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.AtomicReference;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.BiFunction;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.observers.SerializedObserver;

public final class ObservableWithLatestFrom<T, U, R> extends AbstractObservableWithUpstream<T, R> {
    final BiFunction<? super T, ? super U, ? extends R> combiner;
    final ObservableSource<? extends U> other;
    public ObservableWithLatestFrom(ObservableSource<T> source,
            BiFunction<? super T, ? super U, ? extends R> combiner, ObservableSource<? extends U> other) {
        super(source);
        this.combiner = combiner;
        this.other = other;
    }

    @Override
    public void subscribeActual(Observer<? super R> t) {
        final SerializedObserver<R> serial = new SerializedObserver<R>(t);
        final WithLatestFromObserver<T, U, R> wlf = new WithLatestFromObserver<T, U, R>(serial, combiner);

        serial.onSubscribe(wlf);

        other.subscribe(new WithLatestFromOtherObserver(wlf));

        source.subscribe(wlf);
    }

    static final class WithLatestFromObserver<T, U, R> extends AtomicReference<U> implements Observer<T>, Disposable {

        private static final long serialVersionUID = -312246233408980075L;

        final Observer<? super R> downstream;

        final BiFunction<? super T, ? super U, ? extends R> combiner;

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

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

        WithLatestFromObserver(Observer<? super R> actual, BiFunction<? super T, ? super U, ? extends R> combiner) {
            this.downstream = actual;
            this.combiner = combiner;
        }

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

        @Override
        public void onNext(T t) {
            U u = get();
            if (u != null) {
                R r;
                try {
                    r = ObjectHelper.requireNonNull(combiner.apply(t, u), "The combiner returned a null value");
                } catch (Throwable e) {
                    Exceptions.throwIfFatal(e);
                    dispose();
                    downstream.onError(e);
                    return;
                }
                downstream.onNext(r);
            }
        }

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

        @Override
        public void onComplete() {
            DisposableHelper.dispose(other);
            downstream.onComplete();
        }

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

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

        public boolean setOther(Disposable o) {
            return DisposableHelper.setOnce(other, o);
        }

        public void otherError(Throwable e) {
            DisposableHelper.dispose(upstream);
            downstream.onError(e);
        }
    }

    final class WithLatestFromOtherObserver implements Observer<U> {
        private final WithLatestFromObserver<T, U, R> parent;

        WithLatestFromOtherObserver(WithLatestFromObserver<T, U, R> parent) {
            this.parent = parent;
        }

        @Override
        public void onSubscribe(Disposable d) {
            parent.setOther(d);
        }

        @Override
        public void onNext(U t) {
            parent.lazySet(t);
        }

        @Override
        public void onError(Throwable t) {
            parent.otherError(t);
        }

        @Override
        public void onComplete() {
            // nothing to do, the wlf will complete on its own pace
        }
    }
}