trait WebformAjaxFormTrait in Webform 8.5

trait WebformAjaxFormTrait {

  /**
   * Returns if webform is using Ajax.
   *
   * @return bool
   *   TRUE if webform is using Ajax.
   */
  protected abstract function isAjax();

  /**
   * Cancel form #ajax callback.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return \Drupal\Core\Ajax\AjaxResponse
   *   An Ajax response that display validation error messages or redirects
   *   to a URL
   */
  public abstract function cancelAjaxForm(array &$form, FormStateInterface $form_state);

  /**
   * Get default ajax callback settings.
   *
   * @return array
   *   An associative array containing default ajax callback settings.
   */
  protected function getDefaultAjaxSettings() {
    return [
      'disable-refocus' => TRUE,
      'effect' => 'fade',
      'speed' => 1000,
      'progress' => [
        'type' => 'throbber',
        'message' => '',
      ],
    ];
  }

  /**
   * Is the current request for an Ajax modal/dialog.
   *
   * @return bool
   *   TRUE if the current request is for an Ajax modal/dialog.
   */
  protected function isDialog() {
    $wrapper_format = $this
      ->getRequest()
      ->get(MainContentViewSubscriber::WRAPPER_FORMAT);
    return in_array($wrapper_format, [
      'drupal_ajax',
      'drupal_modal',
      'drupal_dialog',
      'drupal_dialog.off_canvas',
    ]) ? TRUE : FALSE;
  }

  /**
   * Is the current request for an off canvas dialog.
   *
   * @return bool
   *   TRUE if the current request is for an off canvas dialog.
   */
  protected function isOffCanvasDialog() {
    $wrapper_format = $this
      ->getRequest()
      ->get(MainContentViewSubscriber::WRAPPER_FORMAT);
    return in_array($wrapper_format, [
      'drupal_dialog.off_canvas',
    ]) ? TRUE : FALSE;
  }

  /**
   * Get the form's Ajax wrapper id.
   *
   * @return string
   *   The form's Ajax wrapper id.
   */
  protected function getWrapperId() {
    $form_id = method_exists($this, 'getBaseFormId') ? $this
      ->getBaseFormId() : $this
      ->getFormId();
    return Html::getId($form_id . '-ajax');
  }

  /**
   * Add Ajax support to a form.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   * @param array $settings
   *   Ajax settings.
   *
   * @return array
   *   The form with Ajax callbacks.
   */
  protected function buildAjaxForm(array &$form, FormStateInterface $form_state, array $settings = []) {
    if (!$this
      ->isAjax()) {
      return $form;
    }

    // Apply default settings.
    $settings += $this
      ->getDefaultAjaxSettings();

    // Add Ajax callback to all submit buttons.
    foreach (Element::children($form) as $element_key) {
      if (!WebformElementHelper::isType($form[$element_key], 'actions')) {
        continue;
      }
      $actions =& $form[$element_key];
      foreach (Element::children($actions) as $action_key) {
        if (WebformElementHelper::isType($actions[$action_key], 'submit')) {
          $actions[$action_key]['#ajax'] = [
            'callback' => '::submitAjaxForm',
            'event' => 'click',
          ] + $settings;
        }
      }
    }

    // Add Ajax wrapper with wrapper content bookmark around the form.
    // @see Drupal.AjaxCommands.prototype.webformScrollTop
    $wrapper_id = $this
      ->getWrapperId();
    $wrapper_attributes = [];
    $wrapper_attributes['id'] = $wrapper_id;
    $wrapper_attributes['class'] = [
      'webform-ajax-form-wrapper',
    ];
    if (isset($settings['effect'])) {
      $wrapper_attributes['data-effect'] = $settings['effect'];
    }
    if (isset($settings['progress']['type'])) {
      $wrapper_attributes['data-progress-type'] = $settings['progress']['type'];
    }
    $wrapper_attributes = new Attribute($wrapper_attributes);
    $form['#form_wrapper_id'] = $wrapper_id;
    $form['#prefix'] = '<span id="' . $wrapper_id . '-content"></span>';
    $form['#prefix'] .= '<div' . $wrapper_attributes . '>';
    $form['#suffix'] = '</div>';

    // Add Ajax library which contains 'Scroll to top' Ajax command and
    // Ajax callback for confirmation back to link.
    $form['#attached']['library'][] = 'webform/webform.ajax';

    // Add validate Ajax form.
    $form['#validate'][] = '::validateAjaxForm';
    return $form;
  }

  /**
   * Submit form #ajax callback.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return \Drupal\Core\Ajax\AjaxResponse
   *   An Ajax response that display validation error messages or redirects
   *   to a URL
   */
  public function submitAjaxForm(array &$form, FormStateInterface $form_state) {
    $scroll_top_target = isset($form['#webform_ajax_scroll_top']) ? $form['#webform_ajax_scroll_top'] : 'form';
    if ($form_state
      ->hasAnyErrors()) {

      // Display validation errors and scroll to the top of the page.
      $response = $this
        ->replaceForm($form, $form_state);
      if ($scroll_top_target) {
        $response
          ->addCommand(new WebformScrollTopCommand('#' . $this
          ->getWrapperId(), $scroll_top_target));
      }

      // Announce validation errors.
      $this
        ->announce($this
        ->t('Form validation errors have been found.'));
    }
    elseif ($form_state
      ->getResponse() instanceof AjaxResponse) {

      // Allow developers via form_alter hooks to set their own Ajax response.
      // The custom Ajax response could be used to close modals and refresh
      // selected regions and blocks on the page.
      $response = $form_state
        ->getResponse();
    }
    elseif ($form_state
      ->isRebuilding()) {

      // Rebuild form.
      $response = $this
        ->replaceForm($form, $form_state);
      if ($scroll_top_target) {
        $response
          ->addCommand(new WebformScrollTopCommand('#' . $this
          ->getWrapperId(), $scroll_top_target));
      }
    }
    elseif ($redirect_url = $this
      ->getFormStateRedirectUrl($form_state)) {

      // Redirect to URL.
      $response = $this
        ->createAjaxResponse($form, $form_state);
      $response
        ->addCommand(new WebformCloseDialogCommand());
      $response
        ->addCommand(new WebformRefreshCommand($redirect_url));
    }
    else {
      $response = $this
        ->cancelAjaxForm($form, $form_state);
    }

    // Add announcements to Ajax response and then reset the announcements.
    // @see \Drupal\webform\Form\WebformAjaxFormTrait::announce
    $announcements = $this
      ->getAnnouncements();
    foreach ($announcements as $announcement) {
      $response
        ->addCommand(new AnnounceCommand($announcement['text'], $announcement['priority']));
    }
    $this
      ->resetAnnouncements();
    return $response;
  }

  /**
   * Validate form #ajax callback.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  public function validateAjaxForm(array &$form, FormStateInterface $form_state) {
    if (!$this
      ->isCallableAjaxCallback($form, $form_state)) {
      $this
        ->missingAjaxCallback($form, $form_state);
    }
  }

  /**
   * Determine if Ajax callback is callable.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return bool
   *   TRUE if if Ajax callback exists.
   */
  protected function isCallableAjaxCallback(array &$form, FormStateInterface $form_state) {

    // Make sure the ajax callback exists.
    // @see \Drupal\Core\Form\FormAjaxResponseBuilder::buildResponse
    $callback = NULL;
    if (($triggering_element = $form_state
      ->getTriggeringElement()) && isset($triggering_element['#ajax']['callback'])) {
      $callback = $triggering_element['#ajax']['callback'];
    }
    $callback = $form_state
      ->prepareCallback($callback);
    return empty($callback) || !is_callable($callback) ? FALSE : TRUE;
  }

  /**
   * Handle missing Ajax callback.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  protected function missingAjaxCallback(array &$form, FormStateInterface $form_state) {
    $command = new WebformConfirmReloadCommand($this
      ->t('We are unable to complete the current request.') . PHP_EOL . PHP_EOL . $this
      ->t('Do you want to reload the current page?'));
    print Json::encode([
      $command
        ->render(),
    ]);
    exit;
  }

  /**
   * Empty submit callback used to only have the submit button to use an #ajax submit callback.
   *
   * This allows modal dialog to using ::submitCallback to validate and submit
   * the form via one ajax request.
   */
  public function noSubmit(array &$form, FormStateInterface $form_state) {

    // Do nothing.
  }

  /**
   * Create an AjaxResponse or WebformAjaxResponse object.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return \Drupal\Core\Ajax\AjaxResponse
   *   An AjaxResponse or WebformAjaxResponse object
   */
  protected function createAjaxResponse(array $form, FormStateInterface $form_state) {
    $form_object = $form_state
      ->getFormObject();
    if ($form_object instanceof WebformSubmissionForm) {

      /** @var \Drupal\webform\WebformSubmissionInterface $webform_submission */
      $webform_submission = $form_object
        ->getEntity();
      $response = new WebformSubmissionAjaxResponse();
      $response
        ->setWebformSubmission($webform_submission);
      return $response;
    }
    else {
      return new AjaxResponse();
    }
  }

  /**
   * Replace form via an Ajax response.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return \Drupal\Core\Ajax\AjaxResponse
   *   An Ajax response that replaces a form.
   */
  protected function replaceForm(array $form, FormStateInterface $form_state) {

    // Display messages first by prefixing it the form and setting its weight
    // to -1000.
    $form = [
      'status_messages' => [
        '#type' => 'status_messages',
        '#weight' => -1000,
      ],
    ] + $form;

    // Remove wrapper.
    unset($form['#prefix'], $form['#suffix']);
    $response = $this
      ->createAjaxResponse($form, $form_state);
    $response
      ->addCommand(new HtmlCommand('#' . $this
      ->getWrapperId(), $form));
    return $response;
  }

  /**
   * Get redirect URL from the form's state.
   *
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return bool|\Drupal\Core\GeneratedUrl|string
   *   The redirect URL or FALSE if the form is not redirecting.
   */
  protected function getFormStateRedirectUrl(FormStateInterface $form_state) {

    // Always check the ?destination which is used by the off-canvas/system tray.
    if ($this
      ->getRequest()
      ->get('destination')) {
      $destination = $this
        ->getRedirectDestination()
        ->get();
      return strpos($destination, $destination) === 0 ? $destination : base_path() . $destination;
    }

    // ISSUE:
    // Can't get the redirect URL from the form state during an AJAX submission.
    //
    // WORKAROUND:
    // Re-enable redirect, grab the URL, and then disable again.
    $no_redirect = $form_state
      ->isRedirectDisabled();
    $form_state
      ->disableRedirect(FALSE);
    $redirect = $form_state
      ->getResponse() ?: $form_state
      ->getRedirect();
    $form_state
      ->disableRedirect($no_redirect);
    if ($redirect instanceof RedirectResponse) {
      return $redirect
        ->getTargetUrl();
    }
    elseif ($redirect instanceof Url) {
      return $redirect
        ->setAbsolute()
        ->toString();
    }
    else {
      return FALSE;
    }
  }

  /****************************************************************************/

  // Drupal.announce handling.
  //
  // Announcements are stored in the user session because the $form_state
  // is already serialized (and can't be altered) when announcements
  // are added to Ajax response.
  // @see \Drupal\webform\Form\WebformAjaxFormTrait::submitAjaxForm

  /****************************************************************************/

  /**
   * Queue announcement with Ajax response.
   *
   * @param string $text
   *   A string to be read by the UA.
   * @param string $priority
   *   A string to indicate the priority of the message. Can be either
   *   'polite' or 'assertive'.
   *
   * @see \Drupal\Core\Ajax\AnnounceCommand
   * @see \Drupal\webform\Form\WebformAjaxFormTrait::submitAjaxForm
   */
  protected function announce($text, $priority = 'polite') {
    $announcements =& drupal_static('webform_announcements', []);
    $announcements[] = [
      'text' => $text,
      'priority' => $priority,
    ];
  }

  /**
   * Get announcements.
   *
   * @return array
   *   An associative array of announcements.
   */
  protected function getAnnouncements() {
    return drupal_static('webform_announcements', []);
  }

  /**
   * Set announcements.
   *
   * @param array $announcements
   *   An associative array of announcements.
   */
  protected function setAnnouncements(array $announcements) {
    $this
      ->resetAnnouncements();
    drupal_static('webform_announcements', $announcements);
  }

  /**
   * Reset announcements.
   */
  protected function resetAnnouncements() {
    drupal_static_reset('webform_announcements');
  }

}