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());
        }
    }

}