class BlockEntitySettingTrayForm

class BlockEntitySettingTrayForm extends BlockForm {
    use AjaxFormHelperTrait;
    
    /**
     * Provides a title callback to get the block's admin label.
     *
     * @param \Drupal\block\BlockInterface $block
     *   The block entity.
     *
     * @return \Drupal\Core\StringTranslation\TranslatableMarkup
     *   The title.
     */
    public function title(BlockInterface $block) {
        // @todo Wrap "Configure " in <span class="visually-hidden"></span> once
        //   https://www.drupal.org/node/2359901 is fixed.
        return $this->t('Configure @block', [
            '@block' => $block->getPlugin()
                ->getPluginDefinition()['admin_label'],
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $form = parent::form($form, $form_state);
        // Create link to full block form.
        $query = [];
        if ($destination = $this->getRequest()->query
            ->get('destination')) {
            $query['destination'] = $destination;
        }
        $form['advanced_link'] = [
            '#type' => 'link',
            '#title' => $this->t('Advanced block options'),
            '#url' => $this->entity
                ->toUrl('edit-form', [
                'query' => $query,
            ]),
            '#weight' => 1000,
        ];
        // Remove the ID and region elements.
        unset($form['id'], $form['region'], $form['settings']['admin_label']);
        if (isset($form['settings']['label_display']) && isset($form['settings']['label'])) {
            // Only show the label input if the label will be shown on the page.
            $form['settings']['label_display']['#weight'] = -100;
            $form['settings']['label']['#states']['visible'] = [
                ':input[name="settings[label_display]"]' => [
                    'checked' => TRUE,
                ],
            ];
            // Relabel to "Block title" because on the front-end this may be confused
            // with page title.
            $form['settings']['label']['#title'] = $this->t("Block title");
            $form['settings']['label_display']['#title'] = $this->t("Display block title");
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function actions(array $form, FormStateInterface $form_state) {
        $actions = parent::actions($form, $form_state);
        $actions['submit']['#value'] = $this->t('Save @block', [
            '@block' => $this->entity
                ->getPlugin()
                ->getPluginDefinition()['admin_label'],
        ]);
        $actions['delete']['#access'] = FALSE;
        return $actions;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function buildVisibilityInterface(array $form, FormStateInterface $form_state) {
        // Do not display the visibility.
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    protected function validateVisibility(array $form, FormStateInterface $form_state) {
        // Intentionally empty.
    }
    
    /**
     * {@inheritdoc}
     */
    protected function submitVisibility(array $form, FormStateInterface $form_state) {
        // Intentionally empty.
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getPluginForm(BlockPluginInterface $block) {
        if ($block instanceof PluginWithFormsInterface) {
            return $this->pluginFormFactory
                ->createInstance($block, 'settings_tray', 'configure');
        }
        return $block;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form = parent::buildForm($form, $form_state);
        $form['actions']['submit']['#ajax'] = [
            'callback' => '::ajaxSubmit',
        ];
        $form['#attached']['library'][] = 'core/drupal.dialog.ajax';
        // static::ajaxSubmit() requires data-drupal-selector to be the same between
        // the various Ajax requests. A bug in \Drupal\Core\Form\FormBuilder
        // prevents that from happening unless $form['#id'] is also the same.
        // Normally, #id is set to a unique HTML ID via Html::getUniqueId(), but
        // here we bypass that in order to work around the data-drupal-selector bug.
        // This is okay so long as we assume that this form only ever occurs once on
        // a page.
        // @todo Remove this workaround once https://www.drupal.org/node/2897377 is
        //   fixed.
        $form['#id'] = Html::getId($form_state->getBuildInfo()['form_id']);
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function successfulAjaxSubmit(array $form, FormStateInterface $form_state) {
        if ($redirect_url = $this->getRedirectUrl()) {
            $command = new RedirectCommand($redirect_url->setAbsolute()
                ->toString());
        }
        else {
            // Settings Tray always provides a destination.
            throw new \Exception("No destination provided by Settings Tray form");
        }
        $response = new AjaxResponse();
        return $response->addCommand($command);
    }
    
    /**
     * Gets the form's redirect URL from 'destination' provide in the request.
     *
     * @return \Drupal\Core\Url|null
     *   The redirect URL or NULL if dialog should just be closed.
     */
    protected function getRedirectUrl() {
        // \Drupal\Core\Routing\RedirectDestination::get() cannot be used directly
        // because it will use <current> if 'destination' is not in the query
        // string.
        if ($this->getRequest()->query
            ->has('destination') && ($destination = $this->getRedirectDestination()
            ->get())) {
            return Url::fromUserInput('/' . $destination);
        }
    }

}