From 3224dc7f1db77b865ca01ce9fb2574f56656edb6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tobias=20Sch=C3=BCrg?= <tobiasschuerg@gmail.com>
Date: Mon, 29 Aug 2022 13:13:15 +0200
Subject: [PATCH] feat: add sum functions for Money collections

---
 .../java/de/tobiasschuerg/money/MoneyUtils.kt | 20 +++++++++++++++++++
 .../de/tobiasschuerg/money/MoneyListTest.kt   | 18 +++++++++++++++--
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/money/src/main/java/de/tobiasschuerg/money/MoneyUtils.kt b/money/src/main/java/de/tobiasschuerg/money/MoneyUtils.kt
index daec31e..8a54ce9 100644
--- a/money/src/main/java/de/tobiasschuerg/money/MoneyUtils.kt
+++ b/money/src/main/java/de/tobiasschuerg/money/MoneyUtils.kt
@@ -3,3 +3,23 @@ package de.tobiasschuerg.money
 fun Money.toFloat(): Float = amount.toFloat()
 
 fun Money.toDouble(): Double = amount.toDouble()
+
+/**
+ * Sum all amounts on the collection.
+ * Will throw if currencies does not match.
+ * @see [sum(currency)]
+ */
+fun Collection<Money>.sum(): Money {
+    return fold(Money.ZERO) { acc, money ->
+        if (money.isZero()) acc else acc + money
+    }
+}
+
+/**
+ * Sum all amounts on the collection and auto apply currency conversion.
+ */
+fun Collection<Money>.sum(currency: Currency): Money {
+    return fold(Money.ZERO) { acc, money ->
+        if (money.isZero()) acc else acc + money.convertInto(currency)
+    }
+}
diff --git a/money/src/test/java/de/tobiasschuerg/money/MoneyListTest.kt b/money/src/test/java/de/tobiasschuerg/money/MoneyListTest.kt
index 2b79f1a..f0e52c5 100644
--- a/money/src/test/java/de/tobiasschuerg/money/MoneyListTest.kt
+++ b/money/src/test/java/de/tobiasschuerg/money/MoneyListTest.kt
@@ -1,5 +1,6 @@
 package de.tobiasschuerg.money
 
+import de.tobiasschuerg.money.Currencies.EURO
 import org.junit.Assert
 import org.junit.Test
 
@@ -8,8 +9,8 @@ import org.junit.Test
  */
 class MoneyListTest {
 
-    private val currency = Currency("EUR", "Euro", 1.0)
-    private val list = MoneyList(currency)
+    private val currency = EURO
+    private val list = MoneyList(EURO)
 
     init {
         list.add(Money(3, currency))
@@ -58,4 +59,17 @@ class MoneyListTest {
         Assert.assertEquals(1, sublist.min()?.amount?.intValueExact())
         Assert.assertEquals(6, sublist.max()?.amount?.intValueExact())
     }
+
+    @Test
+    fun `test that sum of same currencies is calculated correctly`() {
+        val result = list.sum()
+        Assert.assertEquals(45.00, result.amount.toDouble(), 0.01)
+    }
+
+    @Test
+    fun `test that sum of different currencies is calculated correctly`() {
+        val list2: List<Money> = list.plus(Money(5.37, Currencies.USDOLLAR))
+        val result = list2.sum(EURO)
+        Assert.assertEquals(49.93, result.amount.toDouble(), 0.01)
+    }
 }