class MetadataGenerator

class MetadataGenerator implements MetadataGeneratorInterface {
    
    /**
     * An object that checks if a user has access to edit a given entity field.
     *
     * @var \Drupal\quickedit\Access\QuickEditEntityFieldAccessCheckInterface
     */
    protected $accessChecker;
    
    /**
     * An object that determines which editor to attach to a given field.
     *
     * @var \Drupal\quickedit\EditorSelectorInterface
     */
    protected $editorSelector;
    
    /**
     * The manager for editor plugins.
     *
     * @var \Drupal\Component\Plugin\PluginManagerInterface
     */
    protected $editorManager;
    
    /**
     * Constructs a new MetadataGenerator.
     *
     * @param \Drupal\quickedit\Access\QuickEditEntityFieldAccessCheckInterface $access_checker
     *   An object that checks if a user has access to edit a given field.
     * @param \Drupal\quickedit\EditorSelectorInterface $editor_selector
     *   An object that determines which editor to attach to a given field.
     * @param \Drupal\Component\Plugin\PluginManagerInterface $editor_manager
     *   The manager for editor plugins.
     */
    public function __construct(QuickEditEntityFieldAccessCheckInterface $access_checker, EditorSelectorInterface $editor_selector, PluginManagerInterface $editor_manager) {
        $this->accessChecker = $access_checker;
        $this->editorSelector = $editor_selector;
        $this->editorManager = $editor_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public function generateEntityMetadata(EntityInterface $entity) {
        return [
            'label' => $entity->label(),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function generateFieldMetadata(FieldItemListInterface $items, $view_mode) {
        $entity = $items->getEntity();
        $field_name = $items->getFieldDefinition()
            ->getName();
        // Early-return if user does not have access.
        $access = $this->accessChecker
            ->accessEditEntityField($entity, $field_name);
        if (!$access->isAllowed()) {
            return [
                'access' => FALSE,
            ];
        }
        // Early-return if no editor is available.
        $formatter_id = EntityViewDisplay::collectRenderDisplay($entity, $view_mode)->getRenderer($field_name)
            ->getPluginId();
        $editor_id = $this->editorSelector
            ->getEditor($formatter_id, $items);
        if (!isset($editor_id)) {
            return [
                'access' => FALSE,
            ];
        }
        // Gather metadata, allow the editor to add additional metadata of its own.
        $label = $items->getFieldDefinition()
            ->getLabel();
        $editor = $this->editorManager
            ->createInstance($editor_id);
        $metadata = [
            'label' => $label,
            'access' => TRUE,
            'editor' => $editor_id,
        ];
        $custom_metadata = $editor->getMetadata($items);
        if (count($custom_metadata)) {
            $metadata['custom'] = $custom_metadata;
        }
        return $metadata;
    }

}