class UserRegistrationResource

class UserRegistrationResource extends ResourceBase {
  use EntityResourceValidationTrait;
  use EntityResourceAccessTrait;
  
  /**
   * User settings config instance.
   *
   * @var \Drupal\Core\Config\ImmutableConfig
   */
  protected $userSettings;
  
  /**
   * The current user.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $currentUser;
  
  /**
   * Constructs a new UserRegistrationResource instance.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param array $serializer_formats
   *   The available serialization formats.
   * @param \Psr\Log\LoggerInterface $logger
   *   A logger instance.
   * @param \Drupal\Core\Config\ImmutableConfig $user_settings
   *   A user settings config instance.
   * @param \Drupal\Core\Session\AccountInterface $current_user
   *   The current user.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, array $serializer_formats, LoggerInterface $logger, ImmutableConfig $user_settings, AccountInterface $current_user) {
    parent::__construct($configuration, $plugin_id, $plugin_definition, $serializer_formats, $logger);
    $this->userSettings = $user_settings;
    $this->currentUser = $current_user;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->getParameter('serializer.formats'), $container->get('logger.factory')
      ->get('rest'), $container->get('config.factory')
      ->get('user.settings'), $container->get('current_user'));
  }
  
  /**
   * Responds to user registration POST request.
   *
   * @param \Drupal\user\UserInterface $account
   *   The user account entity.
   *
   * @return \Drupal\rest\ModifiedResourceResponse
   *   The HTTP response object.
   *
   * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
   * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
   */
  public function post(UserInterface $account = NULL) {
    $this->ensureAccountCanRegister($account);
    // Only activate new users if visitors are allowed to register and no email
    // verification required.
    if ($this->userSettings
      ->get('register') == UserInterface::REGISTER_VISITORS && !$this->userSettings
      ->get('verify_mail')) {
      $account->activate();
    }
    else {
      $account->block();
    }
    $this->checkEditFieldAccess($account);
    // Make sure that the user entity is valid (email and name are valid).
    $this->validate($account);
    // Create the account.
    $account->save();
    $this->sendEmailNotifications($account);
    return new ModifiedResourceResponse($account, 200);
  }
  
  /**
   * Ensure the account can be registered in this request.
   *
   * @param \Drupal\user\UserInterface $account
   *   The user account to register.
   */
  protected function ensureAccountCanRegister(UserInterface $account = NULL) {
    if ($account === NULL) {
      throw new BadRequestHttpException('No user account data for registration received.');
    }
    // POSTed user accounts must not have an ID set, because we always want to
    // create new entities here.
    if (!$account->isNew()) {
      throw new BadRequestHttpException('An ID has been set and only new user accounts can be registered.');
    }
    // Only allow anonymous users to register, authenticated users with the
    // necessary permissions can POST a new user to the "user" REST resource.
    // @see \Drupal\rest\Plugin\rest\resource\EntityResource
    if (!$this->currentUser
      ->isAnonymous()) {
      throw new AccessDeniedHttpException('Only anonymous users can register a user.');
    }
    // Verify that the current user can register a user account.
    if ($this->userSettings
      ->get('register') == UserInterface::REGISTER_ADMINISTRATORS_ONLY) {
      throw new AccessDeniedHttpException('You cannot register a new user account.');
    }
    if (!$this->userSettings
      ->get('verify_mail')) {
      if (empty($account->getPassword())) {
        // If no e-mail verification then the user must provide a password.
        throw new UnprocessableEntityHttpException('No password provided.');
      }
    }
    else {
      if (!empty($account->getPassword())) {
        // If e-mail verification required then a password cannot provided.
        // The password will be set when the user logs in.
        throw new UnprocessableEntityHttpException('A Password cannot be specified. It will be generated on login.');
      }
    }
  }
  
  /**
   * Sends email notifications if necessary for user that was registered.
   *
   * @param \Drupal\user\UserInterface $account
   *   The user account.
   */
  protected function sendEmailNotifications(UserInterface $account) {
    $approval_settings = $this->userSettings
      ->get('register');
    // No e-mail verification is required. Activating the user.
    if ($approval_settings == UserInterface::REGISTER_VISITORS) {
      if ($this->userSettings
        ->get('verify_mail')) {
        // No administrator approval required.
        _user_mail_notify('register_no_approval_required', $account);
      }
    }
    elseif ($approval_settings == UserInterface::REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL) {
      _user_mail_notify('register_pending_approval', $account);
    }
  }

}