class Rss

class Rss extends RssPluginBase {
  
  /**
   * The base table for this row plugin.
   *
   * @var string
   */
  public $base_table = 'node_field_data';
  
  /**
   * The base field for this row plugin.
   *
   * @var string
   */
  public $base_field = 'nid';
  
  /**
   * Stores the nodes loaded with preRender.
   *
   * @var array
   */
  public $nodes = [];
  
  /**
   * {@inheritdoc}
   */
  protected $entityTypeId = 'node';
  
  /**
   * {@inheritdoc}
   */
  public function buildOptionsForm_summary_options() {
    $options = parent::buildOptionsForm_summary_options();
    $options['title'] = $this->t('Title only');
    $options['default'] = $this->t('Use site default RSS settings');
    return $options;
  }
  public function summaryTitle() {
    $options = $this->buildOptionsForm_summary_options();
    return $options[$this->options['view_mode']];
  }
  public function preRender($values) {
    $nids = [];
    foreach ($values as $row) {
      $nids[] = $row->{$this->field_alias};
    }
    if (!empty($nids)) {
      $this->nodes = $this->entityTypeManager
        ->getStorage('node')
        ->loadMultiple($nids);
    }
  }
  public function render($row) {
    global $base_url;
    $nid = $row->{$this->field_alias};
    if (!is_numeric($nid)) {
      return;
    }
    $display_mode = $this->options['view_mode'];
    if ($display_mode == 'default') {
      $display_mode = \Drupal::config('system.rss')->get('items.view_mode');
    }
    // Load the specified node:
    /** @var \Drupal\node\NodeInterface $node */
    $node = $this->nodes[$nid];
    if (empty($node)) {
      return;
    }
    $node->rss_namespaces = [];
    $node->rss_elements = [
      [
        'key' => 'pubDate',
        'value' => gmdate('r', $node->getCreatedTime()),
      ],
      [
        'key' => 'dc:creator',
        'value' => $node->getOwner()
          ->getDisplayName(),
      ],
      [
        'key' => 'guid',
        'value' => $node->id() . ' at ' . $base_url,
        'attributes' => [
          'isPermaLink' => 'false',
        ],
      ],
    ];
    // The node gets built and modules add to or modify $node->rss_elements
    // and $node->rss_namespaces.
    $build_mode = $display_mode;
    $build = \Drupal::entityTypeManager()->getViewBuilder('node')
      ->view($node, $build_mode);
    unset($build['#theme']);
    if (!empty($node->rss_namespaces)) {
      $this->view->style_plugin->namespaces = array_merge($this->view->style_plugin->namespaces, $node->rss_namespaces);
    }
    $item = new \stdClass();
    if ($display_mode != 'title') {
      // We render node contents.
      $item->description = $build;
    }
    $item->title = $node->label();
    $item->link = $node->toUrl('canonical', [
      'absolute' => TRUE,
    ])
      ->toString();
    // Provide a reference so that the render call in
    // template_preprocess_views_view_row_rss() can still access it.
    $item->elements =& $node->rss_elements;
    $item->nid = $node->id();
    $build = [
      '#theme' => $this->themeFunctions(),
      '#view' => $this->view,
      '#options' => $this->options,
      '#row' => $item,
    ];
    return $build;
  }

}