package ch.becompany.authn

trait Dsl[F[_]] {
  …
}

object Dsl {

  type UserRepository = List[User]

  type UserRepositoryState[A] = State[UserRepository, A]

  implicit object StateInterpreter extends Dsl[UserRepositoryState] {

     override def register(email: String @@ EmailAddress, password: String):
         UserRepositoryState[Either[RegistrationError, User]] =
       State { users =>
         if (users.exists(_.email === email))
           (users, RegistrationError("User already exists").asLeft)
         else {
           val user = User(email, password)
           (users :+ user, user.asRight)
         }
       }

     override def authn(email: String @@ EmailAddress, password: String):
         UserRepositoryState[Either[AuthnError, User]] =
       State.inspect(_
         .find(user => user.email === email && user.password === password)
         .toRight(AuthnError("Authentication failed")))
   }

}