class EntityDisplayModeListBuilder

class EntityDisplayModeListBuilder extends ConfigEntityListBuilder {
  
  /**
   * All entity types.
   *
   * @var \Drupal\Core\Entity\EntityTypeInterface[]
   */
  protected $entityTypes;
  
  /**
   * Constructs a new EntityDisplayModeListBuilder object.
   *
   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
   *   The entity type definition.
   * @param \Drupal\Core\Entity\EntityStorageInterface $storage
   *   The entity storage class.
   * @param \Drupal\Core\Entity\EntityTypeInterface[] $entity_types
   *   List of all entity types.
   */
  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, array $entity_types) {
    parent::__construct($entity_type, $storage);
    // Override the default limit (50) in order to display all view modes.
    $this->limit = FALSE;
    $this->entityTypes = $entity_types;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
    $entity_type_manager = $container->get('entity_type.manager');
    return new static($entity_type, $entity_type_manager->getStorage($entity_type->id()), $entity_type_manager->getDefinitions());
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildHeader() {
    $header['label'] = $this->t('Name');
    $header['description'] = $this->t('Description');
    return $header + parent::buildHeader();
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildRow(EntityInterface $entity) {
    $row['label'] = $entity->label();
    $row['description'] = $entity->getDescription();
    return $row + parent::buildRow($entity);
  }
  
  /**
   * {@inheritdoc}
   */
  public function getOperations(EntityInterface $entity) {
    // Make the edit form render in a dialog, like the add form.
    // The edit form also contains an option to delete the view mode, which
    // also spawns a dialog. Rather than have nested dialogs, we allow the
    // existing dialog to be replaced, so users will be shown the list again
    // if they cancel deleting the view mode.
    $operations = parent::getOperations($entity);
    if (isset($operations['edit'])) {
      $operations['edit'] = NestedArray::mergeDeepArray([
        [
          'attributes' => [
            'class' => [
              'button',
              'use-ajax',
            ],
            'data-dialog-type' => 'modal',
            'data-dialog-options' => Json::encode([
              'width' => '880',
            ]),
          ],
        ],
        $operations['edit'],
      ]);
    }
    return $operations;
  }
  
  /**
   * {@inheritdoc}
   */
  public function load() {
    $entities = [];
    foreach (parent::load() as $entity) {
      $entities[$entity->getTargetType()][] = $entity;
    }
    return $entities;
  }
  
  /**
   * {@inheritdoc}
   */
  public function render() {
    $build = [];
    foreach ($this->load() as $entity_type => $entities) {
      if (!isset($this->entityTypes[$entity_type])) {
        continue;
      }
      // Filter entities.
      if (!$this->isValidEntity($entity_type)) {
        continue;
      }
      $table = [
        '#prefix' => '<h2>' . $this->entityTypes[$entity_type]
          ->getLabel() . '</h2>',
        '#type' => 'table',
        '#header' => $this->buildHeader(),
        '#rows' => [],
        '#attributes' => [
          'class' => [
            'display-mode-table',
          ],
        ],
      ];
      foreach ($entities as $entity) {
        if ($row = $this->buildRow($entity)) {
          $table['#rows'][$entity->id()] = $row;
        }
      }
      // Move content at the top.
      if ($entity_type == 'node') {
        $table['#weight'] = -10;
      }
      $short_type = str_replace([
        'entity_',
        '_mode',
      ], '', $this->entityTypeId);
      $table['#rows']['_add_new'][] = [
        'data' => [
          '#type' => 'link',
          '#url' => Url::fromRoute($short_type == 'view' ? 'entity.entity_view_mode.add_form' : 'entity.entity_form_mode.add_form', [
            'entity_type_id' => $entity_type,
          ]),
          '#title' => $this->t('Add %label for @entity-type', [
            '@entity-type' => $this->entityTypes[$entity_type]
              ->getLabel(),
            '%label' => $this->entityType
              ->getSingularLabel(),
          ]),
          '#button_type' => 'primary',
          '#attributes' => [
            'class' => [
              'button',
              'use-ajax',
              'button--small',
            ],
            'data-dialog-type' => 'modal',
            'data-dialog-options' => Json::encode([
              'width' => '880',
            ]),
          ],
          '#attached' => [
            'library' => [
              'core/drupal.dialog.ajax',
              'field_ui/drupal.field_ui_table',
            ],
          ],
        ],
        'colspan' => count($table['#header']),
      ];
      $build[$entity_type] = $table;
    }
    return $build;
  }
  
  /**
   * Filters entities based on their view builder handlers.
   *
   * @param $entity_type
   *   The entity type of the entity that needs to be validated.
   *
   * @return bool
   *   TRUE if the entity has the correct view builder handler, FALSE if the
   *   entity doesn't have the correct view builder handler.
   */
  protected function isValidEntity($entity_type) {
    return $this->entityTypes[$entity_type]
      ->get('field_ui_base_route') && $this->entityTypes[$entity_type]
      ->hasViewBuilderClass();
  }

}