class Feed

class Feed extends PathPluginBase implements ResponseDisplayPluginInterface {
    
    /**
     * Whether the display allows the use of AJAX or not.
     *
     * @var bool
     */
    protected $ajaxEnabled = FALSE;
    
    /**
     * Whether the display allows the use of a pager or not.
     *
     * @var bool
     */
    protected $usesPager = FALSE;
    
    /**
     * The renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * Constructs a PathPluginBase 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\Routing\RouteProviderInterface $route_provider
     *   The route provider.
     * @param \Drupal\Core\State\StateInterface $state
     *   The state key value store.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, RouteProviderInterface $route_provider, StateInterface $state, RendererInterface $renderer) {
        parent::__construct($configuration, $plugin_id, $plugin_definition, $route_provider, $state);
        $this->renderer = $renderer;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('router.route_provider'), $container->get('state'), $container->get('renderer'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getType() {
        return 'feed';
    }
    
    /**
     * {@inheritdoc}
     */
    public static function buildResponse($view_id, $display_id, array $args = []) {
        $build = static::buildBasicRenderable($view_id, $display_id, $args);
        // Set up an empty response, so for example RSS can set the proper
        // Content-Type header.
        $response = new CacheableResponse('', 200);
        $build['#response'] = $response;
        
        /** @var \Drupal\Core\Render\RendererInterface $renderer */
        $renderer = \Drupal::service('renderer');
        $output = (string) $renderer->renderRoot($build);
        if (empty($output)) {
            throw new NotFoundHttpException();
        }
        $response->setContent($output);
        $cache_metadata = CacheableMetadata::createFromRenderArray($build);
        $response->addCacheableDependency($cache_metadata);
        // Set the HTTP headers and status code on the response if any bubbled.
        if (!empty($build['#attached']['http_header'])) {
            static::setHeaders($response, $build['#attached']['http_header']);
        }
        return $response;
    }
    
    /**
     * Sets headers on a response object.
     *
     * @param \Drupal\Core\Cache\CacheableResponse $response
     *   The HTML response to update.
     * @param array $headers
     *   The headers to set, as an array. The items in this array should be as
     *   follows:
     *   - The header name.
     *   - The header value.
     *   - (optional) Whether to replace a current value with the new one, or add
     *     it to the others. If the value is not replaced, it will be appended,
     *     resulting in a header like this: 'Header: value1,value2'.
     *
     * @see \Drupal\Core\Render\HtmlResponseAttachmentsProcessor::setHeaders()
     */
    protected static function setHeaders(CacheableResponse $response, array $headers) : void {
        foreach ($headers as $values) {
            $name = $values[0];
            $value = $values[1];
            $replace = !empty($values[2]);
            // Drupal treats the HTTP response status code like a header, even though
            // it really is not.
            if (strtolower($name) === 'status') {
                $response->setStatusCode($value);
            }
            else {
                $response->headers
                    ->set($name, $value, $replace);
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function execute() {
        parent::execute();
        return $this->view
            ->render();
    }
    
    /**
     * {@inheritdoc}
     */
    public function preview() {
        $output = $this->view
            ->render();
        if (!empty($this->view->live_preview)) {
            $output = [
                '#prefix' => '<pre>',
                '#plain_text' => $this->renderer
                    ->renderRoot($output),
                '#suffix' => '</pre>',
            ];
        }
        return $output;
    }
    
    /**
     * {@inheritdoc}
     */
    public function render() {
        $build = $this->view->style_plugin
            ->render($this->view->result);
        $this->applyDisplayCacheabilityMetadata($build);
        return $build;
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultableSections($section = NULL) {
        $sections = parent::defaultableSections($section);
        if (in_array($section, [
            'style',
            'row',
        ])) {
            return FALSE;
        }
        // Tell views our sitename_title option belongs in the title section.
        if ($section == 'title') {
            $sections[] = 'sitename_title';
        }
        elseif (!$section) {
            $sections['title'][] = 'sitename_title';
        }
        return $sections;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['displays'] = [
            'default' => [],
        ];
        // Overrides for standard stuff.
        $options['style']['contains']['type']['default'] = 'rss';
        $options['style']['contains']['options']['default'] = [
            'description' => '',
        ];
        $options['sitename_title']['default'] = FALSE;
        $options['row']['contains']['type']['default'] = 'rss_fields';
        $options['defaults']['default']['style'] = FALSE;
        $options['defaults']['default']['row'] = FALSE;
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function newDisplay() {
        parent::newDisplay();
        // Set the default row style. Ideally this would be part of the option
        // definition, but in this case it's dependent on the view's base table,
        // which we don't know until init().
        if (empty($this->options['row']['type']) || $this->options['row']['type'] === 'rss_fields') {
            $row_plugins = Views::fetchPluginNames('row', $this->getType(), [
                $this->view->storage
                    ->get('base_table'),
            ]);
            $default_row_plugin = key($row_plugins);
            $options = $this->getOption('row');
            $options['type'] = $default_row_plugin;
            $this->setOption('row', $options);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function optionsSummary(&$categories, &$options) {
        parent::optionsSummary($categories, $options);
        // Since we're childing off the 'path' type, we'll still *call* our
        // category 'page' but let's override it so it says feed settings.
        $categories['page'] = [
            'title' => $this->t('Feed settings'),
            'column' => 'second',
            'build' => [
                '#weight' => -10,
            ],
        ];
        if ($this->getOption('sitename_title')) {
            $options['title']['value'] = $this->t('Using the site name');
        }
        $displays = array_filter($this->getOption('displays'));
        if (count($displays) > 1) {
            $attach_to = $this->t('Multiple displays');
        }
        elseif (count($displays) == 1) {
            $display = array_shift($displays);
            $displays = $this->view->storage
                ->get('display');
            if (!empty($displays[$display])) {
                $attach_to = $displays[$display]['display_title'];
            }
        }
        if (!isset($attach_to)) {
            $attach_to = $this->t('None');
        }
        $options['displays'] = [
            'category' => 'page',
            'title' => $this->t('Attach to'),
            'value' => $attach_to,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        // It is very important to call the parent function here.
        parent::buildOptionsForm($form, $form_state);
        switch ($form_state->get('section')) {
            case 'title':
                $title = $form['title'];
                // A little juggling to move the 'title' field beyond our checkbox.
                unset($form['title']);
                $form['sitename_title'] = [
                    '#type' => 'checkbox',
                    '#title' => $this->t('Use the site name for the title'),
                    '#default_value' => $this->getOption('sitename_title'),
                ];
                $form['title'] = $title;
                $form['title']['#states'] = [
                    'visible' => [
                        ':input[name="sitename_title"]' => [
                            'checked' => FALSE,
                        ],
                    ],
                ];
                break;
            case 'displays':
                $form['#title'] .= $this->t('Attach to');
                $displays = [];
                foreach ($this->view->storage
                    ->get('display') as $display_id => $display) {
                    // @todo The display plugin should have display_title and id as well.
                    if ($this->view->displayHandlers
                        ->has($display_id) && $this->view->displayHandlers
                        ->get($display_id)
                        ->acceptAttachments()) {
                        $displays[$display_id] = $display['display_title'];
                    }
                }
                $form['displays'] = [
                    '#title' => $this->t('Displays'),
                    '#type' => 'checkboxes',
                    '#description' => $this->t('The feed icon will be available only to the selected displays.'),
                    '#options' => array_map('\\Drupal\\Component\\Utility\\Html::escape', $displays),
                    '#default_value' => $this->getOption('displays'),
                ];
                break;
            case 'path':
                $form['path']['#description'] = $this->t('This view will be displayed by visiting this path on your site. It is recommended that the path be something like "path/%/%/feed" or "path/%/%/rss.xml", putting one % in the path for each contextual filter you have defined in the view.');
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitOptionsForm(&$form, FormStateInterface $form_state) {
        parent::submitOptionsForm($form, $form_state);
        $section = $form_state->get('section');
        switch ($section) {
            case 'title':
                $this->setOption('sitename_title', $form_state->getValue('sitename_title'));
                break;
            case 'displays':
                $this->setOption($section, $form_state->getValue($section));
                break;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function attachTo(ViewExecutable $view, $display_id, array &$build) {
        $displays = $this->getOption('displays');
        if (empty($displays[$display_id])) {
            return;
        }
        // Defer to the feed style; it may put in meta information, and/or
        // attach a feed icon.
        $view->setArguments($this->view->args);
        $view->setDisplay($this->display['id']);
        $view->buildTitle();
        if ($plugin = $view->display_handler
            ->getPlugin('style')) {
            $plugin->attachTo($build, $display_id, $view->getUrl(), $view->getTitle());
            foreach ($view->feedIcons as $feed_icon) {
                $this->view->feedIcons[] = $feed_icon;
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function usesLinkDisplay() {
        return TRUE;
    }

}