class HostnameValidator

class HostnameValidator extends ConstraintValidator {
    
    /**
     * https://tools.ietf.org/html/rfc2606.
     */
    private const RESERVED_TLDS = [
        'example',
        'invalid',
        'localhost',
        'test',
    ];
    public function validate(mixed $value, Constraint $constraint) : void {
        if (!$constraint instanceof Hostname) {
            throw new UnexpectedTypeException($constraint, Hostname::class);
        }
        if (null === $value || '' === $value) {
            return;
        }
        if (!\is_scalar($value) && !$value instanceof \Stringable) {
            throw new UnexpectedValueException($value, 'string');
        }
        $value = (string) $value;
        if ('' === $value) {
            return;
        }
        if (!$this->isValid($value) || $constraint->requireTld && !$this->hasValidTld($value)) {
            $this->context
                ->buildViolation($constraint->message)
                ->setParameter('{{ value }}', $this->formatValue($value))
                ->setCode(Hostname::INVALID_HOSTNAME_ERROR)
                ->addViolation();
        }
    }
    private function isValid(string $domain) : bool {
        return false !== filter_var($domain, \FILTER_VALIDATE_DOMAIN, \FILTER_FLAG_HOSTNAME);
    }
    private function hasValidTld(string $domain) : bool {
        return str_contains($domain, '.') && !\in_array(substr($domain, strrpos($domain, '.') + 1), self::RESERVED_TLDS, true);
    }

}