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path: root/cashier/src/main/java/net/taler/cashier/MainViewModel.kt
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/*
 * 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.cashier

import android.annotation.SuppressLint
import android.app.Application
import android.util.Log
import androidx.annotation.UiThread
import androidx.annotation.WorkerThread
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.viewModelScope
import androidx.security.crypto.EncryptedSharedPreferences
import androidx.security.crypto.EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV
import androidx.security.crypto.EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
import androidx.security.crypto.MasterKeys
import androidx.security.crypto.MasterKeys.AES256_GCM_SPEC
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch
import net.taler.cashier.HttpHelper.makeJsonGetRequest
import net.taler.cashier.withdraw.WithdrawManager
import net.taler.common.AmountParserException
import net.taler.common.SignedAmount
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"
private const val PREF_KEY_PASSWORD = "password"
private const val PREF_KEY_CURRENCY = "currency"

class MainViewModel(private val app: Application) : AndroidViewModel(app) {

    val configDestination = ConfigFragmentDirections.actionGlobalConfigFragment()

    private val masterKeyAlias = MasterKeys.getOrCreate(AES256_GCM_SPEC)
    private val prefs = EncryptedSharedPreferences.create(
        PREF_NAME, masterKeyAlias, app, AES256_SIV, AES256_GCM
    )

    internal var config = Config(
        bankUrl = prefs.getString(PREF_KEY_BANK_URL, "")!!,
        username = prefs.getString(PREF_KEY_USERNAME, "")!!,
        password = prefs.getString(PREF_KEY_PASSWORD, "")!!
    )

    private val mCurrency = MutableLiveData<String>(
        prefs.getString(PREF_KEY_CURRENCY, null)
    )
    internal val currency: LiveData<String> = mCurrency

    private val mConfigResult = MutableLiveData<ConfigResult>()
    val configResult: LiveData<ConfigResult> = mConfigResult

    private val mBalance = MutableLiveData<BalanceResult>()
    val balance: LiveData<BalanceResult> = mBalance

    internal val withdrawManager = WithdrawManager(app, this)

    fun hasConfig() = config.bankUrl.isNotEmpty()
            && config.username.isNotEmpty()
            && config.password.isNotEmpty()

    /**
     * Start observing [configResult] after calling this to get the result async.
     * Warning: Ignore null results that are used to reset old results.
     */
    @UiThread
    fun checkAndSaveConfig(config: Config) {
        mConfigResult.value = null
        viewModelScope.launch(Dispatchers.IO) {
            val url = "${config.bankUrl}/config"
            Log.d(TAG, "Checking config: $url")
            val result = when (val response = makeJsonGetRequest(url, config)) {
                is HttpJsonResult.Success -> {
                    val version = response.json.getString("version")
                    // TODO check if version is compatible
                    val currency = response.json.getString("currency")
                    try {
                        mCurrency.postValue(currency)
                        prefs.edit().putString(PREF_KEY_CURRENCY, currency).apply()
                        // save config
                        saveConfig(config)
                        ConfigResult.Success
                    } catch (e: Exception) {
                        ConfigResult.Error(false, "Invalid Config: ${response.json}")
                    }
                }
                is HttpJsonResult.Error -> {
                    if (response.statusCode > 0 && app.isOnline()) {
                        ConfigResult.Error(response.statusCode == 401, response.msg)
                    } else {
                        ConfigResult.Offline
                    }
                }
            }
            mConfigResult.postValue(result)
        }
    }

    @WorkerThread
    @SuppressLint("ApplySharedPref")
    private fun saveConfig(config: Config) {
        this.config = config
        prefs.edit()
            .putString(PREF_KEY_BANK_URL, config.bankUrl)
            .putString(PREF_KEY_USERNAME, config.username)
            .putString(PREF_KEY_PASSWORD, config.password)
            .commit()
    }

    fun getBalance() = viewModelScope.launch(Dispatchers.IO) {
        check(hasConfig()) { "No config to get balance" }
        val url = "${config.bankUrl}/accounts/${config.username}/balance"
        Log.d(TAG, "Checking balance at $url")
        val result = when (val response = makeJsonGetRequest(url, config)) {
            is HttpJsonResult.Success -> {
                val balance = response.json.getString("balance")
                try {
                    BalanceResult.Success(SignedAmount.fromJSONString(balance))
                } catch (e: AmountParserException) {
                    BalanceResult.Error("invalid amount: $balance")
                }
            }
            is HttpJsonResult.Error -> {
                if (app.isOnline()) BalanceResult.Error(response.msg)
                else BalanceResult.Offline
            }
        }
        mBalance.postValue(result)
    }

    fun lock() {
        saveConfig(config.copy(password = ""))
    }

}

data class Config(
    val bankUrl: String,
    val username: String,
    val password: String
)

sealed class ConfigResult {
    class Error(val authError: Boolean, val msg: String) : ConfigResult()
    object Offline : ConfigResult()
    object Success : ConfigResult()
}