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;
    }

}