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');
    }

}