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.functions.Function;
import io.reactivex.internal.disposables.*;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.util.AtomicThrowable;
import io.reactivex.plugins.RxJavaPlugins;

public final class ObservableCombineLatest<T, R> extends Observable<R> {
    final ObservableSource<? extends T>[] sources;
    final Iterable<? extends ObservableSource<? extends T>> sourcesIterable;
    final Function<? super Object[], ? extends R> combiner;
    final int bufferSize;
    final boolean delayError;

    public ObservableCombineLatest(ObservableSource<? extends T>[] sources,
            Iterable<? extends ObservableSource<? extends T>> sourcesIterable,
            Function<? super Object[], ? extends R> combiner, int bufferSize,
            boolean delayError) {
        this.sources = sources;
        this.sourcesIterable = sourcesIterable;
        this.combiner = combiner;
        this.bufferSize = bufferSize;
        this.delayError = delayError;
    }

    @Override
    @SuppressWarnings("unchecked")
    public void subscribeActual(Observer<? super R> observer) {
        ObservableSource<? extends T>[] sources = this.sources;
        int count = 0;
        if (sources == null) {
            sources = new Observable[8];
            for (ObservableSource<? extends T> p : sourcesIterable) {
                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;
            }
        } else {
            count = sources.length;
        }

        if (count == 0) {
            EmptyDisposable.complete(observer);
            return;
        }

        LatestCoordinator<T, R> lc = new LatestCoordinator<T, R>(observer, combiner, count, bufferSize, delayError);
        lc.subscribe(sources);
    }

    static final class LatestCoordinator<T, R> extends AtomicInteger implements Disposable {

        private static final long serialVersionUID = 8567835998786448817L;
        final Observer<? super R> downstream;
        final Function<? super Object[], ? extends R> combiner;
        final CombinerObserver<T, R>[] observers;
        Object[] latest;
        final SpscLinkedArrayQueue<Object[]> queue;
        final boolean delayError;

        volatile boolean cancelled;

        volatile boolean done;

        final AtomicThrowable errors = new AtomicThrowable();

        int active;
        int complete;

        @SuppressWarnings("unchecked")
        LatestCoordinator(Observer<? super R> actual,
                Function<? super Object[], ? extends R> combiner,
                int count, int bufferSize, boolean delayError) {
            this.downstream = actual;
            this.combiner = combiner;
            this.delayError = delayError;
            this.latest = new Object[count];
            CombinerObserver<T, R>[] as = new CombinerObserver[count];
            for (int i = 0; i < count; i++) {
                as[i] = new CombinerObserver<T, R>(this, i);
            }
            this.observers = as;
            this.queue = new SpscLinkedArrayQueue<Object[]>(bufferSize);
        }

        public void subscribe(ObservableSource<? extends T>[] sources) {
            Observer<T>[] as = observers;
            int len = as.length;
            downstream.onSubscribe(this);
            for (int i = 0; i < len; i++) {
                if (done || cancelled) {
                    return;
                }
                sources[i].subscribe(as[i]);
            }
        }

        @Override
        public void dispose() {
            if (!cancelled) {
                cancelled = true;
                cancelSources();
                if (getAndIncrement() == 0) {
                    clear(queue);
                }
            }
        }

        @Override
        public boolean isDisposed() {
            return cancelled;
        }

        void cancelSources() {
            for (CombinerObserver<T, R> observer : observers) {
                observer.dispose();
            }
        }

        void clear(SpscLinkedArrayQueue<?> q) {
            synchronized (this) {
                latest = null;
            }
            q.clear();
        }

        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }

            final SpscLinkedArrayQueue<Object[]> q = queue;
            final Observer<? super R> a = downstream;
            final boolean delayError = this.delayError;

            int missed = 1;
            for (;;) {

                for (;;) {
                    if (cancelled) {
                        clear(q);
                        return;
                    }

                    if (!delayError && errors.get() != null) {
                        cancelSources();
                        clear(q);
                        a.onError(errors.terminate());
                        return;
                    }

                    boolean d = done;
                    Object[] s = q.poll();
                    boolean empty = s == null;

                    if (d && empty) {
                        clear(q);
                        Throwable ex = errors.terminate();
                        if (ex == null) {
                            a.onComplete();
                        } else {
                            a.onError(ex);
                        }
                        return;
                    }

                    if (empty) {
                        break;
                    }

                    R v;

                    try {
                        v = ObjectHelper.requireNonNull(combiner.apply(s), "The combiner returned a null value");
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);
                        errors.addThrowable(ex);
                        cancelSources();
                        clear(q);
                        ex = errors.terminate();
                        a.onError(ex);
                        return;
                    }

                    a.onNext(v);
                }

                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }

        void innerNext(int index, T item) {
            boolean shouldDrain = false;
            synchronized (this) {
                Object[] latest = this.latest;
                if (latest == null) {
                    return;
                }
                Object o = latest[index];
                int a = active;
                if (o == null) {
                    active = ++a;
                }
                latest[index] = item;
                if (a == latest.length) {
                    queue.offer(latest.clone());
                    shouldDrain = true;
                }
            }
            if (shouldDrain) {
                drain();
            }
        }

        void innerError(int index, Throwable ex) {
            if (errors.addThrowable(ex)) {
                boolean cancelOthers = true;
                if (delayError) {
                    synchronized (this) {
                        Object[] latest = this.latest;
                        if (latest == null) {
                            return;
                        }

                        cancelOthers = latest[index] == null;
                        if (cancelOthers || ++complete == latest.length) {
                            done = true;
                        }
                    }
                }
                if (cancelOthers) {
                    cancelSources();
                }
                drain();
            } else {
                RxJavaPlugins.onError(ex);
            }
        }

        void innerComplete(int index) {
            boolean cancelOthers = false;
            synchronized (this) {
                Object[] latest = this.latest;
                if (latest == null) {
                    return;
                }

                cancelOthers = latest[index] == null;
                if (cancelOthers || ++complete == latest.length) {
                    done = true;
                }
            }
            if (cancelOthers) {
                cancelSources();
            }
            drain();
        }

    }

    static final class CombinerObserver<T, R> extends AtomicReference<Disposable> implements Observer<T> {
        private static final long serialVersionUID = -4823716997131257941L;

        final LatestCoordinator<T, R> parent;

        final int index;

        CombinerObserver(LatestCoordinator<T, R> parent, int index) {
            this.parent = parent;
            this.index = index;
        }

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

        @Override
        public void onNext(T t) {
            parent.innerNext(index, t);
        }

        @Override
        public void onError(Throwable t) {
            parent.innerError(index, t);
        }

        @Override
        public void onComplete() {
            parent.innerComplete(index);
        }

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