pekko/akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala

/**
 * Copyright (C) 2009-2014 Typesafe Inc. <http://www.typesafe.com>
 */
package akka.stream.impl.fusing

import akka.event.Logging.LogLevel
import akka.event.{ LogSource, Logging, LoggingAdapter }
import akka.stream.Attributes.{ InputBuffer, LogLevels }
import akka.stream.DelayOverflowStrategy.EmitEarly
import akka.stream.impl.Stages.DefaultAttributes
import akka.stream.impl.fusing.GraphStages.SimpleLinearGraphStage
import akka.stream.impl.{ FixedSizeBuffer, BoundedBuffer, ReactiveStreamsCompliance }
import akka.stream.stage._
import akka.stream.{ Supervision, _ }
import scala.annotation.tailrec
import scala.collection.immutable
import scala.collection.immutable.VectorBuilder
import scala.concurrent.Future
import scala.util.control.NonFatal
import scala.util.{ Failure, Success, Try }
import akka.stream.ActorAttributes.SupervisionStrategy
import scala.concurrent.duration.{ FiniteDuration, _ }
import akka.stream.impl.Stages.DefaultAttributes

/**
 * INTERNAL API
 */
private[akka] final case class Map[In, Out](f: In ⇒ Out, decider: Supervision.Decider) extends PushStage[In, Out] {
  override def onPush(elem: In, ctx: Context[Out]): SyncDirective = ctx.push(f(elem))

  override def decide(t: Throwable): Supervision.Directive = decider(t)
}

/**
 * INTERNAL API
 */
private[akka] final case class Filter[T](p: T ⇒ Boolean, decider: Supervision.Decider) extends PushStage[T, T] {
  override def onPush(elem: T, ctx: Context[T]): SyncDirective =
    if (p(elem)) ctx.push(elem)
    else ctx.pull()

  override def decide(t: Throwable): Supervision.Directive = decider(t)
}

/**
 * INTERNAL API
 */
private[akka] final case class TakeWhile[T](p: T ⇒ Boolean, decider: Supervision.Decider) extends PushStage[T, T] {

  override def onPush(elem: T, ctx: Context[T]): SyncDirective =
    if (p(elem))
      ctx.push(elem)
    else
      ctx.finish()

  override def decide(t: Throwable): Supervision.Directive = decider(t)
}

/**
 * INTERNAL API
 */
private[akka] final case class DropWhile[T](p: T ⇒ Boolean, decider: Supervision.Decider) extends PushStage[T, T] {
  var taking = false

  override def onPush(elem: T, ctx: Context[T]): SyncDirective =
    if (taking || !p(elem)) {
      taking = true
      ctx.push(elem)
    } else {
      ctx.pull()
    }

  override def decide(t: Throwable): Supervision.Directive = decider(t)
}

private[akka] object Collect {
  // Cached function that can be used with PartialFunction.applyOrElse to ensure that A) the guard is only applied once,
  // and the caller can check the returned value with Collect.notApplied to query whether the PF was applied or not.
  // Prior art: https://github.com/scala/scala/blob/v2.11.4/src/library/scala/collection/immutable/List.scala#L458
  final val NotApplied: Any ⇒ Any = _ ⇒ Collect.NotApplied
}

private[akka] final case class Collect[In, Out](pf: PartialFunction[In, Out], decider: Supervision.Decider) extends PushStage[In, Out] {

  import Collect.NotApplied

  override def onPush(elem: In, ctx: Context[Out]): SyncDirective =
    pf.applyOrElse(elem, NotApplied) match {
      case NotApplied             ⇒ ctx.pull()
      case result: Out @unchecked ⇒ ctx.push(result)
    }

  override def decide(t: Throwable): Supervision.Directive = decider(t)
}

/**
 * INTERNAL API
 */
private[akka] final case class Recover[T](pf: PartialFunction[Throwable, T]) extends PushPullStage[T, T] {
  import Collect.NotApplied
  var recovered: Option[T] = None

  override def onPush(elem: T, ctx: Context[T]): SyncDirective = {
    ctx.push(elem)
  }

  override def onPull(ctx: Context[T]): SyncDirective =
    recovered match {
      case Some(value) ⇒ ctx.pushAndFinish(value)
      case None        ⇒ ctx.pull()
    }

  override def onUpstreamFailure(t: Throwable, ctx: Context[T]): TerminationDirective = {
    pf.applyOrElse(t, NotApplied) match {
      case NotApplied ⇒ ctx.fail(t)
      case result: T @unchecked ⇒
        recovered = Some(result)
        ctx.absorbTermination()
    }
  }

}

/**
 * INTERNAL API
 */
private[akka] final case class MapConcat[In, Out](f: In ⇒ immutable.Iterable[Out], decider: Supervision.Decider) extends PushPullStage[In, Out] {
  private var currentIterator: Iterator[Out] = Iterator.empty

  override def onPush(elem: In, ctx: Context[Out]): SyncDirective = {
    currentIterator = f(elem).iterator
    if (!currentIterator.hasNext) ctx.pull()
    else ctx.push(currentIterator.next())
  }

  override def onPull(ctx: Context[Out]): SyncDirective =
    if (ctx.isFinishing) {
      if (currentIterator.hasNext) {
        val elem = currentIterator.next()
        if (currentIterator.hasNext) ctx.push(elem)
        else ctx.pushAndFinish(elem)
      } else ctx.finish()
    } else {
      if (currentIterator.hasNext) ctx.push(currentIterator.next())
      else ctx.pull()
    }

  override def onUpstreamFinish(ctx: Context[Out]): TerminationDirective =
    if (currentIterator.hasNext) ctx.absorbTermination()
    else ctx.finish()

  override def decide(t: Throwable): Supervision.Directive = decider(t)

  override def restart(): MapConcat[In, Out] = copy()
}

/**
 * INTERNAL API
 */
private[akka] final case class Take[T](count: Long) extends PushPullStage[T, T] {
  private var left: Long = count

  override def onPush(elem: T, ctx: Context[T]): SyncDirective = {
    left -= 1
    if (left > 0) ctx.push(elem)
    else if (left == 0) ctx.pushAndFinish(elem)
    else ctx.finish() //Handle negative take counts
  }

  override def onPull(ctx: Context[T]): SyncDirective =
    if (left <= 0) ctx.finish()
    else ctx.pull()
}

/**
 * INTERNAL API
 */
private[akka] final case class Drop[T](count: Long) extends PushStage[T, T] {
  private var left: Long = count

  override def onPush(elem: T, ctx: Context[T]): SyncDirective =
    if (left > 0) {
      left -= 1
      ctx.pull()
    } else ctx.push(elem)
}

/**
 * INTERNAL API
 */
private[akka] final case class Scan[In, Out](zero: Out, f: (Out, In) ⇒ Out, decider: Supervision.Decider) extends PushPullStage[In, Out] {
  private var aggregator = zero
  private var pushedZero = false

  override def onPush(elem: In, ctx: Context[Out]): SyncDirective = {
    if (pushedZero) {
      aggregator = f(aggregator, elem)
      ctx.push(aggregator)
    } else {
      aggregator = f(zero, elem)
      ctx.push(zero)
    }
  }

  override def onPull(ctx: Context[Out]): SyncDirective =
    if (!pushedZero) {
      pushedZero = true
      if (ctx.isFinishing) ctx.pushAndFinish(aggregator) else ctx.push(aggregator)
    } else ctx.pull()

  override def onUpstreamFinish(ctx: Context[Out]): TerminationDirective =
    if (pushedZero) ctx.finish()
    else ctx.absorbTermination()

  override def decide(t: Throwable): Supervision.Directive = decider(t)

  override def restart(): Scan[In, Out] = copy()
}

/**
 * INTERNAL API
 */
private[akka] final case class Fold[In, Out](zero: Out, f: (Out, In) ⇒ Out, decider: Supervision.Decider) extends PushPullStage[In, Out] {
  private[this] var aggregator: Out = zero

  override def onPush(elem: In, ctx: Context[Out]): SyncDirective = {
    aggregator = f(aggregator, elem)
    ctx.pull()
  }

  override def onPull(ctx: Context[Out]): SyncDirective =
    if (ctx.isFinishing) ctx.pushAndFinish(aggregator)
    else ctx.pull()

  override def onUpstreamFinish(ctx: Context[Out]): TerminationDirective = ctx.absorbTermination()

  override def decide(t: Throwable): Supervision.Directive = decider(t)

  override def restart(): Fold[In, Out] = copy()
}

/**
 * INTERNAL API
 */
final case class Intersperse[T](start: Option[T], inject: T, end: Option[T]) extends GraphStage[FlowShape[T, T]] {
  ReactiveStreamsCompliance.requireNonNullElement(inject)
  if (start.isDefined) ReactiveStreamsCompliance.requireNonNullElement(start.get)
  if (end.isDefined) ReactiveStreamsCompliance.requireNonNullElement(end.get)

  private val in = Inlet[T]("in")
  private val out = Outlet[T]("out")

  override val shape = FlowShape(in, out)

  override def createLogic(attr: Attributes): GraphStageLogic = new GraphStageLogic(shape) {
    val startInHandler = new InHandler {
      override def onPush(): Unit = {
        // if else (to avoid using Iterator[T].flatten in hot code)
        if (start.isDefined) emitMultiple(out, Iterator(start.get, grab(in)))
        else emit(out, grab(in))
        setHandler(in, restInHandler) // switch handler
      }

      override def onUpstreamFinish(): Unit = {
        emitMultiple(out, Iterator(start, end).flatten)
        completeStage()
      }
    }

    val restInHandler = new InHandler {
      override def onPush(): Unit = emitMultiple(out, Iterator(inject, grab(in)))

      override def onUpstreamFinish(): Unit = {
        if (end.isDefined) emit(out, end.get)
        completeStage()
      }
    }

    val outHandler = new OutHandler {
      override def onPull(): Unit = pull(in)
    }

    setHandler(in, startInHandler)
    setHandler(out, outHandler)
  }
}

/**
 * INTERNAL API
 */
private[akka] final case class Grouped[T](n: Int) extends PushPullStage[T, immutable.Seq[T]] {
  private val buf = {
    val b = Vector.newBuilder[T]
    b.sizeHint(n)
    b
  }
  private var left = n

  override def onPush(elem: T, ctx: Context[immutable.Seq[T]]): SyncDirective = {
    buf += elem
    left -= 1
    if (left == 0) {
      val emit = buf.result()
      buf.clear()
      left = n
      ctx.push(emit)
    } else ctx.pull()
  }

  override def onPull(ctx: Context[immutable.Seq[T]]): SyncDirective =
    if (ctx.isFinishing) {
      val elem = buf.result()
      buf.clear()
      left = n
      ctx.pushAndFinish(elem)
    } else ctx.pull()

  override def onUpstreamFinish(ctx: Context[immutable.Seq[T]]): TerminationDirective =
    if (left == n) ctx.finish()
    else ctx.absorbTermination()
}

/**
 * INTERNAL API
 */

private[akka] final case class LimitWeighted[T](n: Long, costFn: T ⇒ Long) extends PushStage[T, T] {
  private var left = n

  override def onPush(elem: T, ctx: Context[T]): SyncDirective = {
    left -= costFn(elem)
    if (left >= 0) ctx.push(elem)
    else ctx.fail(new StreamLimitReachedException(n))
  }
}

/**
 * INTERNAL API
 */
private[akka] final case class Sliding[T](n: Int, step: Int) extends PushPullStage[T, immutable.Seq[T]] {
  private var buf = Vector.empty[T]

  override def onPush(elem: T, ctx: Context[immutable.Seq[T]]): SyncDirective = {
    buf :+= elem
    if (buf.size < n) {
      ctx.pull()
    } else if (buf.size == n) {
      ctx.push(buf)
    } else if (step > n) {
      if (buf.size == step)
        buf = Vector.empty
      ctx.pull()
    } else {
      buf = buf.drop(step)
      if (buf.size == n) ctx.push(buf)
      else ctx.pull()
    }
  }

  override def onPull(ctx: Context[immutable.Seq[T]]): SyncDirective =
    if (!ctx.isFinishing) ctx.pull()
    else if (buf.size >= n) ctx.finish()
    else ctx.pushAndFinish(buf)

  override def onUpstreamFinish(ctx: Context[immutable.Seq[T]]): TerminationDirective =
    if (buf.isEmpty) ctx.finish()
    else ctx.absorbTermination()
}

/**
 * INTERNAL API
 */
private[akka] final case class Buffer[T](size: Int, overflowStrategy: OverflowStrategy) extends DetachedStage[T, T] {

  import OverflowStrategy._

  private val buffer = FixedSizeBuffer[T](size)

  override def onPush(elem: T, ctx: DetachedContext[T]): UpstreamDirective =
    if (ctx.isHoldingDownstream) ctx.pushAndPull(elem)
    else enqueueAction(ctx, elem)

  override def onPull(ctx: DetachedContext[T]): DownstreamDirective = {
    if (ctx.isFinishing) {
      val elem = buffer.dequeue()
      if (buffer.isEmpty) ctx.pushAndFinish(elem)
      else ctx.push(elem)
    } else if (ctx.isHoldingUpstream) ctx.pushAndPull(buffer.dequeue())
    else if (buffer.isEmpty) ctx.holdDownstream()
    else ctx.push(buffer.dequeue())
  }

  override def onUpstreamFinish(ctx: DetachedContext[T]): TerminationDirective =
    if (buffer.isEmpty) ctx.finish()
    else ctx.absorbTermination()

  val enqueueAction: (DetachedContext[T], T) ⇒ UpstreamDirective = {
    (overflowStrategy: @unchecked) match {
      case DropHead ⇒ (ctx, elem) ⇒
        if (buffer.isFull) buffer.dropHead()
        buffer.enqueue(elem)
        ctx.pull()
        case DropTail ⇒ (ctx, elem) ⇒
        if (buffer.isFull) buffer.dropTail()
        buffer.enqueue(elem)
        ctx.pull()
        case DropBuffer ⇒ (ctx, elem) ⇒
        if (buffer.isFull) buffer.clear()
        buffer.enqueue(elem)
        ctx.pull()
        case DropNew ⇒ (ctx, elem) ⇒
        if (!buffer.isFull) buffer.enqueue(elem)
        ctx.pull()
        case Backpressure ⇒ (ctx, elem) ⇒
        buffer.enqueue(elem)
        if (buffer.isFull) ctx.holdUpstream()
        else ctx.pull()
        case Fail ⇒ (ctx, elem) ⇒
        if (buffer.isFull) ctx.fail(new Fail.BufferOverflowException(s"Buffer overflow (max capacity was: $size)!"))
        else {
          buffer.enqueue(elem)
          ctx.pull()
        }
    }
  }
}

/**
 * INTERNAL API
 */
private[akka] final case class Completed[T]() extends PushPullStage[T, T] {
  override def onPush(elem: T, ctx: Context[T]): SyncDirective = ctx.finish()

  override def onPull(ctx: Context[T]): SyncDirective = ctx.finish()
}

/**
 * INTERNAL API
 */
private[akka] final case class Conflate[In, Out](seed: In ⇒ Out, aggregate: (Out, In) ⇒ Out,
                                                 decider: Supervision.Decider) extends DetachedStage[In, Out] {
  private var agg: Any = null

  override def onPush(elem: In, ctx: DetachedContext[Out]): UpstreamDirective = {
    agg =
      if (agg == null) seed(elem)
      else aggregate(agg.asInstanceOf[Out], elem)

    if (!ctx.isHoldingDownstream) ctx.pull()
    else {
      val result = agg.asInstanceOf[Out]
      agg = null
      ctx.pushAndPull(result)
    }
  }

  override def onPull(ctx: DetachedContext[Out]): DownstreamDirective = {
    if (ctx.isFinishing) {
      if (agg == null) ctx.finish()
      else {
        val result = agg.asInstanceOf[Out]
        agg = null
        ctx.pushAndFinish(result)
      }
    } else if (agg == null) ctx.holdDownstream()
    else {
      val result = agg.asInstanceOf[Out]
      if (result == null) throw new NullPointerException
      agg = null
      ctx.push(result)
    }
  }

  override def onUpstreamFinish(ctx: DetachedContext[Out]): TerminationDirective = ctx.absorbTermination()

  override def decide(t: Throwable): Supervision.Directive = decider(t)

  override def restart(): Conflate[In, Out] = copy()
}

/**
 * INTERNAL API
 */
private[akka] final case class Batch[In, Out](max: Long, costFn: In ⇒ Long, seed: In ⇒ Out, aggregate: (Out, In) ⇒ Out)
  extends GraphStage[FlowShape[In, Out]] {

  val in = Inlet[In]("Batch.in")
  val out = Outlet[Out]("Batch.out")

  override val shape: FlowShape[In, Out] = FlowShape.of(in, out)

  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new GraphStageLogic(shape) {
    private var agg: Out = null.asInstanceOf[Out]
    private var left: Long = max
    private var pending: In = null.asInstanceOf[In]

    private def flush(): Unit = {
      push(out, agg)
      left = max
      if (pending != null) {
        val elem = pending
        agg = seed(elem)
        left -= costFn(elem)
        pending = null.asInstanceOf[In]
      } else {
        agg = null.asInstanceOf[Out]
      }
    }

    override def preStart() = pull(in)

    setHandler(in, new InHandler {

      override def onPush(): Unit = {
        val elem = grab(in)
        val cost = costFn(elem)
        if (agg == null) {
          left -= cost
          agg = seed(elem)
        } else if (left < cost) {
          pending = elem
        } else {
          left -= cost
          agg = aggregate(agg, elem)
        }

        if (isAvailable(out)) flush()
        if (pending == null) pull(in)
      }

      override def onUpstreamFinish(): Unit = {
        if (agg == null) completeStage()
      }
    })

    setHandler(out, new OutHandler {

      override def onPull(): Unit = {
        if (agg == null) {
          if (isClosed(in)) completeStage()
          else if (!hasBeenPulled(in)) pull(in)
        } else if (isClosed(in)) {
          push(out, agg)
          if (pending == null) completeStage()
          else {
            agg = seed(pending)
            pending = null.asInstanceOf[In]
          }
        } else {
          flush()
          if (!hasBeenPulled(in)) pull(in)
        }
      }
    })
  }
}

/**
 * INTERNAL API
 */
private[akka] final class Expand[In, Out](extrapolate: In ⇒ Iterator[Out]) extends GraphStage[FlowShape[In, Out]] {
  private val in = Inlet[In]("expand.in")
  private val out = Outlet[Out]("expand.out")

  override def initialAttributes = DefaultAttributes.expand
  override val shape = FlowShape(in, out)

  override def createLogic(attr: Attributes) = new GraphStageLogic(shape) {
    private var iterator: Iterator[Out] = Iterator.empty
    private var expanded = false

    override def preStart(): Unit = pull(in)

    setHandler(in, new InHandler {
      override def onPush(): Unit = {
        iterator = extrapolate(grab(in))
        if (iterator.hasNext) {
          if (isAvailable(out)) {
            expanded = true
            pull(in)
            push(out, iterator.next())
          } else expanded = false
        } else pull(in)
      }
      override def onUpstreamFinish(): Unit = {
        if (iterator.hasNext && !expanded) () // need to wait
        else completeStage()
      }
    })

    setHandler(out, new OutHandler {
      override def onPull(): Unit = {
        if (iterator.hasNext) {
          if (expanded == false) {
            expanded = true
            if (isClosed(in)) {
              push(out, iterator.next())
              completeStage()
            } else {
              // expand needs to pull first to be “fair” when upstream is not actually slow
              pull(in)
              push(out, iterator.next())
            }
          } else push(out, iterator.next())
        }
      }
    })
  }
}

/**
 * INTERNAL API
 */
private[akka] object MapAsync {
  final class Holder[T](var elem: T)
  val NotYetThere = Failure(new Exception)
}

/**
 * INTERNAL API
 */
private[akka] final case class MapAsync[In, Out](parallelism: Int, f: In ⇒ Future[Out])
  extends GraphStage[FlowShape[In, Out]] {

  import MapAsync._

  private val in = Inlet[In]("in")
  private val out = Outlet[Out]("out")

  override def initialAttributes = DefaultAttributes.mapAsync
  override val shape = FlowShape(in, out)

  override def createLogic(inheritedAttributes: Attributes) = new GraphStageLogic(shape) {
    override def toString = s"MapAsync.Logic(buffer=$buffer)"

    //FIXME Put Supervision.stoppingDecider as a SupervisionStrategy on DefaultAttributes.mapAsync?
    val decider = inheritedAttributes.getAttribute(classOf[SupervisionStrategy]).map(_.decider).getOrElse(Supervision.stoppingDecider)

    val buffer = new BoundedBuffer[Holder[Try[Out]]](parallelism)
    def todo = buffer.used

    @tailrec private def pushOne(): Unit =
      if (buffer.isEmpty) {
        if (isClosed(in)) completeStage()
        else if (!hasBeenPulled(in)) pull(in)
      } else if (buffer.peek.elem == NotYetThere) {
        if (todo < parallelism && !hasBeenPulled(in)) tryPull(in)
      } else buffer.dequeue().elem match {
        case Failure(ex) ⇒ pushOne()
        case Success(elem) ⇒
          push(out, elem)
          if (todo < parallelism && !hasBeenPulled(in)) tryPull(in)
      }

    def failOrPull(holder: Holder[Try[Out]], f: Failure[Out]) =
      if (decider(f.exception) == Supervision.Stop) failStage(f.exception)
      else {
        holder.elem = f
        if (isAvailable(out)) pushOne()
      }

    val futureCB =
      getAsyncCallback[(Holder[Try[Out]], Try[Out])]({
        case (holder, f: Failure[_]) ⇒ failOrPull(holder, f)
        case (holder, s @ Success(elem)) ⇒
          if (elem == null) {
            val ex = ReactiveStreamsCompliance.elementMustNotBeNullException
            failOrPull(holder, Failure(ex))
          } else {
            holder.elem = s
            if (isAvailable(out)) pushOne()
          }
      })

    setHandler(in, new InHandler {
      override def onPush(): Unit = {
        try {
          val future = f(grab(in))
          val holder = new Holder[Try[Out]](NotYetThere)
          buffer.enqueue(holder)
          future.onComplete(result ⇒ futureCB.invoke(holder -> result))(akka.dispatch.ExecutionContexts.sameThreadExecutionContext)
        } catch {
          case NonFatal(ex) ⇒
            if (decider(ex) == Supervision.Stop) failStage(ex)
        }
        if (todo < parallelism) tryPull(in)
      }
      override def onUpstreamFinish(): Unit = {
        if (todo == 0) completeStage()
      }
    })

    setHandler(out, new OutHandler {
      override def onPull(): Unit = pushOne()
    })
  }
}

/**
 * INTERNAL API
 */
private[akka] final case class MapAsyncUnordered[In, Out](parallelism: Int, f: In ⇒ Future[Out])
  extends GraphStage[FlowShape[In, Out]] {

  private val in = Inlet[In]("in")
  private val out = Outlet[Out]("out")

  override def initialAttributes = DefaultAttributes.mapAsyncUnordered
  override val shape = FlowShape(in, out)

  override def createLogic(inheritedAttributes: Attributes) = new GraphStageLogic(shape) {
    override def toString = s"MapAsyncUnordered.Logic(inFlight=$inFlight, buffer=$buffer)"

    val decider =
      inheritedAttributes.getAttribute(classOf[SupervisionStrategy])
        .map(_.decider).getOrElse(Supervision.stoppingDecider)

    var inFlight = 0
    val buffer = new BoundedBuffer[Out](parallelism)
    def todo = inFlight + buffer.used

    def failOrPull(ex: Throwable) =
      if (decider(ex) == Supervision.Stop) failStage(ex)
      else if (isClosed(in) && todo == 0) completeStage()
      else if (!hasBeenPulled(in)) tryPull(in)

    val futureCB =
      getAsyncCallback((result: Try[Out]) ⇒ {
        inFlight -= 1
        result match {
          case Failure(ex) ⇒ failOrPull(ex)
          case Success(elem) ⇒
            if (elem == null) {
              val ex = ReactiveStreamsCompliance.elementMustNotBeNullException
              failOrPull(ex)
            } else if (isAvailable(out)) {
              if (!hasBeenPulled(in)) tryPull(in)
              push(out, elem)
            } else buffer.enqueue(elem)
        }
      }).invoke _

    setHandler(in, new InHandler {
      override def onPush(): Unit = {
        try {
          val future = f(grab(in))
          inFlight += 1
          future.onComplete(futureCB)(akka.dispatch.ExecutionContexts.sameThreadExecutionContext)
        } catch {
          case NonFatal(ex) ⇒
            if (decider(ex) == Supervision.Stop) failStage(ex)
        }
        if (todo < parallelism) tryPull(in)
      }
      override def onUpstreamFinish(): Unit = {
        if (todo == 0) completeStage()
      }
    })

    setHandler(out, new OutHandler {
      override def onPull(): Unit = {
        if (!buffer.isEmpty) push(out, buffer.dequeue())
        else if (isClosed(in) && todo == 0) completeStage()
        if (todo < parallelism && !hasBeenPulled(in)) tryPull(in)
      }
    })
  }
}

/**
 * INTERNAL API
 */
private[akka] final case class Log[T](name: String, extract: T ⇒ Any,
                                      logAdapter: Option[LoggingAdapter],
                                      decider: Supervision.Decider) extends PushStage[T, T] {

  import Log._

  private var logLevels: LogLevels = _
  private var log: LoggingAdapter = _

  // TODO more optimisations can be done here - prepare logOnPush function etc

  override def preStart(ctx: LifecycleContext): Unit = {
    logLevels = ctx.attributes.get[LogLevels](DefaultLogLevels)
    log = logAdapter match {
      case Some(l) ⇒ l
      case _ ⇒
        val mat = try ActorMaterializer.downcast(ctx.materializer)
        catch {
          case ex: Exception ⇒
            throw new RuntimeException("Log stage can only provide LoggingAdapter when used with ActorMaterializer! " +
              "Provide a LoggingAdapter explicitly or use the actor based flow materializer.", ex)
        }

        Logging(mat.system, ctx)(fromLifecycleContext)
    }
  }

  override def onPush(elem: T, ctx: Context[T]): SyncDirective = {
    if (isEnabled(logLevels.onElement))
      log.log(logLevels.onElement, "[{}] Element: {}", name, extract(elem))

    ctx.push(elem)
  }

  override def onUpstreamFailure(cause: Throwable, ctx: Context[T]): TerminationDirective = {
    if (isEnabled(logLevels.onFailure))
      logLevels.onFailure match {
        case Logging.ErrorLevel ⇒ log.error(cause, "[{}] Upstream failed.", name)
        case level              ⇒ log.log(level, "[{}] Upstream failed, cause: {}: {}", name, Logging.simpleName(cause.getClass), cause.getMessage)
      }

    super.onUpstreamFailure(cause, ctx)
  }

  override def onUpstreamFinish(ctx: Context[T]): TerminationDirective = {
    if (isEnabled(logLevels.onFinish))
      log.log(logLevels.onFinish, "[{}] Upstream finished.", name)

    super.onUpstreamFinish(ctx)
  }

  override def onDownstreamFinish(ctx: Context[T]): TerminationDirective = {
    if (isEnabled(logLevels.onFinish))
      log.log(logLevels.onFinish, "[{}] Downstream finished.", name)

    super.onDownstreamFinish(ctx)
  }

  private def isEnabled(l: LogLevel): Boolean = l.asInt != OffInt

  override def decide(t: Throwable): Supervision.Directive = decider(t)
}

/**
 * INTERNAL API
 */
private[akka] object Log {

  /**
   * Must be located here to be visible for implicit resolution, when LifecycleContext is passed to [[Logging]]
   * More specific LogSource than `fromString`, which would add the ActorSystem name in addition to the supervision to the log source.
   */
  final val fromLifecycleContext = new LogSource[LifecycleContext] {

    // do not expose private context classes (of OneBoundedInterpreter)
    override def getClazz(t: LifecycleContext): Class[_] = classOf[Materializer]

    override def genString(t: LifecycleContext): String = {
      try s"$DefaultLoggerName(${ActorMaterializer.downcast(t.materializer).supervisor.path})"
      catch {
        case ex: Exception ⇒ LogSource.fromString.genString(DefaultLoggerName)
      }
    }

  }

  private final val DefaultLoggerName = "akka.stream.Log"
  private final val OffInt = LogLevels.Off.asInt
  private final val DefaultLogLevels = LogLevels(onElement = Logging.DebugLevel, onFinish = Logging.DebugLevel, onFailure = Logging.ErrorLevel)
}

/**
 * INTERNAL API
 */
private[stream] object TimerKeys {
  case object TakeWithinTimerKey
  case object DropWithinTimerKey
  case object GroupedWithinTimerKey
}

private[stream] final class GroupedWithin[T](n: Int, d: FiniteDuration) extends GraphStage[FlowShape[T, immutable.Seq[T]]] {
  require(n > 0, "n must be greater than 0")
  require(d > Duration.Zero)

  val in = Inlet[T]("in")
  val out = Outlet[immutable.Seq[T]]("out")
  override def initialAttributes = DefaultAttributes.groupedWithin
  val shape = FlowShape(in, out)

  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new TimerGraphStageLogic(shape) {
    private val buf: VectorBuilder[T] = new VectorBuilder
    // True if:
    // - buf is nonEmpty
    //       AND
    // - timer fired OR group is full
    private var groupClosed = false
    private var finished = false
    private var elements = 0

    private val GroupedWithinTimer = "GroupedWithinTimer"

    override def preStart() = {
      schedulePeriodically(GroupedWithinTimer, d)
      pull(in)
    }

    private def nextElement(elem: T): Unit = {
      buf += elem
      elements += 1
      if (elements == n) {
        schedulePeriodically(GroupedWithinTimer, d)
        closeGroup()
      } else pull(in)
    }

    private def closeGroup(): Unit = {
      groupClosed = true
      if (isAvailable(out)) emitGroup()
    }

    private def emitGroup(): Unit = {
      push(out, buf.result())
      buf.clear()
      if (!finished) startNewGroup()
      else completeStage()
    }

    private def startNewGroup(): Unit = {
      elements = 0
      groupClosed = false
      if (isAvailable(in)) nextElement(grab(in))
      else if (!hasBeenPulled(in)) pull(in)
    }

    setHandler(in, new InHandler {
      override def onPush(): Unit =
        if (!groupClosed) nextElement(grab(in)) // otherwise keep the element for next round
      override def onUpstreamFinish(): Unit = {
        finished = true
        if (!groupClosed && elements > 0) closeGroup()
        else completeStage()
      }
      override def onUpstreamFailure(ex: Throwable): Unit = failStage(ex)
    })

    setHandler(out, new OutHandler {
      override def onPull(): Unit = if (groupClosed) emitGroup()
      override def onDownstreamFinish(): Unit = completeStage()
    })

    override protected def onTimer(timerKey: Any) =
      if (elements > 0) closeGroup()
  }
}

private[stream] final class Delay[T](d: FiniteDuration, strategy: DelayOverflowStrategy) extends SimpleLinearGraphStage[T] {
  private[this] def timerName = "DelayedTimer"
  override def initialAttributes: Attributes = DefaultAttributes.delay
  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new TimerGraphStageLogic(shape) {
    val size =
      inheritedAttributes.getAttribute(classOf[InputBuffer]) match {
        case None                        ⇒ throw new IllegalStateException(s"Couldn't find InputBuffer Attribute for $this")
        case Some(InputBuffer(min, max)) ⇒ max
      }

    val buffer = FixedSizeBuffer[(Long, T)](size) // buffer has pairs timestamp with upstream element
    var willStop = false

    setHandler(in, handler = new InHandler {
      //FIXME rewrite into distinct strategy functions to avoid matching on strategy for every input when full
      override def onPush(): Unit = {
        if (buffer.isFull) (strategy: @unchecked) match {
          case EmitEarly ⇒
            if (!isTimerActive(timerName))
              push(out, buffer.dequeue()._2)
            else {
              cancelTimer(timerName)
              onTimer(timerName)
            }
          case DelayOverflowStrategy.DropHead ⇒
            buffer.dropHead()
            grabAndPull(true)
          case DelayOverflowStrategy.DropTail ⇒
            buffer.dropTail()
            grabAndPull(true)
          case DelayOverflowStrategy.DropNew ⇒
            grab(in)
            if (!isTimerActive(timerName)) scheduleOnce(timerName, d)
          case DelayOverflowStrategy.DropBuffer ⇒
            buffer.clear()
            grabAndPull(true)
          case DelayOverflowStrategy.Fail ⇒
            failStage(new DelayOverflowStrategy.Fail.BufferOverflowException(s"Buffer overflow for delay combinator (max capacity was: $size)!"))
          case DelayOverflowStrategy.Backpressure ⇒ throw new IllegalStateException("Delay buffer must never overflow in Backpressure mode")
        }
        else {
          grabAndPull(strategy != DelayOverflowStrategy.Backpressure || buffer.size < size - 1)
          if (!isTimerActive(timerName)) scheduleOnce(timerName, d)
        }
      }

      def grabAndPull(pullCondition: Boolean): Unit = {
        buffer.enqueue((System.nanoTime(), grab(in)))
        if (pullCondition) pull(in)
      }

      override def onUpstreamFinish(): Unit = {
        if (isAvailable(out) && isTimerActive(timerName)) willStop = true
        else completeStage()
      }
    })

    setHandler(out, new OutHandler {
      override def onPull(): Unit = {
        if (!isTimerActive(timerName) && !buffer.isEmpty && nextElementWaitTime() < 0)
          push(out, buffer.dequeue()._2)

        if (!willStop && !hasBeenPulled(in)) pull(in)
        completeIfReady()
      }
    })

    def completeIfReady(): Unit = if (willStop && buffer.isEmpty) completeStage()

    def nextElementWaitTime(): Long = d.toMillis - (System.nanoTime() - buffer.peek()._1) * 1000 * 1000

    final override protected def onTimer(key: Any): Unit = {
      push(out, buffer.dequeue()._2)
      if (!buffer.isEmpty) {
        val waitTime = nextElementWaitTime()
        if (waitTime > 10) scheduleOnce(timerName, waitTime.millis)
      }
      completeIfReady()
    }
  }

  override def toString = "Delay"
}

private[stream] final class TakeWithin[T](timeout: FiniteDuration) extends SimpleLinearGraphStage[T] {

  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new TimerGraphStageLogic(shape) {
    setHandler(in, new InHandler {
      override def onPush(): Unit = push(out, grab(in))
    })

    setHandler(out, new OutHandler {
      override def onPull(): Unit = pull(in)
    })

    final override protected def onTimer(key: Any): Unit =
      completeStage()

    override def preStart(): Unit = scheduleOnce("TakeWithinTimer", timeout)
  }

  override def toString = "TakeWithin"
}

private[stream] final class DropWithin[T](timeout: FiniteDuration) extends SimpleLinearGraphStage[T] {
  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new TimerGraphStageLogic(shape) {

    private var allow = false

    setHandler(in, new InHandler {
      override def onPush(): Unit =
        if (allow) push(out, grab(in))
        else pull(in)
    })

    setHandler(out, new OutHandler {
      override def onPull(): Unit = pull(in)
    })

    final override protected def onTimer(key: Any): Unit = allow = true

    override def preStart(): Unit = scheduleOnce("DropWithinTimer", timeout)
  }

  override def toString = "DropWithin"
}