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.*;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  
  /**
   * Maps a value into a SingleSource and relays its signal.
   *
   * @param <T> the source value type
   * @param <R> the result value type
   * @since 3.0.0
   */
  public final class SingleFlatMapNotification<T, R> extends Single<R> {
  
      final SingleSource<T> source;
  
      final Function<? super T, ? extends SingleSource<? extends R>> onSuccessMapper;
  
      final Function<? super Throwable, ? extends SingleSource<? extends R>> onErrorMapper;
  
      public SingleFlatMapNotification(SingleSource<T> source,
              Function<? super T, ? extends SingleSource<? extends R>> onSuccessMapper,
              Function<? super Throwable, ? extends SingleSource<? extends R>> onErrorMapper) {
          this.source = source;
          this.onSuccessMapper = onSuccessMapper;
          this.onErrorMapper = onErrorMapper;
      }
  
      @Override
      protected void subscribeActual(SingleObserver<? super R> observer) {
          source.subscribe(new FlatMapSingleObserver<>(observer, onSuccessMapper, onErrorMapper));
      }
  
      static final class FlatMapSingleObserver<T, R>
      extends AtomicReference<Disposable>
      implements SingleObserver<T>, Disposable {
  
          private static final long serialVersionUID = 4375739915521278546L;
  
          final SingleObserver<? super R> downstream;
  
          final Function<? super T, ? extends SingleSource<? extends R>> onSuccessMapper;
  
          final Function<? super Throwable, ? extends SingleSource<? extends R>> onErrorMapper;
  
          Disposable upstream;
  
          FlatMapSingleObserver(SingleObserver<? super R> actual,
                  Function<? super T, ? extends SingleSource<? extends R>> onSuccessMapper,
                  Function<? super Throwable, ? extends SingleSource<? extends R>> onErrorMapper) {
              this.downstream = actual;
              this.onSuccessMapper = onSuccessMapper;
              this.onErrorMapper = onErrorMapper;
          }
  
          @Override
          public void dispose() {
              DisposableHelper.dispose(this);
              upstream.dispose();
          }
  
          @Override
          public boolean isDisposed() {
              return DisposableHelper.isDisposed(get());
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
  
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onSuccess(T value) {
              SingleSource<? extends R> source;
  
              try {
                  source = Objects.requireNonNull(onSuccessMapper.apply(value), "The onSuccessMapper returned a null SingleSource");
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  downstream.onError(ex);
                  return;
              }
  
              if (!isDisposed()) {
                  source.subscribe(new InnerObserver());
              }
          }
  
          @Override
          public void onError(Throwable e) {
              SingleSource<? extends R> source;
  
              try {
                  source = Objects.requireNonNull(onErrorMapper.apply(e), "The onErrorMapper returned a null SingleSource");
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  downstream.onError(new CompositeException(e, ex));
                  return;
              }
  
              if (!isDisposed()) {
                  source.subscribe(new InnerObserver());
              }
          }
  
          final class InnerObserver implements SingleObserver<R> {
  
              @Override
              public void onSubscribe(Disposable d) {
                  DisposableHelper.setOnce(FlatMapSingleObserver.this, d);
              }
  
              @Override
              public void onSuccess(R value) {
                  downstream.onSuccess(value);
              }
  
              @Override
              public void onError(Throwable e) {
                  downstream.onError(e);
              }
          }
      }
  }
  