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}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('current_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',
        ];
    }

}