trait FieldLayoutEntityDisplayFormTrait

trait FieldLayoutEntityDisplayFormTrait {
    
    /**
     * The field layout plugin manager.
     *
     * @var \Drupal\Core\Layout\LayoutPluginManagerInterface
     */
    protected $layoutPluginManager;
    
    /**
     * Overrides \Drupal\field_ui\Form\EntityDisplayFormBase::getRegions().
     */
    public function getRegions() {
        $regions = [];
        $layout_definition = $this->layoutPluginManager
            ->getDefinition($this->getEntity()
            ->getLayoutId());
        foreach ($layout_definition->getRegions() as $name => $region) {
            $regions[$name] = [
                'title' => $region['label'],
                'message' => $this->t('No field is displayed.'),
            ];
        }
        $regions['hidden'] = [
            'title' => $this->t('Disabled', [], [
                'context' => 'Plural',
            ]),
            'message' => $this->t('No field is hidden.'),
        ];
        return $regions;
    }
    
    /**
     * Overrides \Drupal\field_ui\Form\EntityDisplayFormBase::form().
     */
    public function form(array $form, FormStateInterface $form_state) {
        $form = parent::form($form, $form_state);
        $form['field_layouts'] = [
            '#type' => 'details',
            '#title' => $this->t('Layout settings'),
        ];
        $layout_plugin = $this->getLayout($this->getEntity(), $form_state);
        $form['field_layouts']['field_layout'] = [
            '#type' => 'select',
            '#title' => $this->t('Select a layout'),
            '#options' => $this->layoutPluginManager
                ->getLayoutOptions(),
            '#default_value' => $layout_plugin->getPluginId(),
            '#ajax' => [
                'callback' => '::settingsAjax',
                'wrapper' => 'field-layout-settings-wrapper',
                'trigger_as' => [
                    'name' => 'field_layout_change',
                ],
            ],
        ];
        $form['field_layouts']['submit'] = [
            '#type' => 'submit',
            '#name' => 'field_layout_change',
            '#value' => $this->t('Change layout'),
            '#submit' => [
                '::settingsAjaxSubmit',
            ],
            '#attributes' => [
                'class' => [
                    'js-hide',
                ],
            ],
            '#ajax' => [
                'callback' => '::settingsAjax',
                'wrapper' => 'field-layout-settings-wrapper',
            ],
        ];
        $form['field_layouts']['settings_wrapper'] = [
            '#type' => 'container',
            '#id' => 'field-layout-settings-wrapper',
            '#tree' => TRUE,
        ];
        $form['field_layouts']['settings_wrapper']['icon'] = $layout_plugin->getPluginDefinition()
            ->getIcon();
        if ($layout_plugin instanceof PluginFormInterface) {
            $form['field_layouts']['settings_wrapper']['layout_settings'] = [];
            $subform_state = SubformState::createForSubform($form['field_layouts']['settings_wrapper']['layout_settings'], $form, $form_state);
            $form['field_layouts']['settings_wrapper']['layout_settings'] = $layout_plugin->buildConfigurationForm($form['field_layouts']['settings_wrapper']['layout_settings'], $subform_state);
        }
        return $form;
    }
    
    /**
     * Gets the layout plugin for the currently selected field layout.
     *
     * @param \Drupal\field_layout\Display\EntityDisplayWithLayoutInterface $entity
     *   The current form entity.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @return \Drupal\Core\Layout\LayoutInterface
     *   The layout plugin.
     */
    protected function getLayout(EntityDisplayWithLayoutInterface $entity, FormStateInterface $form_state) {
        if (!($layout_plugin = $form_state->get('layout_plugin'))) {
            $stored_layout_id = $entity->getLayoutId();
            // Use selected layout if it exists, falling back to the stored layout.
            $layout_id = $form_state->getValue('field_layout', $stored_layout_id);
            // If the current layout is the stored layout, use the stored layout
            // settings. Otherwise leave the settings empty.
            $layout_settings = $layout_id === $stored_layout_id ? $entity->getLayoutSettings() : [];
            $layout_plugin = $this->layoutPluginManager
                ->createInstance($layout_id, $layout_settings);
            $form_state->set('layout_plugin', $layout_plugin);
        }
        return $layout_plugin;
    }
    
    /**
     * Ajax callback for the field layout settings form.
     */
    public static function settingsAjax($form, FormStateInterface $form_state) {
        return $form['field_layouts']['settings_wrapper'];
    }
    
    /**
     * Submit handler for the non-JS case.
     */
    public function settingsAjaxSubmit($form, FormStateInterface $form_state) {
        $form_state->set('layout_plugin', NULL);
        $form_state->setRebuild();
    }
    
    /**
     * Overrides \Drupal\field_ui\Form\EntityDisplayFormBase::validateForm().
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        parent::validateForm($form, $form_state);
        $layout_plugin = $this->getLayout($this->getEntity(), $form_state);
        if ($layout_plugin instanceof PluginFormInterface) {
            $subform_state = SubformState::createForSubform($form['field_layouts']['settings_wrapper']['layout_settings'], $form, $form_state);
            $layout_plugin->validateConfigurationForm($form['field_layouts']['settings_wrapper']['layout_settings'], $subform_state);
        }
    }
    
    /**
     * Overrides \Drupal\field_ui\Form\EntityDisplayFormBase::submitForm().
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        parent::submitForm($form, $form_state);
        $entity = $this->getEntity();
        $layout_plugin = $this->getLayout($entity, $form_state);
        if ($layout_plugin instanceof PluginFormInterface) {
            $subform_state = SubformState::createForSubform($form['field_layouts']['settings_wrapper']['layout_settings'], $form, $form_state);
            $layout_plugin->submitConfigurationForm($form['field_layouts']['settings_wrapper']['layout_settings'], $subform_state);
        }
        $entity->setLayout($layout_plugin);
    }
    
    /**
     * Gets the form entity.
     *
     * @return \Drupal\field_layout\Display\EntityDisplayWithLayoutInterface
     *   The current form entity.
     */
    public abstract function getEntity();

}