korolev.effect.Decoder.scala Maven / Gradle / Ivy
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package korolev.effect
import korolev.effect.Decoder.Action
import korolev.effect.syntax._
class Decoder[F[_]: Effect, A](upstream: Stream[F, A]) extends Stream[F, A] { self =>
@volatile private var takenBackQueue: List[A] = Nil
def pull(): F[Option[A]] = Effect[F].delayAsync {
takenBackQueue match {
case Nil => upstream.pull()
case x :: xs =>
takenBackQueue = xs
Effect[F].pure(Option(x))
}
}
def cancel(): F[Unit] =
upstream.cancel()
private def unsafeTakeBack(item: A): Unit =
takenBackQueue = item :: takenBackQueue
def decode[S, B](default: => S)(f: (S, A) => (S, Action[A, B])): Decoder[F, B] =
decodeAsync(default)((s, a) => Effect[F].pure(f(s, a)))
def decodeAsync[S, B](default: => S)(f: (S, A) => F[(S, Action[A, B])]): Decoder[F, B] = Decoder(
new Stream[F, B] {
var state: S = default
var finished = false
def pull(): F[Option[B]] = Effect[F].delayAsync {
if (finished) Effect[F].pure(None)
else {
self.pull().flatMap {
case Some(x) =>
f(state, x) flatMap {
case (newState, Action.PushFinish(value)) =>
state = newState
finished = true
Effect[F].pure(Some(value))
case (newState, Action.Push(value)) =>
state = newState
Effect[F].pure(Some(value))
case (newState, Action.Fork(value, takenBack)) =>
state = newState
unsafeTakeBack(takenBack)
Effect[F].pure(Some(value))
case (newState, Action.ForkFinish(value, takenBack)) =>
state = newState
finished = true
unsafeTakeBack(takenBack)
Effect[F].pure(Some(value))
case (newState, Action.TakeBack(takenBack)) =>
state = newState
unsafeTakeBack(takenBack)
pull()
case (newState, Action.TakeBackFinish(takenBack)) =>
state = newState
finished = true
unsafeTakeBack(takenBack)
pull()
case (newState, Action.TakeNext) =>
state = newState
pull()
case (newState, Action.Finish) =>
state = newState
finished = true
Effect[F].pure(None)
}
case None => Effect[F].pure(None)
}
}
}
def cancel(): F[Unit] =
self.cancel()
}
)
}
object Decoder {
sealed trait Action[+From, +To]
object Action {
case class Push[+To](value: To) extends Action[Nothing, To]
case class PushFinish[+To](value: To) extends Action[Nothing, To]
case class Fork[+From, +To](value: To, takeBack: From) extends Action[From, To]
case class ForkFinish[+From, +To](value: To, takeBack: From) extends Action[From, To]
case class TakeBack[+From](value: From) extends Action[From, Nothing]
case class TakeBackFinish[+From](value: From) extends Action[From, Nothing]
case object TakeNext extends Action[Nothing, Nothing]
case object Finish extends Action[Nothing, Nothing]
}
def apply[F[_]: Effect, A](upstream: Stream[F, A]): Decoder[F, A] =
new Decoder(upstream)
}