class NodeForm

class NodeForm extends ContentEntityForm {

  /**
   * The tempstore factory.
   *
   * @var \Drupal\Core\TempStore\PrivateTempStoreFactory
   */
  protected $tempStoreFactory;

  /**
   * The Current User object.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $currentUser;

  /**
   * The date formatter service.
   *
   * @var \Drupal\Core\Datetime\DateFormatterInterface
   */
  protected $dateFormatter;

  /**
   * Constructs a NodeForm object.
   *
   * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
   *   The entity repository.
   * @param \Drupal\Core\TempStore\PrivateTempStoreFactory $temp_store_factory
   *   The factory for the temp store object.
   * @param \Drupal\Core\Entity\EntityTypeBundleInfoInterface $entity_type_bundle_info
   *   The entity type bundle service.
   * @param \Drupal\Component\Datetime\TimeInterface $time
   *   The time service.
   * @param \Drupal\Core\Session\AccountInterface $current_user
   *   The current user.
   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
   *   The date formatter service.
   */
  public function __construct(EntityRepositoryInterface $entity_repository, PrivateTempStoreFactory $temp_store_factory, EntityTypeBundleInfoInterface $entity_type_bundle_info = NULL, TimeInterface $time = NULL, AccountInterface $current_user, DateFormatterInterface $date_formatter) {
    parent::__construct($entity_repository, $entity_type_bundle_info, $time);
    $this->tempStoreFactory = $temp_store_factory;
    $this->currentUser = $current_user;
    $this->dateFormatter = $date_formatter;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container
      ->get('entity.repository'), $container
      ->get('tempstore.private'), $container
      ->get('entity_type.bundle.info'), $container
      ->get('datetime.time'), $container
      ->get('current_user'), $container
      ->get('date.formatter'));
  }

  /**
   * {@inheritdoc}
   */
  public function form(array $form, FormStateInterface $form_state) {

    // Try to restore from temp store, this must be done before calling
    // parent::form().
    $store = $this->tempStoreFactory
      ->get('node_preview');

    // Attempt to load from preview when the uuid is present unless we are
    // rebuilding the form.
    $request_uuid = \Drupal::request()->query
      ->get('uuid');
    if (!$form_state
      ->isRebuilding() && $request_uuid && ($preview = $store
      ->get($request_uuid))) {

      /** @var \Drupal\Core\Form\FormStateInterface $preview */
      $form_state
        ->setStorage($preview
        ->getStorage());
      $form_state
        ->setUserInput($preview
        ->getUserInput());

      // Rebuild the form.
      $form_state
        ->setRebuild();

      // The combination of having user input and rebuilding the form means
      // that it will attempt to cache the form state which will fail if it is
      // a GET request.
      $form_state
        ->setRequestMethod('POST');
      $this->entity = $preview
        ->getFormObject()
        ->getEntity();
      $this->entity->in_preview = NULL;
      $form_state
        ->set('has_been_previewed', TRUE);
    }

    /** @var \Drupal\node\NodeInterface $node */
    $node = $this->entity;
    if ($this->operation == 'edit') {
      $form['#title'] = $this
        ->t('<em>Edit @type</em> @title', [
        '@type' => node_get_type_label($node),
        '@title' => $node
          ->label(),
      ]);
    }

    // Changed must be sent to the client, for later overwrite error checking.
    $form['changed'] = [
      '#type' => 'hidden',
      '#default_value' => $node
        ->getChangedTime(),
    ];
    $form = parent::form($form, $form_state);
    $form['advanced']['#attributes']['class'][] = 'entity-meta';
    $form['meta'] = [
      '#type' => 'details',
      '#group' => 'advanced',
      '#weight' => -10,
      '#title' => $this
        ->t('Status'),
      '#attributes' => [
        'class' => [
          'entity-meta__header',
        ],
      ],
      '#tree' => TRUE,
      '#access' => $this->currentUser
        ->hasPermission('administer nodes'),
    ];
    $form['meta']['published'] = [
      '#type' => 'item',
      '#markup' => $node
        ->isPublished() ? $this
        ->t('Published') : $this
        ->t('Not published'),
      '#access' => !$node
        ->isNew(),
      '#wrapper_attributes' => [
        'class' => [
          'entity-meta__title',
        ],
      ],
    ];
    $form['meta']['changed'] = [
      '#type' => 'item',
      '#title' => $this
        ->t('Last saved'),
      '#markup' => !$node
        ->isNew() ? $this->dateFormatter
        ->format($node
        ->getChangedTime(), 'short') : $this
        ->t('Not saved yet'),
      '#wrapper_attributes' => [
        'class' => [
          'entity-meta__last-saved',
        ],
      ],
    ];
    $form['meta']['author'] = [
      '#type' => 'item',
      '#title' => $this
        ->t('Author'),
      '#markup' => $node
        ->getOwner()
        ->getAccountName(),
      '#wrapper_attributes' => [
        'class' => [
          'entity-meta__author',
        ],
      ],
    ];
    $form['status']['#group'] = 'footer';

    // Node author information for administrators.
    $form['author'] = [
      '#type' => 'details',
      '#title' => $this
        ->t('Authoring information'),
      '#group' => 'advanced',
      '#attributes' => [
        'class' => [
          'node-form-author',
        ],
      ],
      '#attached' => [
        'library' => [
          'node/drupal.node',
        ],
      ],
      '#weight' => 90,
      '#optional' => TRUE,
    ];
    if (isset($form['uid'])) {
      $form['uid']['#group'] = 'author';
    }
    if (isset($form['created'])) {
      $form['created']['#group'] = 'author';
    }

    // Node options for administrators.
    $form['options'] = [
      '#type' => 'details',
      '#title' => $this
        ->t('Promotion options'),
      '#group' => 'advanced',
      '#attributes' => [
        'class' => [
          'node-form-options',
        ],
      ],
      '#attached' => [
        'library' => [
          'node/drupal.node',
        ],
      ],
      '#weight' => 95,
      '#optional' => TRUE,
    ];
    if (isset($form['promote'])) {
      $form['promote']['#group'] = 'options';
    }
    if (isset($form['sticky'])) {
      $form['sticky']['#group'] = 'options';
    }
    $form['#attached']['library'][] = 'node/form';
    return $form;
  }

  /**
   * {@inheritdoc}
   */
  protected function actions(array $form, FormStateInterface $form_state) {
    $element = parent::actions($form, $form_state);
    $node = $this->entity;
    $preview_mode = $node->type->entity
      ->getPreviewMode();
    $element['submit']['#access'] = $preview_mode != DRUPAL_REQUIRED || $form_state
      ->get('has_been_previewed');
    $element['preview'] = [
      '#type' => 'submit',
      '#access' => $preview_mode != DRUPAL_DISABLED && ($node
        ->access('create') || $node
        ->access('update')),
      '#value' => $this
        ->t('Preview'),
      '#weight' => 20,
      '#submit' => [
        '::submitForm',
        '::preview',
      ],
    ];
    if (array_key_exists('delete', $element)) {
      $element['delete']['#weight'] = 100;
    }
    return $element;
  }

  /**
   * Form submission handler for the 'preview' action.
   *
   * @param $form
   *   An associative array containing the structure of the form.
   * @param $form_state
   *   The current state of the form.
   */
  public function preview(array $form, FormStateInterface $form_state) {
    $store = $this->tempStoreFactory
      ->get('node_preview');
    $this->entity->in_preview = TRUE;
    $store
      ->set($this->entity
      ->uuid(), $form_state);
    $route_parameters = [
      'node_preview' => $this->entity
        ->uuid(),
      'view_mode_id' => 'full',
    ];
    $options = [];
    $query = $this
      ->getRequest()->query;
    if ($query
      ->has('destination')) {
      $options['query']['destination'] = $query
        ->get('destination');
      $query
        ->remove('destination');
    }
    $form_state
      ->setRedirect('entity.node.preview', $route_parameters, $options);
  }

  /**
   * {@inheritdoc}
   */
  public function save(array $form, FormStateInterface $form_state) {
    $node = $this->entity;
    $insert = $node
      ->isNew();
    $node
      ->save();
    $node_link = $node
      ->toLink($this
      ->t('View'))
      ->toString();
    $context = [
      '@type' => $node
        ->getType(),
      '%title' => $node
        ->label(),
      'link' => $node_link,
    ];
    $t_args = [
      '@type' => node_get_type_label($node),
      '%title' => $node
        ->toLink()
        ->toString(),
    ];
    if ($insert) {
      $this
        ->logger('content')
        ->info('@type: added %title.', $context);
      $this
        ->messenger()
        ->addStatus($this
        ->t('@type %title has been created.', $t_args));
    }
    else {
      $this
        ->logger('content')
        ->info('@type: updated %title.', $context);
      $this
        ->messenger()
        ->addStatus($this
        ->t('@type %title has been updated.', $t_args));
    }
    if ($node
      ->id()) {
      $form_state
        ->setValue('nid', $node
        ->id());
      $form_state
        ->set('nid', $node
        ->id());
      if ($node
        ->access('view')) {
        $form_state
          ->setRedirect('entity.node.canonical', [
          'node' => $node
            ->id(),
        ]);
      }
      else {
        $form_state
          ->setRedirect('<front>');
      }

      // Remove the preview entry from the temp store, if any.
      $store = $this->tempStoreFactory
        ->get('node_preview');
      $store
        ->delete($node
        ->uuid());
    }
    else {

      // In the unlikely case something went wrong on save, the node will be
      // rebuilt and node form redisplayed the same way as in preview.
      $this
        ->messenger()
        ->addError($this
        ->t('The post could not be saved.'));
      $form_state
        ->setRebuild();
    }
  }

}