class Actions

class Actions extends Container {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        $class = static::class;
        return [
            '#process' => [
                // @todo Move this to #pre_render.
[
                    $class,
                    'preRenderActionsDropbutton',
                ],
                [
                    $class,
                    'processActions',
                ],
                [
                    $class,
                    'processContainer',
                ],
            ],
            '#weight' => 100,
            '#theme_wrappers' => [
                'container',
            ],
        ];
    }
    
    /**
     * Processes a form actions container element.
     *
     * @param array $element
     *   An associative array containing the properties and children of the
     *   form actions container.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param array $complete_form
     *   The complete form structure.
     *
     * @return array
     *   The processed element.
     */
    public static function processActions(&$element, FormStateInterface $form_state, &$complete_form) {
        $element['#attributes']['class'][] = 'form-actions';
        return $element;
    }
    
    /**
     * #pre_render callback for #type 'actions'.
     *
     * This callback iterates over all child elements of the #type 'actions'
     * container to look for elements with a #dropbutton property, so as to group
     * those elements into dropbuttons. As such, it works similar to #group, but is
     * specialized for dropbuttons.
     *
     * The value of #dropbutton denotes the dropbutton to group the child element
     * into. For example, two different values of 'foo' and 'bar' on child elements
     * would generate two separate dropbuttons, which each contain the corresponding
     * buttons.
     *
     * @param array $element
     *   The #type 'actions' element to process.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param array $complete_form
     *   The complete form structure.
     *
     * @return array
     *   The processed #type 'actions' element, including individual buttons grouped
     *   into new #type 'dropbutton' elements.
     */
    public static function preRenderActionsDropbutton(&$element, FormStateInterface $form_state, &$complete_form) {
        $dropbuttons = [];
        foreach (Element::children($element, TRUE) as $key) {
            if (isset($element[$key]['#dropbutton'])) {
                $dropbutton = $element[$key]['#dropbutton'];
                // If there is no dropbutton for this button group yet, create one.
                if (!isset($dropbuttons[$dropbutton])) {
                    $dropbuttons[$dropbutton] = [
                        '#type' => 'dropbutton',
                    ];
                }
                // Add this button to the corresponding dropbutton.
                // @todo Change #type 'dropbutton' to be based on item-list.html.twig
                //   instead of links.html.twig to avoid this preemptive rendering.
                $button = \Drupal::service('renderer')->renderPlain($element[$key]);
                $dropbuttons[$dropbutton]['#links'][$key] = [
                    'title' => $button,
                ];
                // Merge metadata like drupalSettings.
                BubbleableMetadata::createFromRenderArray($dropbuttons[$dropbutton])->merge(BubbleableMetadata::createFromRenderArray($element[$key]))
                    ->applyTo($dropbuttons[$dropbutton]);
            }
        }
        // @todo For now, all dropbuttons appear first. Consider to invent a more
        //   fancy sorting/injection algorithm here.
        return $dropbuttons + $element;
    }

}