package util

import language._

import scala.concurrent.duration.Duration

import scalaz._
import scalaz.effect._
import scalaz.syntax.monad._

// note that F[A] === F[TimeoutT[Identity, A]]
final class TimeoutT[F[_], A] private[util] (private[util] val fa: F[A], private[util] val delay: Duration, private[util] val transform: A => TimeoutT[F, A]) {
  private[this] val init = System.currentTimeMillis

  def run(implicit FL: LiftIO[F], F: Monad[F]): F[A] = {
    val back = if (delay.isFinite) {
      val check = FL.liftIO(IO { System.currentTimeMillis < init + delay.toMillis })

      check flatMap { flag =>
        if (flag)
          fa
        else
          fa flatMap { transform(_).run }
      }
    } else {
      fa
    }

    back
  }

  def flatMap[B](f: A => TimeoutT[F, B])(implicit FL: LiftIO[F], F: Monad[F]): TimeoutT[F, B] = {
    val fa = run flatMap { fa =>
      f(fa).run
    }

    TimeoutT(fa)
  }

  def map[B](f: A => B)(implicit FL: LiftIO[F], F: Monad[F]): TimeoutT[F, B] = TimeoutT(run map f)
}

object TimeoutT extends TimeoutTInstances {
  def apply[F[_], A](fa: F[A]): TimeoutT[F, A] =
    new TimeoutT(fa, Duration.Inf, { _: A => sys.error("assertion error") })        // definitional failure if we hit this case

  def setTimeout[F[_], A](a: F[A], delay: Duration)(transform: A => TimeoutT[F, A]): TimeoutT[F, A] =
    new TimeoutT(a, delay, transform)
}

sealed abstract class TimeoutTInstances1 {
  implicit def timeoutTFunctor[F[_], A](implicit FL0: LiftIO[F], F0: Monad[F]): Functor[({ type λ[α] = TimeoutT[F, α] })#λ] = new TimeoutTFunctor[F] {
    def FL = FL0
    def F = F0
  }
}

sealed abstract class TimeoutTInstances0 extends TimeoutTInstances1 {
  implicit def timeoutTMonad[F[_], A](implicit FL0: LiftIO[F], F0: Monad[F]): Monad[({ type λ[α] = TimeoutT[F, α] })#λ] = new TimeoutTMonad[F] {
    def FL = FL0
    def F = F0
  }
}

sealed abstract class TimeoutTInstances extends TimeoutTInstances0 {
  implicit val timeoutTMonadTrans: Hoist[TimeoutT] = new TimeoutTHoist {}
}

private trait TimeoutTFunctor[F[_]] extends Functor[({ type λ[α] = TimeoutT[F, α] })#λ] {
  implicit def FL: LiftIO[F]
  implicit def F: Monad[F]

  override def map[A, B](fa: TimeoutT[F, A])(f: A => B): TimeoutT[F, B] = fa map f
}

private trait TimeoutTMonad[F[_]] extends Monad[({ type λ[α] = TimeoutT[F, α] })#λ] {
  implicit def FL: LiftIO[F]
  implicit def F: Monad[F]

  def point[A](a: => A): TimeoutT[F, A] = TimeoutT(F point a)

  def bind[A, B](fa: TimeoutT[F, A])(f: A => TimeoutT[F, B]): TimeoutT[F, B] = fa flatMap f
}

private trait TimeoutTHoist extends Hoist[TimeoutT] {
  // monad constraint is actually unnecessary here except to preserve signature
  def liftM[G[_]: Monad, A](a: G[A]): TimeoutT[G, A] = TimeoutT(a)

  def hoist[M[_]: Monad, N[_]](f: M ~> N) = new (({ type λ[α] = TimeoutT[M, α] })#λ ~> ({ type λ[α] = TimeoutT[N, α] })#λ) {
    def apply[A](fa: TimeoutT[M, A]): TimeoutT[N, A] = {
      new TimeoutT(f(fa.fa), fa.delay, fa.transform andThen apply)
    }
  }

  def apply[G[_]: Monad]: Monad[({ type λ[α] = TimeoutT[G, α] })#λ] = ???
}