class SwitchUserPageForm

class SwitchUserPageForm extends FormBase {
  
  /**
   * The FormBuilder object.
   */
  protected FormBuilderInterface $formBuilder;
  
  /**
   * A helper for creating the user list form.
   */
  protected SwitchUserListHelper $switchUserListHelper;
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) : static {
    $instance = parent::create($container);
    $instance->switchUserListHelper = $container->get('devel.switch_user_list_helper');
    $instance->formBuilder = $container->get('form_builder');
    return $instance;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getFormId() : string {
    return 'devel_switchuser_page_form';
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) : array {
    if ($accounts = $this->switchUserListHelper
      ->getUsers()) {
      $form['devel_links'] = $this->switchUserListHelper
        ->buildUserList($accounts);
      $form['devel_form'] = $this->formBuilder
        ->getForm(SwitchUserForm::class);
    }
    else {
      $this->messenger
        ->addStatus('There are no user accounts present!');
    }
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, FormStateInterface $form_state) : void {
    // Nothing to do here. This is delegated to devel.switch via http call.
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) : void {
    // Nothing to do here. This is delegated to devel.switch via http call.
  }

}