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.single;
  
  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;
  
  public final class SingleFlatMapMaybe<T, R> extends Maybe<R> {
  
      final SingleSource<? extends T> source;
  
      final Function<? super T, ? extends MaybeSource<? extends R>> mapper;
  
      public SingleFlatMapMaybe(SingleSource<? extends T> source, Function<? super T, ? extends MaybeSource<? extends R>> mapper) {
          this.mapper = mapper;
          this.source = source;
      }
  
      @Override
      protected void subscribeActual(MaybeObserver<? super R> downstream) {
          source.subscribe(new FlatMapSingleObserver<T, R>(downstream, mapper));
      }
  
      static final class FlatMapSingleObserver<T, R>
      extends AtomicReference<Disposable>
      implements SingleObserver<T>, Disposable {
  
          private static final long serialVersionUID = -5843758257109742742L;
  
          final MaybeObserver<? super R> downstream;
  
          final Function<? super T, ? extends MaybeSource<? extends R>> mapper;
  
          FlatMapSingleObserver(MaybeObserver<? super R> actual, Function<? super T, ? extends MaybeSource<? extends R>> mapper) {
              this.downstream = actual;
              this.mapper = mapper;
          }
  
          @Override
          public void dispose() {
              DisposableHelper.dispose(this);
          }
  
          @Override
          public boolean isDisposed() {
              return DisposableHelper.isDisposed(get());
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.setOnce(this, d)) {
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onSuccess(T value) {
              MaybeSource<? extends R> ms;
  
              try {
                  ms = Objects.requireNonNull(mapper.apply(value), "The mapper returned a null MaybeSource");
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  onError(ex);
                  return;
              }
  
              if (!isDisposed()) {
                  ms.subscribe(new FlatMapMaybeObserver<R>(this, downstream));
              }
          }
  
          @Override
          public void onError(Throwable e) {
              downstream.onError(e);
          }
      }
  
      static final class FlatMapMaybeObserver<R> implements MaybeObserver<R> {
  
          final AtomicReference<Disposable> parent;
  
          final MaybeObserver<? super R> downstream;
  
          FlatMapMaybeObserver(AtomicReference<Disposable> parent, MaybeObserver<? super R> downstream) {
              this.parent = parent;
              this.downstream = downstream;
          }
  
          @Override
          public void onSubscribe(final Disposable d) {
              DisposableHelper.replace(parent, d);
          }
  
          @Override
          public void onSuccess(final R value) {
              downstream.onSuccess(value);
          }
  
          @Override
          public void onError(final Throwable e) {
              downstream.onError(e);
          }
  
          @Override
          public void onComplete() {
              downstream.onComplete();
          }
      }
  }
  