class CKEditor5MediaController

class CKEditor5MediaController extends ControllerBase {
    
    /**
     * The currently authenticated user.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $currentUser;
    
    /**
     * The entity repository.
     *
     * @var \Drupal\Core\Entity\EntityRepositoryInterface
     */
    protected $entityRepository;
    
    /**
     * The request stack.
     *
     * @var \Symfony\Component\HttpFoundation\RequestStack
     */
    protected $requestStack;
    
    /**
     * Constructs a new CKEditor5MediaController.
     *
     * @param \Drupal\Core\Session\AccountInterface $current_user
     *   The currently authenticated user.
     * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
     *   The entity repository.
     * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
     *   The request stack.
     */
    public function __construct(AccountInterface $current_user, EntityRepositoryInterface $entity_repository, RequestStack $request_stack) {
        $this->currentUser = $current_user;
        $this->entityRepository = $entity_repository;
        $this->requestStack = $request_stack;
    }
    
    /**
     * Returns JSON response containing metadata about media entity.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The current request object.
     *
     * @return \Symfony\Component\HttpFoundation\JsonResponse
     *   A JSON object including the response.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown when no media UUID is provided.
     * @throws \Symfony\Component\HttpKernel\Exception\NotFoundHttpException
     *   Thrown when no media with the provided UUID exists.
     */
    public function mediaEntityMetadata(Request $request) {
        $uuid = $request->query
            ->get('uuid');
        if (!$uuid || !Uuid::isValid($uuid)) {
            throw new BadRequestHttpException();
        }
        // Access is enforced on route level.
        // @see \Drupal\ckeditor5\Controller\CKEditor5MediaController::access().
        if (!($media = $this->entityRepository
            ->loadEntityByUuid('media', $uuid))) {
            throw new NotFoundHttpException();
        }
        $image_field = $this->getMediaImageSourceFieldName($media);
        $response = [];
        $response['type'] = $media->bundle();
        // If this uses the image media source and the "alt" field is enabled,
        // expose additional metadata.
        // @see \Drupal\media\Plugin\media\Source\Image
        // @see core/modules/ckeditor5/js/ckeditor5_plugins/drupalMedia/src/mediaimagetextalternative/mediaimagetextalternativeui.js
        if ($image_field) {
            $settings = $media->{$image_field}
                ->getItemDefinition()
                ->getSettings();
            if (!empty($settings['alt_field'])) {
                $response['imageSourceMetadata'] = [
                    'alt' => $this->entityRepository
                        ->getTranslationFromContext($media)->{$image_field}->alt,
                ];
            }
        }
        // Note that we intentionally do not use:
        // - \Drupal\Core\Cache\CacheableResponse because caching it on the server
        //   side is wasteful, hence there is no need for cacheability metadata.
        // - \Drupal\Core\Render\HtmlResponse because there is no need for
        //   attachments nor cacheability metadata.
        return (new JsonResponse($response, 200))->setPrivate()
            ->setMaxAge(300);
    }
    
    /**
     * Additional access check for ::isMediaImage().
     *
     * This grants access if media embed filter is enabled on the filter format
     * and user has access to view the media entity.
     *
     * Note that access to the filter format is not checked here because the route
     * is configured to check entity access to the filter format.
     *
     * @param \Drupal\editor\Entity\Editor $editor
     *   The text editor.
     *
     * @return \Drupal\Core\Access\AccessResultInterface
     *   The access result.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
     *   Thrown when no media UUID is provided.
     * @throws \Symfony\Component\HttpKernel\Exception\NotFoundHttpException
     *   Thrown when no media with the provided UUID exists.
     */
    public function access(Editor $editor) : AccessResultInterface {
        if ($editor->getEditor() !== 'ckeditor5') {
            return AccessResult::forbidden();
        }
        // @todo add current request as an argument after
        // https://www.drupal.org/project/drupal/issues/2786941 has been resolved.
        $request = $this->requestStack
            ->getCurrentRequest();
        $uuid = $request->query
            ->get('uuid');
        if (!$uuid || !Uuid::isValid($uuid)) {
            throw new BadRequestHttpException();
        }
        $media = $this->entityRepository
            ->loadEntityByUuid('media', $uuid);
        if (!$media) {
            throw new NotFoundHttpException();
        }
        $filters = $editor->getFilterFormat()
            ->filters();
        return AccessResult::allowedIf($filters->has('media_embed') && $filters->get('media_embed')->status)
            ->andIf($media->access('view', $this->currentUser, TRUE))
            ->addCacheableDependency($editor->getFilterFormat());
    }
    
    /**
     * Gets the name of an image media item's source field.
     *
     * @param \Drupal\media\MediaInterface $media
     *   The media item being embedded.
     *
     * @return string|null
     *   The name of the image source field configured for the media item, or
     *   NULL if the source field is not an image field.
     */
    protected function getMediaImageSourceFieldName(MediaInterface $media) {
        $field_definition = $media->getSource()
            ->getSourceFieldDefinition($media->bundle->entity);
        $item_class = $field_definition->getItemDefinition()
            ->getClass();
        if (is_a($item_class, ImageItem::class, TRUE)) {
            return $field_definition->getName();
        }
        return NULL;
    }

}