kt
+++ b/wallet/src/main/java/net/taler/wallet/MainViewModel.kt
@@ -24,10 +24,13 @@ import androidx.lifecycle.LiveData
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.distinctUntilChanged
 import androidx.lifecycle.viewModelScope
+import com.fasterxml.jackson.databind.DeserializationFeature
 import com.fasterxml.jackson.databind.DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES
 import com.fasterxml.jackson.databind.ObjectMapper
 import com.fasterxml.jackson.module.kotlin.KotlinModule
 import com.fasterxml.jackson.module.kotlin.readValue
+import net.taler.common.Amount
+import net.taler.common.AmountMixin
 import net.taler.common.Event
 import net.taler.common.assertUiThread
 import net.taler.common.toEvent
@@ -91,6 +94,8 @@ class MainViewModel(val app: Application) : AndroidViewModel(app) {
     private val mapper = ObjectMapper()
         .registerModule(KotlinModule())
         .configure(FAIL_ON_UNKNOWN_PROPERTIES, false)
+        .addMixIn(Amount::class.java, AmountMixin::class.java)
+        .enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT)
 
     val withdrawManager = WithdrawManager(walletBackendApi, mapper)
     val paymentManager = PaymentManager(walletBackendApi, mapper)
diff --git a/wallet/src/main/java/net/taler/wallet/exchanges/ExchangeFees.kt b/wallet/src/main/java/net/taler/wallet/exchanges/ExchangeFees.kt
index ae90b98..a026283 100644
--- a/wallet/src/main/java/net/taler/wallet/exchanges/ExchangeFees.kt
+++ b/wallet/src/main/java/net/taler/wallet/exchanges/ExchangeFees.kt
@@ -18,7 +18,6 @@ package net.taler.wallet.exchanges
 
 import net.taler.common.Amount
 import net.taler.common.Timestamp
-import org.json.JSONObject
 
 data class CoinFee(
     val coin: Amount,
@@ -42,54 +41,4 @@ data class ExchangeFees(
     val earliestDepositExpiration: Timestamp,
     val coinFees: List<CoinFee>,
     val wireFees: List<WireFee>
-) {
-    companion object {
-        fun fromExchangeWithdrawDetailsJson(json: JSONObject): ExchangeFees {
-            val earliestDepositExpiration =
-                json.getJSONObject("earliestDepositExpiration").getLong("t_ms")
-            val selectedDenoms = json.getJSONObject("selectedDenoms")
-            val denoms = selectedDenoms.getJSONArray("selectedDenoms")
-            val coinFees = ArrayList<CoinFee>(denoms.length())
-            for (i in 0 until denoms.length()) {
-                val denom = denoms.getJSONObject(i)
-                val d = denom.getJSONObject("denom")
-                val coinFee = CoinFee(
-                    coin = Amount.fromJsonObject(d.getJSONObject("value")),
-                    quantity = denom.getInt("count"),
-                    feeDeposit = Amount.fromJsonObject(d.getJSONObject("feeDeposit")),
-                    feeRefresh = Amount.fromJsonObject(d.getJSONObject("feeRefresh")),
-                    feeRefund = Amount.fromJsonObject(d.getJSONObject("feeRefund")),
-                    feeWithdraw = Amount.fromJsonObject(d.getJSONObject("feeWithdraw"))
-                )
-                coinFees.add(coinFee)
-            }
-
-            val wireFeesJson = json.getJSONObject("wireFees")
-            val feesForType = wireFeesJson.getJSONObject("feesForType")
-            val bankFees = feesForType.getJSONArray("x-taler-bank")
-            val wireFees = ArrayList<WireFee>(bankFees.length())
-            for (i in 0 until bankFees.length()) {
-                val fee = bankFees.getJSONObject(i)
-                val startStamp =
-                    fee.getJSONObject("startStamp").getLong("t_ms")
-                val endStamp =
-                    fee.getJSONObject("endStamp").getLong("t_ms")
-                val wireFee = WireFee(
-                    start = Timestamp(startStamp),
-                    end = Timestamp(endStamp),
-                    wireFee = Amount.fromJsonObject(fee.getJSONObject("wireFee")),
-                    closingFee = Amount.fromJsonObject(fee.getJSONObject("closingFee"))
-                )
-                wireFees.add(wireFee)
-            }
-
-            return ExchangeFees(
-                withdrawFee = Amount.fromJsonObject(json.getJSONObject("withdrawFee")),
-                overhead = Amount.fromJsonObject(json.getJSONObject("overhead")),
-                earliestDepositExpiration = Timestamp(earliestDepositExpiration),
-                coinFees = coinFees,
-                wireFees = wireFees
-            )
-        }
-    }
-}
+)
diff --git a/wallet/src/main/java/net/taler/wallet/payment/PaymentResponses.kt b/wallet/src/main/java/net/taler/wallet/payment/PaymentResponses.kt
index 4c5b010..d2f8e6c 100644
--- a/wallet/src/main/java/net/taler/wallet/payment/PaymentResponses.kt
+++ b/wallet/src/main/java/net/taler/wallet/payment/PaymentResponses.kt
@@ -16,23 +16,12 @@
 
 package net.taler.wallet.payment
 
-import com.fasterxml.jackson.annotation.JsonSubTypes
-import com.fasterxml.jackson.annotation.JsonSubTypes.Type
 import com.fasterxml.jackson.annotation.JsonTypeInfo
-import com.fasterxml.jackson.annotation.JsonTypeInfo.As.PROPERTY
 import com.fasterxml.jackson.annotation.JsonTypeInfo.Id.NAME
 import com.fasterxml.jackson.annotation.JsonTypeName
 import net.taler.common.ContractTerms
-import net.taler.wallet.payment.PreparePayResponse.AlreadyConfirmedResponse
-import net.taler.wallet.payment.PreparePayResponse.InsufficientBalanceResponse
-import net.taler.wallet.payment.PreparePayResponse.PaymentPossibleResponse
 
-@JsonTypeInfo(use = NAME, include = PROPERTY, property = "status")
-@JsonSubTypes(
-    Type(value = PaymentPossibleResponse::class, name = "payment-possible"),
-    Type(value = AlreadyConfirmedResponse::class, name = "already-confirmed"),
-    Type(value = InsufficientBalanceResponse::class, name = "insufficient-balance")
-)
+@JsonTypeInfo(use = NAME, property = "status")
 sealed class PreparePayResponse(open val proposalId: String) {
     @JsonTypeName("payment-possible")
     data class PaymentPossibleResponse(
-- 
cgit v1.2.3