Add LanguageCode rule

README.md

@@ -351,6 +351,18 @@ The field under validation must be a valid country code according to ISO 3166-1
 
 The country code has three different format `ALPHA2`, `ALPHA3` or `NUMERIC`. Select the format you want to check. Default `Iso3166::ALPHA2`.
 
+### Language Code (ISO 639-1)
+
+The field under validation must be a valid language code according to ISO ISO 639-1.
+
+    public Intervention\Validation\Rules\Iso3166::__construct(bool $strict = true)
+
+#### Parameters
+
+**strict**
+
+If `strict` is `true`, the language code must be passed in lowercase. Otherwise, the case doesn't matter.
+
 ## Development & Testing
 
 With this package comes a Docker image to build a test suite container. To

src/Rules/LanguageCode.php

@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Intervention\Validation\Rules;
+
+use Intervention\Validation\AbstractRule;
+
+class LanguageCode extends AbstractRule
+{
+    private const VALUES = [
+        'aa', 'ab', 'ae', 'af', 'ak', 'am', 'an', 'ar', 'as', 'av', 'ay', 'az', 'ba', 'be', 'bg', 'bh', 'bi', 'bm',
+        'bn', 'bo', 'br', 'bs', 'ca', 'ce', 'ch', 'co', 'cr', 'cs', 'cu', 'cv', 'cy', 'da', 'de', 'dv', 'dz', 'ee',
+        'el', 'en', 'eo', 'es', 'et', 'eu', 'fa', 'ff', 'fi', 'fj', 'fo', 'fr', 'fy', 'ga', 'gd', 'gl', 'gn', 'gu',
+        'gv', 'ha', 'he', 'hi', 'ho', 'hr', 'ht', 'hu', 'hy', 'hz', 'ia', 'id', 'ie', 'ig', 'ii', 'ik', 'io', 'is',
+        'it', 'iu', 'ja', 'jv', 'ka', 'kg', 'ki', 'kj', 'kk', 'kl', 'km', 'kn', 'ko', 'kr', 'ks', 'ku', 'kv', 'kw',
+        'ky', 'la', 'lb', 'lg', 'li', 'ln', 'lo', 'lt', 'lu', 'lv', 'mg', 'mh', 'mi', 'mk', 'ml', 'mn', 'mr', 'ms',
+        'mt', 'my', 'na', 'nb', 'nd', 'ne', 'ng', 'nl', 'nn', 'no', 'nr', 'nv', 'ny', 'oc', 'oj', 'om', 'or', 'os',
+        'pa', 'pi', 'pl', 'ps', 'pt', 'qu', 'rm', 'rn', 'ro', 'ru', 'rw', 'sa', 'sc', 'sd', 'se', 'sg', 'si', 'sk',
+        'sl', 'sm', 'sn', 'so', 'sq', 'sr', 'ss', 'st', 'su', 'sv', 'sw', 'ta', 'te', 'tg', 'th', 'ti', 'tk', 'tl',
+        'tn', 'to', 'tr', 'ts', 'tt', 'tw', 'ty', 'ug', 'uk', 'ur', 'uz', 've', 'vi', 'vo', 'wa', 'wo', 'xh', 'yi',
+        'yo', 'za', 'zh', 'zu',
+    ];
+
+    public function __construct(protected bool $strict = true)
+    {
+        //
+    }
+
+    /**
+     * {@inheritdoc}
+     *
+     * @see Rule::isValid()
+     */
+    public function isValid(mixed $value): bool
+    {
+        $value = strval($value);
+
+        if ($this->strict === false) {
+            $value = strtolower($value);
+        }
+
+        return in_array($value, self::VALUES, strict: true);
+    }
+}

tests/Rules/LanguageCodeTest.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Intervention\Validation\Tests\Rules;
+
+use Generator;
+use Intervention\Validation\Rules\LanguageCode;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+
+final class LanguageCodeTest extends TestCase
+{
+    #[DataProvider('dataProvider')]
+    public function testValidationAlpha2(bool $result, string $value, bool $strict): void
+    {
+        $valid = (new LanguageCode($strict))->isValid($value);
+        $this->assertEquals($result, $valid);
+    }
+
+    public static function dataProvider(): Generator
+    {
+        yield [true, 'de', true];
+        yield [true, 'en', true];
+        yield [true, 'se', true];
+        yield [true, 'cs', true];
+        yield [true, 'EN', false];
+        yield [false, 'cz', true];
+        yield [false, 'us', true];
+        yield [false, 'EN', true];
+        yield [false, 'xx', true];
+    }
+}