class ImageEffectFormBase

abstract class ImageEffectFormBase extends FormBase {
  
  /**
   * The image style.
   *
   * @var \Drupal\image\ImageStyleInterface
   */
  protected $imageStyle;
  
  /**
   * The image effect.
   *
   * @var \Drupal\image\ImageEffectInterface|\Drupal\image\ConfigurableImageEffectInterface
   */
  protected $imageEffect;
  
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'image_effect_form';
  }
  
  /**
   * {@inheritdoc}
   *
   * @param array $form
   *   A nested array form elements comprising the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   * @param \Drupal\image\ImageStyleInterface $image_style
   *   The image style.
   * @param string $image_effect
   *   The image effect ID.
   *
   * @return array
   *   The form structure.
   *
   * @throws \Symfony\Component\HttpKernel\Exception\NotFoundHttpException
   */
  public function buildForm(array $form, FormStateInterface $form_state, ?ImageStyleInterface $image_style = NULL, $image_effect = NULL) {
    $this->imageStyle = $image_style;
    try {
      $this->imageEffect = $this->prepareImageEffect($image_effect);
    } catch (PluginNotFoundException $e) {
      throw new NotFoundHttpException("Invalid effect id: '{$image_effect}'.");
    }
    $request = $this->getRequest();
    if (!$this->imageEffect instanceof ConfigurableImageEffectInterface) {
      throw new NotFoundHttpException();
    }
    $form['#attached']['library'][] = 'image/admin';
    $form['uuid'] = [
      '#type' => 'value',
      '#value' => $this->imageEffect
        ->getUuid(),
    ];
    $form['id'] = [
      '#type' => 'value',
      '#value' => $this->imageEffect
        ->getPluginId(),
    ];
    $form['data'] = [];
    $subform_state = SubformState::createForSubform($form['data'], $form, $form_state);
    $form['data'] = $this->imageEffect
      ->buildConfigurationForm($form['data'], $subform_state);
    $form['data']['#tree'] = TRUE;
    // Check the URL for a weight, then the image effect, otherwise use default.
    $form['weight'] = [
      '#type' => 'hidden',
      '#value' => $request->query
        ->has('weight') ? (int) $request->query
        ->get('weight') : $this->imageEffect
        ->getWeight(),
    ];
    $form['actions'] = [
      '#type' => 'actions',
    ];
    $form['actions']['submit'] = [
      '#type' => 'submit',
      '#button_type' => 'primary',
    ];
    $form['actions']['cancel'] = [
      '#type' => 'link',
      '#title' => $this->t('Cancel'),
      '#url' => $this->imageStyle
        ->toUrl('edit-form'),
      '#attributes' => [
        'class' => [
          'button',
        ],
      ],
    ];
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    // The image effect configuration is stored in the 'data' key in the form,
    // pass that through for validation.
    $this->imageEffect
      ->validateConfigurationForm($form['data'], SubformState::createForSubform($form['data'], $form, $form_state));
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $form_state->cleanValues();
    // The image effect configuration is stored in the 'data' key in the form,
    // pass that through for submission.
    $this->imageEffect
      ->submitConfigurationForm($form['data'], SubformState::createForSubform($form['data'], $form, $form_state));
    $this->imageEffect
      ->setWeight($form_state->getValue('weight'));
    if ($uuid = $this->imageEffect
      ->getUuid()) {
      $this->imageStyle
        ->getEffect($uuid)
        ->setConfiguration($this->imageEffect
        ->getConfiguration());
    }
    else {
      $this->imageStyle
        ->addImageEffect($this->imageEffect
        ->getConfiguration());
    }
    $this->imageStyle
      ->save();
    $this->messenger()
      ->addStatus($this->t('The image effect was successfully applied.'));
    $form_state->setRedirectUrl($this->imageStyle
      ->toUrl('edit-form'));
  }
  
  /**
   * Converts an image effect ID into an object.
   *
   * @param string $image_effect
   *   The image effect ID.
   *
   * @return \Drupal\image\ImageEffectInterface
   *   The image effect object.
   */
  abstract protected function prepareImageEffect($image_effect);

}