class PathProcessorTest

class PathProcessorTest implements InboundPathProcessorInterface, OutboundPathProcessorInterface {

  /**
   * {@inheritdoc}
   */
  public function processInbound($path, Request $request) {

    // Rewrite user/username to user/uid.
    if (preg_match('!^/user/([^/]+)(/.*)?!', $path, $matches)) {
      if ($account = user_load_by_name($matches[1])) {
        $matches += [
          2 => '',
        ];
        $path = '/user/' . $account
          ->id() . $matches[2];
      }
    }
    if ($path == '/url-alter-test/bar') {
      $path = '/url-alter-test/foo';
    }
    return $path;
  }

  /**
   * {@inheritdoc}
   */
  public function processOutbound($path, &$options = [], Request $request = NULL, BubbleableMetadata $bubbleable_metadata = NULL) {

    // Rewrite user/uid to user/username.
    if (preg_match('!^/user/([0-9]+)(/.*)?!', $path, $matches)) {
      if ($account = User::load($matches[1])) {
        $matches += [
          2 => '',
        ];
        $path = '/user/' . $account
          ->getAccountName() . $matches[2];
        if ($bubbleable_metadata) {
          $bubbleable_metadata
            ->addCacheTags($account
            ->getCacheTags());
        }
      }
    }

    // Verify that $options are alterable.
    if ($path == '/user/login') {
      $options['query']['foo'] = 'bar';
    }
    return $path;
  }

}