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.exceptions.Exceptions;
import io.reactivex.functions.BiFunction;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.fuseable.ConditionalSubscriber;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.subscribers.SerializedSubscriber;

public final class FlowableWithLatestFrom<T, U, R> extends AbstractFlowableWithUpstream<T, R> {
    final BiFunction<? super T, ? super U, ? extends R> combiner;
    final Publisher<? extends U> other;
    public FlowableWithLatestFrom(Flowable<T> source, BiFunction<? super T, ? super U, ? extends R> combiner, Publisher<? extends U> other) {
        super(source);
        this.combiner = combiner;
        this.other = other;
    }

    @Override
    protected void subscribeActual(Subscriber<? super R> s) {
        final SerializedSubscriber<R> serial = new SerializedSubscriber<R>(s);
        final WithLatestFromSubscriber<T, U, R> wlf = new WithLatestFromSubscriber<T, U, R>(serial, combiner);

        serial.onSubscribe(wlf);

        other.subscribe(new FlowableWithLatestSubscriber(wlf));

        source.subscribe(wlf);
    }

    static final class WithLatestFromSubscriber<T, U, R> extends AtomicReference<U>
    implements ConditionalSubscriber<T>, Subscription {

        private static final long serialVersionUID = -312246233408980075L;

        final Subscriber<? super R> downstream;

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

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

        final AtomicLong requested = new AtomicLong();

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

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

        @Override
        public void onSubscribe(Subscription s) {
            SubscriptionHelper.deferredSetOnce(this.upstream, requested, s);
        }

        @Override
        public void onNext(T t) {
            if (!tryOnNext(t)) {
                upstream.get().request(1);
            }
        }

        @Override
        public boolean tryOnNext(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);
                    cancel();
                    downstream.onError(e);
                    return false;
                }
                downstream.onNext(r);
                return true;
            } else {
                return false;
            }
        }

        @Override
        public void onError(Throwable t) {
            SubscriptionHelper.cancel(other);
            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            SubscriptionHelper.cancel(other);
            downstream.onComplete();
        }

        @Override
        public void request(long n) {
            SubscriptionHelper.deferredRequest(upstream, requested, n);
        }

        @Override
        public void cancel() {
            SubscriptionHelper.cancel(upstream);
            SubscriptionHelper.cancel(other);
        }

        public boolean setOther(Subscription o) {
            return SubscriptionHelper.setOnce(other, o);
        }

        public void otherError(Throwable e) {
            SubscriptionHelper.cancel(upstream);
            downstream.onError(e);
        }
    }

    final class FlowableWithLatestSubscriber implements FlowableSubscriber<U> {
        private final WithLatestFromSubscriber<T, U, R> wlf;

        FlowableWithLatestSubscriber(WithLatestFromSubscriber<T, U, R> wlf) {
            this.wlf = wlf;
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (wlf.setOther(s)) {
                s.request(Long.MAX_VALUE);
            }
        }

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

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

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