class User

class User extends ArgumentDefaultPluginBase implements CacheableDependencyInterface {
  
  /**
   * The route match.
   *
   * @var \Drupal\Core\Routing\RouteMatchInterface
   */
  protected $routeMatch;
  
  /**
   * Constructs a new User instance.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin ID for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
   *   The route match.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, RouteMatchInterface $route_match) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->routeMatch = $route_match;
  }
  
  /**
   * {@inheritdoc}
   */
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['user'] = [
      'default' => '',
    ];
    return $options;
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    $form['user'] = [
      '#type' => 'checkbox',
      '#title' => $this->t('Also look for a node and use the node author'),
      '#default_value' => $this->options['user'],
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function getArgument() {
    // If there is a user object in the current route.
    if ($user = $this->routeMatch
      ->getParameter('user')) {
      if ($user instanceof UserInterface) {
        return $user->id();
      }
    }
    // If option to use node author; and node in current route.
    if (!empty($this->options['user']) && $node = $this->routeMatch
      ->getParameter('node')) {
      if ($node instanceof NodeInterface) {
        return $node->getOwnerId();
      }
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public function getCacheMaxAge() {
    return Cache::PERMANENT;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getCacheContexts() {
    return [
      'url',
    ];
  }

}