class QuickEditFieldForm

class QuickEditFieldForm extends FormBase {
    
    /**
     * Stores the tempstore factory.
     *
     * @var \Drupal\Core\TempStore\PrivateTempStoreFactory
     */
    protected $tempStoreFactory;
    
    /**
     * The module handler.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * The node type storage.
     *
     * @var \Drupal\Core\Entity\EntityStorageInterface
     */
    protected $nodeTypeStorage;
    
    /**
     * Constructs a new EditFieldForm.
     *
     * @param \Drupal\Core\TempStore\PrivateTempStoreFactory $temp_store_factory
     *   The tempstore factory.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     * @param \Drupal\Core\Entity\EntityStorageInterface $node_type_storage
     *   The node type storage.
     */
    public function __construct(PrivateTempStoreFactory $temp_store_factory, ModuleHandlerInterface $module_handler, EntityStorageInterface $node_type_storage) {
        $this->moduleHandler = $module_handler;
        $this->nodeTypeStorage = $node_type_storage;
        $this->tempStoreFactory = $temp_store_factory;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('tempstore.private'), $container->get('module_handler'), $container->get('entity_type.manager')
            ->getStorage('node_type'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'quickedit_field_form';
    }
    
    /**
     * {@inheritdoc}
     *
     * Builds a form for a single entity field.
     */
    public function buildForm(array $form, FormStateInterface $form_state, EntityInterface $entity = NULL, $field_name = NULL) {
        if (!$form_state->has('entity')) {
            $this->init($form_state, $entity, $field_name);
        }
        // Add the field form.
        $form_state->get('form_display')
            ->buildForm($entity, $form, $form_state);
        // Add a dummy changed timestamp field to attach form errors to.
        if ($entity instanceof EntityChangedInterface) {
            $form['changed_field'] = [
                '#type' => 'hidden',
                '#value' => $entity->getChangedTime(),
            ];
        }
        // Add a submit button. Give it a class for easy JavaScript targeting.
        $form['actions'] = [
            '#type' => 'actions',
        ];
        $form['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Save'),
            '#attributes' => [
                'class' => [
                    'quickedit-form-submit',
                ],
            ],
        ];
        // Use the non-inline form error display for Quick Edit forms, because in
        // this case the errors are already near the form element.
        $form['#disable_inline_form_errors'] = TRUE;
        // Simplify it for optimal in-place use.
        $this->simplify($form, $form_state);
        return $form;
    }
    
    /**
     * Initialize the form state and the entity before the first form build.
     */
    protected function init(FormStateInterface $form_state, EntityInterface $entity, $field_name) {
        // @todo Rather than special-casing $node->revision, invoke prepareEdit()
        //   once https://www.drupal.org/node/1863258 lands.
        if ($entity->getEntityTypeId() == 'node') {
            $node_type = $this->nodeTypeStorage
                ->load($entity->bundle());
            $entity->setNewRevision($node_type->shouldCreateNewRevision());
            $entity->revision_log = NULL;
        }
        $form_state->set('entity', $entity);
        $form_state->set('field_name', $field_name);
        // Fetch the display used by the form. It is the display for the 'default'
        // form mode, with only the current field visible.
        $display = EntityFormDisplay::collectRenderDisplay($entity, 'default');
        foreach ($display->getComponents() as $name => $options) {
            if ($name != $field_name) {
                $display->removeComponent($name);
            }
        }
        $form_state->set('form_display', $display);
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        $entity = $this->buildEntity($form, $form_state);
        $form_state->get('form_display')
            ->validateFormValues($entity, $form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     *
     * Saves the entity with updated values for the edited field.
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $entity = $this->buildEntity($form, $form_state);
        $form_state->set('entity', $entity);
        // Store entity in tempstore with its UUID as tempstore key.
        $this->tempStoreFactory
            ->get('quickedit')
            ->set($entity->uuid(), $entity);
    }
    
    /**
     * Returns a cloned entity containing updated field values.
     *
     * Calling code may then validate the returned entity, and if valid, transfer
     * it back to the form state and save it.
     */
    protected function buildEntity(array $form, FormStateInterface $form_state) {
        
        /** @var \Drupal\Core\Entity\EntityInterface $entity */
        $entity = clone $form_state->get('entity');
        $field_name = $form_state->get('field_name');
        $form_state->get('form_display')
            ->extractFormValues($entity, $form, $form_state);
        // @todo Refine automated log messages and abstract them to all entity
        //   types: https://www.drupal.org/node/1678002.
        if ($entity->getEntityTypeId() == 'node' && $entity->isNewRevision() && $entity->revision_log
            ->isEmpty()) {
            $entity->revision_log = $this->t('Updated the %field-name field through in-place editing.', [
                '%field-name' => $entity->get($field_name)
                    ->getFieldDefinition()
                    ->getLabel(),
            ]);
        }
        return $entity;
    }
    
    /**
     * Simplifies the field edit form for in-place editing.
     *
     * This function:
     * - Hides the field label inside the form, because JavaScript displays it
     *   outside the form.
     * - Adjusts textarea elements to fit their content.
     *
     * @param array &$form
     *   A reference to an associative array containing the structure of the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    protected function simplify(array &$form, FormStateInterface $form_state) {
        $field_name = $form_state->get('field_name');
        $widget_element =& $form[$field_name]['widget'];
        // Hide the field label from displaying within the form, because JavaScript
        // displays the equivalent label that was provided within an HTML data
        // attribute of the field's display element outside of the form. Do this for
        // widgets without child elements (like Option widgets) as well as for ones
        // with per-delta elements. Skip single checkboxes, because their title is
        // key to their UI. Also skip widgets with multiple subelements, because in
        // that case, per-element labeling is informative.
        $num_children = count(Element::children($widget_element));
        if ($num_children == 0 && $widget_element['#type'] != 'checkbox') {
            $widget_element['#title_display'] = 'invisible';
        }
        if ($num_children == 1 && isset($widget_element[0]['value'])) {
            // @todo While most widgets name their primary element 'value', not all
            //   do, so generalize this.
            $widget_element[0]['value']['#title_display'] = 'invisible';
        }
        // Adjust textarea elements to fit their content.
        if (isset($widget_element[0]['value']['#type']) && $widget_element[0]['value']['#type'] == 'textarea') {
            $lines = count(explode("\n", $widget_element[0]['value']['#default_value']));
            $widget_element[0]['value']['#rows'] = $lines + 1;
        }
    }

}