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.single;

import java.util.concurrent.atomic.AtomicBoolean;

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

public final class SingleAmb<T> extends Single<T> {
    private final SingleSource<? extends T>[] sources;
    private final Iterable<? extends SingleSource<? extends T>> sourcesIterable;

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

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

        final AtomicBoolean winner = new AtomicBoolean();
        final CompositeDisposable set = new CompositeDisposable();

        observer.onSubscribe(set);

        for (int i = 0; i < count; i++) {
            SingleSource<? extends T> s1 = sources[i];
            if (set.isDisposed()) {
                return;
            }

            if (s1 == null) {
                set.dispose();
                Throwable e = new NullPointerException("One of the sources is null");
                if (winner.compareAndSet(false, true)) {
                    observer.onError(e);
                } else {
                    RxJavaPlugins.onError(e);
                }
                return;
            }

            s1.subscribe(new AmbSingleObserver<T>(observer, set, winner));
        }
    }

    static final class AmbSingleObserver<T> implements SingleObserver<T> {

        final CompositeDisposable set;

        final SingleObserver<? super T> downstream;

        final AtomicBoolean winner;

        Disposable upstream;

        AmbSingleObserver(SingleObserver<? super T> observer, CompositeDisposable set, AtomicBoolean winner) {
            this.downstream = observer;
            this.set = set;
            this.winner = winner;
        }

        @Override
        public void onSubscribe(Disposable d) {
            this.upstream = d;
            set.add(d);
        }

        @Override
        public void onSuccess(T value) {
            if (winner.compareAndSet(false, true)) {
                set.delete(upstream);
                set.dispose();
                downstream.onSuccess(value);
            }
        }

        @Override
        public void onError(Throwable e) {
            if (winner.compareAndSet(false, true)) {
                set.delete(upstream);
                set.dispose();
                downstream.onError(e);
            } else {
                RxJavaPlugins.onError(e);
            }
        }
    }

}