class AjaxRenderer

class AjaxRenderer implements MainContentRendererInterface {
    
    /**
     * The element info manager.
     *
     * @var \Drupal\Core\Render\ElementInfoManagerInterface
     */
    protected $elementInfoManager;
    
    /**
     * The renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * Constructs a new AjaxRenderer instance.
     *
     * @param \Drupal\Core\Render\ElementInfoManagerInterface $element_info_manager
     *   The element info manager.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer.
     */
    public function __construct(ElementInfoManagerInterface $element_info_manager, RendererInterface $renderer) {
        $this->elementInfoManager = $element_info_manager;
        $this->renderer = $renderer;
    }
    
    /**
     * {@inheritdoc}
     */
    public function renderResponse(array $main_content, Request $request, RouteMatchInterface $route_match) {
        $response = new AjaxResponse();
        if (isset($main_content['#type']) && $main_content['#type'] == 'ajax') {
            // Complex Ajax callbacks can return a result that contains an error
            // message or a specific set of commands to send to the browser.
            $main_content += $this->elementInfoManager
                ->getInfo('ajax');
            $error = $main_content['#error'];
            if (!empty($error)) {
                // Fall back to some default message otherwise use the specific one.
                if (!is_string($error)) {
                    $error = 'An error occurred while handling the request: The server received invalid input.';
                }
                $response->addCommand(new AlertCommand($error));
            }
        }
        $html = $this->renderer
            ->renderRoot($main_content);
        $response->setAttachments($main_content['#attached']);
        // The selector for the insert command is NULL as the new content will
        // replace the element making the Ajax call. The default 'replaceWith'
        // behavior can be changed with #ajax['method'].
        $response->addCommand(new InsertCommand(NULL, $html));
        $status_messages = [
            '#type' => 'status_messages',
        ];
        $output = $this->renderer
            ->renderRoot($status_messages);
        if (!empty($output)) {
            $response->addCommand(new PrependCommand(NULL, $output));
        }
        return $response;
    }

}