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 java.util.concurrent.atomic.AtomicInteger;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.BiPredicate;
import io.reactivex.internal.disposables.ArrayCompositeDisposable;
import io.reactivex.internal.fuseable.FuseToObservable;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.plugins.RxJavaPlugins;

public final class ObservableSequenceEqualSingle<T> extends Single<Boolean> implements FuseToObservable<Boolean> {
    final ObservableSource<? extends T> first;
    final ObservableSource<? extends T> second;
    final BiPredicate<? super T, ? super T> comparer;
    final int bufferSize;

    public ObservableSequenceEqualSingle(ObservableSource<? extends T> first, ObservableSource<? extends T> second,
                                   BiPredicate<? super T, ? super T> comparer, int bufferSize) {
        this.first = first;
        this.second = second;
        this.comparer = comparer;
        this.bufferSize = bufferSize;
    }

    @Override
    public void subscribeActual(SingleObserver<? super Boolean> observer) {
        EqualCoordinator<T> ec = new EqualCoordinator<T>(observer, bufferSize, first, second, comparer);
        observer.onSubscribe(ec);
        ec.subscribe();
    }

    @Override
    public Observable<Boolean> fuseToObservable() {
        return RxJavaPlugins.onAssembly(new ObservableSequenceEqual<T>(first, second, comparer, bufferSize));
    }

    static final class EqualCoordinator<T> extends AtomicInteger implements Disposable {

        private static final long serialVersionUID = -6178010334400373240L;
        final SingleObserver<? super Boolean> downstream;
        final BiPredicate<? super T, ? super T> comparer;
        final ArrayCompositeDisposable resources;
        final ObservableSource<? extends T> first;
        final ObservableSource<? extends T> second;
        final EqualObserver<T>[] observers;

        volatile boolean cancelled;

        T v1;

        T v2;

        EqualCoordinator(SingleObserver<? super Boolean> actual, int bufferSize,
                                ObservableSource<? extends T> first, ObservableSource<? extends T> second,
                                BiPredicate<? super T, ? super T> comparer) {
            this.downstream = actual;
            this.first = first;
            this.second = second;
            this.comparer = comparer;
            @SuppressWarnings("unchecked")
            EqualObserver<T>[] as = new EqualObserver[2];
            this.observers = as;
            as[0] = new EqualObserver<T>(this, 0, bufferSize);
            as[1] = new EqualObserver<T>(this, 1, bufferSize);
            this.resources = new ArrayCompositeDisposable(2);
        }

        boolean setDisposable(Disposable d, int index) {
            return resources.setResource(index, d);
        }

        void subscribe() {
            EqualObserver<T>[] as = observers;
            first.subscribe(as[0]);
            second.subscribe(as[1]);
        }

        @Override
        public void dispose() {
            if (!cancelled) {
                cancelled = true;
                resources.dispose();

                if (getAndIncrement() == 0) {
                    EqualObserver<T>[] as = observers;
                    as[0].queue.clear();
                    as[1].queue.clear();
                }
            }
        }

        @Override
        public boolean isDisposed() {
            return cancelled;
        }

        void cancel(SpscLinkedArrayQueue<T> q1, SpscLinkedArrayQueue<T> q2) {
            cancelled = true;
            q1.clear();
            q2.clear();
        }

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

            int missed = 1;
            EqualObserver<T>[] as = observers;

            final EqualObserver<T> observer1 = as[0];
            final SpscLinkedArrayQueue<T> q1 = observer1.queue;
            final EqualObserver<T> observer2 = as[1];
            final SpscLinkedArrayQueue<T> q2 = observer2.queue;

            for (;;) {

                for (;;) {
                    if (cancelled) {
                        q1.clear();
                        q2.clear();
                        return;
                    }

                    boolean d1 = observer1.done;

                    if (d1) {
                        Throwable e = observer1.error;
                        if (e != null) {
                            cancel(q1, q2);

                            downstream.onError(e);
                            return;
                        }
                    }

                    boolean d2 = observer2.done;
                    if (d2) {
                        Throwable e = observer2.error;
                        if (e != null) {
                            cancel(q1, q2);

                            downstream.onError(e);
                            return;
                        }
                    }

                    if (v1 == null) {
                        v1 = q1.poll();
                    }
                    boolean e1 = v1 == null;

                    if (v2 == null) {
                        v2 = q2.poll();
                    }
                    boolean e2 = v2 == null;

                    if (d1 && d2 && e1 && e2) {
                        downstream.onSuccess(true);
                        return;
                    }
                    if ((d1 && d2) && (e1 != e2)) {
                        cancel(q1, q2);

                        downstream.onSuccess(false);
                        return;
                    }

                    if (!e1 && !e2) {
                        boolean c;

                        try {
                            c = comparer.test(v1, v2);
                        } catch (Throwable ex) {
                            Exceptions.throwIfFatal(ex);
                            cancel(q1, q2);

                            downstream.onError(ex);
                            return;
                        }

                        if (!c) {
                            cancel(q1, q2);

                            downstream.onSuccess(false);
                            return;
                        }

                        v1 = null;
                        v2 = null;
                    }

                    if (e1 || e2) {
                        break;
                    }
                }

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

    static final class EqualObserver<T> implements Observer<T> {
        final EqualCoordinator<T> parent;
        final SpscLinkedArrayQueue<T> queue;
        final int index;

        volatile boolean done;
        Throwable error;

        EqualObserver(EqualCoordinator<T> parent, int index, int bufferSize) {
            this.parent = parent;
            this.index = index;
            this.queue = new SpscLinkedArrayQueue<T>(bufferSize);
        }

        @Override
        public void onSubscribe(Disposable d) {
            parent.setDisposable(d, index);
        }

        @Override
        public void onNext(T t) {
            queue.offer(t);
            parent.drain();
        }

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

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