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.mixed;
  
  import java.util.Objects;
  import java.util.concurrent.atomic.AtomicReference;
  
  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.*;
  import io.reactivex.rxjava3.operators.SimpleQueue;
  
  /**
   * Maps the upstream items into {@link CompletableSource}s and subscribes to them one after the
   * other completes or terminates (in error-delaying mode).
   * <p>History: 2.1.11 - experimental
   * @param <T> the upstream value type
   * @since 2.2
   */
  public final class FlowableConcatMapCompletable<T> extends Completable {
  
      final Flowable<T> source;
  
      final Function<? super T, ? extends CompletableSource> mapper;
  
      final ErrorMode errorMode;
  
      final int prefetch;
  
      public FlowableConcatMapCompletable(Flowable<T> source,
              Function<? super T, ? extends CompletableSource> mapper,
              ErrorMode errorMode,
              int prefetch) {
          this.source = source;
          this.mapper = mapper;
          this.errorMode = errorMode;
          this.prefetch = prefetch;
      }
  
      @Override
      protected void subscribeActual(CompletableObserver observer) {
          source.subscribe(new ConcatMapCompletableObserver<>(observer, mapper, errorMode, prefetch));
      }
  
      static final class ConcatMapCompletableObserver<T>
      extends ConcatMapXMainSubscriber<T>
      implements Disposable {
  
          private static final long serialVersionUID = 3610901111000061034L;
  
          final CompletableObserver downstream;
  
          final Function<? super T, ? extends CompletableSource> mapper;
  
          final ConcatMapInnerObserver inner;
  
          volatile boolean active;
  
          int consumed;
  
          ConcatMapCompletableObserver(CompletableObserver downstream,
                  Function<? super T, ? extends CompletableSource> mapper,
                  ErrorMode errorMode, int prefetch) {
              super(prefetch, errorMode);
              this.downstream = downstream;
              this.mapper = mapper;
              this.inner = new ConcatMapInnerObserver(this);
          }
  
          @Override
          void onSubscribeDownstream() {
              downstream.onSubscribe(this);
          }
  
          @Override
          void disposeInner() {
              inner.dispose();
          }
  
          @Override
          public void dispose() {
              stop();
          }
  
          @Override
          public boolean isDisposed() {
              return cancelled;
          }
  
          void innerError(Throwable ex) {
              if (errors.tryAddThrowableOrReport(ex)) {
                  if (errorMode == ErrorMode.IMMEDIATE) {
                      upstream.cancel();
                      errors.tryTerminateConsumer(downstream);
                      if (getAndIncrement() == 0) {
                          queue.clear();
                      }
                  } else {
                      active = false;
                      drain();
                  }
              }
          }
  
          void innerComplete() {
              active = false;
              drain();
          }
  
          @Override
          void drain() {
              if (getAndIncrement() != 0) {
                  return;
              }
  
              ErrorMode errorMode = this.errorMode;
              SimpleQueue<T> queue = this.queue;
              AtomicThrowable errors = this.errors;
              boolean syncFused = this.syncFused;
  
              do {
                  if (cancelled) {
                      queue.clear();
                      return;
                  }
  
                  if (errors.get() != null) {
                      if (errorMode == ErrorMode.IMMEDIATE
                              || (errorMode == ErrorMode.BOUNDARY && !active)) {
                          queue.clear();
                          errors.tryTerminateConsumer(downstream);
                          return;
                      }
                  }
  
                  if (!active) {
  
                      boolean d = done;
                      T v;
                      try {
                          v = queue.poll();
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
                          upstream.cancel();
                          errors.tryAddThrowableOrReport(ex);
                          errors.tryTerminateConsumer(downstream);
                          return;
                      }
                      boolean empty = v == null;
  
                      if (d && empty) {
                          errors.tryTerminateConsumer(downstream);
                          return;
                      }
  
                      if (!empty) {
  
                          int limit = prefetch - (prefetch >> 1);
  
                          if (!syncFused) {
                              int c = consumed + 1;
                              if (c == limit) {
                                  consumed = 0;
                                  upstream.request(limit);
                              } else {
                                  consumed = c;
                              }
                          }
  
                          CompletableSource cs;
  
                          try {
                              cs = Objects.requireNonNull(mapper.apply(v), "The mapper returned a null CompletableSource");
                          } catch (Throwable ex) {
                              Exceptions.throwIfFatal(ex);
                              queue.clear();
                              upstream.cancel();
                              errors.tryAddThrowableOrReport(ex);
                              errors.tryTerminateConsumer(downstream);
                              return;
                          }
                          active = true;
                          cs.subscribe(inner);
                      }
                  }
              } while (decrementAndGet() != 0);
          }
  
          static final class ConcatMapInnerObserver extends AtomicReference<Disposable>
          implements CompletableObserver {
  
              private static final long serialVersionUID = 5638352172918776687L;
  
              final ConcatMapCompletableObserver<?> parent;
  
              ConcatMapInnerObserver(ConcatMapCompletableObserver<?> parent) {
                  this.parent = parent;
              }
  
              @Override
              public void onSubscribe(Disposable d) {
                  DisposableHelper.replace(this, d);
              }
  
              @Override
              public void onError(Throwable e) {
                  parent.innerError(e);
              }
  
              @Override
              public void onComplete() {
                  parent.innerComplete();
              }
  
              void dispose() {
                  DisposableHelper.dispose(this);
              }
          }
      }
  }
  