Allow divisor in mod to be a number as well

Fixes #687

src/Money.php

@@ -272,14 +272,22 @@ public function divide(int|string $divisor, int $roundingMode = self::ROUND_HALF
      * the remainder after dividing the value by
      * the given factor.
      */
-    public function mod(Money $divisor): Money
+    public function mod(Money|int|string $divisor): Money
     {
-        // Note: non-strict equality is intentional here, since `Currency` is `final` and reliable.
-        if ($this->currency != $divisor->currency) {
-            throw new InvalidArgumentException('Currencies must be identical');
+        if ($divisor instanceof self) {
+            // Note: non-strict equality is intentional here, since `Currency` is `final` and reliable.
+            if ($this->currency != $divisor->currency) {
+                throw new InvalidArgumentException('Currencies must be identical');
+            }
+            $amount = $divisor->amount;
+        } else {
+            if (is_int($divisor)) {
+                $divisor = (string) $divisor;
+            }
+            $amount = $divisor;
         }
 
-        return new self(self::$calculator::mod($this->amount, $divisor->amount), $this->currency);
+        return new self(self::$calculator::mod($this->amount, $amount), $this->currency);
     }
 
     /**

tests/MoneyTest.php

@@ -257,6 +257,24 @@ public function itCalculatesTheModulusOfAnAmount($left, $right, $expected): void
         self::assertEquals($expected, $money->getAmount());
     }
 
+    /**
+     * @psalm-param positive-int $left
+     * @psalm-param positive-int $right
+     * @psalm-param numeric-string $expected
+     *
+     * @dataProvider modExamples
+     * @test
+     */
+    public function itCalculatesTheModulusOfNumber($left, $right, $expected): void
+    {
+        $money = new Money($left, new Currency(self::CURRENCY));
+
+        $money = $money->mod($right);
+
+        self::assertInstanceOf(Money::class, $money);
+        self::assertEquals($expected, $money->getAmount());
+    }
+
     /**
      * @test
      */