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.observable;
  
  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.*;
  import io.reactivex.rxjava3.subjects.PublishSubject;
  
  /**
   * Shares a source Observable for the duration of a selector function.
   * @param <T> the input value type
   * @param <R> the output value type
   */
  public final class ObservablePublishSelector<T, R> extends AbstractObservableWithUpstream<T, R> {
  
      final Function<? super Observable<T>, ? extends ObservableSource<R>> selector;
  
      public ObservablePublishSelector(final ObservableSource<T> source,
                                                final Function<? super Observable<T>, ? extends ObservableSource<R>> selector) {
          super(source);
          this.selector = selector;
      }
  
      @Override
      protected void subscribeActual(Observer<? super R> observer) {
          PublishSubject<T> subject = PublishSubject.create();
  
          ObservableSource<? extends R> target;
  
          try {
              target = Objects.requireNonNull(selector.apply(subject), "The selector returned a null ObservableSource");
          } catch (Throwable ex) {
              Exceptions.throwIfFatal(ex);
              EmptyDisposable.error(ex, observer);
              return;
          }
  
          TargetObserver<R> o = new TargetObserver<>(observer);
  
          target.subscribe(o);
  
          source.subscribe(new SourceObserver<>(subject, o));
      }
  
      static final class SourceObserver<T> implements Observer<T> {
  
          final PublishSubject<T> subject;
  
          final AtomicReference<Disposable> target;
  
          SourceObserver(PublishSubject<T> subject, AtomicReference<Disposable> target) {
              this.subject = subject;
              this.target = target;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              DisposableHelper.setOnce(target, d);
          }
  
          @Override
          public void onNext(T value) {
              subject.onNext(value);
          }
  
          @Override
          public void onError(Throwable e) {
              subject.onError(e);
          }
  
          @Override
          public void onComplete() {
              subject.onComplete();
          }
      }
  
      static final class TargetObserver<R>
      extends AtomicReference<Disposable> implements Observer<R>, Disposable {
          private static final long serialVersionUID = 854110278590336484L;
  
          final Observer<? super R> downstream;
  
          Disposable upstream;
  
          TargetObserver(Observer<? super R> downstream) {
              this.downstream = downstream;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
  
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(R value) {
              downstream.onNext(value);
          }
  
          @Override
          public void onError(Throwable e) {
              DisposableHelper.dispose(this);
              downstream.onError(e);
          }
  
          @Override
          public void onComplete() {
              DisposableHelper.dispose(this);
              downstream.onComplete();
          }
  
          @Override
          public void dispose() {
              upstream.dispose();
              DisposableHelper.dispose(this);
          }
  
          @Override
          public boolean isDisposed() {
              return upstream.isDisposed();
          }
      }
  }
  