public function encode_form_data( $request ) {
    global $wp_widget_factory;

    $id            = $request['id'];
    $widget_object = $wp_widget_factory->get_widget_object( $id );

    if ( ! $widget_object ) {
      return new WP_Error(
        'rest_invalid_widget',
        __( 'Cannot preview a widget that does not extend WP_Widget.' ),
        array( 'status' => 400 )
      );
    }

    /*
		 * Set the widget's number so that the id attributes in the HTML that we
		 * return are predictable.
		 */
    if ( isset( $request['number'] ) && is_numeric( $request['number'] ) ) {
      $widget_object->_set( (int) $request['number'] );
    } else {
      $widget_object->_set( -1 );
    }

    if ( isset( $request['instance']['encoded'], $request['instance']['hash'] ) ) {
      $serialized_instance = base64_decode( $request['instance']['encoded'] );
      if ( ! hash_equals( wp_hash( $serialized_instance ), $request['instance']['hash'] ) ) {
        return new WP_Error(
          'rest_invalid_widget',
          __( 'The provided instance is malformed.' ),
          array( 'status' => 400 )
        );
      }
      $instance = unserialize( $serialized_instance );
    } else {
      $instance = array();
    }

    if (
      isset( $request['form_data'][ "widget-$id" ] ) &&
      is_array( $request['form_data'][ "widget-$id" ] )
    ) {
      $new_instance = array_values( $request['form_data'][ "widget-$id" ] )[0];
      $old_instance = $instance;

      $instance = $widget_object->update( $new_instance, $old_instance );

      
/** This filter is documented in wp-includes/class-wp-widget.php */
      $instance = apply_filters(
        'widget_update_callback',
        $instance,
        $new_instance,
        $old_instance,
        $widget_object
      );
    }

    $serialized_instance = serialize( $instance );
    $widget_key          = $wp_widget_factory->get_widget_key( $id );

    $response = array(
      'form'     => trim(
        $this->get_widget_form(
          $widget_object,
          $instance
        )
      ),
      'preview'  => trim(
        $this->get_widget_preview(
          $widget_key,
          $instance
        )
      ),
      'instance' => array(
        'encoded' => base64_encode( $serialized_instance ),
        'hash'    => wp_hash( $serialized_instance ),
      ),
    );

    if ( ! empty( $widget_object->widget_options['show_instance_in_rest'] ) ) {
      // Use new stdClass so that JSON result is {} and not [].
      $response['instance']['raw'] = empty( $instance ) ? new stdClass() : $instance;
    }

    return rest_ensure_response( $response );
  }