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Reactive Extensions for Java
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/**
 * 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.internal.operators.observable;

import java.util.concurrent.atomic.AtomicReference;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.disposables.*;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.subjects.PublishSubject;

/**
 * Shares a source Observable for the duration of a selector function.
 * @param  the input value type
 * @param  the output value type
 */
public final class ObservablePublishSelector extends AbstractObservableWithUpstream {

    final Function, ? extends ObservableSource> selector;

    public ObservablePublishSelector(final ObservableSource source,
                                              final Function, ? extends ObservableSource> selector) {
        super(source);
        this.selector = selector;
    }

    @Override
    protected void subscribeActual(Observer observer) {
        PublishSubject subject = PublishSubject.create();

        ObservableSource target;

        try {
            target = ObjectHelper.requireNonNull(selector.apply(subject), "The selector returned a null ObservableSource");
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            EmptyDisposable.error(ex, observer);
            return;
        }

        TargetObserver o = new TargetObserver(observer);

        target.subscribe(o);

        source.subscribe(new SourceObserver(subject, o));
    }

    static final class SourceObserver implements Observer {

        final PublishSubject subject;

        final AtomicReference target;

        SourceObserver(PublishSubject subject, AtomicReference 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
    extends AtomicReference implements Observer, Disposable {
        private static final long serialVersionUID = 854110278590336484L;

        final Observer downstream;

        Disposable upstream;

        TargetObserver(Observer 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();
        }
    }
}