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.maybe;
  
  import java.util.Iterator;
  import java.util.Objects;
  import java.util.concurrent.atomic.*;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.internal.disposables.SequentialDisposable;
  import io.reactivex.rxjava3.internal.subscriptions.*;
  import io.reactivex.rxjava3.internal.util.*;
  
  /**
   * Concatenate values of each MaybeSource provided by an Iterable.
   *
   * @param <T> the value type
   */
  public final class MaybeConcatIterable<T> extends Flowable<T> {
  
      final Iterable<? extends MaybeSource<? extends T>> sources;
  
      public MaybeConcatIterable(Iterable<? extends MaybeSource<? extends T>> sources) {
          this.sources = sources;
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super T> s) {
  
          Iterator<? extends MaybeSource<? extends T>> it;
  
          try {
              it = Objects.requireNonNull(sources.iterator(), "The sources Iterable returned a null Iterator");
          } catch (Throwable ex) {
              Exceptions.throwIfFatal(ex);
              EmptySubscription.error(ex, s);
              return;
          }
  
          ConcatMaybeObserver<T> parent = new ConcatMaybeObserver<>(s, it);
          s.onSubscribe(parent);
          parent.drain();
      }
  
      static final class ConcatMaybeObserver<T>
      extends AtomicInteger
      implements MaybeObserver<T>, Subscription {
  
          private static final long serialVersionUID = 3520831347801429610L;
  
          final Subscriber<? super T> downstream;
  
          final AtomicLong requested;
  
          final AtomicReference<Object> current;
  
          final SequentialDisposable disposables;
  
          final Iterator<? extends MaybeSource<? extends T>> sources;
  
          long produced;
  
          ConcatMaybeObserver(Subscriber<? super T> actual, Iterator<? extends MaybeSource<? extends T>> sources) {
              this.downstream = actual;
              this.sources = sources;
              this.requested = new AtomicLong();
              this.disposables = new SequentialDisposable();
              this.current = new AtomicReference<>(NotificationLite.COMPLETE); // as if a previous completed
          }
  
          @Override
          public void request(long n) {
              if (SubscriptionHelper.validate(n)) {
                  BackpressureHelper.add(requested, n);
                  drain();
              }
          }
  
          @Override
          public void cancel() {
              disposables.dispose();
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              disposables.replace(d);
          }
  
          @Override
          public void onSuccess(T value) {
              current.lazySet(value);
              drain();
          }
  
          @Override
          public void onError(Throwable e) {
              downstream.onError(e);
          }
  
          @Override
          public void onComplete() {
              current.lazySet(NotificationLite.COMPLETE);
              drain();
          }
  
          @SuppressWarnings("unchecked")
          void drain() {
              if (getAndIncrement() != 0) {
                  return;
              }
  
              AtomicReference<Object> c = current;
              Subscriber<? super T> a = downstream;
              Disposable cancelled = disposables;
  
              for (;;) {
                  if (cancelled.isDisposed()) {
                      c.lazySet(null);
                      return;
                  }
  
                  Object o = c.get();
  
                  if (o != null) {
                      boolean goNextSource;
                      if (o != NotificationLite.COMPLETE) {
                          long p = produced;
                          if (p != requested.get()) {
                              produced = p + 1;
                              c.lazySet(null);
                              goNextSource = true;
  
                              a.onNext((T)o);
                          } else {
                              goNextSource = false;
                          }
                      } else {
                          goNextSource = true;
                          c.lazySet(null);
                      }
  
                      if (goNextSource && !cancelled.isDisposed()) {
                          boolean b;
  
                          try {
                              b = sources.hasNext();
                          } catch (Throwable ex) {
                              Exceptions.throwIfFatal(ex);
                              a.onError(ex);
                              return;
                          }
  
                          if (b) {
                              MaybeSource<? extends T> source;
  
                              try {
                                  source = Objects.requireNonNull(sources.next(), "The source Iterator returned a null MaybeSource");
                              } catch (Throwable ex) {
                                  Exceptions.throwIfFatal(ex);
                                  a.onError(ex);
                                  return;
                              }
  
                              source.subscribe(this);
                          } else {
                              a.onComplete();
                          }
                      }
                  }
  
                  if (decrementAndGet() == 0) {
                      break;
                  }
              }
          }
      }
  }
  