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.*;
  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.SpscLinkedArrayQueue;
  
  /**
   * Maps upstream values into MaybeSources and merges their signals into one sequence.
   * @param <T> the source value type
   * @param <R> the result value type
   */
  public final class ObservableFlatMapMaybe<T, R> extends AbstractObservableWithUpstream<T, R> {
  
      final Function<? super T, ? extends MaybeSource<? extends R>> mapper;
  
      final boolean delayErrors;
  
      public ObservableFlatMapMaybe(ObservableSource<T> source, Function<? super T, ? extends MaybeSource<? extends R>> mapper,
              boolean delayError) {
          super(source);
          this.mapper = mapper;
          this.delayErrors = delayError;
      }
  
      @Override
      protected void subscribeActual(Observer<? super R> observer) {
          source.subscribe(new FlatMapMaybeObserver<>(observer, mapper, delayErrors));
      }
  
      static final class FlatMapMaybeObserver<T, R>
      extends AtomicInteger
      implements Observer<T>, Disposable {
  
          private static final long serialVersionUID = 8600231336733376951L;
  
          final Observer<? super R> downstream;
  
          final boolean delayErrors;
  
          final CompositeDisposable set;
  
          final AtomicInteger active;
  
          final AtomicThrowable errors;
  
          final Function<? super T, ? extends MaybeSource<? extends R>> mapper;
  
          final AtomicReference<SpscLinkedArrayQueue<R>> queue;
  
          Disposable upstream;
  
          volatile boolean cancelled;
  
          FlatMapMaybeObserver(Observer<? super R> actual,
                  Function<? super T, ? extends MaybeSource<? extends R>> mapper, boolean delayErrors) {
              this.downstream = actual;
              this.mapper = mapper;
              this.delayErrors = delayErrors;
              this.set = new CompositeDisposable();
              this.errors = new AtomicThrowable();
              this.active = new AtomicInteger(1);
              this.queue = new AtomicReference<>();
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
  
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(T t) {
              MaybeSource<? extends R> ms;
  
              try {
                  ms = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null MaybeSource");
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  upstream.dispose();
                  onError(ex);
                  return;
              }
  
              active.getAndIncrement();
  
              InnerObserver inner = new InnerObserver();
  
              if (!cancelled && set.add(inner)) {
                  ms.subscribe(inner);
              }
          }
  
          @Override
          public void onError(Throwable t) {
              active.decrementAndGet();
              if (errors.tryAddThrowableOrReport(t)) {
                  if (!delayErrors) {
                      set.dispose();
                  }
                  drain();
              }
          }
  
          @Override
          public void onComplete() {
              active.decrementAndGet();
              drain();
          }
  
          @Override
          public void dispose() {
              cancelled = true;
              upstream.dispose();
              set.dispose();
              errors.tryTerminateAndReport();
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
  
          void innerSuccess(InnerObserver inner, R value) {
              set.delete(inner);
              if (get() == 0 && compareAndSet(0, 1)) {
                  downstream.onNext(value);
  
                  boolean d = active.decrementAndGet() == 0;
                  SpscLinkedArrayQueue<R> q = queue.get();
  
                  if (d && (q == null || q.isEmpty())) {
                      errors.tryTerminateConsumer(downstream);
                      return;
                  }
                  if (decrementAndGet() == 0) {
                      return;
                  }
              } else {
                  SpscLinkedArrayQueue<R> q = getOrCreateQueue();
                  synchronized (q) {
                      q.offer(value);
                  }
                  active.decrementAndGet();
                  if (getAndIncrement() != 0) {
                      return;
                  }
              }
              drainLoop();
          }
  
          SpscLinkedArrayQueue<R> getOrCreateQueue() {
              SpscLinkedArrayQueue<R> current = queue.get();
              if (current != null) {
                  return current;
              }
              current = new SpscLinkedArrayQueue<>(Observable.bufferSize());
              if (queue.compareAndSet(null, current)) {
                  return current;
              }
              return queue.get();
          }
  
          void innerError(InnerObserver inner, Throwable e) {
              set.delete(inner);
              if (errors.tryAddThrowableOrReport(e)) {
                  if (!delayErrors) {
                      upstream.dispose();
                      set.dispose();
                  }
                  active.decrementAndGet();
                  drain();
              }
          }
  
          void innerComplete(InnerObserver inner) {
              set.delete(inner);
  
              if (get() == 0 && compareAndSet(0, 1)) {
                  boolean d = active.decrementAndGet() == 0;
                  SpscLinkedArrayQueue<R> q = queue.get();
  
                  if (d && (q == null || q.isEmpty())) {
                      errors.tryTerminateConsumer(downstream);
                      return;
                  }
                  if (decrementAndGet() == 0) {
                      return;
                  }
                  drainLoop();
              } else {
                  active.decrementAndGet();
                  drain();
              }
          }
  
          void drain() {
              if (getAndIncrement() == 0) {
                  drainLoop();
              }
          }
  
          void clear() {
              SpscLinkedArrayQueue<R> q = queue.get();
              if (q != null) {
                  q.clear();
              }
          }
  
          void drainLoop() {
              int missed = 1;
              Observer<? super R> a = downstream;
              AtomicInteger n = active;
              AtomicReference<SpscLinkedArrayQueue<R>> qr = queue;
  
              for (;;) {
                  for (;;) {
                      if (cancelled) {
                          clear();
                          return;
                      }
  
                      if (!delayErrors) {
                          Throwable ex = errors.get();
                          if (ex != null) {
                              clear();
                              errors.tryTerminateConsumer(a);
                              return;
                          }
                      }
  
                      boolean d = n.get() == 0;
                      SpscLinkedArrayQueue<R> q = qr.get();
                      R v = q != null ? q.poll() : null;
                      boolean empty = v == null;
  
                      if (d && empty) {
                          errors.tryTerminateConsumer(a);
                          return;
                      }
  
                      if (empty) {
                          break;
                      }
  
                      a.onNext(v);
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          final class InnerObserver extends AtomicReference<Disposable>
          implements MaybeObserver<R>, Disposable {
              private static final long serialVersionUID = -502562646270949838L;
  
              @Override
              public void onSubscribe(Disposable d) {
                  DisposableHelper.setOnce(this, d);
              }
  
              @Override
              public void onSuccess(R value) {
                  innerSuccess(this, value);
              }
  
              @Override
              public void onError(Throwable e) {
                  innerError(this, e);
              }
  
              @Override
              public void onComplete() {
                  innerComplete(this);
              }
  
              @Override
              public boolean isDisposed() {
                  return DisposableHelper.isDisposed(get());
              }
  
              @Override
              public void dispose() {
                  DisposableHelper.dispose(this);
              }
          }
      }
  }
  