class RssPluginBase

abstract class RssPluginBase extends RowPluginBase {
  
  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;
  
  /**
   * The entity display repository.
   *
   * @var \Drupal\Core\Entity\EntityDisplayRepositoryInterface
   */
  protected $entityDisplayRepository;
  
  /**
   * Constructs a RssPluginBase  object.
   *
   * @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\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   * @param \Drupal\Core\Entity\EntityDisplayRepositoryInterface $entity_display_repository
   *   The entity display repository.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, EntityDisplayRepositoryInterface $entity_display_repository) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->entityTypeManager = $entity_type_manager;
    $this->entityDisplayRepository = $entity_display_repository;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('entity_type.manager'), $container->get('entity_display.repository'));
  }
  
  /**
   * The ID of the entity type for which this is an RSS row plugin.
   *
   * @var string
   */
  protected $entityTypeId;
  
  /**
   * {@inheritdoc}
   */
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['view_mode'] = [
      'default' => 'default',
    ];
    return $options;
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    parent::buildOptionsForm($form, $form_state);
    $form['view_mode'] = [
      '#type' => 'select',
      '#title' => $this->t('Display type'),
      '#options' => $this->buildOptionsForm_summary_options(),
      '#default_value' => $this->options['view_mode'],
    ];
  }
  
  /**
   * Return the main options, which are shown in the summary title.
   */
  public function buildOptionsForm_summary_options() {
    $view_modes = $this->entityDisplayRepository
      ->getViewModes($this->entityTypeId);
    $options = [];
    foreach ($view_modes as $mode => $settings) {
      $options[$mode] = $settings['label'];
    }
    return $options;
  }
  
  /**
   * {@inheritdoc}
   */
  public function calculateDependencies() {
    $dependencies = parent::calculateDependencies();
    $view_mode = $this->entityTypeManager
      ->getStorage('entity_view_mode')
      ->load($this->entityTypeId . '.' . $this->options['view_mode']);
    if ($view_mode) {
      $dependencies[$view_mode->getConfigDependencyKey()][] = $view_mode->getConfigDependencyName();
    }
    return $dependencies;
  }

}