class ContentEntityConfirmFormBase

abstract class ContentEntityConfirmFormBase extends ContentEntityForm implements ConfirmFormInterface {
  
  /**
   * {@inheritdoc}
   */
  public function getBaseFormId() {
    return $this->entity
      ->getEntityTypeId() . '_confirm_form';
  }
  
  /**
   * {@inheritdoc}
   */
  public function getDescription() {
    return $this->t('This action cannot be undone.');
  }
  
  /**
   * {@inheritdoc}
   */
  public function getConfirmText() {
    return $this->t('Confirm');
  }
  
  /**
   * {@inheritdoc}
   */
  public function getCancelText() {
    return $this->t('Cancel');
  }
  
  /**
   * {@inheritdoc}
   */
  public function getFormName() {
    return 'confirm';
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form = parent::buildForm($form, $form_state);
    $form['#title'] = $this->getQuestion();
    $form['#attributes']['class'][] = 'confirmation';
    $form['description'] = [
      '#markup' => $this->getDescription(),
    ];
    $form[$this->getFormName()] = [
      '#type' => 'hidden',
      '#value' => 1,
    ];
    // By default, render the form using theme_confirm_form().
    if (!isset($form['#theme'])) {
      $form['#theme'] = 'confirm_form';
    }
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function form(array $form, FormStateInterface $form_state) {
    // Do not attach fields to the confirm form.
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  protected function actions(array $form, FormStateInterface $form_state) {
    return [
      'submit' => [
        '#type' => 'submit',
        '#value' => $this->getConfirmText(),
        '#submit' => [
          [
            $this,
            'submitForm',
          ],
        ],
      ],
      'cancel' => ConfirmFormHelper::buildCancelLink($this, $this->getRequest()),
    ];
  }
  
  /**
   * {@inheritdoc}
   *
   * The save() method is not used in ContentEntityConfirmFormBase. This
   * overrides the default implementation that saves the entity.
   *
   * Confirmation forms should override submitForm() instead for their logic.
   */
  public function save(array $form, FormStateInterface $form_state) {
  }
  
  /**
   * {@inheritdoc}
   *
   * The delete() method is not used in ContentEntityConfirmFormBase. This
   * overrides the default implementation that redirects to the delete-form
   * confirmation form.
   *
   * Confirmation forms should override submitForm() instead for their logic.
   */
  public function delete(array $form, FormStateInterface $form_state) {
  }
  
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) {
    // Override the default validation implementation as it is not necessary
    // nor possible to validate an entity in a confirmation form.
    return $this->entity;
  }

}