class EntityDisplayModeController

class EntityDisplayModeController extends ControllerBase {
  
  /**
   * Provides a list of eligible entity types for adding view modes.
   *
   * @return array
   *   A list of entity types to add a view mode for.
   */
  public function viewModeTypeSelection() {
    $entity_types = [];
    foreach ($this->entityTypeManager()
      ->getDefinitions() as $entity_type_id => $entity_type) {
      if ($entity_type->get('field_ui_base_route') && $entity_type->hasViewBuilderClass()) {
        $entity_types[$entity_type_id] = [
          'title' => $entity_type->getLabel(),
          'url' => Url::fromRoute('entity.entity_view_mode.add_form', [
            'entity_type_id' => $entity_type_id,
          ])->setOption('attributes', [
            'class' => [
              'use-ajax',
            ],
            'data-dialog-type' => 'modal',
            'data-dialog-options' => Json::encode([
              'width' => '880',
            ]),
          ]),
        ];
      }
    }
    // Move content at the top.
    array_splice($entity_types, 0, 0, array_splice($entity_types, array_search('node', array_keys($entity_types)), 1));
    return [
      '#theme' => 'admin_block_content',
      '#content' => $entity_types,
      '#attached' => [
        'library' => [
          'core/drupal.dialog.ajax',
        ],
      ],
    ];
  }
  
  /**
   * Provides a list of eligible entity types for adding form modes.
   *
   * @return array
   *   A list of entity types to add a form mode for.
   */
  public function formModeTypeSelection() {
    $entity_types = [];
    foreach ($this->entityTypeManager()
      ->getDefinitions() as $entity_type_id => $entity_type) {
      if ($entity_type->get('field_ui_base_route') && $entity_type->hasFormClasses()) {
        $entity_types[$entity_type_id] = [
          'title' => $entity_type->getLabel(),
          'url' => Url::fromRoute('entity.entity_form_mode.add_form', [
            'entity_type_id' => $entity_type_id,
          ])->setOption('attributes', [
            'class' => [
              'use-ajax',
            ],
            'data-dialog-type' => 'modal',
            'data-dialog-options' => Json::encode([
              'width' => '880',
            ]),
          ]),
        ];
      }
    }
    // Move content at the top.
    array_splice($entity_types, 0, 0, array_splice($entity_types, array_search('node', array_keys($entity_types)), 1));
    return [
      '#theme' => 'admin_block_content',
      '#content' => $entity_types,
      '#attached' => [
        'library' => [
          'core/drupal.dialog.ajax',
        ],
      ],
    ];
  }

}