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.flowable;
  
  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.*;
  import io.reactivex.rxjava3.functions.Function;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.internal.util.BackpressureHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  import io.reactivex.rxjava3.subscribers.*;
  
  public final class FlowableDebounce<T, U> extends AbstractFlowableWithUpstream<T, T> {
      final Function<? super T, ? extends Publisher<U>> debounceSelector;
  
      public FlowableDebounce(Flowable<T> source, Function<? super T, ? extends Publisher<U>> debounceSelector) {
          super(source);
          this.debounceSelector = debounceSelector;
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super T> s) {
          source.subscribe(new DebounceSubscriber<>(new SerializedSubscriber<>(s), debounceSelector));
      }
  
      static final class DebounceSubscriber<T, U> extends AtomicLong
      implements FlowableSubscriber<T>, Subscription {
  
          private static final long serialVersionUID = 6725975399620862591L;
          final Subscriber<? super T> downstream;
          final Function<? super T, ? extends Publisher<U>> debounceSelector;
  
          Subscription upstream;
  
          final AtomicReference<Disposable> debouncer = new AtomicReference<>();
  
          volatile long index;
  
          boolean done;
  
          DebounceSubscriber(Subscriber<? super T> actual,
                  Function<? super T, ? extends Publisher<U>> debounceSelector) {
              this.downstream = actual;
              this.debounceSelector = debounceSelector;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
                  downstream.onSubscribe(this);
                  s.request(Long.MAX_VALUE);
              }
          }
  
          @Override
          public void onNext(T t) {
              if (done) {
                  return;
              }
  
              long idx = index + 1;
              index = idx;
  
              Disposable d = debouncer.get();
              if (d != null) {
                  d.dispose();
              }
  
              Publisher<U> p;
  
              try {
                  p = Objects.requireNonNull(debounceSelector.apply(t), "The publisher supplied is null");
              } catch (Throwable e) {
                  Exceptions.throwIfFatal(e);
                  cancel();
                  downstream.onError(e);
                  return;
              }
  
              DebounceInnerSubscriber<T, U> dis = new DebounceInnerSubscriber<>(this, idx, t);
  
              if (debouncer.compareAndSet(d, dis)) {
                  p.subscribe(dis);
              }
          }
  
          @Override
          public void onError(Throwable t) {
              DisposableHelper.dispose(debouncer);
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              if (done) {
                  return;
              }
              done = true;
              Disposable d = debouncer.get();
              if (!DisposableHelper.isDisposed(d)) {
                  @SuppressWarnings("unchecked")
                  DebounceInnerSubscriber<T, U> dis = (DebounceInnerSubscriber<T, U>)d;
                  if (dis != null) {
                      dis.emit();
                  }
                  DisposableHelper.dispose(debouncer);
                  downstream.onComplete();
              }
          }
  
          @Override
          public void request(long n) {
              if (SubscriptionHelper.validate(n)) {
                  BackpressureHelper.add(this, n);
              }
          }
  
          @Override
          public void cancel() {
              upstream.cancel();
              DisposableHelper.dispose(debouncer);
          }
  
          void emit(long idx, T value) {
              if (idx == index) {
                  long r = get();
                  if (r != 0L) {
                      downstream.onNext(value);
                      BackpressureHelper.produced(this, 1);
                  } else {
                      cancel();
                      downstream.onError(MissingBackpressureException.createDefault());
                  }
              }
          }
  
          static final class DebounceInnerSubscriber<T, U> extends DisposableSubscriber<U> {
              final DebounceSubscriber<T, U> parent;
              final long index;
              final T value;
  
              boolean done;
  
              final AtomicBoolean once = new AtomicBoolean();
  
              DebounceInnerSubscriber(DebounceSubscriber<T, U> parent, long index, T value) {
                  this.parent = parent;
                  this.index = index;
                  this.value = value;
              }
  
              @Override
              public void onNext(U t) {
                  if (done) {
                      return;
                  }
                  done = true;
                  cancel();
                  emit();
              }
  
              void emit() {
                  if (once.compareAndSet(false, true)) {
                      parent.emit(index, value);
                  }
              }
  
              @Override
              public void onError(Throwable t) {
                  if (done) {
                      RxJavaPlugins.onError(t);
                      return;
                  }
                  done = true;
                  parent.onError(t);
              }
  
              @Override
              public void onComplete() {
                  if (done) {
                      return;
                  }
                  done = true;
                  emit();
              }
          }
      }
  }
  