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.*;

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

public final class ObservableAmb<T> extends Observable<T> {
    final ObservableSource<? extends T>[] sources;
    final Iterable<? extends ObservableSource<? extends T>> sourcesIterable;

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

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

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

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

    static final class AmbCoordinator<T> implements Disposable {
        final Observer<? super T> downstream;
        final AmbInnerObserver<T>[] observers;

        final AtomicInteger winner = new AtomicInteger();

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

        public void subscribe(ObservableSource<? extends T>[] sources) {
            AmbInnerObserver<T>[] as = observers;
            int len = as.length;
            for (int i = 0; i < len; i++) {
                as[i] = new AmbInnerObserver<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]);
            }
        }

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

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

                for (AmbInnerObserver<T> a : observers) {
                    a.dispose();
                }
            }
        }

        @Override
        public boolean isDisposed() {
            return winner.get() == -1;
        }
    }

    static final class AmbInnerObserver<T> extends AtomicReference<Disposable> implements Observer<T> {

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

        boolean won;

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

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

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

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

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

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