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.maybe;

import java.util.concurrent.atomic.*;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.BiPredicate;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.plugins.RxJavaPlugins;

Compares two MaybeSources to see if they are both empty or emit the same value compared
via a BiPredicate.
Type parameters:
<T> – the common base type of the sources/**
 * Compares two MaybeSources to see if they are both empty or emit the same value compared
 * via a BiPredicate.
 *
 * @param <T> the common base type of the sources
 */
public final class MaybeEqualSingle<T> extends Single<Boolean> {
    final MaybeSource<? extends T> source1;

    final MaybeSource<? extends T> source2;

    final BiPredicate<? super T, ? super T> isEqual;

    public MaybeEqualSingle(MaybeSource<? extends T> source1, MaybeSource<? extends T> source2,
            BiPredicate<? super T, ? super T> isEqual) {
        this.source1 = source1;
        this.source2 = source2;
        this.isEqual = isEqual;
    }

    @Override
    protected void subscribeActual(SingleObserver<? super Boolean> observer) {
        EqualCoordinator<T> parent = new EqualCoordinator<T>(observer, isEqual);
        observer.onSubscribe(parent);
        parent.subscribe(source1, source2);
    }

    @SuppressWarnings("serial")
    static final class EqualCoordinator<T>
    extends AtomicInteger
    implements Disposable {
        final SingleObserver<? super Boolean> downstream;

        final EqualObserver<T> observer1;

        final EqualObserver<T> observer2;

        final BiPredicate<? super T, ? super T> isEqual;

        EqualCoordinator(SingleObserver<? super Boolean> actual, BiPredicate<? super T, ? super T> isEqual) {
            super(2);
            this.downstream = actual;
            this.isEqual = isEqual;
            this.observer1 = new EqualObserver<T>(this);
            this.observer2 = new EqualObserver<T>(this);
        }

        void subscribe(MaybeSource<? extends T> source1, MaybeSource<? extends T> source2) {
            source1.subscribe(observer1);
            source2.subscribe(observer2);
        }

        @Override
        public void dispose() {
            observer1.dispose();
            observer2.dispose();
        }

        @Override
        public boolean isDisposed() {
            return DisposableHelper.isDisposed(observer1.get());
        }

        @SuppressWarnings("unchecked")
        void done() {
            if (decrementAndGet() == 0) {
                Object o1 = observer1.value;
                Object o2 = observer2.value;

                if (o1 != null && o2 != null) {
                    boolean b;

                    try {
                        b = isEqual.test((T)o1, (T)o2);
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);
                        downstream.onError(ex);
                        return;
                    }

                    downstream.onSuccess(b);
                } else {
                    downstream.onSuccess(o1 == null && o2 == null);
                }
            }
        }

        void error(EqualObserver<T> sender, Throwable ex) {
            if (getAndSet(0) > 0) {
                if (sender == observer1) {
                    observer2.dispose();
                } else {
                    observer1.dispose();
                }
                downstream.onError(ex);
            } else {
                RxJavaPlugins.onError(ex);
            }
        }
    }

    static final class EqualObserver<T>
    extends AtomicReference<Disposable>
    implements MaybeObserver<T> {

        private static final long serialVersionUID = -3031974433025990931L;

        final EqualCoordinator<T> parent;

        Object value;

        EqualObserver(EqualCoordinator<T> parent) {
            this.parent = parent;
        }

        public void dispose() {
            DisposableHelper.dispose(this);
        }

        @Override
        public void onSubscribe(Disposable d) {
            DisposableHelper.setOnce(this, d);
        }

        @Override
        public void onSuccess(T value) {
            this.value = value;
            parent.done();
        }

        @Override
        public void onError(Throwable e) {
            parent.error(this, e);
        }

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

    }
}