1 files changed, 100 insertions, 0 deletions
diff --git a/common/src/main/kotlin/TalerCommon.kt b/common/src/main/kotlin/TalerCommon.kt
new file mode 100644
index 00000000..96d20a86
--- /dev/null
+++ b/common/src/main/kotlin/TalerCommon.kt
@@ -0,0 +1,100 @@
+/*
+ * This file is part of LibEuFin.
+ * Copyright (C) 2024 Taler Systems S.A.
+ *
+ * LibEuFin is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation; either version 3, or
+ * (at your option) any later version.
+ *
+ * LibEuFin 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 Affero General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License along with LibEuFin; see the file COPYING.  If not, see
+ * <http://www.gnu.org/licenses/>
+ */
+
+package tech.libeufin.common
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+import kotlinx.serialization.json.*
+
+sealed class CommonError(msg: String): Exception(msg) {
+    class AmountFormat(msg: String): CommonError(msg)
+    class AmountNumberTooBig(msg: String): CommonError(msg)
+}
+
+@Serializable(with = TalerAmount.Serializer::class)
+class TalerAmount {
+    val value: Long
+    val frac: Int
+    val currency: String
+
+    constructor(value: Long, frac: Int, currency: String) {
+        this.value = value
+        this.frac = frac
+        this.currency = currency
+    }
+    constructor(encoded: String) {
+        val match = PATTERN.matchEntire(encoded) ?: 
+            throw CommonError.AmountFormat("Invalid amount format");
+        val (currency, value, frac) = match.destructured
+        this.currency = currency
+        this.value = value.toLongOrNull() ?: 
+            throw CommonError.AmountFormat("Invalid value")
+        if (this.value > MAX_VALUE) 
+            throw CommonError.AmountNumberTooBig("Value specified in amount is too large")
+        this.frac = if (frac.isEmpty()) {
+            0
+        } else {
+            var tmp = frac.toIntOrNull() ?: 
+                throw CommonError.AmountFormat("Invalid fractional value")
+            if (tmp > FRACTION_BASE) 
+                throw CommonError.AmountFormat("Fractional calue specified in amount is too large")
+            repeat(8 - frac.length) {
+                tmp *= 10
+            }
+            tmp
+        }
+    }
+
+    override fun equals(other: Any?): Boolean {
+        return other is TalerAmount &&
+                other.value == this.value &&
+                other.frac == this.frac &&
+                other.currency == this.currency
+    }
+
+    override fun toString(): String {
+        if (frac == 0) {
+            return "$currency:$value"
+        } else {
+            return "$currency:$value.${frac.toString().padStart(8, '0')}"
+                .dropLastWhile { it == '0' } // Trim useless fractional trailing 0
+        }
+    }
+
+    internal object Serializer : KSerializer<TalerAmount> {
+        override val descriptor: SerialDescriptor =
+        PrimitiveSerialDescriptor("TalerAmount", PrimitiveKind.STRING)
+    
+        override fun serialize(encoder: Encoder, value: TalerAmount) {
+            encoder.encodeString(value.toString())
+        }
+    
+        override fun deserialize(decoder: Decoder): TalerAmount {
+            return TalerAmount(decoder.decodeString())
+        }
+    }
+
+    companion object {
+        const val FRACTION_BASE = 100000000
+        const val MAX_VALUE = 4503599627370496L; // 2^52
+        private val PATTERN = Regex("([A-Z]{1,11}):([0-9]+)(?:\\.([0-9]{1,8}))?");
+    }
+}
+\ No newline at end of file