feat(validation): add HexColor validation rule

Author: tizianozonta

packages/validation/src/Rules/HexColor.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\Validation\Rules;
+
+use Attribute;
+use Tempest\Validation\Rule;
+
+#[Attribute]
+final readonly class HexColor implements Rule
+{
+    public function __construct(
+        private bool $orNull = false,
+    )
+    {
+    }
+
+    public function isValid(mixed $value): bool
+    {
+        if ($this->orNull && $value === null) {
+            return true;
+        }
+
+        if (! is_string($value)) {
+            return false;
+        }
+
+        return preg_match('/^#(?:(?:[0-9a-f]{3}){1,2}|(?:[0-9a-f]{4}){1,2})$/i', $value) === 1;
+    }
+
+    public function message(): string
+    {
+        return 'Value should be a valid hexadecimal color.';
+    }
+}

packages/validation/tests/Rules/HexColorTest.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tempest\Validation\Tests\Rules;
+
+use PHPUnit\Framework\TestCase;
+use Tempest\Validation\Rules\HexColor;
+
+/**
+ * @internal
+ */
+final class HexColorTest extends TestCase
+{
+    public function test_uuid(): void
+    {
+        $rule = new HexColor();
+
+        $this->assertSame('Value should be a valid hexadecimal color.', $rule->message());
+
+        $this->assertFalse($rule->isValid('string_123'));
+        $this->assertFalse($rule->isValid([])); // Should return false, not a TypeError from preg_match
+        $this->assertFalse($rule->isValid('ffffff'));
+        $this->assertFalse($rule->isValid('#fffffff'));
+
+        $this->assertTrue($rule->isValid('#ffffff'));
+        $this->assertTrue($rule->isValid('#FFFFFF'));
+        $this->assertTrue($rule->isValid('#fff'));
+    }
+}