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.TimeUnit;
import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

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

Emits the next or latest item when the given time elapses.

The operator emits the next item, then starts a timer. When the timer fires,
it tries to emit the latest item from upstream. If there was no upstream item,
in the meantime, the next upstream item is emitted immediately and the
timed process repeats.
History: 2.1.14 - experimental
Type parameters:
<T> – the upstream and downstream value type
Since:
2.2/**
 * Emits the next or latest item when the given time elapses.
 * <p>
 * The operator emits the next item, then starts a timer. When the timer fires,
 * it tries to emit the latest item from upstream. If there was no upstream item,
 * in the meantime, the next upstream item is emitted immediately and the
 * timed process repeats.
 * <p>History: 2.1.14 - experimental
 * @param <T> the upstream and downstream value type
 * @since 2.2
 */
public final class FlowableThrottleLatest<T> extends AbstractFlowableWithUpstream<T, T> {

    final long timeout;

    final TimeUnit unit;

    final Scheduler scheduler;

    final boolean emitLast;

    public FlowableThrottleLatest(Flowable<T> source,
            long timeout, TimeUnit unit, Scheduler scheduler,
            boolean emitLast) {
        super(source);
        this.timeout = timeout;
        this.unit = unit;
        this.scheduler = scheduler;
        this.emitLast = emitLast;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {
        source.subscribe(new ThrottleLatestSubscriber<T>(s, timeout, unit, scheduler.createWorker(), emitLast));
    }

    static final class ThrottleLatestSubscriber<T>
    extends AtomicInteger
    implements FlowableSubscriber<T>, Subscription, Runnable {

        private static final long serialVersionUID = -8296689127439125014L;

        final Subscriber<? super T> downstream;

        final long timeout;

        final TimeUnit unit;

        final Scheduler.Worker worker;

        final boolean emitLast;

        final AtomicReference<T> latest;

        final AtomicLong requested;

        Subscription upstream;

        volatile boolean done;
        Throwable error;

        volatile boolean cancelled;

        volatile boolean timerFired;

        long emitted;

        boolean timerRunning;

        ThrottleLatestSubscriber(Subscriber<? super T> downstream,
                long timeout, TimeUnit unit, Scheduler.Worker worker,
                boolean emitLast) {
            this.downstream = downstream;
            this.timeout = timeout;
            this.unit = unit;
            this.worker = worker;
            this.emitLast = emitLast;
            this.latest = new AtomicReference<T>();
            this.requested = new AtomicLong();
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(upstream, s)) {
                upstream = s;
                downstream.onSubscribe(this);
                s.request(Long.MAX_VALUE);
            }
        }

        @Override
        public void onNext(T t) {
            latest.set(t);
            drain();
        }

        @Override
        public void onError(Throwable t) {
            error = t;
            done = true;
            drain();
        }

        @Override
        public void onComplete() {
            done = true;
            drain();
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                BackpressureHelper.add(requested, n);
            }
        }

        @Override
        public void cancel() {
            cancelled = true;
            upstream.cancel();
            worker.dispose();
            if (getAndIncrement() == 0) {
                latest.lazySet(null);
            }
        }

        @Override
        public void run() {
            timerFired = true;
            drain();
        }

        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }

            int missed = 1;

            AtomicReference<T> latest = this.latest;
            AtomicLong requested = this.requested;
            Subscriber<? super T> downstream = this.downstream;

            for (;;) {

                for (;;) {
                    if (cancelled) {
                        latest.lazySet(null);
                        return;
                    }

                    boolean d = done;

                    if (d && error != null) {
                        latest.lazySet(null);
                        downstream.onError(error);
                        worker.dispose();
                        return;
                    }

                    T v = latest.get();
                    boolean empty = v == null;

                    if (d) {
                        if (!empty && emitLast) {
                            v = latest.getAndSet(null);
                            long e = emitted;
                            if (e != requested.get()) {
                                emitted = e + 1;
                                downstream.onNext(v);
                                downstream.onComplete();
                            } else {
                                downstream.onError(new MissingBackpressureException(
                                        "Could not emit final value due to lack of requests"));
                            }
                        } else {
                            latest.lazySet(null);
                            downstream.onComplete();
                        }
                        worker.dispose();
                        return;
                    }

                    if (empty) {
                        if (timerFired) {
                            timerRunning = false;
                            timerFired = false;
                        }
                        break;
                    }

                    if (!timerRunning || timerFired) {
                        v = latest.getAndSet(null);
                        long e = emitted;
                        if (e != requested.get()) {
                            downstream.onNext(v);
                            emitted = e + 1;
                        } else {
                            upstream.cancel();
                            downstream.onError(new MissingBackpressureException(
                                    "Could not emit value due to lack of requests"));
                            worker.dispose();
                            return;
                        }

                        timerFired = false;
                        timerRunning = true;
                        worker.schedule(this, timeout, unit);
                    } else {
                        break;
                    }
                }

                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }
    }
}