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 (!$this->imageEffect
            ->getUuid()) {
            $this->imageStyle
                ->addImageEffect($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 $image_effect
     *   The image effect ID.
     *
     * @return \Drupal\image\ImageEffectInterface
     *   The image effect object.
     */
    protected abstract function prepareImageEffect($image_effect);

}