pekko/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala

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

import akka.stream.impl.Stages.{ MaterializingStageFactory, StageModule }
import akka.stream.{ SourceShape, Inlet, Outlet }
import akka.stream.impl.StreamLayout.{ EmptyModule, Module }
import akka.stream.stage.{ TerminationDirective, Directive, Context, PushPullStage }

import scala.annotation.unchecked.uncheckedVariance
import scala.language.higherKinds
import akka.actor.Props
import akka.stream.impl.{ EmptyPublisher, ErrorPublisher, SynchronousIterablePublisher }
import org.reactivestreams.Publisher
import scala.collection.immutable
import scala.concurrent.duration.FiniteDuration
import scala.concurrent.{ ExecutionContext, Future }
import akka.stream.{ ActorFlowMaterializer, Graph }
import akka.stream.impl._
import akka.actor.Cancellable
import akka.actor.ActorRef
import scala.concurrent.Promise
import org.reactivestreams.Subscriber

/**
 * A `Source` is a set of stream processing steps that has one open output. It can comprise
 * any number of internal sources and transformations that are wired together, or it can be
 * an “atomic” source, e.g. from a collection or a file. Materialization turns a Source into
 * a Reactive Streams `Publisher` (at least conceptually).
 */
final class Source[+Out, +Mat](private[stream] override val module: Module)
  extends FlowOps[Out, Mat] with Graph[SourceShape[Out], Mat] {

  override type Repr[+O, +M] = Source[O, M]

  override val shape: SourceShape[Out] = module.shape.asInstanceOf[SourceShape[Out]]

  /**
   * Transform this [[akka.stream.scaladsl.Source]] by appending the given processing stages.
   */
  def via[T, Mat2](flow: Flow[Out, T, Mat2]): Source[T, Mat] = viaMat(flow)(Keep.left)

  /**
   * Transform this [[akka.stream.scaladsl.Source]] by appending the given processing stages.
   */
  def viaMat[T, Mat2, Mat3](flow: Flow[Out, T, Mat2])(combine: (Mat, Mat2) ⇒ Mat3): Source[T, Mat3] = {
    if (flow.isIdentity) this.asInstanceOf[Source[T, Mat3]]
    else {
      val flowCopy = flow.module.carbonCopy
      new Source(
        module
          .growConnect(flowCopy, shape.outlet, flowCopy.shape.inlets.head, combine)
          .replaceShape(SourceShape(flowCopy.shape.outlets.head)))
    }
  }

  /**
   * Connect this [[akka.stream.scaladsl.Source]] to a [[akka.stream.scaladsl.Sink]],
   * concatenating the processing steps of both.
   */
  def to[Mat2](sink: Sink[Out, Mat2]): RunnableFlow[Mat] = toMat(sink)(Keep.left)

  /**
   * Connect this [[akka.stream.scaladsl.Source]] to a [[akka.stream.scaladsl.Sink]],
   * concatenating the processing steps of both.
   */
  def toMat[Mat2, Mat3](sink: Sink[Out, Mat2])(combine: (Mat, Mat2) ⇒ Mat3): RunnableFlow[Mat3] = {
    val sinkCopy = sink.module.carbonCopy
    RunnableFlow(module.growConnect(sinkCopy, shape.outlet, sinkCopy.shape.inlets.head, combine))
  }

  /**
   * Transform only the materialized value of this Source, leaving all other properties as they were.
   */
  def mapMaterialized[Mat2](f: Mat ⇒ Mat2): Repr[Out, Mat2] =
    new Source(module.transformMaterializedValue(f.asInstanceOf[Any ⇒ Any]))

  /** INTERNAL API */
  override private[scaladsl] def andThen[U](op: StageModule): Repr[U, Mat] = {
    // No need to copy here, op is a fresh instance
    new Source(
      module
        .growConnect(op, shape.outlet, op.inPort)
        .replaceShape(SourceShape(op.outPort)))
  }

  override private[scaladsl] def andThenMat[U, Mat2](op: MaterializingStageFactory): Repr[U, Mat2] = {
    new Source(
      module
        .growConnect(op, shape.outlet, op.inPort, Keep.right)
        .replaceShape(SourceShape(op.outPort)))
  }

  /**
   * Connect this `Source` to a `Sink` and run it. The returned value is the materialized value
   * of the `Sink`, e.g. the `Publisher` of a [[akka.stream.scaladsl.Sink#publisher]].
   */
  def runWith[Mat2](sink: Sink[Out, Mat2])(implicit materializer: ActorFlowMaterializer): Mat2 = toMat(sink)(Keep.right).run()

  /**
   * Shortcut for running this `Source` with a fold function.
   * The given function is invoked for every received element, giving it its previous
   * output (or the given `zero` value) and the element as input.
   * The returned [[scala.concurrent.Future]] will be completed with value of the final
   * function evaluation when the input stream ends, or completed with `Failure`
   * if there is a failure signaled in the stream.
   */
  def runFold[U](zero: U)(f: (U, Out) ⇒ U)(implicit materializer: ActorFlowMaterializer): Future[U] =
    runWith(Sink.fold(zero)(f))

  /**
   * Shortcut for running this `Source` with a foreach procedure. The given procedure is invoked
   * for each received element.
   * The returned [[scala.concurrent.Future]] will be completed with `Success` when reaching the
   * normal end of the stream, or completed with `Failure` if there is a failure signaled in
   * the stream.
   */
  def runForeach(f: Out ⇒ Unit)(implicit materializer: ActorFlowMaterializer): Future[Unit] = runWith(Sink.foreach(f))

  /**
   * Concatenates a second source so that the first element
   * emitted by that source is emitted after the last element of this
   * source.
   */
  def concat[Out2 >: Out, M](second: Source[Out2, M]): Source[Out2, (Mat, M)] = Source.concat(this, second)

  /**
   * Concatenates a second source so that the first element
   * emitted by that source is emitted after the last element of this
   * source.
   *
   * This is a shorthand for [[concat]]
   */
  def ++[Out2 >: Out, M](second: Source[Out2, M]): Source[Out2, (Mat, M)] = concat(second)

  /**
   * Applies given [[OperationAttributes]] to a given section.
   */
  def section[O, O2 >: Out, Mat2, Mat3](attributes: OperationAttributes, combine: (Mat, Mat2) ⇒ Mat3)(section: Flow[O2, O2, Unit] ⇒ Flow[O2, O, Mat2]): Source[O, Mat3] = {
    val subFlow = section(Flow[O2]).module.carbonCopy.withAttributes(attributes).wrap()
    new Source(
      module
        .growConnect(subFlow, shape.outlet, subFlow.shape.inlets.head, combine)
        .replaceShape(SourceShape(subFlow.shape.outlets.head)))
  }

  def section[O, O2 >: Out, Mat2](attributes: OperationAttributes)(section: Flow[O2, O2, Unit] ⇒ Flow[O2, O, Mat2]): Source[O, Mat2] = {
    this.section[O, O2, Mat2, Mat2](attributes, (parentm: Mat, subm: Mat2) ⇒ subm)(section)
  }

  override def withAttributes(attr: OperationAttributes): Repr[Out, Mat] =
    new Source(module.withAttributes(attr).wrap())

}

object Source extends SourceApply {

  import OperationAttributes.{ none, name ⇒ named }

  private[stream] def apply[Out, Mat](module: SourceModule[Out, Mat]): Source[Out, Mat] =
    new Source(module)

  private def shape[T](name: String): SourceShape[T] = SourceShape(new Outlet(name + ".out"))

  /**
   * Helper to create [[Source]] from `Publisher`.
   *
   * Construct a transformation starting with given publisher. The transformation steps
   * are executed by a series of [[org.reactivestreams.Processor]] instances
   * that mediate the flow of elements downstream and the propagation of
   * back-pressure upstream.
   */
  def apply[T](publisher: Publisher[T]): Source[T, Unit] =
    new Source(new PublisherSource(publisher, none, shape("PublisherSource")))

  /**
   * Helper to create [[Source]] from `Publisher`.
   *
   * Construct a transformation starting with given publisher. The transformation steps
   * are executed by a series of [[org.reactivestreams.Processor]] instances
   * that mediate the flow of elements downstream and the propagation of
   * back-pressure upstream.
   */
  def apply[T](publisher: Publisher[T], name: String): Source[T, Unit] =
    new Source(new PublisherSource(publisher, named(name), shape(name)))

  /**
   * Helper to create [[Source]] from `Iterator`.
   * Example usage: `Source(() => Iterator.from(0))`
   *
   * Start a new `Source` from the given function that produces anIterator.
   * The produced stream of elements will continue until the iterator runs empty
   * or fails during evaluation of the `next()` method.
   * Elements are pulled out of the iterator in accordance with the demand coming
   * from the downstream transformation steps.
   */
  def apply[T](f: () ⇒ Iterator[T]): Source[T, Unit] = {
    apply(new immutable.Iterable[T] {
      override def iterator: Iterator[T] = f()
    })
  }

  /**
   * Helper to create [[Source]] from `Iterator`.
   * Example usage: `Source(() => Iterator.from(0))`
   *
   * Start a new `Source` from the given function that produces anIterator.
   * The produced stream of elements will continue until the iterator runs empty
   * or fails during evaluation of the `next()` method.
   * Elements are pulled out of the iterator in accordance with the demand coming
   * from the downstream transformation steps.
   */
  def apply[T](f: () ⇒ Iterator[T], name: String): Source[T, Unit] = {
    apply(new immutable.Iterable[T] {
      override def iterator: Iterator[T] = f()
    })
  }

  /**
   * A graph with the shape of a source logically is a source, this method makes
   * it so also in type.
   */
  def wrap[T, M](g: Graph[SourceShape[T], M]): Source[T, M] = new Source(g.module)

  /**
   * Helper to create [[Source]] from `Iterable`.
   * Example usage: `Source(Seq(1,2,3))`
   *
   * Starts a new `Source` from the given `Iterable`. This is like starting from an
   * Iterator, but every Subscriber directly attached to the Publisher of this
   * stream will see an individual flow of elements (always starting from the
   * beginning) regardless of when they subscribed.
   */
  def apply[T](iterable: immutable.Iterable[T]): Source[T, Unit] = { // FIXME add naming of outlet

    Source.empty.transform(() ⇒ {
      new PushPullStage[Nothing, T] {
        var iterator: Iterator[T] = null

        // Delayed init so we onError instead of failing during construction of the Source
        def initIterator(): Unit = if (iterator eq null) iterator = iterable.iterator

        // Upstream is guaranteed to be empty
        override def onPush(elem: Nothing, ctx: Context[T]): Directive =
          throw new UnsupportedOperationException("The IterableSource stage cannot be pushed")

        override def onUpstreamFinish(ctx: Context[T]): TerminationDirective = {
          initIterator()
          if (iterator.hasNext) ctx.absorbTermination()
          else ctx.finish()
        }

        override def onPull(ctx: Context[T]): Directive = {
          if (!ctx.isFinishing) {
            initIterator()
            ctx.pull()
          } else {
            val elem = iterator.next()
            if (iterator.hasNext) ctx.push(elem)
            else ctx.pushAndFinish(elem)
          }
        }
      }

    }).withAttributes(OperationAttributes.name("iterable"))
  }

  /**
   * Start a new `Source` from the given `Future`. The stream will consist of
   * one element when the `Future` is completed with a successful value, which
   * may happen before or after materializing the `Flow`.
   * The stream terminates with an error if the `Future` is completed with a failure.
   */
  def apply[T](future: Future[T]): Source[T, Unit] =
    new Source(new FutureSource(future, none, shape("FutureSource")))

  /**
   * Start a new `Source` from the given `Future`. The stream will consist of
   * one element when the `Future` is completed with a successful value, which
   * may happen before or after materializing the `Flow`.
   * The stream terminates with a failure if the `Future` is completed with a failure.
   */
  def apply[T](future: Future[T], name: String): Source[T, Unit] =
    new Source(new FutureSource(future, named(name), shape(name)))

  /**
   * Elements are emitted periodically with the specified interval.
   * The tick element will be delivered to downstream consumers that has requested any elements.
   * If a consumer has not requested any elements at the point in time when the tick
   * element is produced it will not receive that tick element later. It will
   * receive new tick elements as soon as it has requested more elements.
   */
  def apply[T](initialDelay: FiniteDuration, interval: FiniteDuration, tick: T): Source[T, Cancellable] =
    new Source(new TickSource(initialDelay, interval, tick, none, shape("TickSource")))

  /**
   * Elements are emitted periodically with the specified interval.
   * The tick element will be delivered to downstream consumers that has requested any elements.
   * If a consumer has not requested any elements at the point in time when the tick
   * element is produced it will not receive that tick element later. It will
   * receive new tick elements as soon as it has requested more elements.
   */
  def apply[T](initialDelay: FiniteDuration, interval: FiniteDuration, tick: T, name: String): Source[T, Cancellable] =
    new Source(new TickSource(initialDelay, interval, tick, named(name), shape(name)))

  /**
   * Creates a `Source` that is materialized to an [[akka.actor.ActorRef]] which points to an Actor
   * created according to the passed in [[akka.actor.Props]]. Actor created by the `props` should
   * be [[akka.stream.actor.ActorPublisher]].
   */
  def apply[T](props: Props): Source[T, ActorRef] = new Source(new PropsSource(props, none, shape("PropsSource")))

  /**
   * Creates a `Source` that is materialized to an [[akka.actor.ActorRef]] which points to an Actor
   * created according to the passed in [[akka.actor.Props]]. Actor created by the `props` should
   * be [[akka.stream.actor.ActorPublisher]].
   */
  def apply[T](props: Props, name: String): Source[T, ActorRef] = new Source(new PropsSource(props, named(name), shape(name)))

  /**
   * Create a `Source` with one element.
   * Every connected `Sink` of this stream will see an individual stream consisting of one element.
   */
  def single[T](element: T): Source[T, Unit] = apply(SynchronousIterablePublisher(List(element), "single")) // FIXME optimize

  /**
   * Create a `Source` that will continually emit the given element.
   */
  def repeat[T](element: T): Source[T, Unit] = apply(() ⇒ Iterator.continually(element)) // FIXME optimize

  /**
   * A `Source` with no elements, i.e. an empty stream that is completed immediately for every connected `Sink`.
   */
  def empty[T](): Source[T, Unit] = _empty
  private[this] val _empty: Source[Nothing, Unit] = apply(EmptyPublisher, "EmptySource")

  /**
   * Create a `Source` with no elements, which does not complete its downstream,
   * until externally triggered to do so.
   *
   * It materializes a [[scala.concurrent.Promise]] which will be completed
   * when the downstream stage of this source cancels. This promise can also
   * be used to externally trigger completion, which the source then signalls
   * to its downstream.
   */
  def lazyEmpty[T](): Source[T, Promise[Unit]] = new Source(new LazyEmptySource[T](none, shape("LazyEmptySource")))

  /**
   * Create a `Source` with no elements, which does not complete its downstream,
   * until externally triggered to do so.
   *
   * It materializes a [[scala.concurrent.Promise]] which will be completed
   * when the downstream stage of this source cancels. This promise can also
   * be used to externally trigger completion, which the source then signalls
   * to its downstream.
   */
  def lazyEmpty[T](name: String): Source[T, Promise[Unit]] = new Source(new LazyEmptySource[T](named(name), shape(name)))

  /**
   * Create a `Source` that immediately ends the stream with the `cause` error to every connected `Sink`.
   */
  def failed[T](cause: Throwable): Source[T, Unit] = apply(ErrorPublisher(cause, "failed"), "FailedSource")

  /**
   * Create a `Source` that immediately ends the stream with the `cause` failure to every connected `Sink`.
   */
  def failed[T](cause: Throwable, name: String): Source[T, Unit] = apply(ErrorPublisher(cause, "failed"), name)

  /**
   * Concatenates two sources so that the first element
   * emitted by the second source is emitted after the last element of the first
   * source.
   */
  def concat[T, Mat1, Mat2](source1: Source[T, Mat1], source2: Source[T, Mat2]): Source[T, (Mat1, Mat2)] =
    wrap(FlowGraph.partial(source1, source2)(Keep.both) { implicit b ⇒
      (s1, s2) ⇒
        import FlowGraph.Implicits._
        val c = b.add(Concat[T]())
        s1.outlet ~> c.in(0)
        s2.outlet ~> c.in(1)
        SourceShape(c.out)
    })

  /**
   * Creates a `Source` that is materialized as a [[org.reactivestreams.Subscriber]]
   */
  def subscriber[T](): Source[T, Subscriber[T]] = new Source(new SubscriberSource[T](none, shape("SubscriberSource")))

  /**
   * Creates a `Source` that is materialized as a [[org.reactivestreams.Subscriber]]
   */
  def subscriber[T](name: String): Source[T, Subscriber[T]] = new Source(new SubscriberSource[T](named(name), shape(name)))

}