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;
  
  /**
   * Maps the success value of a Maybe onto an ObservableSource and
   * relays its signals to the downstream observer.
   *
   * @param <T> the success value type of the Maybe source
   * @param <R> the result type of the ObservableSource and this operator
   * @since 2.1.15
   */
  public final class MaybeFlatMapObservable<T, R> extends Observable<R> {
  
      final MaybeSource<T> source;
  
      final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
  
      public MaybeFlatMapObservable(MaybeSource<T> source,
              Function<? super T, ? extends ObservableSource<? extends R>> mapper) {
          this.source = source;
          this.mapper = mapper;
      }
  
      @Override
      protected void subscribeActual(Observer<? super R> observer) {
          FlatMapObserver<T, R> parent = new FlatMapObserver<>(observer, mapper);
          observer.onSubscribe(parent);
          source.subscribe(parent);
      }
  
      static final class FlatMapObserver<T, R>
      extends AtomicReference<Disposable>
      implements Observer<R>, MaybeObserver<T>, Disposable {
  
          private static final long serialVersionUID = -8948264376121066672L;
  
          final Observer<? super R> downstream;
  
          final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
  
          FlatMapObserver(Observer<? super R> downstream, Function<? super T, ? extends ObservableSource<? extends R>> mapper) {
              this.downstream = downstream;
              this.mapper = mapper;
          }
  
          @Override
          public void onNext(R t) {
              downstream.onNext(t);
          }
  
          @Override
          public void onError(Throwable t) {
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              downstream.onComplete();
          }
  
          @Override
          public void dispose() {
              DisposableHelper.dispose(this);
          }
  
          @Override
          public boolean isDisposed() {
              return DisposableHelper.isDisposed(get());
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              DisposableHelper.replace(this, d);
          }
  
          @Override
          public void onSuccess(T t) {
              ObservableSource<? extends R> o;
  
              try {
                  o = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null Publisher");
              } catch (Throwable ex) {
                  Exceptions.throwIfFatal(ex);
                  downstream.onError(ex);
                  return;
              }
  
              if (!isDisposed()) {
                  o.subscribe(this);
              }
          }
  
      }
  }
  