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.operators.observable;
  
  import java.util.Objects;
  import java.util.concurrent.atomic.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.Function;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.util.AtomicThrowable;
  import io.reactivex.rxjava3.operators.QueueDisposable;
  import io.reactivex.rxjava3.operators.SimpleQueue;
  import io.reactivex.rxjava3.operators.SpscLinkedArrayQueue;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  public final class ObservableSwitchMap<T, R> extends AbstractObservableWithUpstream<T, R> {
      final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
      final int bufferSize;
  
      final boolean delayErrors;
  
      public ObservableSwitchMap(ObservableSource<T> source,
                                 Function<? super T, ? extends ObservableSource<? extends R>> mapper, int bufferSize,
                                         boolean delayErrors) {
          super(source);
          this.mapper = mapper;
          this.bufferSize = bufferSize;
          this.delayErrors = delayErrors;
      }
  
      @Override
      public void subscribeActual(Observer<? super R> t) {
  
          if (ObservableScalarXMap.tryScalarXMapSubscribe(source, t, mapper)) {
              return;
          }
  
          source.subscribe(new SwitchMapObserver<>(t, mapper, bufferSize, delayErrors));
      }
  
      static final class SwitchMapObserver<T, R> extends AtomicInteger implements Observer<T>, Disposable {
  
          private static final long serialVersionUID = -3491074160481096299L;
          final Observer<? super R> downstream;
          final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
          final int bufferSize;
  
          final boolean delayErrors;
  
          final AtomicThrowable errors;
  
          volatile boolean done;
  
          volatile boolean cancelled;
  
          Disposable upstream;
  
          final AtomicReference<SwitchMapInnerObserver<T, R>> active = new AtomicReference<>();
  
          static final SwitchMapInnerObserver<Object, Object> CANCELLED;
          static {
              CANCELLED = new SwitchMapInnerObserver<>(null, -1L, 1);
              CANCELLED.cancel();
          }
  
          volatile long unique;
  
          SwitchMapObserver(Observer<? super R> actual,
                  Function<? super T, ? extends ObservableSource<? extends R>> mapper, int bufferSize,
                          boolean delayErrors) {
              this.downstream = actual;
              this.mapper = mapper;
              this.bufferSize = bufferSize;
              this.delayErrors = delayErrors;
              this.errors = new AtomicThrowable();
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(T t) {
              long c = unique + 1;
              unique = c;
  
              SwitchMapInnerObserver<T, R> inner = active.get();
              if (inner != null) {
                  inner.cancel();
              }
  
              ObservableSource<? extends R> p;
              try {
                  p = Objects.requireNonNull(mapper.apply(t), "The ObservableSource returned is null");
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  upstream.dispose();
                  onError(e);
                  return;
              }
  
              SwitchMapInnerObserver<T, R> nextInner = new SwitchMapInnerObserver<>(this, c, bufferSize);
  
              for (;;) {
                  inner = active.get();
                  if (inner == CANCELLED) {
                      break;
                  }
                  if (active.compareAndSet(inner, nextInner)) {
                      p.subscribe(nextInner);
                      break;
                  }
              }
          }
  
          @Override
          public void onError(Throwable t) {
              if (!done && errors.tryAddThrowable(t)) {
                  if (!delayErrors) {
                      disposeInner();
                  }
                  done = true;
                  drain();
              } else {
                  RxJavaPlugins.onError(t);
              }
          }
  
          @Override
          public void onComplete() {
              if (!done) {
                  done = true;
                  drain();
              }
          }
  
          @Override
          public void dispose() {
              if (!cancelled) {
                  cancelled = true;
                  upstream.dispose();
                  disposeInner();
  
                  errors.tryTerminateAndReport();
              }
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
  
          @SuppressWarnings("unchecked")
          void disposeInner() {
              SwitchMapInnerObserver<T, R> a = active.getAndSet((SwitchMapInnerObserver<T, R>)CANCELLED);
              if (a != null) {
                  a.cancel();
              }
          }
  
          void drain() {
              if (getAndIncrement() != 0) {
                  return;
              }
  
              final Observer<? super R> a = downstream;
              final AtomicReference<SwitchMapInnerObserver<T, R>> active = this.active;
              final boolean delayErrors = this.delayErrors;
  
              int missing = 1;
  
              for (;;) {
  
                  if (cancelled) {
                      return;
                  }
  
                  if (done) {
                      boolean empty = active.get() == null;
                      if (delayErrors) {
                          if (empty) {
                              Throwable ex = errors.get();
                              if (ex != null) {
                                  a.onError(ex);
                              } else {
                                  a.onComplete();
                              }
                              return;
                          }
                      } else {
                          Throwable ex = errors.get();
                          if (ex != null) {
                              errors.tryTerminateConsumer(a);
                              return;
                          }
                          if (empty) {
                              a.onComplete();
                              return;
                          }
                      }
                  }
  
                  SwitchMapInnerObserver<T, R> inner = active.get();
  
                  if (inner != null) {
                      SimpleQueue<R> q = inner.queue;
  
                      if (q != null) {
  
                          boolean retry = false;
  
                          for (;;) {
                              if (cancelled) {
                                  return;
                              }
                              if (inner != active.get()) {
                                  retry = true;
                                  break;
                              }
  
                              if (!delayErrors) {
                                  Throwable ex = errors.get();
                                  if (ex != null) {
                                      errors.tryTerminateConsumer(a);
                                      return;
                                  }
                              }
  
                              boolean d = inner.done;
                              R v;
  
                              try {
                                  v = q.poll();
                              } catch (Throwable ex) {
                                  Exceptions.throwIfFatal(ex);
                                  errors.tryAddThrowableOrReport(ex);
                                  active.compareAndSet(inner, null);
                                  if (!delayErrors) {
                                      disposeInner();
                                      upstream.dispose();
                                      done = true;
                                  } else {
                                      inner.cancel();
                                  }
                                  v = null;
                                  retry = true;
                              }
                              boolean empty = v == null;
  
                              if (d && empty) {
                                  active.compareAndSet(inner, null);
                                  retry = true;
                                  break;
                              }
  
                              if (empty) {
                                  break;
                              }
  
                              a.onNext(v);
                          }
  
                          if (retry) {
                              continue;
                          }
                      }
                  }
  
                  missing = addAndGet(-missing);
                  if (missing == 0) {
                      break;
                  }
              }
          }
  
          void innerError(SwitchMapInnerObserver<T, R> inner, Throwable ex) {
              if (inner.index == unique && errors.tryAddThrowable(ex)) {
                  if (!delayErrors) {
                      upstream.dispose();
                      done = true;
                  }
                  inner.done = true;
                  drain();
              } else {
                  RxJavaPlugins.onError(ex);
              }
          }
      }
  
      static final class SwitchMapInnerObserver<T, R> extends AtomicReference<Disposable> implements Observer<R> {
  
          private static final long serialVersionUID = 3837284832786408377L;
          final SwitchMapObserver<T, R> parent;
          final long index;
  
          final int bufferSize;
  
          volatile SimpleQueue<R> queue;
  
          volatile boolean done;
  
          SwitchMapInnerObserver(SwitchMapObserver<T, R> parent, long index, int bufferSize) {
              this.parent = parent;
              this.index = index;
              this.bufferSize = bufferSize;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.setOnce(this, d)) {
                  if (d instanceof QueueDisposable) {
                      @SuppressWarnings("unchecked")
                      QueueDisposable<R> qd = (QueueDisposable<R>) d;
  
                      int m = qd.requestFusion(QueueDisposable.ANY | QueueDisposable.BOUNDARY);
                      if (m == QueueDisposable.SYNC) {
                          queue = qd;
                          done = true;
                          parent.drain();
                          return;
                      }
                      if (m == QueueDisposable.ASYNC) {
                          queue = qd;
                          return;
                      }
                  }
  
                  queue = new SpscLinkedArrayQueue<>(bufferSize);
              }
          }
  
          @Override
          public void onNext(R t) {
              if (index == parent.unique) {
                  if (t != null) {
                      queue.offer(t);
                  }
                  parent.drain();
              }
          }
  
          @Override
          public void onError(Throwable t) {
              parent.innerError(this, t);
          }
  
          @Override
          public void onComplete() {
              if (index == parent.unique) {
                  done = true;
                  parent.drain();
              }
          }
  
          public void cancel() {
              DisposableHelper.dispose(this);
          }
      }
  }
  