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);
    }

}