add aggregate functions, fixes moneyphp#473 (moneyphp#478)

src/Money.php

@@ -515,6 +515,66 @@ public function jsonSerialize()
         ];
     }
 
+    /**
+     * @param Money $first
+     * @param Money ...$collection
+     *
+     * @return Money
+     */
+    public static function min(self $first, self ...$collection)
+    {
+        $min = $first;
+
+        foreach ($collection as $money) {
+            if ($money->lessThan($min)) {
+                $min = $money;
+            }
+        }
+
+        return $min;
+    }
+
+    /**
+     * @param Money $first
+     * @param Money ...$collection
+     *
+     * @return Money
+     */
+    public static function max(self $first, self ...$collection)
+    {
+        $max = $first;
+
+        foreach ($collection as $money) {
+            if ($money->greaterThan($max)) {
+                $max = $money;
+            }
+        }
+
+        return $max;
+    }
+
+    /**
+     * @param Money $first
+     * @param Money ...$collection
+     *
+     * @return Money
+     */
+    public static function sum(self $first, self ...$collection)
+    {
+        return $first->add(...$collection);
+    }
+
+    /**
+     * @param Money $first
+     * @param Money ...$collection
+     *
+     * @return Money
+     */
+    public static function avg(self $first, self ...$collection)
+    {
+        return $first->add(...$collection)->divide(func_num_args());
+    }
+
     /**
      * @param string $calculator
      */

tests/AggregateExamples.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Tests\Money;
+
+use Money\Money;
+
+trait AggregateExamples
+{
+    public function sumExamples()
+    {
+        return [
+            [[Money::EUR(5), Money::EUR(10), Money::EUR(15)], Money::EUR(30)],
+            [[Money::EUR(-5), Money::EUR(-10), Money::EUR(-15)], Money::EUR(-30)],
+            [[Money::EUR(0)], Money::EUR(0)],
+        ];
+    }
+
+    public function minExamples()
+    {
+        return [
+            [[Money::EUR(5), Money::EUR(10), Money::EUR(15)], Money::EUR(5)],
+            [[Money::EUR(-5), Money::EUR(-10), Money::EUR(-15)], Money::EUR(-15)],
+            [[Money::EUR(0)], Money::EUR(0)],
+        ];
+    }
+
+    public function maxExamples()
+    {
+        return [
+            [[Money::EUR(5), Money::EUR(10), Money::EUR(15)], Money::EUR(15)],
+            [[Money::EUR(-5), Money::EUR(-10), Money::EUR(-15)], Money::EUR(-5)],
+            [[Money::EUR(0)], Money::EUR(0)],
+        ];
+    }
+
+    public function avgExamples()
+    {
+        return [
+            [[Money::EUR(5), Money::EUR(10), Money::EUR(15)], Money::EUR(10)],
+            [[Money::EUR(-5), Money::EUR(-10), Money::EUR(-15)], Money::EUR(-10)],
+            [[Money::EUR(0)], Money::EUR(0)],
+        ];
+    }
+}

tests/MoneyTest.php

@@ -8,7 +8,7 @@
 
 final class MoneyTest extends TestCase
 {
-    use RoundExamples;
+    use AggregateExamples, RoundExamples;
 
     const AMOUNT = 10;
 
@@ -259,6 +259,82 @@ public function it_throws_when_calculating_ratio_of_zero()
         $six->ratioOf($zero);
     }
 
+    /**
+     * @dataProvider sumExamples
+     * @test
+     */
+    public function it_calculates_sum($values, $sum)
+    {
+        $this->assertEquals($sum, Money::sum(...$values));
+    }
+
+    /**
+     * @dataProvider minExamples
+     * @test
+     */
+    public function it_calculates_min($values, $min)
+    {
+        $this->assertEquals($min, Money::min(...$values));
+    }
+
+    /**
+     * @dataProvider maxExamples
+     * @test
+     */
+    public function it_calculates_max($values, $max)
+    {
+        $this->assertEquals($max, Money::max(...$values));
+    }
+
+    /**
+     * @dataProvider avgExamples
+     * @test
+     */
+    public function it_calculates_avg($values, $avg)
+    {
+        $this->assertEquals($avg, Money::avg(...$values));
+    }
+
+    /**
+     * @test
+     * @requires PHP 7.0
+     */
+    public function it_throws_when_calculating_min_with_zero_arguments()
+    {
+        $this->expectException(\Throwable::class);
+        Money::min(...[]);
+    }
+
+    /**
+     * @test
+     * @requires PHP 7.0
+     */
+    public function it_throws_when_calculating_max_with_zero_arguments()
+    {
+        $this->expectException(\Throwable::class);
+        Money::max(...[]);
+    }
+
+    /**
+     * @test
+     * @requires PHP 7.0
+     */
+    public function it_throws_when_calculating_sum_with_zero_arguments()
+    {
+        $this->expectException(\Throwable::class);
+        Money::sum(...[]);
+    }
+
+    /**
+     * @test
+     * @requires PHP 7.0
+     */
+    public function it_throws_when_calculating_avg_with_zero_arguments()
+    {
+        $this->expectException(\Throwable::class);
+        Money::avg(...[]);
+    }
+
     public function equalityExamples()
     {
         return [