EitherFuture

EtherFutureValidation.scala

  type Result = String
  type Error = String

  sealed trait DError
  case object NotFound extends DError
  case class ValidationErrors(err: Set[Error]) extends DError

  val id = "10"
  val data = "data"

  val b: Future[Either[DError, Result]] = for {
    content <- loadA(id)
    validatedContent <- validateAndLift(content)
    res <- updateAndLift(content)
  } yield content

  def validateAndLift(c: Either[DError, Nothing]) =
    c.right.map(content => validateAsEither(content))
      .fold(err => failedValidation(err), a => a)

  def validateAsEither(content: Nothing) = {
    validate(data, content)
      .map(err => if (err.isEmpty) Right(content) else Left(ValidationErrors(err)))
  }

  def updateAndLift(c: Either[DError, Nothing]) =
    c.right.map(g => updateA(id, g))
      .fold(err => failedValidation(err), a => a.map(res => Right(res)))

  def failedValidation(err: DError) = Future.successful(Left(err))

  def loadA[A](id: String): Future[Either[DError, A]] = ???

  def validate[A](data: Any, stuff: A): Future[Set[Error]] = ???

  def updateA(id: String, data: Any): Future[Result] = ???