class ViewsSelection

class ViewsSelection extends SelectionPluginBase implements ContainerFactoryPluginInterface {
    use StringTranslationTrait;
    
    /**
     * The loaded View object.
     *
     * @var \Drupal\views\ViewExecutable
     */
    protected $view;
    
    /**
     * The entity type manager service.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The module handler service.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * The current user.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $currentUser;
    
    /**
     * The renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * Constructs a new ViewsSelection 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 service.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler service.
     * @param \Drupal\Core\Session\AccountInterface $current_user
     *   The current user.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, ModuleHandlerInterface $module_handler, AccountInterface $current_user, RendererInterface $renderer) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->entityTypeManager = $entity_type_manager;
        $this->moduleHandler = $module_handler;
        $this->currentUser = $current_user;
        $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('entity_type.manager'), $container->get('module_handler'), $container->get('current_user'), $container->get('renderer'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'view' => [
                'view_name' => NULL,
                'display_name' => NULL,
                'arguments' => [],
            ],
        ] + parent::defaultConfiguration();
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $form = parent::buildConfigurationForm($form, $form_state);
        $view_settings = $this->getConfiguration()['view'];
        $displays = Views::getApplicableViews('entity_reference_display');
        // Filter views that list the entity type we want, and group the separate
        // displays by view.
        $entity_type = $this->entityTypeManager
            ->getDefinition($this->configuration['target_type']);
        $view_storage = $this->entityTypeManager
            ->getStorage('view');
        $options = [];
        foreach ($displays as $data) {
            [
                $view_id,
                $display_id,
            ] = $data;
            $view = $view_storage->load($view_id);
            if (in_array($view->get('base_table'), [
                $entity_type->getBaseTable(),
                $entity_type->getDataTable(),
            ])) {
                $display = $view->get('display');
                $options[$view_id . ':' . $display_id] = $view_id . ' - ' . $display[$display_id]['display_title'];
            }
        }
        // The value of the 'view_and_display' select below will need to be split
        // into 'view_name' and 'view_display' in the final submitted values, so
        // we massage the data at validate time on the wrapping element (not
        // ideal).
        $form['view']['#element_validate'] = [
            [
                static::class,
                'settingsFormValidate',
            ],
        ];
        if ($options) {
            $default = !empty($view_settings['view_name']) ? $view_settings['view_name'] . ':' . $view_settings['display_name'] : NULL;
            $form['view']['view_and_display'] = [
                '#type' => 'select',
                '#title' => $this->t('View used to select the entities'),
                '#required' => TRUE,
                '#options' => $options,
                '#default_value' => $default,
                '#description' => '<p>' . $this->t('Choose the view and display that select the entities that can be referenced.<br />Only views with a display of type "Entity Reference" are eligible.') . '</p>',
            ];
            $default = !empty($view_settings['arguments']) ? implode(', ', $view_settings['arguments']) : '';
            $form['view']['arguments'] = [
                '#type' => 'textfield',
                '#title' => $this->t('View arguments'),
                '#default_value' => $default,
                '#required' => FALSE,
                '#description' => $this->t('Provide a comma separated list of arguments to pass to the view.'),
            ];
        }
        else {
            if ($this->currentUser
                ->hasPermission('administer views') && $this->moduleHandler
                ->moduleExists('views_ui')) {
                $form['view']['no_view_help'] = [
                    '#markup' => '<p>' . $this->t('No eligible views were found. <a href=":create">Create a view</a> with an <em>Entity Reference</em> display, or add such a display to an <a href=":existing">existing view</a>.', [
                        ':create' => Url::fromRoute('views_ui.add')->toString(),
                        ':existing' => Url::fromRoute('entity.view.collection')->toString(),
                    ]) . '</p>',
                ];
            }
            else {
                $form['view']['no_view_help']['#markup'] = '<p>' . $this->t('No eligible views were found.') . '</p>';
            }
        }
        return $form;
    }
    
    /**
     * Initializes a view.
     *
     * @param string|null $match
     *   (Optional) Text to match the label against. Defaults to NULL.
     * @param string $match_operator
     *   (Optional) The operation the matching should be done with. Defaults
     *   to "CONTAINS".
     * @param int $limit
     *   Limit the query to a given number of items. Defaults to 0, which
     *   indicates no limiting.
     * @param array|null $ids
     *   Array of entity IDs. Defaults to NULL.
     *
     * @return bool
     *   Return TRUE if the view was initialized, FALSE otherwise.
     */
    protected function initializeView($match = NULL, $match_operator = 'CONTAINS', $limit = 0, $ids = NULL) {
        $view_name = $this->getConfiguration()['view']['view_name'];
        $display_name = $this->getConfiguration()['view']['display_name'];
        // Check that the view is valid and the display still exists.
        $this->view = Views::getView($view_name);
        if (!$this->view || !$this->view
            ->access($display_name)) {
            \Drupal::messenger()->addWarning($this->t('The reference view %view_name cannot be found.', [
                '%view_name' => $view_name,
            ]));
            return FALSE;
        }
        $this->view
            ->setDisplay($display_name);
        // Pass options to the display handler to make them available later.
        $entity_reference_options = [
            'match' => $match,
            'match_operator' => $match_operator,
            'limit' => $limit,
            'ids' => $ids,
        ];
        $this->view->displayHandlers
            ->get($display_name)
            ->setOption('entity_reference_options', $entity_reference_options);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getReferenceableEntities($match = NULL, $match_operator = 'CONTAINS', $limit = 0) {
        $entities = [];
        if ($display_execution_results = $this->getDisplayExecutionResults($match, $match_operator, $limit)) {
            $entities = $this->stripAdminAndAnchorTagsFromResults($display_execution_results);
        }
        return $entities;
    }
    
    /**
     * Fetches the results of executing the display.
     *
     * @param string|null $match
     *   (Optional) Text to match the label against. Defaults to NULL.
     * @param string $match_operator
     *   (Optional) The operation the matching should be done with. Defaults
     *   to "CONTAINS".
     * @param int $limit
     *   Limit the query to a given number of items. Defaults to 0, which
     *   indicates no limiting.
     * @param array|null $ids
     *   Array of entity IDs. Defaults to NULL.
     *
     * @return array
     *   The results.
     */
    protected function getDisplayExecutionResults(string $match = NULL, string $match_operator = 'CONTAINS', int $limit = 0, array $ids = NULL) {
        $display_name = $this->getConfiguration()['view']['display_name'];
        $arguments = $this->getConfiguration()['view']['arguments'];
        $results = [];
        if ($this->initializeView($match, $match_operator, $limit, $ids)) {
            $results = $this->view
                ->executeDisplay($display_name, $arguments);
        }
        return $results;
    }
    
    /**
     * Strips all admin and anchor tags from a result list.
     *
     * These results are usually displayed in an autocomplete field, which is
     * surrounded by anchor tags. Most tags are allowed inside anchor tags, except
     * for other anchor tags.
     *
     * @param array $results
     *   The result list.
     *
     * @return array
     *   The provided result list with anchor tags removed.
     */
    protected function stripAdminAndAnchorTagsFromResults(array $results) {
        $allowed_tags = Xss::getAdminTagList();
        if (($key = array_search('a', $allowed_tags)) !== FALSE) {
            unset($allowed_tags[$key]);
        }
        $stripped_results = [];
        foreach (Element::children($results) as $id) {
            $entity = $results[$id]['#row']->_entity;
            $stripped_results[$entity->bundle()][$id] = ViewsRenderPipelineMarkup::create(Xss::filter($this->renderer
                ->renderPlain($results[$id]), $allowed_tags));
        }
        return $stripped_results;
    }
    
    /**
     * {@inheritdoc}
     */
    public function countReferenceableEntities($match = NULL, $match_operator = 'CONTAINS') {
        $this->getReferenceableEntities($match, $match_operator);
        return $this->view->pager
            ->getTotalItems();
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateReferenceableEntities(array $ids) {
        $entities = $this->getDisplayExecutionResults(NULL, 'CONTAINS', 0, $ids);
        $result = [];
        if ($entities) {
            $result = array_keys($entities);
        }
        return $result;
    }
    
    /**
     * Element validate; Check View is valid.
     */
    public static function settingsFormValidate($element, FormStateInterface $form_state, $form) {
        // Split view name and display name from the 'view_and_display' value.
        if (!empty($element['view_and_display']['#value'])) {
            [
                $view,
                $display,
            ] = explode(':', $element['view_and_display']['#value']);
        }
        else {
            $form_state->setError($element, new TranslatableMarkup('The views entity selection mode requires a view.'));
            return;
        }
        // Explode the 'arguments' string into an actual array. Beware, explode()
        // turns an empty string into an array with one empty string. We'll need an
        // empty array instead.
        $arguments_string = trim($element['arguments']['#value']);
        if ($arguments_string === '') {
            $arguments = [];
        }
        else {
            // array_map() is called to trim whitespaces from the arguments.
            $arguments = array_map('trim', explode(',', $arguments_string));
        }
        $value = [
            'view_name' => $view,
            'display_name' => $display,
            'arguments' => $arguments,
        ];
        $form_state->setValueForElement($element, $value);
    }

}