class FieldConfigAddController

final class FieldConfigAddController extends ControllerBase {
    
    /**
     * FieldConfigAddController constructor.
     *
     * @param \Drupal\Core\TempStore\PrivateTempStore $tempStore
     *   The private tempstore.
     */
    public function __construct(PrivateTempStore $tempStore) {
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('tempstore.private')
            ->get('field_ui'));
    }
    
    /**
     * Builds the field config instance form.
     *
     * @param string $entity_type
     *   The entity type.
     * @param string $field_name
     *   The name of the field to create.
     *
     * @return array
     *   The field instance edit form.
     */
    public function fieldConfigAddConfigureForm(string $entity_type, string $field_name) : array {
        // @see \Drupal\field_ui\Form\FieldStorageAddForm::submitForm
        $temp_storage = $this->tempStore
            ->get($entity_type . ':' . $field_name);
        if (!$temp_storage) {
            throw new NotFoundHttpException();
        }
        
        /** @var \Drupal\Core\Field\FieldConfigInterface $entity */
        $entity = $this->entityTypeManager()
            ->getStorage('field_config')
            ->create([
            $temp_storage['field_config_values'],
            'field_storage' => $temp_storage['field_storage'],
        ]);
        return $this->entityFormBuilder()
            ->getForm($entity, 'default', [
            'default_options' => $temp_storage['default_options'],
        ]);
    }

}