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.single;

import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;

import org.reactivestreams.Publisher;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;

import io.reactivex.Flowable;
import io.reactivex.FlowableSubscriber;
import io.reactivex.Scheduler;
import io.reactivex.SingleObserver;
import io.reactivex.SingleSource;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscriptions.SubscriptionHelper;

A Flowable that emits items based on applying a specified function to the item emitted by the
source Single, where that function returns a Publisher.



 
Backpressure:
 
The returned Flowable honors the backpressure of the downstream consumer and the Publisher returned by the mapper function is expected to honor it as well.
Scheduler:
flatMapPublisher does not operate by default on a particular Scheduler.

Type parameters:
<T> – the source value type
<R> – the result value type
See Also:
ReactiveX operators documentation: FlatMap
Since:
2.1.15/**
 * A Flowable that emits items based on applying a specified function to the item emitted by the
 * source Single, where that function returns a Publisher.
 * <p>
 * <img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.flatMapPublisher.png" alt="">
 * <dl>
 *  <dt><b>Backpressure:</b></dt>
 *  <dd>The returned {@code Flowable} honors the backpressure of the downstream consumer
 *  and the {@code Publisher} returned by the mapper function is expected to honor it as well.</dd>
 * <dt><b>Scheduler:</b></dt>
 * <dd>{@code flatMapPublisher} does not operate by default on a particular {@link Scheduler}.</dd>
 * </dl>
 * 
 * @param <T> the source value type
 * @param <R> the result value type
 * 
 * @see <a href="http://reactivex.io/documentation/operators/flatmap.html">ReactiveX operators documentation: FlatMap</a>
 * @since 2.1.15
 */
public final class SingleFlatMapPublisher<T, R> extends Flowable<R> {

    final SingleSource<T> source;
    final Function<? super T, ? extends Publisher<? extends R>> mapper;

    public SingleFlatMapPublisher(SingleSource<T> source,
            Function<? super T, ? extends Publisher<? extends R>> mapper) {
        this.source = source;
        this.mapper = mapper;
    }

    @Override
    protected void subscribeActual(Subscriber<? super R> downstream) {
        source.subscribe(new SingleFlatMapPublisherObserver<T, R>(downstream, mapper));
    }

    static final class SingleFlatMapPublisherObserver<S, T> extends AtomicLong
            implements SingleObserver<S>, FlowableSubscriber<T>, Subscription {

        private static final long serialVersionUID = 7759721921468635667L;

        final Subscriber<? super T> downstream;
        final Function<? super S, ? extends Publisher<? extends T>> mapper;
        final AtomicReference<Subscription> parent;
        Disposable disposable;

        SingleFlatMapPublisherObserver(Subscriber<? super T> actual,
                Function<? super S, ? extends Publisher<? extends T>> mapper) {
            this.downstream = actual;
            this.mapper = mapper;
            this.parent = new AtomicReference<Subscription>();
        }

        @Override
        public void onSubscribe(Disposable d) {
            this.disposable = d;
            downstream.onSubscribe(this);
        }

        @Override
        public void onSuccess(S value) {
            Publisher<? extends T> f;
            try {
                f = ObjectHelper.requireNonNull(mapper.apply(value), "the mapper returned a null Publisher");
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                downstream.onError(e);
                return;
            }
            f.subscribe(this);
        }

        @Override
        public void onSubscribe(Subscription s) {
            SubscriptionHelper.deferredSetOnce(parent, this, s);
        }

        @Override
        public void onNext(T t) {
            downstream.onNext(t);
        }

        @Override
        public void onComplete() {
            downstream.onComplete();
        }

        @Override
        public void onError(Throwable e) {
            downstream.onError(e);
        }

        @Override
        public void request(long n) {
            SubscriptionHelper.deferredRequest(parent, this, n);
        }

        @Override
        public void cancel() {
            disposable.dispose();
            SubscriptionHelper.cancel(parent);
        }
    }

}