class ImageStyleFormBase

abstract class ImageStyleFormBase extends EntityForm {
    
    /**
     * The entity being used by this form.
     *
     * @var \Drupal\image\ImageStyleInterface
     */
    protected $entity;
    
    /**
     * The image style entity storage.
     *
     * @var \Drupal\Core\Entity\EntityStorageInterface
     */
    protected $imageStyleStorage;
    
    /**
     * Constructs a base class for image style add and edit forms.
     *
     * @param \Drupal\Core\Entity\EntityStorageInterface $image_style_storage
     *   The image style entity storage.
     */
    public function __construct(EntityStorageInterface $image_style_storage) {
        $this->imageStyleStorage = $image_style_storage;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager')
            ->getStorage('image_style'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $form['label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Image style name'),
            '#default_value' => $this->entity
                ->label(),
            '#required' => TRUE,
        ];
        $form['name'] = [
            '#type' => 'machine_name',
            '#machine_name' => [
                'exists' => [
                    $this->imageStyleStorage,
                    'load',
                ],
            ],
            '#default_value' => $this->entity
                ->id(),
            '#required' => TRUE,
        ];
        return parent::form($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function save(array $form, FormStateInterface $form_state) {
        parent::save($form, $form_state);
        $form_state->setRedirectUrl($this->entity
            ->toUrl('edit-form'));
    }

}