Locale Value Object

Locale.php

<?php
  
namespace ValueObject;

use ResourceBundle;
use Stringable;

final readonly class Locale implements Stringable
{
    private function __construct(public string $locale) {}

    public static function from(string $locale): self
    {
        static $locales = null;
        static $instances = [];
        if ($locales === null) {
            $locales = ResourceBundle::getLocales('');
        }
        $parts = \Locale::parseLocale($locale);
        if (! isset($parts['language'], $parts['region'])) {
            throw new InvalidArgumentException("Invalid locale $locale provided");
        }
        $normalizedLocale = $parts['language'] . '_' . strtoupper($parts['region']);
        if (!in_array($normalizedLocale, $locales, true)) {
            throw new InvalidArgumentException("Invalid locale $locale provided");
        }
        if (! isset($instances[$normalizedLocale])) {
            $instances[$normalizedLocale] = new self($normalizedLocale);
        }
        return $instances[$normalizedLocale];
    }

    public function __toString(): string
    {
        return $this->locale;
    }
}

LocaleTest.php

<?php

namespace Test\ValueObject;

use ValueObject\InvalidArgumentException;
use ValueObject\Locale;
use PHPUnit\Framework\Attributes\TestDox;
use PHPUnit\Framework\Attributes\TestWith;
use PHPUnit\Framework\TestCase;

class LocaleTest extends TestCase
{
    #[TestWith(['fr_FR', 'fr_FR'])]
    #[TestWith(['fr_CA', 'fr_CA'])]
    #[TestWith(['en_US', 'en_US'])]
    #[TestWith(['en_GB', 'en_GB'])]
    #[TestWith(['de-DE', 'de_DE'])]
    #[TestWith(['de-CH', 'de_CH'])]
    #[TestWith(['fr_CA.ISO-8895-1@euro', 'fr_CA'])]
    #[TestWith(['fr-CA-u-ca-gregorian-nu-arab', 'fr_CA'])]
    #[TestDox('Create locale $localeToTest with should return Locale instance with $expected value')]
    public function testValidLocaleShouldReturnLocaleInstance(string $localeToTest, string $expected): void
    {
        $locale = Locale::from($localeToTest);
        self::assertSame($expected, $locale->locale);
    }

    #[TestWith(['fr_DE'])]
    #[TestWith(['en_UK'])]
    #[TestWith(['foobar'])]
    #[TestDox('Create locale $localeToTest with should fail')]
    public function testWithInvalidLocaleShouldFail(string $localeToTest): void
    {
        $this->expectException(InvalidArgumentException::class);
        Locale::from($localeToTest);
    }
    
    public function testInstantiateTwiceSameLocaleReturnsSameInstance(): void
    {
        self::assertSame(
            Locale::from('fr_CA'),
            Locale::from('fr-CA-u-ca-gregorian-nu-arab')
        );
    }
}