class BlockController

class BlockController extends ControllerBase {
    
    /**
     * The theme handler.
     *
     * @var \Drupal\Core\Extension\ThemeHandlerInterface
     */
    protected $themeHandler;
    
    /**
     * Constructs a new BlockController instance.
     *
     * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
     *   The theme handler.
     */
    public function __construct(ThemeHandlerInterface $theme_handler) {
        $this->themeHandler = $theme_handler;
    }
    
    /**
     * Calls a method on a block and reloads the listing page.
     *
     * @param \Drupal\block\BlockInterface $block
     *   The block being acted upon.
     * @param string $op
     *   The operation to perform, e.g., 'enable' or 'disable'.
     *
     * @return \Symfony\Component\HttpFoundation\RedirectResponse
     *   A redirect back to the listing page.
     */
    public function performOperation(BlockInterface $block, $op) {
        $block->{$op}()
            ->save();
        $this->messenger()
            ->addStatus($this->t('The block settings have been updated.'));
        return $this->redirect('block.admin_display');
    }
    
    /**
     * Returns a block theme demo page.
     *
     * @param string $theme
     *   The name of the theme.
     *
     * @return array
     *   A #type 'page' render array containing the block region demo.
     */
    public function demo($theme) {
        if (!$this->themeHandler
            ->hasUi($theme)) {
            throw new NotFoundHttpException();
        }
        $page = [
            '#title' => Html::escape($this->themeHandler
                ->getName($theme)),
            '#type' => 'page',
            '#attached' => [
                'drupalSettings' => [
                    // The block demonstration page is not marked as an administrative
                    // page by \Drupal::service('router.admin_context')->isAdminRoute()
                    // function in order to use the frontend theme. Since JavaScript
                    // relies on a proper separation of admin pages, it needs to know this
                    // is an actual administrative page.
'path' => [
                        'currentPathIsAdmin' => TRUE,
                    ],
                ],
                'library' => [
                    'block/drupal.block.admin',
                ],
            ],
        ];
        // Show descriptions in each visible page region, nothing else.
        $visible_regions = $this->getVisibleRegionNames($theme);
        foreach (array_keys($visible_regions) as $region) {
            $page[$region]['block_description'] = [
                '#type' => 'inline_template',
                '#template' => '<div class="block-region demo-block">{{ region_name }}</div>',
                '#context' => [
                    'region_name' => $visible_regions[$region],
                ],
            ];
        }
        return $page;
    }
    
    /**
     * Returns the human-readable list of regions keyed by machine name.
     *
     * @param string $theme
     *   The name of the theme.
     *
     * @return array
     *   An array of human-readable region names keyed by machine name.
     */
    protected function getVisibleRegionNames($theme) {
        return system_region_list($theme, REGIONS_VISIBLE);
    }

}