class ViewAddForm

class ViewAddForm extends ViewFormBase {

  /**
   * The wizard plugin manager.
   *
   * @var \Drupal\views\Plugin\ViewsPluginManager
   */
  protected $wizardManager;

  /**
   * The module handler service.
   *
   * @var \Drupal\Core\Extension\ModuleHandlerInterface
   */
  protected $moduleHandler;

  /**
   * Constructs a new ViewAddForm object.
   *
   * @param \Drupal\views\Plugin\ViewsPluginManager $wizard_manager
   *   The wizard plugin manager.
   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
   *   The module handler service.
   */
  public function __construct(ViewsPluginManager $wizard_manager, ModuleHandlerInterface $module_handler) {
    $this->wizardManager = $wizard_manager;
    $this->moduleHandler = $module_handler;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container
      ->get('plugin.manager.views.wizard'), $container
      ->get('module_handler'));
  }

  /**
   * {@inheritdoc}
   */
  protected function prepareEntity() {

    // Do not prepare the entity while it is being added.
  }

  /**
   * {@inheritdoc}
   */
  public function form(array $form, FormStateInterface $form_state) {
    $form['#attached']['library'][] = 'views_ui/views_ui.admin';
    $form['#attributes']['class'] = [
      'views-admin',
    ];
    $form['name'] = [
      '#type' => 'fieldset',
      '#title' => $this
        ->t('View basic information'),
      '#attributes' => [
        'class' => [
          'fieldset-no-legend',
        ],
      ],
    ];
    $form['name']['label'] = [
      '#type' => 'textfield',
      '#title' => $this
        ->t('View name'),
      '#required' => TRUE,
      '#size' => 32,
      '#default_value' => '',
      '#maxlength' => 255,
    ];
    $form['name']['id'] = [
      '#type' => 'machine_name',
      '#maxlength' => 128,
      '#machine_name' => [
        'exists' => '\\Drupal\\views\\Views::getView',
        'source' => [
          'name',
          'label',
        ],
      ],
      '#description' => $this
        ->t('A unique machine-readable name for this View. It must only contain lowercase letters, numbers, and underscores.'),
    ];
    $form['name']['description_enable'] = [
      '#type' => 'checkbox',
      '#title' => $this
        ->t('Description'),
    ];
    $form['name']['description'] = [
      '#type' => 'textfield',
      '#title' => $this
        ->t('Provide description'),
      '#title_display' => 'invisible',
      '#size' => 64,
      '#default_value' => '',
      '#states' => [
        'visible' => [
          ':input[name="description_enable"]' => [
            'checked' => TRUE,
          ],
        ],
      ],
    ];

    // Create a wrapper for the entire dynamic portion of the form. Everything
    // that can be updated by AJAX goes somewhere inside here. For example, this
    // is needed by "Show" dropdown (below); it changes the base table of the
    // view and therefore potentially requires all options on the form to be
    // dynamically updated.
    $form['displays'] = [];

    // Create the part of the form that allows the user to select the basic
    // properties of what the view will display.
    $form['displays']['show'] = [
      '#type' => 'fieldset',
      '#title' => $this
        ->t('View settings'),
      '#tree' => TRUE,
      '#attributes' => [
        'class' => [
          'container-inline',
        ],
      ],
    ];

    // Create the "Show" dropdown, which allows the base table of the view to be
    // selected.
    $wizard_plugins = $this->wizardManager
      ->getDefinitions();
    $options = [];
    foreach ($wizard_plugins as $key => $wizard) {
      $options[$key] = $wizard['title'];
    }
    $form['displays']['show']['wizard_key'] = [
      '#type' => 'select',
      '#title' => $this
        ->t('Show'),
      '#options' => $options,
      '#sort_options' => TRUE,
    ];
    $show_form =& $form['displays']['show'];
    $default_value = $this->moduleHandler
      ->moduleExists('node') ? 'node' : 'users';
    $show_form['wizard_key']['#default_value'] = WizardPluginBase::getSelected($form_state, [
      'show',
      'wizard_key',
    ], $default_value, $show_form['wizard_key']);

    // Changing this dropdown updates the entire content of $form['displays'] via
    // AJAX.
    views_ui_add_ajax_trigger($show_form, 'wizard_key', [
      'displays',
    ]);

    // Build the rest of the form based on the currently selected wizard plugin.
    $wizard_key = $show_form['wizard_key']['#default_value'];
    $wizard_instance = $this->wizardManager
      ->createInstance($wizard_key);
    $form = $wizard_instance
      ->buildForm($form, $form_state);
    return $form;
  }

  /**
   * {@inheritdoc}
   */
  protected function actions(array $form, FormStateInterface $form_state) {
    $actions = parent::actions($form, $form_state);
    $actions['submit']['#value'] = $this
      ->t('Save and edit');

    // Remove EntityFormController::save() form the submission handlers.
    $actions['submit']['#submit'] = [
      [
        $this,
        'submitForm',
      ],
    ];
    $actions['cancel'] = [
      '#type' => 'submit',
      '#value' => $this
        ->t('Cancel'),
      '#submit' => [
        '::cancel',
      ],
      '#limit_validation_errors' => [],
    ];
    return $actions;
  }

  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    $wizard_type = $form_state
      ->getValue([
      'show',
      'wizard_key',
    ]);
    $wizard_instance = $this->wizardManager
      ->createInstance($wizard_type);
    $form_state
      ->set('wizard', $wizard_instance
      ->getPluginDefinition());
    $form_state
      ->set('wizard_instance', $wizard_instance);
    $path =& $form_state
      ->getValue([
      'page',
      'path',
    ]);
    if (!empty($path)) {

      // @todo https://www.drupal.org/node/2423913 Views should expect and store
      //   a leading /.
      $path = ltrim($path, '/ ');
    }
    $errors = $wizard_instance
      ->validateView($form, $form_state);
    foreach ($errors as $display_errors) {
      foreach ($display_errors as $name => $message) {
        $form_state
          ->setErrorByName($name, $message);
      }
    }
  }

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

      /** @var \Drupal\views\Plugin\views\wizard\WizardInterface $wizard */
      $wizard = $form_state
        ->get('wizard_instance');
      $this->entity = $wizard
        ->createView($form, $form_state);
    } catch (WizardException $e) {
      $this
        ->messenger()
        ->addError($e
        ->getMessage());
      $form_state
        ->setRedirect('entity.view.collection');
      return;
    }
    $this->entity
      ->save();
    $this
      ->messenger()
      ->addStatus($this
      ->t('The view %name has been saved.', [
      '%name' => $form_state
        ->getValue('label'),
    ]));
    $form_state
      ->setRedirectUrl($this->entity
      ->toUrl('edit-form'));
  }

  /**
   * Form submission handler for the 'cancel' action.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  public function cancel(array $form, FormStateInterface $form_state) {
    $form_state
      ->setRedirect('entity.view.collection');
  }

}