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;
  }

}