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.internal.subscriptions.*;
import io.reactivex.plugins.RxJavaPlugins;

public final class FlowableAmb<T> extends Flowable<T> {
    final Publisher<? extends T>[] sources;
    final Iterable<? extends Publisher<? extends T>> sourcesIterable;

    public FlowableAmb(Publisher<? extends T>[] sources, Iterable<? extends Publisher<? extends T>> sourcesIterable) {
        this.sources = sources;
        this.sourcesIterable = sourcesIterable;
    }

    @Override
    @SuppressWarnings("unchecked")
    public void subscribeActual(Subscriber<? super T> s) {
        Publisher<? extends T>[] sources = this.sources;
        int count = 0;
        if (sources == null) {
            sources = new Publisher[8];
            try {
                for (Publisher<? extends T> p : sourcesIterable) {
                    if (p == null) {
                        EmptySubscription.error(new NullPointerException("One of the sources is null"), s);
                        return;
                    }
                    if (count == sources.length) {
                        Publisher<? extends T>[] b = new Publisher[count + (count >> 2)];
                        System.arraycopy(sources, 0, b, 0, count);
                        sources = b;
                    }
                    sources[count++] = p;
                }
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                EmptySubscription.error(e, s);
                return;
            }
        } else {
            count = sources.length;
        }

        if (count == 0) {
            EmptySubscription.complete(s);
            return;
        } else
        if (count == 1) {
            sources[0].subscribe(s);
            return;
        }

        AmbCoordinator<T> ac = new AmbCoordinator<T>(s, count);
        ac.subscribe(sources);
    }

    static final class AmbCoordinator<T> implements Subscription {
        final Subscriber<? super T> downstream;
        final AmbInnerSubscriber<T>[] subscribers;

        final AtomicInteger winner = new AtomicInteger();

        @SuppressWarnings("unchecked")
        AmbCoordinator(Subscriber<? super T> actual, int count) {
            this.downstream = actual;
            this.subscribers = new AmbInnerSubscriber[count];
        }

        public void subscribe(Publisher<? extends T>[] sources) {
            AmbInnerSubscriber<T>[] as = subscribers;
            int len = as.length;
            for (int i = 0; i < len; i++) {
                as[i] = new AmbInnerSubscriber<T>(this, i + 1, downstream);
            }
            winner.lazySet(0); // release the contents of 'as'
            downstream.onSubscribe(this);

            for (int i = 0; i < len; i++) {
                if (winner.get() != 0) {
                    return;
                }

                sources[i].subscribe(as[i]);
            }
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                int w = winner.get();
                if (w > 0) {
                    subscribers[w - 1].request(n);
                } else
                if (w == 0) {
                    for (AmbInnerSubscriber<T> a : subscribers) {
                        a.request(n);
                    }
                }
            }
        }

        public boolean win(int index) {
            int w = winner.get();
            if (w == 0) {
                if (winner.compareAndSet(0, index)) {
                    AmbInnerSubscriber<T>[] a = subscribers;
                    int n = a.length;
                    for (int i = 0; i < n; i++) {
                        if (i + 1 != index) {
                            a[i].cancel();
                        }
                    }
                    return true;
                }
            }
            return false;
        }

        @Override
        public void cancel() {
            if (winner.get() != -1) {
                winner.lazySet(-1);

                for (AmbInnerSubscriber<T> a : subscribers) {
                    a.cancel();
                }
            }
        }
    }

    static final class AmbInnerSubscriber<T> extends AtomicReference<Subscription> implements FlowableSubscriber<T>, Subscription {

        private static final long serialVersionUID = -1185974347409665484L;
        final AmbCoordinator<T> parent;
        final int index;
        final Subscriber<? super T> downstream;

        boolean won;

        final AtomicLong missedRequested = new AtomicLong();

        AmbInnerSubscriber(AmbCoordinator<T> parent, int index, Subscriber<? super T> downstream) {
            this.parent = parent;
            this.index = index;
            this.downstream = downstream;
        }

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

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

        @Override
        public void onNext(T t) {
            if (won) {
                downstream.onNext(t);
            } else {
                if (parent.win(index)) {
                    won = true;
                    downstream.onNext(t);
                } else {
                    get().cancel();
                }
            }
        }

        @Override
        public void onError(Throwable t) {
            if (won) {
                downstream.onError(t);
            } else {
                if (parent.win(index)) {
                    won = true;
                    downstream.onError(t);
                } else {
                    get().cancel();
                    RxJavaPlugins.onError(t);
                }
            }
        }

        @Override
        public void onComplete() {
            if (won) {
                downstream.onComplete();
            } else {
                if (parent.win(index)) {
                    won = true;
                    downstream.onComplete();
                } else {
                    get().cancel();
                }
            }
        }

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

    }
}