class UrlEncode

class UrlEncode extends ProcessPluginBase {

  /**
   * {@inheritdoc}
   */
  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {

    // Only apply to a full URL.
    if (is_string($value) && strpos($value, '://') > 0) {

      // URL encode everything after the hostname.
      $parsed_url = parse_url($value);

      // Fail on seriously malformed URLs.
      if ($parsed_url === FALSE) {
        throw new MigrateException("Value '{$value}' is not a valid URL");
      }

      // Iterate over specific pieces of the URL raw URL encoding each one.
      $url_parts_to_encode = [
        'path',
        'query',
        'fragment',
      ];
      foreach ($parsed_url as $parsed_url_key => $parsed_url_value) {
        if (in_array($parsed_url_key, $url_parts_to_encode)) {

          // urlencode() would convert spaces to + signs.
          $urlencoded_parsed_url_value = rawurlencode($parsed_url_value);

          // Restore special characters depending on which part of the URL this is.
          switch ($parsed_url_key) {
            case 'query':
              $urlencoded_parsed_url_value = str_replace('%26', '&', $urlencoded_parsed_url_value);
              break;
            case 'path':
              $urlencoded_parsed_url_value = str_replace('%2F', '/', $urlencoded_parsed_url_value);
              break;
          }
          $parsed_url[$parsed_url_key] = $urlencoded_parsed_url_value;
        }
      }
      $value = (string) Uri::fromParts($parsed_url);
    }
    return $value;
  }

}