class ImageToolkitForm

class ImageToolkitForm extends ConfigFormBase {
  
  /**
   * An array containing currently available toolkits.
   *
   * @var \Drupal\Core\ImageToolkit\ImageToolkitInterface[]
   */
  protected $availableToolkits = [];
  
  /**
   * Constructs an ImageToolkitForm object.
   *
   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
   *   The factory for configuration objects.
   * @param \Drupal\Core\ImageToolkit\ImageToolkitManager $manager
   *   The image toolkit plugin manager.
   */
  public function __construct(ConfigFactoryInterface $config_factory, ImageToolkitManager $manager) {
    parent::__construct($config_factory);
    foreach ($manager->getAvailableToolkits() as $id => $definition) {
      $this->availableToolkits[$id] = $manager->createInstance($id);
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('config.factory'), $container->get('image.toolkit.manager'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'system_image_toolkit_settings';
  }
  
  /**
   * {@inheritdoc}
   */
  protected function getEditableConfigNames() {
    return [
      'system.image',
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $current_toolkit = $this->config('system.image')
      ->get('toolkit');
    $form['image_toolkit'] = [
      '#type' => 'radios',
      '#title' => $this->t('Select an image processing toolkit'),
      '#default_value' => $current_toolkit,
      '#options' => [],
    ];
    // If we have more than one image toolkit, allow the user to select the one
    // to use, and load each of the toolkits' settings form.
    foreach ($this->availableToolkits as $id => $toolkit) {
      $definition = $toolkit->getPluginDefinition();
      $form['image_toolkit']['#options'][$id] = $definition['title'];
      $form['image_toolkit_settings'][$id] = [
        '#type' => 'details',
        '#title' => $this->t('@toolkit settings', [
          '@toolkit' => $definition['title'],
        ]),
        '#open' => TRUE,
        '#tree' => TRUE,
        '#states' => [
          'visible' => [
            ':radio[name="image_toolkit"]' => [
              'value' => $id,
            ],
          ],
        ],
      ];
      $form['image_toolkit_settings'][$id] += $toolkit->buildConfigurationForm([], $form_state);
    }
    return parent::buildForm($form, $form_state);
  }
  
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    parent::validateForm($form, $form_state);
    // Call the form validation handler for each of the toolkits.
    foreach ($this->availableToolkits as $toolkit) {
      $toolkit->validateConfigurationForm($form, $form_state);
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $this->config('system.image')
      ->set('toolkit', $form_state->getValue('image_toolkit'))
      ->save();
    // Call the form submit handler for each of the toolkits.
    foreach ($this->availableToolkits as $toolkit) {
      $toolkit->submitConfigurationForm($form, $form_state);
    }
    parent::submitForm($form, $form_state);
  }

}