class WorkflowStateAddForm

class WorkflowStateAddForm extends EntityForm {
    
    /**
     * The plugin form factory.
     *
     * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
     */
    protected $pluginFormFactory;
    
    /**
     * Creates an instance of WorkflowStateEditForm.
     *
     * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $pluginFormFactory
     *   The plugin form factory.
     */
    public function __construct(PluginFormFactoryInterface $pluginFormFactory) {
        $this->pluginFormFactory = $pluginFormFactory;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('plugin_form.factory'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'workflow_state_add_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $form = parent::form($form, $form_state);
        
        /** @var \Drupal\workflows\WorkflowInterface $workflow */
        $workflow = $this->getEntity();
        $workflow_type = $workflow->getTypePlugin();
        $form['label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('State label'),
            '#maxlength' => 255,
            '#default_value' => '',
            '#required' => TRUE,
        ];
        $form['id'] = [
            '#type' => 'machine_name',
            '#machine_name' => [
                'exists' => [
                    $this,
                    'exists',
                ],
            ],
        ];
        if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
            $form['type_settings'] = [
                '#tree' => TRUE,
            ];
            $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
            $form['type_settings'] += $this->pluginFormFactory
                ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
                ->buildConfigurationForm($form['type_settings'], $subform_state);
        }
        return $form;
    }
    
    /**
     * Determines if the workflow state already exists.
     *
     * @param string $state_id
     *   The workflow state ID.
     *
     * @return bool
     *   TRUE if the workflow state exists, FALSE otherwise.
     */
    public function exists($state_id) {
        
        /** @var \Drupal\workflows\WorkflowInterface $original_workflow */
        $original_workflow = \Drupal::entityTypeManager()->getStorage('workflow')
            ->loadUnchanged($this->getEntity()
            ->id());
        return $original_workflow->getTypePlugin()
            ->hasState($state_id);
    }
    
    /**
     * Copies top-level form values to entity properties.
     *
     * This form can only change values for a state, which is part of workflow.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity the current form should operate upon.
     * @param array $form
     *   A nested array of form elements comprising the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
        if (!$form_state->isValidationComplete()) {
            // Only do something once form validation is complete.
            return;
        }
        
        /** @var \Drupal\workflows\WorkflowInterface $entity */
        $values = $form_state->getValues();
        $entity->getTypePlugin()
            ->addState($values['id'], $values['label']);
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        parent::validateForm($form, $form_state);
        
        /** @var \Drupal\workflows\WorkflowTypeInterface $workflow_type */
        $workflow = $this->entity;
        $workflow_type = $workflow->getTypePlugin();
        if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
            $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
            $this->pluginFormFactory
                ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
                ->validateConfigurationForm($form['type_settings'], $subform_state);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function save(array $form, FormStateInterface $form_state) {
        
        /** @var \Drupal\workflows\WorkflowInterface $workflow */
        $workflow = $this->entity;
        $workflow_type = $workflow->getTypePlugin();
        $state = $workflow_type->getState($form_state->getValue('id'));
        if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
            $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
            $subform_state->set('state', $state);
            $this->pluginFormFactory
                ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
                ->submitConfigurationForm($form['type_settings'], $subform_state);
        }
        $workflow->save();
        $this->messenger()
            ->addStatus($this->t('Created %label state.', [
            '%label' => $workflow->getTypePlugin()
                ->getState($form_state->getValue('id'))
                ->label(),
        ]));
        $form_state->setRedirectUrl($workflow->toUrl('edit-form'));
    }
    
    /**
     * {@inheritdoc}
     */
    protected function actions(array $form, FormStateInterface $form_state) {
        $actions['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Save'),
            '#submit' => [
                '::submitForm',
                '::save',
            ],
        ];
        return $actions;
    }

}