class VerticalTabs

class VerticalTabs extends RenderElementBase {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        $class = static::class;
        return [
            '#default_tab' => '',
            '#process' => [
                [
                    $class,
                    'processVerticalTabs',
                ],
            ],
            '#pre_render' => [
                [
                    $class,
                    'preRenderVerticalTabs',
                ],
            ],
            '#theme_wrappers' => [
                'vertical_tabs',
                'form_element',
            ],
        ];
    }
    
    /**
     * Prepares a vertical_tabs element for rendering.
     *
     * @param array $element
     *   An associative array containing the properties and children of the
     *   vertical tabs element.
     *
     * @return array
     *   The modified element.
     */
    public static function preRenderVerticalTabs($element) {
        // Do not render the vertical tabs element if it is empty.
        $group = implode('][', $element['#parents']);
        if (!Element::getVisibleChildren($element['group']['#groups'][$group])) {
            $element['#printed'] = TRUE;
        }
        return $element;
    }
    
    /**
     * Creates a group formatted as vertical tabs.
     *
     * @param array $element
     *   An associative array containing the properties and children of the
     *   details element.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param array $complete_form
     *   The complete form structure.
     *
     * @return array
     *   The processed element.
     */
    public static function processVerticalTabs(&$element, FormStateInterface $form_state, &$complete_form) {
        if (isset($element['#access']) && !$element['#access']) {
            return $element;
        }
        // Inject a new details as child, so that form_process_details() processes
        // this details element like any other details.
        $element['group'] = [
            '#type' => 'details',
            '#theme_wrappers' => [],
            '#parents' => $element['#parents'],
        ];
        // Add an invisible label for accessibility.
        if (!isset($element['#title'])) {
            $element['#title'] = t('Vertical Tabs');
            $element['#title_display'] = 'invisible';
        }
        $element['#attached']['library'][] = 'core/drupal.vertical-tabs';
        // The JavaScript stores the currently selected tab in this hidden
        // field so that the active tab can be restored the next time the
        // form is rendered, e.g. on preview pages or when form validation
        // fails.
        $name = implode('__', $element['#parents']);
        if ($form_state->hasValue($name . '__active_tab')) {
            $element['#default_tab'] = $form_state->getValue($name . '__active_tab');
        }
        $element[$name . '__active_tab'] = [
            '#type' => 'hidden',
            '#default_value' => $element['#default_tab'],
            '#attributes' => [
                'class' => [
                    'vertical-tabs__active-tab',
                ],
            ],
        ];
        // Clean up the active tab value so it's not accidentally stored in
        // settings forms.
        $form_state->addCleanValueKey($name . '__active_tab');
        return $element;
    }

}