class UserLocaltyPointsService[F[_] : Monad, S[_] : Monad](ur: UserRepository[F], es: EmailService[S]) {
  def addPoints(userId: UUID, pointsToAdd: Int): F[S[Either[String, Unit]]] = ur.findUser(userId).flatMap {
    case None => implicitly[Monad[F]].pure(implicitly[Monad[S]].pure(Left("User not found")))
    case Some(user) =>
      val updated = user.copy(loyaltyPoints = user.loyaltyPoints + pointsToAdd)
      for {
        _ <- es.sendEmail(user.email, "Points added!", s"You now have ${updated.loyaltyPoints}")
        _ <- ur.updateUser(updated)
      } yield Right(())
  }
}