Add format_money modifier (#92)

Author: duncanmcclean

docs/frontend/modifiers/format_money.md

@@ -0,0 +1,25 @@
+---
+title: Format Money Modifier
+description: "The `format_money` modifier converts an amount (in pence) to a nicely formatted string, like `£190.55`."
+---
+
+The `format_money` modifier converts an amount (in pence) to a nicely formatted string, like `£190.55`.
+
+```php
+special_calculation: '19055'
+```
+
+::tabs
+::tab antlers
+```antlers
+{{ special_calculation | format_money }}
+```
+::tab blade
+```blade
+{{ Statamic::modify($specialCalculation)->formatMoney() }}
+``` 
+::
+
+```php
+£190.55
+```

src/Modifiers/FormatMoney.php

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+<?php
+
+namespace DuncanMcClean\Cargo\Modifiers;
+
+use DuncanMcClean\Cargo\Support\Money;
+use Statamic\Facades\Site;
+use Statamic\Modifiers\Modifier;
+
+class FormatMoney extends Modifier
+{
+    public function index($value, $params, $context)
+    {
+        if (! $value) {
+            return $value;
+        }
+
+        if (! is_numeric($value)) {
+            throw new \Exception('The format_money modifier requires a numeric value.');
+        }
+
+        return Money::format($value, Site::current());
+    }
+}

tests/Modifiers/FormatMoneyTest.php

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+<?php
+
+namespace Tests\Modifiers;
+
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Modifiers\Modify;
+use Tests\TestCase;
+
+class FormatMoneyTest extends TestCase
+{
+    public static function amountProvider(): array
+    {
+        return [
+            [null, null],
+            ['1599', '£15.99'],
+            ['15.99', '£15.99'],
+            [1599, '£15.99'],
+            [15.99, '£15.99'],
+        ];
+    }
+
+    #[Test]
+    #[DataProvider('amountProvider')]
+    public function it_formats_money($input, $expected)
+    {
+        $this->assertEquals($expected, $this->modify($input));
+    }
+
+    #[Test]
+    public function exception_is_thrown_when_non_numeric_value_is_provided()
+    {
+        $this->expectException(\Exception::class);
+        $this->expectExceptionMessage('The format_money modifier requires a numeric value.');
+
+        $this->modify('Hello World!');
+    }
+
+    private function modify($value)
+    {
+        return Modify::value($value)->formatMoney()->fetch();
+    }
+}