pekko/akka-stream/src/main/scala/akka/stream/impl2/ActorBasedFlowMaterializer.scala

/**
 * Copyright (C) 2014 Typesafe Inc. <http://www.typesafe.com>
 */
package akka.stream.impl2

import java.util.concurrent.atomic.AtomicLong
import akka.actor.{ Actor, ActorCell, ActorRef, ActorSystem, ExtendedActorSystem, Extension, ExtensionId, ExtensionIdProvider, LocalActorRef, Props, RepointableActorRef }
import akka.pattern.ask
import org.reactivestreams.{ Processor, Publisher, Subscriber }
import scala.annotation.tailrec
import scala.collection.immutable
import scala.concurrent.{ Await, Future }
import scala.concurrent.duration._
import scala.util.{ Failure, Success }
import akka.stream.Transformer
import akka.stream.scaladsl2.FlowMaterializer
import akka.stream.MaterializerSettings
import akka.stream.impl.ActorPublisher
import akka.stream.impl.IterablePublisher
import akka.stream.impl.TransformProcessorImpl
import akka.stream.impl.ActorProcessor
import akka.stream.impl.ExposedPublisher
import akka.stream.scaladsl2.Source
import akka.stream.scaladsl2.Sink
import akka.stream.scaladsl2.MaterializedFlow
import akka.stream.scaladsl2.IterableSource
import akka.stream.impl.EmptyPublisher

/**
 * INTERNAL API
 */
private[akka] object Ast {
  sealed trait AstNode {
    def name: String
  }

  case class Transform(name: String, mkTransformer: () ⇒ Transformer[Any, Any]) extends AstNode

}

/**
 * INTERNAL API
 */
private[akka] case class ActorBasedFlowMaterializer(
  override val settings: MaterializerSettings,
  supervisor: ActorRef,
  flowNameCounter: AtomicLong,
  namePrefix: String)
  extends FlowMaterializer(settings) {
  import akka.stream.impl2.Ast._

  def withNamePrefix(name: String): FlowMaterializer = this.copy(namePrefix = name)

  private def nextFlowNameCount(): Long = flowNameCounter.incrementAndGet()

  private def createFlowName(): String = s"$namePrefix-${nextFlowNameCount()}"

  @tailrec private def processorChain(topSubscriber: Subscriber[_], ops: immutable.Seq[AstNode],
                                      flowName: String, n: Int): Subscriber[_] = {
    ops match {
      case op :: tail ⇒
        val opProcessor: Processor[Any, Any] = processorForNode(op, flowName, n)
        opProcessor.subscribe(topSubscriber.asInstanceOf[Subscriber[Any]])
        processorChain(opProcessor, tail, flowName, n - 1)
      case _ ⇒ topSubscriber
    }
  }

  // Ops come in reverse order
  override def materialize[In, Out](source: Source[In], sink: Sink[Out], ops: List[Ast.AstNode]): MaterializedFlow = {
    val flowName = createFlowName()
    val (s, p) =
      if (ops.isEmpty) {
        val identityProcessor: Processor[In, Out] = processorForNode(identityTransform, flowName, 1).asInstanceOf[Processor[In, Out]]
        (identityProcessor, identityProcessor)
      } else {
        val opsSize = ops.size
        val outProcessor = processorForNode(ops.head, flowName, opsSize).asInstanceOf[Processor[In, Out]]
        val topSubscriber = processorChain(outProcessor, ops.tail, flowName, opsSize - 1).asInstanceOf[Processor[In, Out]]
        (topSubscriber, outProcessor)
      }
    val sourceValue = source.attach(s, this, flowName)
    val sinkValue = sink.attach(p, this)
    new MaterializedFlow(source, sourceValue, sink, sinkValue)

  }

  private def identityProcessor[I](flowName: String): Processor[I, I] =
    processorForNode(identityTransform, flowName, 1).asInstanceOf[Processor[I, I]]

  private val identityTransform = Transform("identity", () ⇒
    new Transformer[Any, Any] {
      override def onNext(element: Any) = List(element)
    })

  override def materializeSource[In](source: IterableSource[In], flowName: String): Publisher[In] = {
    if (source.iterable.isEmpty) EmptyPublisher[In]
    else ActorPublisher(actorOf(IterablePublisher.props(source.iterable, settings),
      name = s"$flowName-0-iterable"), Some(source.iterable))
  }

  private def processorForNode(op: AstNode, flowName: String, n: Int): Processor[Any, Any] = {
    val impl = actorOf(ActorProcessorFactory.props(settings, op), s"$flowName-$n-${op.name}")
    ActorProcessorFactory(impl)
  }

  private def actorOf(props: Props, name: String): ActorRef = supervisor match {
    case ref: LocalActorRef ⇒
      ref.underlying.attachChild(props, name, systemService = false)
    case ref: RepointableActorRef ⇒
      if (ref.isStarted)
        ref.underlying.asInstanceOf[ActorCell].attachChild(props, name, systemService = false)
      else {
        implicit val timeout = ref.system.settings.CreationTimeout
        val f = (supervisor ? StreamSupervisor.Materialize(props, name)).mapTo[ActorRef]
        Await.result(f, timeout.duration)
      }
    case _ ⇒
      throw new IllegalStateException(s"Stream supervisor must be a local actor, was [${supervisor.getClass.getName}]")
  }

}

/**
 * INTERNAL API
 */
private[akka] object FlowNameCounter extends ExtensionId[FlowNameCounter] with ExtensionIdProvider {
  override def get(system: ActorSystem): FlowNameCounter = super.get(system)
  override def lookup = FlowNameCounter
  override def createExtension(system: ExtendedActorSystem): FlowNameCounter = new FlowNameCounter
}

/**
 * INTERNAL API
 */
private[akka] class FlowNameCounter extends Extension {
  val counter = new AtomicLong(0)
}

/**
 * INTERNAL API
 */
private[akka] object StreamSupervisor {
  def props(settings: MaterializerSettings): Props = Props(new StreamSupervisor(settings))

  case class Materialize(props: Props, name: String)
}

private[akka] class StreamSupervisor(settings: MaterializerSettings) extends Actor {
  import StreamSupervisor._

  def receive = {
    case Materialize(props, name) ⇒
      val impl = context.actorOf(props, name)
      sender() ! impl
  }
}

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

  import Ast._
  def props(settings: MaterializerSettings, op: AstNode): Props =
    (op match {
      case t: Transform ⇒ Props(new TransformProcessorImpl(settings, t.mkTransformer()))
    }).withDispatcher(settings.dispatcher)

  def apply[I, O](impl: ActorRef): ActorProcessor[I, O] = {
    val p = new ActorProcessor[I, O](impl)
    impl ! ExposedPublisher(p.asInstanceOf[ActorPublisher[Any]])
    p
  }
}