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.disposables.Disposable;
import io.reactivex.exceptions.*;
import io.reactivex.functions.Function;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.BackpressureHelper;
import io.reactivex.plugins.RxJavaPlugins;
import io.reactivex.subscribers.*;

public final class FlowableDebounce<T, U> extends AbstractFlowableWithUpstream<T, T> {
    final Function<? super T, ? extends Publisher<U>> debounceSelector;

    public FlowableDebounce(Flowable<T> source, Function<? super T, ? extends Publisher<U>> debounceSelector) {
        super(source);
        this.debounceSelector = debounceSelector;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {
        source.subscribe(new DebounceSubscriber<T, U>(new SerializedSubscriber<T>(s), debounceSelector));
    }

    static final class DebounceSubscriber<T, U> extends AtomicLong
    implements FlowableSubscriber<T>, Subscription {

        private static final long serialVersionUID = 6725975399620862591L;
        final Subscriber<? super T> downstream;
        final Function<? super T, ? extends Publisher<U>> debounceSelector;

        Subscription upstream;

        final AtomicReference<Disposable> debouncer = new AtomicReference<Disposable>();

        volatile long index;

        boolean done;

        DebounceSubscriber(Subscriber<? super T> actual,
                Function<? super T, ? extends Publisher<U>> debounceSelector) {
            this.downstream = actual;
            this.debounceSelector = debounceSelector;
        }

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

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }

            long idx = index + 1;
            index = idx;

            Disposable d = debouncer.get();
            if (d != null) {
                d.dispose();
            }

            Publisher<U> p;

            try {
                p = ObjectHelper.requireNonNull(debounceSelector.apply(t), "The publisher supplied is null");
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                cancel();
                downstream.onError(e);
                return;
            }

            DebounceInnerSubscriber<T, U> dis = new DebounceInnerSubscriber<T, U>(this, idx, t);

            if (debouncer.compareAndSet(d, dis)) {
                p.subscribe(dis);
            }
        }

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

        @Override
        public void onComplete() {
            if (done) {
                return;
            }
            done = true;
            Disposable d = debouncer.get();
            if (!DisposableHelper.isDisposed(d)) {
                @SuppressWarnings("unchecked")
                DebounceInnerSubscriber<T, U> dis = (DebounceInnerSubscriber<T, U>)d;
                if (dis != null) {
                    dis.emit();
                }
                DisposableHelper.dispose(debouncer);
                downstream.onComplete();
            }
        }

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

        @Override
        public void cancel() {
            upstream.cancel();
            DisposableHelper.dispose(debouncer);
        }

        void emit(long idx, T value) {
            if (idx == index) {
                long r = get();
                if (r != 0L) {
                    downstream.onNext(value);
                    BackpressureHelper.produced(this, 1);
                } else {
                    cancel();
                    downstream.onError(new MissingBackpressureException("Could not deliver value due to lack of requests"));
                }
            }
        }

        static final class DebounceInnerSubscriber<T, U> extends DisposableSubscriber<U> {
            final DebounceSubscriber<T, U> parent;
            final long index;
            final T value;

            boolean done;

            final AtomicBoolean once = new AtomicBoolean();

            DebounceInnerSubscriber(DebounceSubscriber<T, U> parent, long index, T value) {
                this.parent = parent;
                this.index = index;
                this.value = value;
            }

            @Override
            public void onNext(U t) {
                if (done) {
                    return;
                }
                done = true;
                cancel();
                emit();
            }

            void emit() {
                if (once.compareAndSet(false, true)) {
                    parent.emit(index, value);
                }
            }

            @Override
            public void onError(Throwable t) {
                if (done) {
                    RxJavaPlugins.onError(t);
                    return;
                }
                done = true;
                parent.onError(t);
            }

            @Override
            public void onComplete() {
                if (done) {
                    return;
                }
                done = true;
                emit();
            }
        }
    }
}