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.
/**
 * 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.
Type parameters:
<T> – the input value type
<R> – the output value type/**
 * 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 = ObjectHelper.requireNonNull(selector.apply(subject), "The selector returned a null ObservableSource");
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            EmptyDisposable.error(ex, observer);
            return;
        }

        TargetObserver<T, R> o = new TargetObserver<T, R>(observer);

        target.subscribe(o);

        source.subscribe(new SourceObserver<T, R>(subject, o));
    }

    static final class SourceObserver<T, R> 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<T, 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();
        }
    }
}