class MediaThumbnailFormatter

class MediaThumbnailFormatter extends ImageFormatter {
  
  /**
   * The renderer service.
   *
   * @var \Drupal\Core\Render\RendererInterface
   */
  protected $renderer;
  
  /**
   * Constructs a MediaThumbnailFormatter object.
   *
   * @param string $plugin_id
   *   The plugin ID for the formatter.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The definition of the field to which the formatter is associated.
   * @param array $settings
   *   The formatter settings.
   * @param string $label
   *   The formatter label display setting.
   * @param string $view_mode
   *   The view mode.
   * @param array $third_party_settings
   *   Any third party settings.
   * @param \Drupal\Core\Session\AccountInterface $current_user
   *   The current user.
   * @param \Drupal\image\ImageStyleStorageInterface $image_style_storage
   *   The image style entity storage handler.
   * @param \Drupal\Core\File\FileUrlGeneratorInterface $file_url_generator
   *   The file URL generator.
   * @param \Drupal\Core\Render\RendererInterface $renderer
   *   The renderer service.
   */
  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, AccountInterface $current_user, ImageStyleStorageInterface $image_style_storage, FileUrlGeneratorInterface $file_url_generator, RendererInterface $renderer) {
    parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings, $current_user, $image_style_storage, $file_url_generator);
    $this->renderer = $renderer;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($plugin_id, $plugin_definition, $configuration['field_definition'], $configuration['settings'], $configuration['label'], $configuration['view_mode'], $configuration['third_party_settings'], $container->get('current_user'), $container->get('entity_type.manager')
      ->getStorage('image_style'), $container->get('file_url_generator'), $container->get('renderer'));
  }
  
  /**
   * {@inheritdoc}
   *
   * This has to be overridden because FileFormatterBase expects $item to be
   * of type \Drupal\file\Plugin\Field\FieldType\FileItem and calls
   * isDisplayed() which is not in FieldItemInterface.
   */
  protected function needsEntityLoad(EntityReferenceItem $item) {
    return !$item->hasNewEntity();
  }
  
  /**
   * {@inheritdoc}
   */
  public function settingsForm(array $form, FormStateInterface $form_state) {
    $element = parent::settingsForm($form, $form_state);
    $link_types = [
      'content' => $this->t('Content'),
      'media' => $this->t('Media item'),
    ];
    $element['image_link']['#options'] = $link_types;
    return $element;
  }
  
  /**
   * {@inheritdoc}
   */
  public function settingsSummary() {
    $summary = parent::settingsSummary();
    // The parent class adds summary text if the image_link setting is
    // 'content'. Here we only have to add summary text if the setting
    // is 'media'.
    if ($this->getSetting('image_link') === 'media') {
      $summary[] = $this->t('Linked to media item');
    }
    return $summary;
  }
  
  /**
   * {@inheritdoc}
   */
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];
    $media_items = $this->getEntitiesToView($items, $langcode);
    // Early opt-out if the field is empty.
    if (empty($media_items)) {
      return $elements;
    }
    $image_style_setting = $this->getSetting('image_style');
    /** @var \Drupal\media\MediaInterface[] $media_items */
    foreach ($media_items as $delta => $media) {
      $elements[$delta] = [
        '#theme' => 'image_formatter',
        '#item' => $media->get('thumbnail')
          ->first(),
        '#item_attributes' => [
          'loading' => $this->getSetting('image_loading')['attribute'],
        ],
        '#image_style' => $this->getSetting('image_style'),
        '#url' => $this->getMediaThumbnailUrl($media, $items->getEntity()),
      ];
      // Add cacheability of each item in the field.
      $this->renderer
        ->addCacheableDependency($elements[$delta], $media);
    }
    // Add cacheability of the image style setting.
    if ($this->getSetting('image_link') && ($image_style = $this->imageStyleStorage
      ->load($image_style_setting))) {
      $this->renderer
        ->addCacheableDependency($elements, $image_style);
    }
    return $elements;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function isApplicable(FieldDefinitionInterface $field_definition) {
    // This formatter is only available for entity types that reference
    // media items.
    return $field_definition->getFieldStorageDefinition()
      ->getSetting('target_type') == 'media';
  }
  
  /**
   * {@inheritdoc}
   */
  protected function checkAccess(EntityInterface $entity) {
    return $entity->access('view', NULL, TRUE)
      ->andIf(parent::checkAccess($entity));
  }
  
  /**
   * Get the URL for the media thumbnail.
   *
   * @param \Drupal\media\MediaInterface $media
   *   The media item.
   * @param \Drupal\Core\Entity\EntityInterface $entity
   *   The entity that the field belongs to.
   *
   * @return \Drupal\Core\Url|null
   *   The URL object for the media item or null if we don't want to add
   *   a link.
   */
  protected function getMediaThumbnailUrl(MediaInterface $media, EntityInterface $entity) {
    $url = NULL;
    $image_link_setting = $this->getSetting('image_link');
    // Check if the formatter involves a link.
    if ($image_link_setting == 'content') {
      if (!$entity->isNew()) {
        $url = $entity->toUrl();
      }
    }
    elseif ($image_link_setting === 'media') {
      $url = $media->toUrl();
    }
    return $url;
  }

}