问如何检查域名是否为punycode？

EN

class PunycodeCheck extends Punycode
{
  public function check_encoded($decoded)
  {
      $extract = self::byteLength(self::punycodePrefix);
      $check_pref = $this->UnicodeTranscoder->utf8_ucs4array(self::punycodePrefix);
      $check_deco = array_slice($decoded, 0, $extract);
      if ($check_pref == $check_deco) 
          return true;
      return false;
   }
}

/**
 * Validate helper.
 *
 * @author Maksim T. <zapalm@yandex.com>
 */
class ValidateHelper
{
    /**
     * Checks if the given domain is in Punycode.
     *
     * @param string $domain The domain to check.
     *
     * @return bool Whether the domain is in Punycode.
     *
     * @see https://developer.mozilla.org/en-US/docs/Mozilla/Internationalized_domain_names_support_in_Mozilla#ASCII-compatible_encoding_.28ACE.29
     *
     * @author Maksim T. <zapalm@yandex.com>
     */
    public static function isPunycodeDomain($domain)
    {
        $hasPunycode = false;

        foreach (explode('.', $domain) as $part) {
            if (false === static::isAscii($part)) {
                return false;
            }

            if (static::isPunycode($part)) {
                $hasPunycode = true;
            }
        }

        return $hasPunycode;
    }

    /**
     * Checks if the given value is in ASCII character encoding.
     *
     * @param string $value The value to check.
     *
     * @return bool Whether the value is in ASCII character encoding.
     *
     * @see https://en.wikipedia.org/wiki/ASCII
     *
     * @author Maksim T. <zapalm@yandex.com>
     */
    public static function isAscii($value)
    {
        return ('ASCII' === mb_detect_encoding($value, 'ASCII', true));
    }

    /**
     * Checks if the given value is in Punycode.
     *
     * @param string $value The value to check.
     *
     * @return bool Whether the value is in Punycode.
     *
     * @throws \LogicException If the string is not encoded by UTF-8.
     *
     * @see https://en.wikipedia.org/wiki/Punycode
     *
     * @author Maksim T. <zapalm@yandex.com>
     */
    public static function isPunycode($value)
    {
        if (false === static::isAscii($value)) {
            return false;
        }

        if ('UTF-8' !== mb_detect_encoding($value, 'UTF-8', true)) {
            throw new \LogicException('The string should be encoded by UTF-8 to do the right check.');
        }

        return (0 === mb_stripos($value, 'xn--', 0, 'UTF-8'));
    }
}

/**
 * Test Punycode domain validator.
 *
 * @author Maksim T. <zapalm@yandex.com>
 */
class Test
{
    /**
     * Run the test.
     *
     * @author Maksim T. <zapalm@yandex.com>
     */
    public static function run()
    {
        $domains = [
            // White list
            'почта@престашоп.рф'          => false, // Russian, Unicode
            'modulez.ru'                  => false, // English, ASCII
            'xn--80aj2abdcii9c.xn--p1ai'  => true,  // Russian, ASCII
            'xn--80a1acn3a.xn--j1amh'     => true,  // Ukrainian, ASCII
            'xn--srensen-90a.example.com' => true,  // German, ASCII
            'xn--mxahbxey0c.xn--xxaf0a'   => true,  // Greek, ASCII
            'xn--fsqu00a.xn--4rr70v'      => true,  // Chinese, ASCII

            // Black List
            'xn--престашоп.xn--рф'        => false, // Russian, Unicode
            'xn--prestashop.рф'           => false, // Russian, Unicode
        ];

        foreach ($domains as $domain => $isPunycode) {
            echo 'TEST: ' . $domain . (ValidateHelper::isPunycodeDomain($domain)
                ? ' is in Punycode [' . ($isPunycode ? 'OK' : 'FAIL') . ']'
                : ' is NOT in Punycode [' . (false === $isPunycode ? 'OK' : 'FAIL') . ']'
            ) . PHP_EOL;
        }
    }
}

Test::run();

// The output result:
//
// TEST: почта@престашоп.рф is NOT in Punycode [OK]
// TEST: modulez.ru is NOT in Punycode [OK]
// TEST: xn--80aj2abdcii9c.xn--p1ai is in Punycode [OK]
// TEST: xn--80a1acn3a.xn--j1amh is in Punycode [OK]
// TEST: xn--srensen-90a.example.com is in Punycode [OK]
// TEST: xn--mxahbxey0c.xn--xxaf0a is in Punycode [OK]
// TEST: xn--fsqu00a.xn--4rr70v is in Punycode [OK]
// TEST: xn--престашоп.xn--рф is NOT in Punycode [OK]
// TEST: xn--prestashop.рф is NOT in Punycode [OK]