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;
    }

}