class Rss

class Rss extends StylePluginBase {
    
    /**
     * {@inheritdoc}
     */
    protected $usesRowPlugin = TRUE;
    public function attachTo(array &$build, $display_id, Url $feed_url, $title) {
        $url_options = [];
        $input = $this->view
            ->getExposedInput();
        if ($input) {
            $url_options['query'] = $input;
        }
        $url_options['absolute'] = TRUE;
        $url = $feed_url->setOptions($url_options)
            ->toString();
        // Add the RSS icon to the view.
        $this->view->feedIcons[] = [
            '#theme' => 'feed_icon',
            '#url' => $url,
            '#title' => $title,
        ];
        // Attach a link to the RSS feed, which is an alternate representation.
        $build['#attached']['html_head_link'][][] = [
            'rel' => 'alternate',
            'type' => 'application/rss+xml',
            'title' => $title,
            'href' => $url,
        ];
    }
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['description'] = [
            'default' => '',
        ];
        return $options;
    }
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        $form['description'] = [
            '#type' => 'textfield',
            '#title' => $this->t('RSS description'),
            '#default_value' => $this->options['description'],
            '#description' => $this->t('This will appear in the RSS feed itself.'),
            '#maxlength' => 1024,
        ];
    }
    
    /**
     * Return an array of additional XHTML elements to add to the channel.
     *
     * @return array
     *   A render array.
     */
    protected function getChannelElements() {
        return [];
    }
    
    /**
     * Get RSS feed description.
     *
     * @return string
     *   The string containing the description with the tokens replaced.
     */
    public function getDescription() {
        $description = $this->options['description'];
        // Allow substitutions from the first row.
        $description = $this->tokenizeValue($description, 0);
        return $description;
    }
    public function render() {
        $rows = [];
        // This will be filled in by the row plugin and is used later on in the
        // theming output.
        $this->namespaces = [
            'xmlns:dc' => 'http://purl.org/dc/elements/1.1/',
        ];
        // Fetch any additional elements for the channel and merge in their
        // namespaces.
        $this->channel_elements = $this->getChannelElements();
        foreach ($this->channel_elements as $element) {
            if (isset($element['namespace'])) {
                $this->namespaces = array_merge($this->namespaces, $element['namespace']);
            }
        }
        foreach ($this->view->result as $row_index => $row) {
            $this->view->row_index = $row_index;
            $rows[] = $this->view->rowPlugin
                ->render($row);
        }
        $build = [
            '#theme' => $this->themeFunctions(),
            '#view' => $this->view,
            '#options' => $this->options,
            '#rows' => $rows,
        ];
        unset($this->view->row_index);
        return $build;
    }

}