trait CommerceElementTrait in Commerce Core 8.2

trait CommerceElementTrait {

  /**
   * Attaches the #commerce_element_submit functionality.
   *
   * @param array $element
   *   The form element being processed.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   * @param array $complete_form
   *   The complete form structure.
   *
   * @return array
   *   The processed form element.
   */
  public static function attachElementSubmit(array $element, FormStateInterface $form_state, array &$complete_form) {
    if (isset($complete_form['#commerce_element_submit_attached'])) {
      return $element;
    }

    // The #validate callbacks of the complete form run last.
    // That allows executeElementSubmitHandlers() to be completely certain that
    // the form has passed validation before proceeding.
    $complete_form['#validate'][] = [
      get_class(),
      'executeElementSubmitHandlers',
    ];
    $complete_form['#commerce_element_submit_attached'] = TRUE;
    return $element;
  }

  /**
   * Confirms that #commerce_element_submit handlers can be run.
   *
   * @param array $element
   *   The form element.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @throws \Exception
   *   Thrown if button-level #validate handlers are detected on the parent
   *   form, as a protection against buggy behavior.
   */
  public static function validateElementSubmit(array &$element, FormStateInterface $form_state) {

    // Button-level #validate handlers replace the form-level ones, which means
    // that executeElementSubmitHandlers() won't be triggered.
    if (self::shouldExecuteElementSubmit($form_state) && $form_state
      ->getValidateHandlers()) {
      throw new \Exception('The triggering element must not have #validate handlers');
    }
  }

  /**
   * Submits elements by calling their #commerce_element_submit callbacks.
   *
   * Form API has no #element_submit, requiring us to simulate it by running
   * the #commerce_element_submit handlers either in the last step of
   * validation, or the first step of submission. In this case it's the last
   * step of validation, allowing thrown exceptions to be converted into form
   * errors.
   *
   * @param array &$form
   *   The form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The form state.
   */
  public static function executeElementSubmitHandlers(array &$form, FormStateInterface $form_state) {
    if (self::shouldExecuteElementSubmit($form_state)) {
      self::doExecuteSubmitHandlers($form, $form_state);
    }
  }

  /**
   * Checks whether #commerce_element_submit callbacks should be executed.
   *
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The form state.
   *
   * @return bool
   *   TRUE if the callbacks can be executed, FALSE otherwise.
   */
  protected static function shouldExecuteElementSubmit(FormStateInterface $form_state) {
    if (!$form_state
      ->isSubmitted() || $form_state
      ->hasAnyErrors()) {

      // The form wasn't submitted (#ajax in progress) or failed validation.
      return FALSE;
    }
    if (count($form_state
      ->getButtons()) === 1) {

      // The form has only one button, no need to guess if it was clicked.
      return TRUE;
    }
    $triggering_element = $form_state
      ->getTriggeringElement();
    $button_type = isset($triggering_element['#button_type']) ? $triggering_element['#button_type'] : '';
    if (in_array($button_type, [
      'primary',
      'secondary',
    ])) {

      // Invoke callbacks only for submit buttons with a known #button_type.
      // Buttons without a #button_type usually rebuild the form.
      // The 'secondary' #button_type was invented by Commerce for buttons
      // which behave like a primary button (e.g. saving the entity), but
      // shouldn't have the styling of a primary button.
      return TRUE;
    }
    return FALSE;
  }

  /**
   * Calls the #commerce_element_submit callbacks recursively.
   *
   * @param array &$element
   *   The current element.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The form state.
   */
  protected static function doExecuteSubmitHandlers(array &$element, FormStateInterface $form_state) {

    // Recurse through all children.
    foreach (Element::children($element) as $key) {
      if (!empty($element[$key])) {
        static::doExecuteSubmitHandlers($element[$key], $form_state);
      }
    }

    // If there are callbacks on this level, run them.
    if (!empty($element['#commerce_element_submit'])) {
      foreach ($element['#commerce_element_submit'] as $callback) {
        call_user_func_array($callback, [
          &$element,
          &$form_state,
        ]);
      }
    }
  }

}