class DevelGenerateForm

class DevelGenerateForm extends FormBase {
    
    /**
     * The manager to be used for instantiating plugins.
     *
     * @var \Drupal\Component\Plugin\PluginManagerInterface
     */
    protected $develGenerateManager;
    
    /**
     * Constructs a new DevelGenerateForm object.
     *
     * @param \Drupal\Component\Plugin\PluginManagerInterface $devel_generate_manager
     *   The manager to be used for instantiating plugins.
     */
    public function __construct(PluginManagerInterface $devel_generate_manager) {
        $this->develGenerateManager = $devel_generate_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('plugin.manager.develgenerate'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'devel_generate_form_' . $this->getPluginIdFromRequest();
    }
    
    /**
     * Returns the value of the param _plugin_id for the current request.
     *
     * @see \Drupal\devel_generate\Routing\DevelGenerateRouteSubscriber
     */
    protected function getPluginIdFromRequest() {
        $request = $this->getRequest();
        return $request->get('_plugin_id');
    }
    
    /**
     * Returns a DevelGenerate plugin instance for a given plugin id.
     *
     * @param string $plugin_id
     *   The plugin_id for the plugin instance.
     *
     * @return \Drupal\devel_generate\DevelGenerateBaseInterface
     *   A DevelGenerate plugin instance.
     */
    public function getPluginInstance($plugin_id) {
        $instance = $this->develGenerateManager
            ->createInstance($plugin_id, array());
        return $instance;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $plugin_id = $this->getPluginIdFromRequest();
        $instance = $this->getPluginInstance($plugin_id);
        $form = $instance->settingsForm($form, $form_state);
        $form['actions'] = [
            '#type' => 'actions',
        ];
        $form['actions']['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Generate'),
            '#button_type' => 'primary',
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        $plugin_id = $this->getPluginIdFromRequest();
        $instance = $this->getPluginInstance($plugin_id);
        $instance->settingsFormValidate($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        try {
            $plugin_id = $this->getPluginIdFromRequest();
            $instance = $this->getPluginInstance($plugin_id);
            $instance->generate($form_state->getValues());
        } catch (DevelGenerateException $e) {
            $this->logger('DevelGenerate', $this->t('Failed to generate elements due to "%error".', array(
                '%error' => $e->getMessage(),
            )));
            drupal_set_message($this->t('Failed to generate elements due to "%error".', array(
                '%error' => $e->getMessage(),
            )));
        }
    }

}