class ConvertImageEffect

class ConvertImageEffect extends ConfigurableImageEffectBase {
    
    /**
     * {@inheritdoc}
     */
    public function applyEffect(ImageInterface $image) {
        if (!$image->convert($this->configuration['extension'])) {
            $this->logger
                ->error('Image convert failed using the %toolkit toolkit on %path (%mimetype)', [
                '%toolkit' => $image->getToolkitId(),
                '%path' => $image->getSource(),
                '%mimetype' => $image->getMimeType(),
            ]);
            return FALSE;
        }
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDerivativeExtension($extension) {
        return $this->configuration['extension'];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getSummary() {
        $summary = [
            '#markup' => mb_strtoupper($this->configuration['extension']),
        ];
        $summary += parent::getSummary();
        return $summary;
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'extension' => NULL,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $extensions = \Drupal::service('image.toolkit.manager')->getDefaultToolkit()
            ->getSupportedExtensions();
        $options = array_combine($extensions, array_map('mb_strtoupper', $extensions));
        $form['extension'] = [
            '#type' => 'select',
            '#title' => $this->t('Convert to'),
            '#default_value' => $this->configuration['extension'],
            '#required' => TRUE,
            '#options' => $options,
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
        parent::submitConfigurationForm($form, $form_state);
        $this->configuration['extension'] = $form_state->getValue('extension');
    }

}