class WorkspaceSelection

class WorkspaceSelection extends DefaultSelection {
    
    /**
     * The workspace repository service.
     *
     * @var \Drupal\workspaces\WorkspaceRepositoryInterface
     */
    protected $workspaceRepository;
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        $instance = parent::create($container, $configuration, $plugin_id, $plugin_definition);
        $instance->workspaceRepository = $container->get('workspaces.repository');
        return $instance;
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'sort' => [
                'field' => 'label',
                'direction' => 'asc',
            ],
        ] + parent::defaultConfiguration();
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $form = parent::buildConfigurationForm($form, $form_state);
        // Sorting is not possible for workspaces because we always sort them by
        // depth and label.
        $form['sort']['#access'] = FALSE;
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getReferenceableEntities($match = NULL, $match_operator = 'CONTAINS', $limit = 0) {
        // Get all the workspace entities and sort them in tree order.
        $storage = $this->entityTypeManager
            ->getStorage('workspace');
        $workspace_tree = $this->workspaceRepository
            ->loadTree();
        $entities = array_replace($workspace_tree, $storage->loadMultiple());
        // If we need to restrict the list of workspaces by searching only a part of
        // their label ($match) or by a number of results ($limit), the workspace
        // tree would be mangled because it wouldn't contain all the tree items.
        if ($match || $limit) {
            $options = parent::getReferenceableEntities($match, $match_operator, $limit);
        }
        else {
            $options = [];
            foreach ($entities as $entity) {
                $options[$entity->bundle()][$entity->id()] = str_repeat('-', $workspace_tree[$entity->id()]['depth']) . Html::escape($this->entityRepository
                    ->getTranslationFromContext($entity)
                    ->label());
            }
        }
        $restricted_access_entities = [];
        foreach ($options as $bundle => $bundle_options) {
            foreach (array_keys($bundle_options) as $id) {
                // If a user can not view a workspace, we need to prevent them from
                // referencing that workspace as well as its descendants.
                if (in_array($id, $restricted_access_entities) || !$entities[$id]->access('view', $this->currentUser)) {
                    $restricted_access_entities += $workspace_tree[$id]['descendants'];
                    unset($options[$bundle][$id]);
                }
            }
        }
        return $options;
    }

}