code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.rxjava3.internal.jdk8;
  
  import java.util.*;
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.stream.Stream;
  
  import io.reactivex.rxjava3.annotations.NonNull;
  import io.reactivex.rxjava3.core.Observable;
  import io.reactivex.rxjava3.core.Observer;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.internal.disposables.*;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Maps the upstream values onto {@link Stream}s and emits their items in order to the downstream.
   *
   * @param <T> the upstream element type
   * @param <R> the inner {@code Stream} and result element type
   * @since 3.0.0
   */
  public final class ObservableFlatMapStream<T, R> extends Observable<R> {
  
      final Observable<T> source;
  
      final Function<? super T, ? extends Stream<? extends R>> mapper;
  
      public ObservableFlatMapStream(Observable<T> source, Function<? super T, ? extends Stream<? extends R>> mapper) {
          this.source = source;
          this.mapper = mapper;
      }
  
      @Override
      protected void subscribeActual(Observer<? super R> observer) {
          if (source instanceof Supplier) {
              Stream<? extends R> stream = null;
              try {
                  @SuppressWarnings("unchecked")
                  T t = ((Supplier<T>)source).get();
                  if (t != null) {
                      stream = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null Stream");
                  }
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  EmptyDisposable.error(ex, observer);
                  return;
              }
  
              if (stream != null) {
                  ObservableFromStream.subscribeStream(observer, stream);
              } else {
                  EmptyDisposable.complete(observer);
              }
          } else {
              source.subscribe(new FlatMapStreamObserver<>(observer, mapper));
          }
      }
  
      static final class FlatMapStreamObserver<T, R> extends AtomicInteger
      implements Observer<T>, Disposable {
  
          private static final long serialVersionUID = -5127032662980523968L;
  
          final Observer<? super R> downstream;
  
          final Function<? super T, ? extends Stream<? extends R>> mapper;
  
          Disposable upstream;
  
          volatile boolean disposed;
  
          boolean done;
  
          FlatMapStreamObserver(Observer<? super R> downstream, Function<? super T, ? extends Stream<? extends R>> mapper) {
              this.downstream = downstream;
              this.mapper = mapper;
          }
  
          @Override
          public void onSubscribe(@NonNull Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
  
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(@NonNull T t) {
              if (done) {
                  return;
              }
              try {
                  try (Stream<? extends R> stream = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null Stream")) {
                      Iterator<? extends R> it = stream.iterator();
                      while (it.hasNext()) {
                          if (disposed) {
                              done = true;
                              break;
                          }
                          R value = Objects.requireNonNull(it.next(), "The Stream's Iterator.next returned a null value");
                          if (disposed) {
                              done = true;
                              break;
                          }
                          downstream.onNext(value);
                          if (disposed) {
                              done = true;
                              break;
                          }
                      }
                  }
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  upstream.dispose();
                  onError(ex);
              }
          }
  
          @Override
          public void onError(@NonNull Throwable e) {
              if (done) {
                  RxJavaPlugins.onError(e);
              } else {
                  done = true;
                  downstream.onError(e);
              }
          }
  
          @Override
          public void onComplete() {
              if (!done) {
                  done = true;
                  downstream.onComplete();
              }
          }
  
          @Override
          public void dispose() {
              disposed = true;
              upstream.dispose();
          }
  
          @Override
          public boolean isDisposed() {
              return disposed;
          }
      }
  }
  