/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * license agreements; and to You under the Apache License, version 2.0:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * This file is part of the Apache Pekko project, which was derived from Akka.
 */

/*
 * Copyright (C) 2018-2022 Lightbend Inc. <https://www.lightbend.com>
 */

package jdocs.stream;

// #imports
import static org.junit.Assert.assertEquals;

import java.util.*;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.TimeUnit;
import jdocs.AbstractJavaTest;
import org.apache.pekko.Done;
import org.apache.pekko.NotUsed;
import org.apache.pekko.actor.ActorSystem;
import org.apache.pekko.japi.Pair;
import org.apache.pekko.japi.function.Function;
import org.apache.pekko.japi.function.Predicate;
import org.apache.pekko.japi.function.Procedure;
import org.apache.pekko.stream.*;
import org.apache.pekko.stream.javadsl.*;
import org.apache.pekko.stream.stage.*;
// #imports
import org.apache.pekko.stream.testkit.TestPublisher;
import org.apache.pekko.stream.testkit.TestSubscriber;
import org.apache.pekko.testkit.javadsl.TestKit;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;
import org.reactivestreams.Subscription;
import scala.concurrent.ExecutionContext;

public class GraphStageDocTest extends AbstractJavaTest {
  static ActorSystem system;

  @BeforeClass
  public static void setup() {
    system = ActorSystem.create("GraphStageDocTest");
  }

  @AfterClass
  public static void tearDown() {
    TestKit.shutdownActorSystem(system);
    system = null;
  }

  // #simple-source
  public class NumbersSource extends GraphStage<SourceShape<Integer>> {
    // Define the (sole) output port of this stage
    public final Outlet<Integer> out = Outlet.create("NumbersSource.out");

    // Define the shape of this stage, which is SourceShape with the port we defined above
    private final SourceShape<Integer> shape = SourceShape.of(out);

    @Override
    public SourceShape<Integer> shape() {
      return shape;
    }

    // This is where the actual (possibly stateful) logic is created
    @Override
    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new GraphStageLogic(shape()) {
        // All state MUST be inside the GraphStageLogic,
        // never inside the enclosing GraphStage.
        // This state is safe to access and modify from all the
        // callbacks that are provided by GraphStageLogic and the
        // registered handlers.
        private int counter = 1;

        {
          setHandler(
              out,
              new AbstractOutHandler() {
                @Override
                public void onPull() throws Exception {
                  push(out, counter);
                  counter += 1;
                }
              });
        }
      };
    }
  }

  // #simple-source

  // #simple-sink
  public class StdoutSink extends GraphStage<SinkShape<Integer>> {
    public final Inlet<Integer> in = Inlet.create("StdoutSink.in");

    private final SinkShape<Integer> shape = SinkShape.of(in);

    @Override
    public SinkShape<Integer> shape() {
      return shape;
    }

    @Override
    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new GraphStageLogic(shape()) {

        // This requests one element at the Sink startup.
        @Override
        public void preStart() {
          pull(in);
        }

        {
          setHandler(
              in,
              new AbstractInHandler() {
                @Override
                public void onPush() throws Exception {
                  Integer element = grab(in);
                  System.out.println(element);
                  pull(in);
                }
              });
        }
      };
    }
  }

  // #simple-sink

  @Test
  public void demonstrateCustomSourceUsage() throws Exception {
    // #simple-source-usage
    // A GraphStage is a proper Graph, just like what GraphDSL.create would return
    Graph<SourceShape<Integer>, NotUsed> sourceGraph = new NumbersSource();

    // Create a Source from the Graph to access the DSL
    Source<Integer, NotUsed> mySource = Source.fromGraph(sourceGraph);

    // Returns 55
    CompletionStage<Integer> result1 =
        mySource.take(10).runFold(0, (sum, next) -> sum + next, system);

    // The source is reusable. This returns 5050
    CompletionStage<Integer> result2 =
        mySource.take(100).runFold(0, (sum, next) -> sum + next, system);
    // #simple-source-usage

    assertEquals(result1.toCompletableFuture().get(3, TimeUnit.SECONDS), (Integer) 55);
    assertEquals(result2.toCompletableFuture().get(3, TimeUnit.SECONDS), (Integer) 5050);
  }

  @Test
  public void demonstrateCustomSinkUsage() throws Exception {
    Graph<SinkShape<Integer>, NotUsed> sinkGraph = new StdoutSink();

    Sink<Integer, NotUsed> mySink = Sink.fromGraph(sinkGraph);

    Source.from(Arrays.asList(1, 2, 3)).runWith(mySink, system);
  }

  // #one-to-one
  public class Map<A, B> extends GraphStage<FlowShape<A, B>> {

    private final Function<A, B> f;

    public Map(Function<A, B> f) {
      this.f = f;
    }

    public final Inlet<A> in = Inlet.create("Map.in");
    public final Outlet<B> out = Outlet.create("Map.out");

    private final FlowShape<A, B> shape = FlowShape.of(in, out);

    @Override
    public FlowShape<A, B> shape() {
      return shape;
    }

    @Override
    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new GraphStageLogic(shape) {

        {
          setHandler(
              in,
              new AbstractInHandler() {
                @Override
                public void onPush() throws Exception {
                  push(out, f.apply(grab(in)));
                }
              });
          setHandler(
              out,
              new AbstractOutHandler() {
                @Override
                public void onPull() throws Exception {
                  pull(in);
                }
              });
        }
      };
    }
  }

  // #one-to-one

  @Test
  public void demonstrateOneToOne() throws Exception {
    // tests:
    final Graph<FlowShape<String, Integer>, NotUsed> stringLength =
        Flow.fromGraph(
            new Map<String, Integer>(
                new Function<String, Integer>() {
                  @Override
                  public Integer apply(String str) {
                    return str.length();
                  }
                }));

    CompletionStage<Integer> result =
        Source.from(Arrays.asList("one", "two", "three"))
            .via(stringLength)
            .runFold(0, (sum, n) -> sum + n, system);

    assertEquals(Integer.valueOf(11), result.toCompletableFuture().get(3, TimeUnit.SECONDS));
  }

  // #many-to-one
  public final class Filter<A> extends GraphStage<FlowShape<A, A>> {

    private final Predicate<A> p;

    public Filter(Predicate<A> p) {
      this.p = p;
    }

    public final Inlet<A> in = Inlet.create("Filter.in");
    public final Outlet<A> out = Outlet.create("Filter.out");

    private final FlowShape<A, A> shape = FlowShape.of(in, out);

    @Override
    public FlowShape<A, A> shape() {
      return shape;
    }

    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new GraphStageLogic(shape) {
        {
          setHandler(
              in,
              new AbstractInHandler() {
                @Override
                public void onPush() {
                  A elem = grab(in);
                  if (p.test(elem)) {
                    push(out, elem);
                  } else {
                    pull(in);
                  }
                }
              });

          setHandler(
              out,
              new AbstractOutHandler() {
                @Override
                public void onPull() throws Exception {
                  pull(in);
                }
              });
        }
      };
    }
  }

  // #many-to-one

  @Test
  public void demonstrateAManyToOneElementGraphStage() throws Exception {

    // tests:
    Graph<FlowShape<Integer, Integer>, NotUsed> evenFilter =
        Flow.fromGraph(new Filter<Integer>(n -> n % 2 == 0));

    CompletionStage<Integer> result =
        Source.from(Arrays.asList(1, 2, 3, 4, 5, 6))
            .via(evenFilter)
            .runFold(0, (elem, sum) -> sum + elem, system);

    assertEquals(Integer.valueOf(12), result.toCompletableFuture().get(3, TimeUnit.SECONDS));
  }

  // #one-to-many
  public class Duplicator<A> extends GraphStage<FlowShape<A, A>> {

    public final Inlet<A> in = Inlet.create("Duplicator.in");
    public final Outlet<A> out = Outlet.create("Duplicator.out");

    private final FlowShape<A, A> shape = FlowShape.of(in, out);

    @Override
    public FlowShape<A, A> shape() {
      return shape;
    }

    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new GraphStageLogic(shape) {
        // Again: note that all mutable state
        // MUST be inside the GraphStageLogic
        Optional<A> lastElem = Optional.empty();

        {
          setHandler(
              in,
              new AbstractInHandler() {
                @Override
                public void onPush() {
                  A elem = grab(in);
                  lastElem = Optional.ofNullable(elem);
                  push(out, elem);
                }

                @Override
                public void onUpstreamFinish() {
                  if (lastElem.isPresent()) {
                    emit(out, lastElem.get());
                  }
                  complete(out);
                }
              });

          setHandler(
              out,
              new AbstractOutHandler() {
                @Override
                public void onPull() throws Exception {
                  if (lastElem.isPresent()) {
                    push(out, lastElem.get());
                    lastElem = Optional.empty();
                  } else {
                    pull(in);
                  }
                }
              });
        }
      };
    }
  }

  // #one-to-many

  @Test
  public void demonstrateAOneToManyElementGraphStage() throws Exception {
    // tests:
    Graph<FlowShape<Integer, Integer>, NotUsed> duplicator =
        Flow.fromGraph(new Duplicator<Integer>());

    CompletionStage<Integer> result =
        Source.from(Arrays.asList(1, 2, 3)).via(duplicator).runFold(0, (n, sum) -> n + sum, system);

    assertEquals(Integer.valueOf(12), result.toCompletableFuture().get(3, TimeUnit.SECONDS));
  }

  // #simpler-one-to-many
  public class Duplicator2<A> extends GraphStage<FlowShape<A, A>> {

    public final Inlet<A> in = Inlet.create("Duplicator.in");
    public final Outlet<A> out = Outlet.create("Duplicator.out");

    private final FlowShape<A, A> shape = FlowShape.of(in, out);

    @Override
    public FlowShape<A, A> shape() {
      return shape;
    }

    @Override
    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new GraphStageLogic(shape) {

        {
          setHandler(
              in,
              new AbstractInHandler() {
                @Override
                public void onPush() {
                  A elem = grab(in);
                  // this will temporarily suspend this handler until the two elems
                  // are emitted and then reinstates it
                  emitMultiple(out, Arrays.asList(elem, elem).iterator());
                }
              });

          setHandler(
              out,
              new AbstractOutHandler() {
                @Override
                public void onPull() throws Exception {
                  pull(in);
                }
              });
        }
      };
    }
  }

  // #simpler-one-to-many

  @Test
  public void demonstrateASimplerOneToManyStage() throws Exception {
    // tests:
    Graph<FlowShape<Integer, Integer>, NotUsed> duplicator =
        Flow.fromGraph(new Duplicator2<Integer>());

    CompletionStage<Integer> result =
        Source.from(Arrays.asList(1, 2, 3)).via(duplicator).runFold(0, (n, sum) -> n + sum, system);

    assertEquals(Integer.valueOf(12), result.toCompletableFuture().get(3, TimeUnit.SECONDS));
  }

  @Test
  public void demonstrateChainingOfGraphStages() throws Exception {
    Graph<SinkShape<Integer>, CompletionStage<String>> sink =
        Sink.fold("", (acc, n) -> acc + n.toString());

    // #graph-operator-chain
    CompletionStage<String> resultFuture =
        Source.from(Arrays.asList(1, 2, 3, 4, 5))
            .via(new Filter<Integer>((n) -> n % 2 == 0))
            .via(new Duplicator<Integer>())
            .via(new Map<Integer, Integer>((n) -> n / 2))
            .runWith(sink, system);

    // #graph-operator-chain

    assertEquals("1122", resultFuture.toCompletableFuture().get(3, TimeUnit.SECONDS));
  }

  // #async-side-channel
  // will close upstream in all materializations of the stage instance
  // when the completion stage completes
  public class KillSwitch<A> extends GraphStage<FlowShape<A, A>> {

    private final CompletionStage<Done> switchF;

    public KillSwitch(CompletionStage<Done> switchF) {
      this.switchF = switchF;
    }

    public final Inlet<A> in = Inlet.create("KillSwitch.in");
    public final Outlet<A> out = Outlet.create("KillSwitch.out");

    private final FlowShape<A, A> shape = FlowShape.of(in, out);

    @Override
    public FlowShape<A, A> shape() {
      return shape;
    }

    @Override
    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new GraphStageLogic(shape) {

        {
          setHandler(
              in,
              new AbstractInHandler() {
                @Override
                public void onPush() {
                  push(out, grab(in));
                }
              });
          setHandler(
              out,
              new AbstractOutHandler() {
                @Override
                public void onPull() throws Exception {
                  pull(in);
                }
              });
        }

        @Override
        public void preStart() {
          AsyncCallback<Done> callback =
              createAsyncCallback(
                  new Procedure<Done>() {
                    @Override
                    public void apply(Done param) throws Exception {
                      completeStage();
                    }
                  });

          ExecutionContext ec = system.dispatcher();
          switchF.thenAccept(callback::invoke);
        }
      };
    }
  }

  // #async-side-channel

  @Test
  public void demonstrateAnAsynchronousSideChannel() throws Exception {

    // tests:
    TestSubscriber.Probe<Integer> out = TestSubscriber.probe(system);
    TestPublisher.Probe<Integer> in = TestPublisher.probe(0, system);

    CompletableFuture<Done> switchF = new CompletableFuture<>();
    Graph<FlowShape<Integer, Integer>, NotUsed> killSwitch =
        Flow.fromGraph(new KillSwitch<>(switchF));

    Source.fromPublisher(in).via(killSwitch).to(Sink.fromSubscriber(out)).run(system);

    out.request(1);
    in.sendNext(1);
    out.expectNext(1);

    switchF.complete(Done.getInstance());

    out.expectComplete();
  }

  // #timed
  // each time an event is pushed through it will trigger a period of silence
  public class TimedGate<A> extends GraphStage<FlowShape<A, A>> {

    private final int silencePeriodInSeconds;

    public TimedGate(int silencePeriodInSeconds) {
      this.silencePeriodInSeconds = silencePeriodInSeconds;
    }

    public final Inlet<A> in = Inlet.create("TimedGate.in");
    public final Outlet<A> out = Outlet.create("TimedGate.out");

    private final FlowShape<A, A> shape = FlowShape.of(in, out);

    @Override
    public FlowShape<A, A> shape() {
      return shape;
    }

    @Override
    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new TimerGraphStageLogic(shape) {

        private boolean open = false;

        {
          setHandler(
              in,
              new AbstractInHandler() {
                @Override
                public void onPush() throws Exception {
                  A elem = grab(in);
                  if (open) pull(in);
                  else {
                    push(out, elem);
                    open = true;
                    scheduleOnce("key", java.time.Duration.ofSeconds(silencePeriodInSeconds));
                  }
                }
              });
          setHandler(
              out,
              new AbstractOutHandler() {
                @Override
                public void onPull() throws Exception {
                  pull(in);
                }
              });
        }

        @Override
        public void onTimer(Object key) {
          if (key.equals("key")) {
            open = false;
          }
        }
      };
    }
  }

  // #timed

  public void demonstrateAGraphStageWithATimer() throws Exception {
    // tests:
    CompletionStage<Integer> result =
        Source.from(Arrays.asList(1, 2, 3))
            .via(new TimedGate<>(2))
            .takeWithin(java.time.Duration.ofMillis(250))
            .runFold(0, (n, sum) -> n + sum, system);

    assertEquals(Integer.valueOf(1), result.toCompletableFuture().get(3, TimeUnit.SECONDS));
  }

  // #materialized
  public class FirstValue<A>
      extends AbstractGraphStageWithMaterializedValue<FlowShape<A, A>, CompletionStage<A>> {

    public final Inlet<A> in = Inlet.create("FirstValue.in");
    public final Outlet<A> out = Outlet.create("FirstValue.out");

    private final FlowShape<A, A> shape = FlowShape.of(in, out);

    @Override
    public FlowShape<A, A> shape() {
      return shape;
    }

    @Override
    public Pair<GraphStageLogic, CompletionStage<A>> createLogicAndMaterializedValuePair(
        Attributes inheritedAttributes) {
      CompletableFuture<A> promise = new CompletableFuture<>();

      GraphStageLogic logic =
          new GraphStageLogic(shape) {
            {
              setHandler(
                  in,
                  new AbstractInHandler() {
                    @Override
                    public void onPush() {
                      A elem = grab(in);
                      promise.complete(elem);
                      push(out, elem);

                      // replace handler with one that only forwards elements
                      setHandler(
                          in,
                          new AbstractInHandler() {
                            @Override
                            public void onPush() {
                              push(out, grab(in));
                            }
                          });
                    }
                  });

              setHandler(
                  out,
                  new AbstractOutHandler() {
                    @Override
                    public void onPull() throws Exception {
                      pull(in);
                    }
                  });
            }
          };

      return new Pair<>(logic, promise);
    }
  }

  // #materialized

  public void demonstrateACustomMaterializedValue() throws Exception {
    // tests:
    RunnableGraph<CompletionStage<Integer>> flow =
        Source.from(Arrays.asList(1, 2, 3))
            .viaMat(new FirstValue<Integer>(), Keep.right())
            .to(Sink.ignore());

    CompletionStage<Integer> result = flow.run(system);

    assertEquals(Integer.valueOf(1), result.toCompletableFuture().get(3, TimeUnit.SECONDS));
  }

  // #detached
  public class TwoBuffer<A> extends GraphStage<FlowShape<A, A>> {

    public final Inlet<A> in = Inlet.create("TwoBuffer.in");
    public final Outlet<A> out = Outlet.create("TwoBuffer.out");

    private final FlowShape<A, A> shape = FlowShape.of(in, out);

    @Override
    public FlowShape<A, A> shape() {
      return shape;
    }

    @Override
    public GraphStageLogic createLogic(Attributes inheritedAttributes) {
      return new GraphStageLogic(shape) {

        private final int SIZE = 2;
        private Queue<A> buffer = new ArrayDeque<>(SIZE);
        private boolean downstreamWaiting = false;

        private boolean isBufferFull() {
          return buffer.size() == SIZE;
        }

        @Override
        public void preStart() {
          // a detached stage needs to start upstream demand
          // itself as it is not triggered by downstream demand
          pull(in);
        }

        {
          setHandler(
              in,
              new AbstractInHandler() {
                @Override
                public void onPush() {
                  A elem = grab(in);
                  buffer.add(elem);
                  if (downstreamWaiting) {
                    downstreamWaiting = false;
                    A bufferedElem = buffer.poll();
                    push(out, bufferedElem);
                  }
                  if (!isBufferFull()) {
                    pull(in);
                  }
                }

                @Override
                public void onUpstreamFinish() {
                  if (!buffer.isEmpty()) {
                    // emit the rest if possible
                    emitMultiple(out, buffer.iterator());
                  }
                  completeStage();
                }
              });

          setHandler(
              out,
              new AbstractOutHandler() {
                @Override
                public void onPull() throws Exception {
                  if (buffer.isEmpty()) {
                    downstreamWaiting = true;
                  } else {
                    A elem = buffer.poll();
                    push(out, elem);
                  }
                  if (!isBufferFull() && !hasBeenPulled(in)) {
                    pull(in);
                  }
                }
              });
        }
      };
    }
  }

  // #detached

  public void demonstrateADetachedGraphStage() throws Exception {
    // tests:
    CompletionStage<Integer> result1 =
        Source.from(Arrays.asList(1, 2, 3))
            .via(new TwoBuffer<>())
            .runFold(0, (acc, n) -> acc + n, system);

    assertEquals(Integer.valueOf(6), result1.toCompletableFuture().get(3, TimeUnit.SECONDS));

    TestSubscriber.ManualProbe<Integer> subscriber = TestSubscriber.manualProbe(system);
    TestPublisher.Probe<Integer> publisher = TestPublisher.probe(0, system);
    RunnableGraph<NotUsed> flow2 =
        Source.fromPublisher(publisher).via(new TwoBuffer<>()).to(Sink.fromSubscriber(subscriber));

    flow2.run(system);

    Subscription sub = subscriber.expectSubscription();
    // this happens even though the subscriber has not signalled any demand
    publisher.sendNext(1);
    publisher.sendNext(2);

    sub.cancel();
  }
}
