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.flowable;

import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.BackpressureHelper;

Subscribes to the source Flowable on the specified Scheduler and makes
sure downstream requests are scheduled there as well.
Type parameters:
<T> – the value type emitted/**
 * Subscribes to the source Flowable on the specified Scheduler and makes
 * sure downstream requests are scheduled there as well.
 *
 * @param <T> the value type emitted
 */
public final class FlowableSubscribeOn<T> extends AbstractFlowableWithUpstream<T , T> {

    final Scheduler scheduler;

    final boolean nonScheduledRequests;

    public FlowableSubscribeOn(Flowable<T> source, Scheduler scheduler, boolean nonScheduledRequests) {
        super(source);
        this.scheduler = scheduler;
        this.nonScheduledRequests = nonScheduledRequests;
    }

    @Override
    public void subscribeActual(final Subscriber<? super T> s) {
        Scheduler.Worker w = scheduler.createWorker();
        final SubscribeOnSubscriber<T> sos = new SubscribeOnSubscriber<T>(s, w, source, nonScheduledRequests);
        s.onSubscribe(sos);

        w.schedule(sos);
    }

    static final class SubscribeOnSubscriber<T> extends AtomicReference<Thread>
    implements FlowableSubscriber<T>, Subscription, Runnable {

        private static final long serialVersionUID = 8094547886072529208L;

        final Subscriber<? super T> downstream;

        final Scheduler.Worker worker;

        final AtomicReference<Subscription> upstream;

        final AtomicLong requested;

        final boolean nonScheduledRequests;

        Publisher<T> source;

        SubscribeOnSubscriber(Subscriber<? super T> actual, Scheduler.Worker worker, Publisher<T> source, boolean requestOn) {
            this.downstream = actual;
            this.worker = worker;
            this.source = source;
            this.upstream = new AtomicReference<Subscription>();
            this.requested = new AtomicLong();
            this.nonScheduledRequests = !requestOn;
        }

        @Override
        public void run() {
            lazySet(Thread.currentThread());
            Publisher<T> src = source;
            source = null;
            src.subscribe(this);
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.setOnce(this.upstream, s)) {
                long r = requested.getAndSet(0L);
                if (r != 0L) {
                    requestUpstream(r, s);
                }
            }
        }

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

        @Override
        public void onError(Throwable t) {
            downstream.onError(t);
            worker.dispose();
        }

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

        @Override
        public void request(final long n) {
            if (SubscriptionHelper.validate(n)) {
                Subscription s = this.upstream.get();
                if (s != null) {
                    requestUpstream(n, s);
                } else {
                    BackpressureHelper.add(requested, n);
                    s = this.upstream.get();
                    if (s != null) {
                        long r = requested.getAndSet(0L);
                        if (r != 0L) {
                            requestUpstream(r, s);
                        }
                    }
                }
            }
        }

        void requestUpstream(final long n, final Subscription s) {
            if (nonScheduledRequests || Thread.currentThread() == get()) {
                s.request(n);
            } else {
                worker.schedule(new Request(s, n));
            }
        }

        @Override
        public void cancel() {
            SubscriptionHelper.cancel(upstream);
            worker.dispose();
        }

        static final class Request implements Runnable {
            final Subscription upstream;
            final long n;

            Request(Subscription s, long n) {
                this.upstream = s;
                this.n = n;
            }

            @Override
            public void run() {
                upstream.request(n);
            }
        }
    }
}