class WizardFactory

class WizardFactory implements WizardFactoryInterface {
    
    /**
     * The Form Builder.
     *
     * @var \Drupal\Core\Form\FormBuilderInterface
     */
    protected $builder;
    
    /**
     * The event dispatcher.
     *
     * @var \Symfony\Component\EventDispatcher\EventDispatcherInterface
     */
    protected $dispatcher;
    
    /**
     * The object renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * The construct method.
     *
     * @param \Drupal\Core\Form\FormBuilderInterface $form_builder
     *   The form builder.
     * @param \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher
     *   The event dispatcher.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The object renderer.
     */
    public function __construct(FormBuilderInterface $form_builder, EventDispatcherInterface $event_dispatcher, RendererInterface $renderer) {
        $this->builder = $form_builder;
        $this->dispatcher = $event_dispatcher;
        $this->renderer = $renderer;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getWizardForm(FormWizardInterface $wizard, array $parameters = [], $ajax = FALSE) {
        $form_state = $this->getFormState($wizard, $parameters, $ajax);
        $form = $this->builder
            ->buildForm($wizard, $form_state);
        if ($ajax) {
            $form['#attached']['library'][] = 'core/drupal.dialog.ajax';
            $status_messages = [
                '#type' => 'status_messages',
            ];
            if ($messages = $this->renderer
                ->renderRoot($status_messages)) {
                if (!empty($form['#prefix'])) {
                    // Form prefix is expected to be a string. Prepend the messages to
                    // that string.
                    $form['#prefix'] = '<div class="wizard-messages">' . $messages . '</div>' . $form['#prefix'];
                }
            }
        }
        return $form;
    }
    
    /**
     * Create form wizard.
     *
     * @param string $class
     *   A class name implementing FormWizardInterface.
     * @param array $parameters
     *   The array of parameters specific to this wizard.
     *
     * @return \Drupal\ctools\Wizard\FormWizardInterface
     *   Return form Wizard.
     */
    public function createWizard($class, array $parameters) {
        $arguments = [];
        $reflection = new \ReflectionClass($class);
        $constructor = $reflection->getMethod('__construct');
        foreach ($constructor->getParameters() as $parameter) {
            if (array_key_exists($parameter->name, $parameters)) {
                $arguments[] = $parameters[$parameter->name];
            }
            elseif ($parameter->isDefaultValueAvailable()) {
                $arguments[] = $parameter->getDefaultValue();
            }
        }
        
        /** @var \Drupal\ctools\Wizard\FormWizardInterface $wizard */
        $wizard = $reflection->newInstanceArgs($arguments);
        return $wizard;
    }
    
    /**
     * Get the wizard form state.
     *
     * @param \Drupal\ctools\Wizard\FormWizardInterface $wizard
     *   The form wizard.
     * @param array $parameters
     *   The array of parameters specific to this wizard.
     * @param bool $ajax
     *   Is ajax or not.
     *
     * @return \Drupal\Core\Form\FormState
     *   Return the form state.
     */
    public function getFormState(FormWizardInterface $wizard, array $parameters, $ajax = FALSE) {
        $form_state = new FormState();
        // If a wizard has no values, initialize them.
        if (!$wizard->getMachineName() || !$wizard->getTempstore()
            ->get($wizard->getMachineName())) {
            $cached_values = $wizard->initValues();
            // Save the cached values that were initialized.
            if ($wizard->getMachineName()) {
                $wizard->getTempstore()
                    ->set($wizard->getMachineName(), $cached_values);
            }
        }
        else {
            $cached_values = $wizard->getTempstore()
                ->get($wizard->getMachineName());
        }
        $form_state->setTemporaryValue('wizard', $cached_values);
        $form_state->set('ajax', $ajax);
        $parameters['form'] = [];
        $parameters['form_state'] = $form_state;
        $method = new \ReflectionMethod($wizard, 'buildForm');
        $arguments = [];
        foreach ($method->getParameters() as $parameter) {
            if (array_key_exists($parameter->name, $parameters)) {
                $arguments[] = $parameters[$parameter->name];
            }
            elseif ($parameter->isDefaultValueAvailable()) {
                $arguments[] = $parameter->getDefaultValue();
            }
        }
        unset($parameters['form'], $parameters['form_state']);
        // Remove $form and $form_state from the arguments, and re-index them.
        unset($arguments[0], $arguments[1]);
        $form_state->addBuildInfo('args', array_values($arguments));
        return $form_state;
    }

}