/*
 * Copyright (C) 2014-2020 Lightbend Inc. <https://www.lightbend.com>
 */

package akka.stream.javadsl;

import akka.Done;
import akka.NotUsed;
import akka.actor.ActorRef;
import akka.actor.Cancellable;
import akka.actor.Status;
import akka.japi.Pair;
import akka.japi.function.*;
import akka.japi.pf.PFBuilder;
// #imports
import akka.stream.*;

// #imports
import akka.stream.scaladsl.FlowSpec;
import akka.util.ConstantFun;
import akka.stream.stage.*;
import akka.testkit.AkkaSpec;
import akka.stream.testkit.TestPublisher;
import akka.testkit.javadsl.TestKit;
import com.google.common.collect.Iterables;
import org.junit.ClassRule;
import org.junit.Test;
import scala.concurrent.duration.FiniteDuration;
import scala.util.Try;
import akka.testkit.AkkaJUnitActorSystemResource;

import java.time.Duration;
import java.util.*;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import static akka.NotUsed.notUsed;
import static akka.stream.testkit.StreamTestKit.PublisherProbeSubscription;
import static akka.stream.testkit.TestPublisher.ManualProbe;
import static org.hamcrest.core.Is.is;
import static org.junit.Assert.*;

@SuppressWarnings("serial")
public class SourceTest extends StreamTest {
  public SourceTest() {
    super(actorSystemResource);
  }

  @ClassRule
  public static AkkaJUnitActorSystemResource actorSystemResource =
      new AkkaJUnitActorSystemResource("SourceTest", AkkaSpec.testConf());

  interface Fruit {}

  static class Apple implements Fruit {};

  static class Orange implements Fruit {};

  public void compileOnlyUpcast() {
    Source<Apple, NotUsed> apples = null;
    Source<Orange, NotUsed> oranges = null;
    Source<Fruit, NotUsed> appleFruits = Source.upcast(apples);
    Source<Fruit, NotUsed> orangeFruits = Source.upcast(oranges);

    Source<Fruit, NotUsed> fruits = appleFruits.merge(orangeFruits);
  }

  @Test
  public void mustBeAbleToUseSimpleOperators() {
    final TestKit probe = new TestKit(system);
    final String[] lookup = {"a", "b", "c", "d", "e", "f"};
    final java.lang.Iterable<Integer> input = Arrays.asList(0, 1, 2, 3, 4, 5);
    final Source<Integer, NotUsed> ints = Source.from(input);

    ints.drop(2)
        .take(3)
        .takeWithin(Duration.ofSeconds(10))
        .map(elem -> lookup[elem])
        .filter(elem -> !elem.equals("c"))
        .grouped(2)
        .mapConcat(elem -> elem)
        .groupedWithin(100, Duration.ofMillis(50))
        .mapConcat(elem -> elem)
        .runFold("", (acc, elem) -> acc + elem, system)
        .thenAccept(elem -> probe.getRef().tell(elem, ActorRef.noSender()));

    probe.expectMsgEquals("de");
  }

  @Test
  public void mustBeAbleToUseVoidTypeInForeach() {
    final TestKit probe = new TestKit(system);
    final java.lang.Iterable<String> input = Arrays.asList("a", "b", "c");
    Source<String, NotUsed> ints = Source.from(input);

    final CompletionStage<Done> completion =
        ints.runForeach(elem -> probe.getRef().tell(elem, ActorRef.noSender()), system);

    completion.thenAccept(elem -> probe.getRef().tell(String.valueOf(elem), ActorRef.noSender()));

    probe.expectMsgEquals("a");
    probe.expectMsgEquals("b");
    probe.expectMsgEquals("c");
    probe.expectMsgEquals("Done");
  }

  @Test
  public void mustBeAbleToUseVia() {
    final TestKit probe = new TestKit(system);
    final Iterable<Integer> input = Arrays.asList(0, 1, 2, 3, 4, 5, 6, 7);
    // duplicate each element, stop after 4 elements, and emit sum to the end
    Source.from(input)
        .via(
            new GraphStage<FlowShape<Integer, Integer>>() {
              public final Inlet<Integer> in = Inlet.create("in");
              public final Outlet<Integer> out = Outlet.create("out");

              @Override
              public GraphStageLogic createLogic(Attributes inheritedAttributes) throws Exception {
                return new GraphStageLogic(shape()) {
                  int sum = 0;
                  int count = 0;

                  {
                    setHandler(
                        in,
                        new AbstractInHandler() {
                          @Override
                          public void onPush() {
                            final Integer element = grab(in);
                            sum += element;
                            count += 1;
                            if (count == 4) {
                              emitMultiple(
                                  out,
                                  Arrays.asList(element, element, sum).iterator(),
                                  () -> completeStage());
                            } else {
                              emitMultiple(out, Arrays.asList(element, element).iterator());
                            }
                          }
                        });
                    setHandler(
                        out,
                        new AbstractOutHandler() {
                          @Override
                          public void onPull() throws Exception {
                            pull(in);
                          }
                        });
                  }
                };
              }

              @Override
              public FlowShape<Integer, Integer> shape() {
                return FlowShape.of(in, out);
              }
            })
        .runForeach(
            (Procedure<Integer>) elem -> probe.getRef().tell(elem, ActorRef.noSender()), system);

    probe.expectMsgEquals(0);
    probe.expectMsgEquals(0);
    probe.expectMsgEquals(1);
    probe.expectMsgEquals(1);
    probe.expectMsgEquals(2);
    probe.expectMsgEquals(2);
    probe.expectMsgEquals(3);
    probe.expectMsgEquals(3);
    probe.expectMsgEquals(6);
  }

  @SuppressWarnings("unchecked")
  @Test
  public void mustBeAbleToUseGroupBy() throws Exception {
    final Iterable<String> input = Arrays.asList("Aaa", "Abb", "Bcc", "Cdd", "Cee");
    final Source<List<String>, NotUsed> source =
        Source.from(input)
            .groupBy(
                3,
                new Function<String, String>() {
                  public String apply(String elem) {
                    return elem.substring(0, 1);
                  }
                })
            .grouped(10)
            .mergeSubstreams();

    final CompletionStage<List<List<String>>> future =
        source.grouped(10).runWith(Sink.<List<List<String>>>head(), system);
    final Object[] result = future.toCompletableFuture().get(1, TimeUnit.SECONDS).toArray();
    Arrays.sort(
        result,
        (Comparator<Object>)
            (Object)
                new Comparator<List<String>>() {
                  @Override
                  public int compare(List<String> o1, List<String> o2) {
                    return o1.get(0).charAt(0) - o2.get(0).charAt(0);
                  }
                });

    assertArrayEquals(
        new Object[] {
          Arrays.asList("Aaa", "Abb"), Arrays.asList("Bcc"), Arrays.asList("Cdd", "Cee")
        },
        result);
  }

  @Test
  public void mustBeAbleToUseSplitWhen() throws Exception {
    final Iterable<String> input = Arrays.asList("A", "B", "C", ".", "D", ".", "E", "F");
    final Source<List<String>, NotUsed> source =
        Source.from(input)
            .splitWhen(
                new Predicate<String>() {
                  public boolean test(String elem) {
                    return elem.equals(".");
                  }
                })
            .grouped(10)
            .concatSubstreams();

    final CompletionStage<List<List<String>>> future =
        source.grouped(10).runWith(Sink.<List<List<String>>>head(), system);
    final List<List<String>> result = future.toCompletableFuture().get(1, TimeUnit.SECONDS);

    assertEquals(
        Arrays.asList(
            Arrays.asList("A", "B", "C"), Arrays.asList(".", "D"), Arrays.asList(".", "E", "F")),
        result);
  }

  @Test
  public void mustBeAbleToUseSplitAfter() throws Exception {
    final Iterable<String> input = Arrays.asList("A", "B", "C", ".", "D", ".", "E", "F");
    final Source<List<String>, NotUsed> source =
        Source.from(input)
            .splitAfter(
                new Predicate<String>() {
                  public boolean test(String elem) {
                    return elem.equals(".");
                  }
                })
            .grouped(10)
            .concatSubstreams();

    final CompletionStage<List<List<String>>> future =
        source.grouped(10).runWith(Sink.<List<List<String>>>head(), system);
    final List<List<String>> result = future.toCompletableFuture().get(1, TimeUnit.SECONDS);

    assertEquals(
        Arrays.asList(
            Arrays.asList("A", "B", "C", "."), Arrays.asList("D", "."), Arrays.asList("E", "F")),
        result);
  }

  @Test
  public void mustBeAbleToUseConcat() {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
    final Iterable<String> input2 = Arrays.asList("D", "E", "F");

    final Source<String, NotUsed> in1 = Source.from(input1);
    final Source<String, NotUsed> in2 = Source.from(input2);

    in1.concat(in2)
        .runForeach(
            new Procedure<String>() {
              public void apply(String elem) {
                probe.getRef().tell(elem, ActorRef.noSender());
              }
            },
            system);

    List<Object> output = probe.receiveN(6);
    assertEquals(Arrays.asList("A", "B", "C", "D", "E", "F"), output);
  }

  @Test
  public void mustBeAbleToUsePrepend() {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
    final Iterable<String> input2 = Arrays.asList("D", "E", "F");

    final Source<String, NotUsed> in1 = Source.from(input1);
    final Source<String, NotUsed> in2 = Source.from(input2);

    in2.prepend(in1)
        .runForeach(
            new Procedure<String>() {
              public void apply(String elem) {
                probe.getRef().tell(elem, ActorRef.noSender());
              }
            },
            system);

    List<Object> output = probe.receiveN(6);
    assertEquals(Arrays.asList("A", "B", "C", "D", "E", "F"), output);
  }

  @Test
  public void mustBeAbleToUseCallableInput() {
    final TestKit probe = new TestKit(system);
    final Iterable<Integer> input1 = Arrays.asList(4, 3, 2, 1, 0);
    final Creator<Iterator<Integer>> input =
        new Creator<Iterator<Integer>>() {
          @Override
          public Iterator<Integer> create() {
            return input1.iterator();
          }
        };
    Source.fromIterator(input)
        .runForeach(
            new Procedure<Integer>() {
              public void apply(Integer elem) {
                probe.getRef().tell(elem, ActorRef.noSender());
              }
            },
            system);

    List<Object> output = probe.receiveN(5);
    assertEquals(Arrays.asList(4, 3, 2, 1, 0), output);
    probe.expectNoMessage(FiniteDuration.create(500, TimeUnit.MILLISECONDS));
  }

  @Test
  public void mustBeAbleToUseOnCompleteSuccess() {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input = Arrays.asList("A", "B", "C");

    Source.from(input)
        .runWith(
            Sink.<String>onComplete(
                new Procedure<Try<Done>>() {
                  @Override
                  public void apply(Try<Done> param) throws Exception {
                    probe.getRef().tell(param.get(), ActorRef.noSender());
                  }
                }),
            system);

    probe.expectMsgClass(Done.class);
  }

  @Test
  public void mustBeAbleToUseOnCompleteError() {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input = Arrays.asList("A", "B", "C");

    Source.from(input)
        .<String>map(
            in -> {
              throw new RuntimeException("simulated err");
            })
        .runWith(Sink.<String>head(), system)
        .whenComplete(
            (s, ex) -> {
              if (ex == null) {
                probe.getRef().tell("done", ActorRef.noSender());
              } else {
                probe.getRef().tell(ex.getMessage(), ActorRef.noSender());
              }
            });

    probe.expectMsgEquals("simulated err");
  }

  @Test
  public void mustBeAbleToUseToFuture() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input = Arrays.asList("A", "B", "C");
    CompletionStage<String> future = Source.from(input).runWith(Sink.<String>head(), system);
    String result = future.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals("A", result);
  }

  @Test
  public void mustBeAbleToUseSingle() throws Exception {
    // #source-single
    CompletionStage<List<String>> future = Source.single("A").runWith(Sink.seq(), system);
    CompletableFuture<List<String>> completableFuture = future.toCompletableFuture();
    completableFuture.thenAccept(result -> System.out.printf("collected elements: %s\n", result));
    // result list will contain exactly one element "A"

    // #source-single
    // DO NOT use get() directly in your production code!
    List<String> result = completableFuture.get();
    assertEquals(1, result.size());
    assertEquals("A", result.get(0));
  }

  @Test
  public void mustBeAbleToUsePrefixAndTail() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<Integer> input = Arrays.asList(1, 2, 3, 4, 5, 6);
    CompletionStage<Pair<List<Integer>, Source<Integer, NotUsed>>> future =
        Source.from(input)
            .prefixAndTail(3)
            .runWith(Sink.<Pair<List<Integer>, Source<Integer, NotUsed>>>head(), system);
    Pair<List<Integer>, Source<Integer, NotUsed>> result =
        future.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(Arrays.asList(1, 2, 3), result.first());

    CompletionStage<List<Integer>> tailFuture =
        result.second().limit(4).runWith(Sink.<Integer>seq(), system);
    List<Integer> tailResult = tailFuture.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(Arrays.asList(4, 5, 6), tailResult);
  }

  @Test
  public void mustBeAbleToUseConcatAllWithSources() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<Integer> input1 = Arrays.asList(1, 2, 3);
    final Iterable<Integer> input2 = Arrays.asList(4, 5);

    final List<Source<Integer, NotUsed>> mainInputs = new ArrayList<Source<Integer, NotUsed>>();
    mainInputs.add(Source.from(input1));
    mainInputs.add(Source.from(input2));

    CompletionStage<List<Integer>> future =
        Source.from(mainInputs)
            .<Integer, NotUsed>flatMapConcat(
                ConstantFun.<Source<Integer, NotUsed>>javaIdentityFunction())
            .grouped(6)
            .runWith(Sink.<List<Integer>>head(), system);

    List<Integer> result = future.toCompletableFuture().get(3, TimeUnit.SECONDS);

    assertEquals(Arrays.asList(1, 2, 3, 4, 5), result);
  }

  @Test
  public void mustBeAbleToUseFlatMapMerge() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<Integer> input1 = Arrays.asList(0, 1, 2, 3, 4, 5, 6, 7, 8, 9);
    final Iterable<Integer> input2 = Arrays.asList(10, 11, 12, 13, 14, 15, 16, 17, 18, 19);
    final Iterable<Integer> input3 = Arrays.asList(20, 21, 22, 23, 24, 25, 26, 27, 28, 29);
    final Iterable<Integer> input4 = Arrays.asList(30, 31, 32, 33, 34, 35, 36, 37, 38, 39);

    final List<Source<Integer, NotUsed>> mainInputs = new ArrayList<Source<Integer, NotUsed>>();
    mainInputs.add(Source.from(input1));
    mainInputs.add(Source.from(input2));
    mainInputs.add(Source.from(input3));
    mainInputs.add(Source.from(input4));

    CompletionStage<List<Integer>> future =
        Source.from(mainInputs)
            .flatMapMerge(3, ConstantFun.<Source<Integer, NotUsed>>javaIdentityFunction())
            .grouped(60)
            .runWith(Sink.<List<Integer>>head(), system);

    List<Integer> result = future.toCompletableFuture().get(3, TimeUnit.SECONDS);
    final Set<Integer> set = new HashSet<Integer>();
    for (Integer i : result) {
      set.add(i);
    }
    final Set<Integer> expected = new HashSet<Integer>();
    for (int i = 0; i < 40; ++i) {
      expected.add(i);
    }

    assertEquals(expected, set);
  }

  @Test
  public void mustBeAbleToUseBuffer() throws Exception {
    final TestKit probe = new TestKit(system);
    final List<String> input = Arrays.asList("A", "B", "C");
    final CompletionStage<List<String>> future =
        Source.from(input)
            .buffer(2, OverflowStrategy.backpressure())
            .grouped(4)
            .runWith(Sink.<List<String>>head(), system);

    List<String> result = future.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(input, result);
  }

  @Test
  public void mustBeAbleToUseConflate() throws Exception {
    final TestKit probe = new TestKit(system);
    final List<String> input = Arrays.asList("A", "B", "C");
    CompletionStage<String> future =
        Source.from(input)
            .conflateWithSeed(s -> s, (aggr, in) -> aggr + in)
            .runFold("", (aggr, in) -> aggr + in, system);
    String result = future.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals("ABC", result);

    final Flow<String, String, NotUsed> flow2 = Flow.of(String.class).conflate((a, b) -> a + b);

    CompletionStage<String> future2 =
        Source.from(input)
            .conflate((String a, String b) -> a + b)
            .runFold("", (a, b) -> a + b, system);
    String result2 = future2.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals("ABC", result2);
  }

  @Test
  public void mustBeAbleToUseExpand() throws Exception {
    final TestKit probe = new TestKit(system);
    final List<String> input = Arrays.asList("A", "B", "C");
    CompletionStage<String> future =
        Source.from(input)
            .expand(in -> Stream.iterate(in, i -> i).iterator())
            .runWith(Sink.<String>head(), system);
    String result = future.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals("A", result);
  }

  @Test
  public void mustProduceTicks() throws Exception {
    final TestKit probe = new TestKit(system);
    Source<String, Cancellable> tickSource =
        Source.tick(Duration.ofSeconds(1), Duration.ofMillis(500), "tick");
    @SuppressWarnings("unused")
    Cancellable cancellable =
        tickSource
            .to(
                Sink.foreach(
                    new Procedure<String>() {
                      public void apply(String elem) {
                        probe.getRef().tell(elem, ActorRef.noSender());
                      }
                    }))
            .run(system);
    probe.expectNoMessage(Duration.ofMillis(600));
    probe.expectMsgEquals("tick");
    probe.expectNoMessage(Duration.ofMillis(200));
    probe.expectMsgEquals("tick");
    probe.expectNoMessage(Duration.ofMillis(200));
    cancellable.cancel();
  }

  @Test
  @SuppressWarnings("unused")
  public void mustCompileMethodsWithJavaDuration() {
    Source<NotUsed, Cancellable> tickSource =
        Source.tick(Duration.ofSeconds(1), Duration.ofMillis(500), notUsed());
  }

  @Test
  public void mustBeAbleToUseMapFuture() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input = Arrays.asList("a", "b", "c");
    Source.from(input)
        .mapAsync(4, elem -> CompletableFuture.completedFuture(elem.toUpperCase()))
        .runForeach(elem -> probe.getRef().tell(elem, ActorRef.noSender()), system);
    probe.expectMsgEquals("A");
    probe.expectMsgEquals("B");
    probe.expectMsgEquals("C");
  }

  @Test
  public void mustBeAbleToUseCollectType() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<FlowSpec.Apple> input = Collections.singletonList(new FlowSpec.Apple());
    final Source<FlowSpec.Apple, ?> appleSource = Source.from(input);
    final Source<FlowSpec.Fruit, ?> fruitSource = appleSource.collectType(FlowSpec.Fruit.class);
    fruitSource
        .collectType(FlowSpec.Apple.class)
        .collectType(FlowSpec.Apple.class)
        .runForeach(
            (elem) -> {
              probe.getRef().tell(elem, ActorRef.noSender());
            },
            system);
    probe.expectMsgAnyClassOf(FlowSpec.Apple.class);
  }

  @Test
  public void mustWorkFromFuture() throws Exception {
    final Iterable<String> input = Arrays.asList("A", "B", "C");
    CompletionStage<String> future1 = Source.from(input).runWith(Sink.<String>head(), system);
    CompletionStage<String> future2 =
        Source.fromCompletionStage(future1).runWith(Sink.<String>head(), system);
    String result = future2.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals("A", result);
  }

  @Test
  public void mustWorkFromFutureVoid() throws Exception {
    CompletionStage<Void> future = CompletableFuture.completedFuture(null);
    CompletionStage<List<Void>> future2 =
        Source.fromCompletionStage(future).runWith(Sink.seq(), system);
    List<Void> result = future2.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(0, result.size());
  }

  @Test
  public void mustWorkFromRange() throws Exception {
    CompletionStage<List<Integer>> f =
        Source.range(0, 10).grouped(20).runWith(Sink.<List<Integer>>head(), system);
    final List<Integer> result = f.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(11, result.size());
    Integer counter = 0;
    for (Integer i : result) assertEquals(i, counter++);
  }

  @Test
  public void mustWorkFromRangeWithStep() throws Exception {
    CompletionStage<List<Integer>> f =
        Source.range(0, 10, 2).grouped(20).runWith(Sink.<List<Integer>>head(), system);
    final List<Integer> result = f.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(6, result.size());
    Integer counter = 0;
    for (Integer i : result) {
      assertEquals(i, counter);
      counter += 2;
    }
  }

  @Test
  public void mustRepeat() throws Exception {
    final CompletionStage<List<Integer>> f =
        Source.repeat(42).grouped(10000).runWith(Sink.<List<Integer>>head(), system);
    final List<Integer> result = f.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(result.size(), 10000);
    for (Integer i : result) assertEquals(i, (Integer) 42);
  }

  @Test
  public void mustRepeatForDocs() throws Exception {
    // #repeat
    Source<Integer, NotUsed> source = Source.repeat(42);
    CompletionStage<Done> f = source.take(4).runWith(Sink.foreach(System.out::println), system);
    // 42
    // 42
    // 42
    // 42
    // #repeat
    final Done result = f.toCompletableFuture().get(3, TimeUnit.SECONDS);
    assertEquals(Done.done(), result);
  }

  @Test
  public void mustBeAbleToUseQueue() throws Exception {
    final Pair<SourceQueueWithComplete<String>, CompletionStage<List<String>>> x =
        Flow.of(String.class).runWith(Source.queue(2, OverflowStrategy.fail()), Sink.seq(), system);
    final SourceQueueWithComplete<String> source = x.first();
    final CompletionStage<List<String>> result = x.second();
    source.offer("hello");
    source.offer("world");
    source.complete();
    assertEquals(
        result.toCompletableFuture().get(3, TimeUnit.SECONDS), Arrays.asList("hello", "world"));
  }

  @Test
  public void mustBeAbleToUseActorRefSource() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<Integer, ActorRef> actorRefSource = Source.actorRef(10, OverflowStrategy.fail());
    final ActorRef ref =
        actorRefSource
            .to(
                Sink.foreach(
                    new Procedure<Integer>() {
                      public void apply(Integer elem) {
                        probe.getRef().tell(elem, ActorRef.noSender());
                      }
                    }))
            .run(system);
    ref.tell(1, ActorRef.noSender());
    probe.expectMsgEquals(1);
    ref.tell(2, ActorRef.noSender());
    probe.expectMsgEquals(2);
    ref.tell(new Status.Success("ok"), ActorRef.noSender());
  }

  @Test
  public void mustBeAbleToUseStatefulMaponcat() throws Exception {
    final TestKit probe = new TestKit(system);
    final java.lang.Iterable<Integer> input = Arrays.asList(1, 2, 3, 4, 5);
    final Source<Integer, NotUsed> ints =
        Source.from(input)
            .statefulMapConcat(
                () -> {
                  int[] state = new int[] {0};
                  return (elem) -> {
                    List<Integer> list = new ArrayList<>(Collections.nCopies(state[0], elem));
                    state[0] = elem;
                    return list;
                  };
                });

    ints.runFold("", (acc, elem) -> acc + elem, system)
        .thenAccept(elem -> probe.getRef().tell(elem, ActorRef.noSender()));

    probe.expectMsgEquals("2334445555");
  }

  @Test
  public void mustBeAbleToUseIntersperse() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<String, NotUsed> source =
        Source.from(Arrays.asList("0", "1", "2", "3")).intersperse("[", ",", "]");

    final CompletionStage<Done> future =
        source.runWith(
            Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), system);

    probe.expectMsgEquals("[");
    probe.expectMsgEquals("0");
    probe.expectMsgEquals(",");
    probe.expectMsgEquals("1");
    probe.expectMsgEquals(",");
    probe.expectMsgEquals("2");
    probe.expectMsgEquals(",");
    probe.expectMsgEquals("3");
    probe.expectMsgEquals("]");
    future.toCompletableFuture().get(3, TimeUnit.SECONDS);
  }

  @Test
  public void mustBeAbleToUseIntersperseAndConcat() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<String, NotUsed> source =
        Source.from(Arrays.asList("0", "1", "2", "3")).intersperse(",");

    final CompletionStage<Done> future =
        Source.single(">> ")
            .concat(source)
            .runWith(Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), system);

    probe.expectMsgEquals(">> ");
    probe.expectMsgEquals("0");
    probe.expectMsgEquals(",");
    probe.expectMsgEquals("1");
    probe.expectMsgEquals(",");
    probe.expectMsgEquals("2");
    probe.expectMsgEquals(",");
    probe.expectMsgEquals("3");
    future.toCompletableFuture().get(3, TimeUnit.SECONDS);
  }

  @Test
  public void mustBeAbleToUseDropWhile() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<Integer, NotUsed> source =
        Source.from(Arrays.asList(0, 1, 2, 3))
            .dropWhile(
                new Predicate<Integer>() {
                  public boolean test(Integer elem) {
                    return elem < 2;
                  }
                });

    final CompletionStage<Done> future =
        source.runWith(
            Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), system);

    probe.expectMsgEquals(2);
    probe.expectMsgEquals(3);
    future.toCompletableFuture().get(3, TimeUnit.SECONDS);
  }

  @Test
  public void mustBeAbleToUseTakeWhile() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<Integer, NotUsed> source =
        Source.from(Arrays.asList(0, 1, 2, 3))
            .takeWhile(
                new Predicate<Integer>() {
                  public boolean test(Integer elem) {
                    return elem < 2;
                  }
                });

    final CompletionStage<Done> future =
        source.runWith(
            Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), system);

    probe.expectMsgEquals(0);
    probe.expectMsgEquals(1);

    Duration duration = Duration.ofMillis(200);

    probe.expectNoMessage(duration);
    future.toCompletableFuture().get(3, TimeUnit.SECONDS);
  }

  @Test
  public void mustBeAbleToRecover() throws Exception {
    final ManualProbe<Integer> publisherProbe = TestPublisher.manualProbe(true, system);
    final TestKit probe = new TestKit(system);

    final Source<Integer, NotUsed> source =
        Source.fromPublisher(publisherProbe)
            .map(
                elem -> {
                  if (elem == 1) throw new RuntimeException("ex");
                  else return elem;
                })
            .recover(new PFBuilder<Throwable, Integer>().matchAny(ex -> 0).build());

    final CompletionStage<Done> future =
        source.runWith(
            Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), system);
    final PublisherProbeSubscription<Integer> s = publisherProbe.expectSubscription();
    s.sendNext(0);
    probe.expectMsgEquals(0);
    s.sendNext(1);
    probe.expectMsgEquals(0);

    future.toCompletableFuture().get(3, TimeUnit.SECONDS);
  }

  @Test
  public void mustBeAbleToCombine() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<Integer, NotUsed> source1 = Source.from(Arrays.asList(0, 1));
    final Source<Integer, NotUsed> source2 = Source.from(Arrays.asList(2, 3));

    final Source<Integer, NotUsed> source =
        Source.combine(
            source1,
            source2,
            new ArrayList<Source<Integer, ?>>(),
            width -> Merge.<Integer>create(width));

    final CompletionStage<Done> future =
        source.runWith(
            Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), system);

    probe.expectMsgAllOf(0, 1, 2, 3);

    future.toCompletableFuture().get(3, TimeUnit.SECONDS);
  }

  @Test
  public void mustBeAbleToCombineMat() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<Integer, SourceQueueWithComplete<Integer>> source1 =
        Source.queue(1, OverflowStrategy.dropNew());
    final Source<Integer, NotUsed> source2 = Source.from(Arrays.asList(2, 3));

    // compiler to check the correct materialized value of type = SourceQueueWithComplete<Integer>
    // available
    final Source<Integer, SourceQueueWithComplete<Integer>> combined =
        Source.combineMat(
            source1,
            source2,
            width -> Concat.<Integer>create(width),
            Keep.left()); // Keep.left() (i.e. preserve queueSource's materialized value)

    SourceQueueWithComplete<Integer> queue =
        combined
            .toMat(
                Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), Keep.left())
            .run(system);

    queue.offer(0);
    queue.offer(1);
    queue.complete(); // complete queueSource so that combined with `Concat` pulls elements from
    // queueSource

    // elements from source1 (i.e. first of combined source) come first, then source2 elements, due
    // to `Concat`
    probe.expectMsgAllOf(0, 1, 2, 3);
  }

  @Test
  public void mustBeAbleToZipN() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<Integer, NotUsed> source1 = Source.from(Arrays.asList(0, 1));
    final Source<Integer, NotUsed> source2 = Source.from(Arrays.asList(2, 3));

    final List<Source<Integer, ?>> sources = Arrays.asList(source1, source2);

    final Source<List<Integer>, ?> source = Source.zipN(sources);

    final CompletionStage<Done> future =
        source.runWith(
            Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), system);

    probe.expectMsgAllOf(Arrays.asList(0, 2), Arrays.asList(1, 3));

    future.toCompletableFuture().get(3, TimeUnit.SECONDS);
  }

  @Test
  public void mustBeAbleToZipWithN() throws Exception {
    final TestKit probe = new TestKit(system);
    final Source<Integer, NotUsed> source1 = Source.from(Arrays.asList(0, 1));
    final Source<Integer, NotUsed> source2 = Source.from(Arrays.asList(2, 3));

    final List<Source<Integer, ?>> sources = Arrays.asList(source1, source2);

    final Source<Boolean, ?> source =
        Source.zipWithN(list -> new Boolean(list.contains(0)), sources);

    final CompletionStage<Done> future =
        source.runWith(
            Sink.foreach(elem -> probe.getRef().tell(elem, ActorRef.noSender())), system);

    probe.expectMsgAllOf(Boolean.TRUE, Boolean.FALSE);

    future.toCompletableFuture().get(3, TimeUnit.SECONDS);
  }

  @Test
  public void mustBeAbleToZipAll() {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input1 =
        Arrays.asList("A", "B", "C", "D", "new kid on the block1", "second newbie");
    final Iterable<Integer> input2 = Arrays.asList(1, 2, 3, 4);

    Source<String, NotUsed> src1 = Source.from(input1);
    Source<Integer, NotUsed> src2 = Source.from(input2);
    Sink<Pair<String, Integer>, CompletionStage<Done>> sink =
        Sink.foreach(
            new Procedure<Pair<String, Integer>>() {
              @Override
              public void apply(Pair<String, Integer> param) throws Exception {
                probe.getRef().tell(param, ActorRef.noSender());
              }
            });
    Source<Pair<String, Integer>, NotUsed> zippedSrc = src1.zipAll(src2, "MISSING", -1);
    zippedSrc.runWith(sink, system);

    List<Object> output = probe.receiveN(6);
    List<Pair<String, Integer>> expected =
        Arrays.asList(
            new Pair<String, Integer>("A", 1),
            new Pair<String, Integer>("B", 2),
            new Pair<String, Integer>("C", 3),
            new Pair<String, Integer>("D", 4),
            new Pair<String, Integer>("new kid on the block1", -1),
            new Pair<String, Integer>("second newbie", -1));
    assertEquals(expected, output);
  }

  @Test
  public void createEmptySource() throws Exception {
    List<Integer> actual =
        Source.empty(Integer.class).runWith(Sink.seq(), system).toCompletableFuture().get();
    assertThat(actual, is(Collections.emptyList()));
  }

  @Test
  public void cycleSourceMustGenerateSameSequenceInRepeatedFashion() throws Exception {
    // #cycle
    final Source<Integer, NotUsed> source = Source.cycle(() -> Arrays.asList(1, 2, 3).iterator());
    CompletionStage<List<Integer>> result = source.grouped(9).runWith(Sink.head(), system);
    List<Integer> emittedValues = result.toCompletableFuture().get();
    assertThat(emittedValues, is(Arrays.asList(1, 2, 3, 1, 2, 3, 1, 2, 3)));
    // #cycle
  }

  @Test(expected = IllegalArgumentException.class)
  public void cycleSourceMustThrow() throws Throwable {

    try {
      // #cycle-error
      Iterator<Integer> emptyIterator = Collections.<Integer>emptyList().iterator();
      Source.cycle(() -> emptyIterator)
          .runWith(Sink.head(), system)
          // stream will be terminated with IllegalArgumentException
          // #cycle-error
          .toCompletableFuture()
          .get();
    } catch (ExecutionException e) {
      throw e.getCause();
    }
  }

  @Test
  public void mustBeAbleToUseMerge() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
    final Iterable<String> input2 = Arrays.asList("D", "E", "F");

    Source.from(input1)
        .merge(Source.from(input2))
        .runForeach(
            new Procedure<String>() {
              public void apply(String elem) {
                probe.getRef().tell(elem, ActorRef.noSender());
              }
            },
            system);

    probe.expectMsgAllOf("A", "B", "C", "D", "E", "F");
  }

  @Test
  public void mustBeAbleToUseZipWith() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
    final Iterable<String> input2 = Arrays.asList("D", "E", "F");

    Source.from(input1)
        .zipWith(
            Source.from(input2),
            new Function2<String, String, String>() {
              public String apply(String s1, String s2) {
                return s1 + "-" + s2;
              }
            })
        .runForeach(
            new Procedure<String>() {
              public void apply(String elem) {
                probe.getRef().tell(elem, ActorRef.noSender());
              }
            },
            system);

    probe.expectMsgEquals("A-D");
    probe.expectMsgEquals("B-E");
    probe.expectMsgEquals("C-F");
  }

  @Test
  public void mustBeAbleToUseZip() throws Exception {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
    final Iterable<String> input2 = Arrays.asList("D", "E", "F");

    Source.from(input1)
        .zip(Source.from(input2))
        .runForeach(
            new Procedure<Pair<String, String>>() {
              public void apply(Pair<String, String> elem) {
                probe.getRef().tell(elem, ActorRef.noSender());
              }
            },
            system);

    probe.expectMsgEquals(new Pair<String, String>("A", "D"));
    probe.expectMsgEquals(new Pair<String, String>("B", "E"));
    probe.expectMsgEquals(new Pair<String, String>("C", "F"));
  }

  @Test
  public void mustBeAbleToUseMerge2() {
    final TestKit probe = new TestKit(system);
    final Iterable<String> input1 = Arrays.asList("A", "B", "C");
    final Iterable<String> input2 = Arrays.asList("D", "E", "F");

    Source.from(input1)
        .merge(Source.from(input2))
        .runForeach(
            new Procedure<String>() {
              public void apply(String elem) {
                probe.getRef().tell(elem, ActorRef.noSender());
              }
            },
            system);

    probe.expectMsgAllOf("A", "B", "C", "D", "E", "F");
  }

  @Test
  public void mustBeAbleToUseInitialTimeout() throws Throwable {
    try {
      try {
        Source.maybe()
            .initialTimeout(Duration.ofSeconds(1))
            .runWith(Sink.head(), system)
            .toCompletableFuture()
            .get(3, TimeUnit.SECONDS);
        org.junit.Assert.fail("A TimeoutException was expected");
      } catch (ExecutionException e) {
        throw e.getCause();
      }
    } catch (TimeoutException e) {
      // expected
    }
  }

  @Test
  public void mustBeAbleToUseCompletionTimeout() throws Throwable {
    try {
      try {
        Source.maybe()
            .completionTimeout(Duration.ofSeconds(1))
            .runWith(Sink.head(), system)
            .toCompletableFuture()
            .get(3, TimeUnit.SECONDS);
        org.junit.Assert.fail("A TimeoutException was expected");
      } catch (ExecutionException e) {
        throw e.getCause();
      }
    } catch (TimeoutException e) {
      // expected
    }
  }

  @Test
  public void mustBeAbleToUseIdleTimeout() throws Throwable {
    try {
      try {
        Source.maybe()
            .idleTimeout(Duration.ofSeconds(1))
            .runWith(Sink.head(), system)
            .toCompletableFuture()
            .get(3, TimeUnit.SECONDS);
        org.junit.Assert.fail("A TimeoutException was expected");
      } catch (ExecutionException e) {
        throw e.getCause();
      }
    } catch (TimeoutException e) {
      // expected
    }
  }

  @Test
  public void mustBeAbleToUseIdleInject() throws Exception {
    Integer result =
        Source.<Integer>maybe()
            .keepAlive(Duration.ofSeconds(1), () -> 0)
            .takeWithin(Duration.ofMillis(1500))
            .runWith(Sink.head(), system)
            .toCompletableFuture()
            .get(3, TimeUnit.SECONDS);

    assertEquals((Object) 0, result);
  }

  public void mustSuitablyOverrideAttributeHandlingMethods() {
    @SuppressWarnings("unused")
    final Source<Integer, NotUsed> f =
        Source.single(42)
            .withAttributes(Attributes.name(""))
            .addAttributes(Attributes.asyncBoundary())
            .named("");
  }

  @Test
  public void mustBeAbleToUseThrottle() throws Exception {
    Integer result =
        Source.from(Arrays.asList(0, 1, 2))
            .throttle(10, Duration.ofSeconds(1), 10, ThrottleMode.shaping())
            .throttle(10, Duration.ofSeconds(1), 10, ThrottleMode.enforcing())
            .runWith(Sink.head(), system)
            .toCompletableFuture()
            .get(3, TimeUnit.SECONDS);

    assertEquals((Object) 0, result);
  }

  @Test
  public void mustBeAbleToUseAlsoTo() {
    final Source<Integer, NotUsed> f = Source.<Integer>empty().alsoTo(Sink.ignore());
    final Source<Integer, String> f2 =
        Source.<Integer>empty().alsoToMat(Sink.ignore(), (i, n) -> "foo");
  }

  @Test
  public void mustBeAbleToUseDivertTo() {
    final Source<Integer, NotUsed> f = Source.<Integer>empty().divertTo(Sink.ignore(), e -> true);
    final Source<Integer, String> f2 =
        Source.<Integer>empty().divertToMat(Sink.ignore(), e -> true, (i, n) -> "foo");
  }

  @Test
  public void mustBeAbleToUsePreMaterialize() {
    final Pair<NotUsed, Source<Integer, NotUsed>> p =
        Source.<Integer>empty().preMaterialize(system);
  }

  @Test
  public void mustBeAbleToConvertToJavaInJava() {
    final akka.stream.scaladsl.Source<Integer, NotUsed> scalaSource =
        akka.stream.scaladsl.Source.empty();
    Source<Integer, NotUsed> javaSource = scalaSource.asJava();
  }

  @Test
  public void mustProperlyIterate() throws Exception {
    final Creator<Iterator<Boolean>> input = () -> Iterables.cycle(false, true).iterator();

    final CompletableFuture<List<Boolean>> future =
        Source.fromIterator(input).grouped(10).runWith(Sink.head(), system).toCompletableFuture();

    assertArrayEquals(
        new Boolean[] {false, true, false, true, false, true, false, true, false, true},
        future.get(1, TimeUnit.SECONDS).toArray());
  }

  @Test
  public void mustRunSourceAndIgnoreElementsItOutputsAndOnlySignalTheCompletion() {
    final Iterator<Integer> iterator = IntStream.range(1, 10).iterator();
    final Creator<Iterator<Integer>> input = () -> iterator;
    final Done completion =
        Source.fromIterator(input).map(it -> it * 10).run(system).toCompletableFuture().join();
    assertEquals(completion, Done.getInstance());
  }

  @Test
  public void mustRunSourceAndIgnoreElementsItOutputsAndOnlySignalTheCompletionWithMaterializer() {
    final Materializer materializer = Materializer.createMaterializer(system);
    final Iterator<Integer> iterator = IntStream.range(1, 10).iterator();
    final Creator<Iterator<Integer>> input = () -> iterator;
    final Done completion =
        Source.fromIterator(input)
            .map(it -> it * 10)
            .run(materializer)
            .toCompletableFuture()
            .join();
    assertEquals(completion, Done.getInstance());
  }
}