class AddSectionController

class AddSectionController implements ContainerInjectionInterface {
  use AjaxHelperTrait;
  use LayoutRebuildTrait;
  
  /**
   * The layout tempstore repository.
   *
   * @var \Drupal\layout_builder\LayoutTempstoreRepositoryInterface
   */
  protected $layoutTempstoreRepository;
  
  /**
   * AddSectionController constructor.
   *
   * @param \Drupal\layout_builder\LayoutTempstoreRepositoryInterface $layout_tempstore_repository
   *   The layout tempstore repository.
   */
  public function __construct(LayoutTempstoreRepositoryInterface $layout_tempstore_repository) {
    $this->layoutTempstoreRepository = $layout_tempstore_repository;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('layout_builder.tempstore_repository'));
  }
  
  /**
   * Adds the new section.
   *
   * @param \Drupal\layout_builder\SectionStorageInterface $section_storage
   *   The section storage.
   * @param int $delta
   *   The delta of the section to splice.
   * @param string $plugin_id
   *   The plugin ID of the layout to add.
   *
   * @return \Symfony\Component\HttpFoundation\Response
   *   The controller response.
   */
  public function build(SectionStorageInterface $section_storage, int $delta, $plugin_id) {
    $section_storage->insertSection($delta, new Section($plugin_id));
    $this->layoutTempstoreRepository
      ->set($section_storage);
    if ($this->isAjax()) {
      return $this->rebuildAndClose($section_storage);
    }
    else {
      $url = $section_storage->getLayoutBuilderUrl();
      return new RedirectResponse($url->setAbsolute()
        ->toString());
    }
  }

}