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 io.reactivex.internal.functions.ObjectHelper;
import java.util.concurrent.atomic.*;

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.observers.*;
import io.reactivex.plugins.RxJavaPlugins;

public final class ObservableDebounce<T, U> extends AbstractObservableWithUpstream<T, T> {
    final Function<? super T, ? extends ObservableSource<U>> debounceSelector;

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

    @Override
    public void subscribeActual(Observer<? super T> t) {
        source.subscribe(new DebounceObserver<T, U>(new SerializedObserver<T>(t), debounceSelector));
    }

    static final class DebounceObserver<T, U>
    implements Observer<T>, Disposable {
        final Observer<? super T> downstream;
        final Function<? super T, ? extends ObservableSource<U>> debounceSelector;

        Disposable upstream;

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

        volatile long index;

        boolean done;

        DebounceObserver(Observer<? super T> actual,
                Function<? super T, ? extends ObservableSource<U>> debounceSelector) {
            this.downstream = actual;
            this.debounceSelector = debounceSelector;
        }

        @Override
        public void onSubscribe(Disposable d) {
            if (DisposableHelper.validate(this.upstream, d)) {
                this.upstream = d;
                downstream.onSubscribe(this);
            }
        }

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

            long idx = index + 1;
            index = idx;

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

            ObservableSource<U> p;

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

            DebounceInnerObserver<T, U> dis = new DebounceInnerObserver<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 (d != DisposableHelper.DISPOSED) {
                @SuppressWarnings("unchecked")
                DebounceInnerObserver<T, U> dis = (DebounceInnerObserver<T, U>)d;
                if (dis != null) {
                    dis.emit();
                }
                DisposableHelper.dispose(debouncer);
                downstream.onComplete();
            }
        }

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

        @Override
        public boolean isDisposed() {
            return upstream.isDisposed();
        }

        void emit(long idx, T value) {
            if (idx == index) {
                downstream.onNext(value);
            }
        }

        static final class DebounceInnerObserver<T, U> extends DisposableObserver<U> {
            final DebounceObserver<T, U> parent;
            final long index;
            final T value;

            boolean done;

            final AtomicBoolean once = new AtomicBoolean();

            DebounceInnerObserver(DebounceObserver<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;
                dispose();
                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();
            }
        }
    }
}