use Symfony\Component\OptionsResolver\OptionsResolver;

class Mailer
{
    protected array $options;

    public function __construct(array $options = [])
    {
        $resolver = new OptionsResolver();
        $this->configureOptions($resolver);
        $this->options = $resolver->resolve($options);
    }

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->setDefaults([
            'host'       => 'smtp.example.org',
            'username'   => 'user',
            'password'   => 'pa$$word',
            'port'       => 25,
            'encryption' => null,
        ]);
    }
}

// Required options (must be provided)
$resolver->setRequired(['host', 'username']);

// Defined options (allowed but no default)
$resolver->setDefined(['port', 'encryption']);

$resolver->setAllowedTypes('host', 'string');
$resolver->setAllowedTypes('port', ['null', 'int']);
$resolver->setAllowedTypes('port', 'int|null');  // Symfony 7.3+
$resolver->setAllowedTypes('dates', 'DateTime[]');
$resolver->setAllowedTypes('logger', 'Psr\Log\LoggerInterface');

$resolver->setAllowedValues('transport', ['sendmail', 'mail', 'smtp']);

// With closure
$resolver->setAllowedValues('port', function ($value): bool {
    return $value > 0 && $value < 65536;
});

use Symfony\Component\OptionsResolver\Options;

$resolver->setNormalizer('host', function (Options $options, string $value): string {
    if (!str_starts_with($value, 'http://')) {
        $value = 'http://' . $value;
    }
    return $value;
});

$resolver->setDefault('port', function (Options $options): int {
    return $options['encryption'] === 'ssl' ? 465 : 25;
});

$resolver->setOptions('spool', function (OptionsResolver $spoolResolver): void {
    $spoolResolver->setDefaults([
        'type' => 'file',
        'path' => '/path/to/spool',
    ]);
    $spoolResolver->setAllowedValues('type', ['file', 'memory']);
});

// Usage
$mailer = new Mailer([
    'spool' => ['type' => 'memory'],
]);

$resolver->define('host')
    ->required()
    ->default('smtp.example.org')
    ->allowedTypes('string')
    ->info('The IP address or hostname');

$resolver->setDeprecated(
    'hostname',
    'acme/package',
    '1.2',
    'The option "%name%" is deprecated, use "host" instead.'
);