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.Iterator;
import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.annotations.*;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.operators.flowable.FlowableMap.MapSubscriber;
import io.reactivex.internal.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.internal.util.*;
import io.reactivex.plugins.RxJavaPlugins;

Combines the latest values from multiple sources through a function.
Type parameters:
<T> – the value type of the sources
<R> – the result type/**
 * Combines the latest values from multiple sources through a function.
 *
 * @param <T> the value type of the sources
 * @param <R> the result type
 */
public final class FlowableCombineLatest<T, R>
extends Flowable<R> {

    @Nullable
    final Publisher<? extends T>[] array;

    @Nullable
    final Iterable<? extends Publisher<? extends T>> iterable;

    final Function<? super Object[], ? extends R> combiner;

    final int bufferSize;

    final boolean delayErrors;

    public FlowableCombineLatest(@NonNull Publisher<? extends T>[] array,
                    @NonNull Function<? super Object[], ? extends R> combiner,
                    int bufferSize, boolean delayErrors) {
        this.array = array;
        this.iterable = null;
        this.combiner = combiner;
        this.bufferSize = bufferSize;
        this.delayErrors = delayErrors;
    }

    public FlowableCombineLatest(@NonNull Iterable<? extends Publisher<? extends T>> iterable,
                    @NonNull Function<? super Object[], ? extends R> combiner,
                    int bufferSize, boolean delayErrors) {
        this.array = null;
        this.iterable = iterable;
        this.combiner = combiner;
        this.bufferSize = bufferSize;
        this.delayErrors = delayErrors;
    }

    @SuppressWarnings("unchecked")
    @Override
    public void subscribeActual(Subscriber<? super R> s) {
        Publisher<? extends T>[] a = array;
        int n;
        if (a == null) {
            n = 0;
            a = new Publisher[8];

            Iterator<? extends Publisher<? extends T>> it;

            try {
                it = ObjectHelper.requireNonNull(iterable.iterator(), "The iterator returned is null");
            } catch (Throwable e) {
                Exceptions.throwIfFatal(e);
                EmptySubscription.error(e, s);
                return;
            }

            for (;;) {

                boolean b;

                try {
                    b = it.hasNext();
                } catch (Throwable e) {
                    Exceptions.throwIfFatal(e);
                    EmptySubscription.error(e, s);
                    return;
                }

                if (!b) {
                    break;
                }

                Publisher<? extends T> p;

                try {
                    p = ObjectHelper.requireNonNull(it.next(), "The publisher returned by the iterator is null");
                } catch (Throwable e) {
                    Exceptions.throwIfFatal(e);
                    EmptySubscription.error(e, s);
                    return;
                }

                if (n == a.length) {
                    Publisher<? extends T>[] c = new Publisher[n + (n >> 2)];
                    System.arraycopy(a, 0, c, 0, n);
                    a = c;
                }
                a[n++] = p;
            }

        } else {
            n = a.length;
        }

        if (n == 0) {
            EmptySubscription.complete(s);
            return;
        }
        if (n == 1) {
            ((Publisher<T>)a[0]).subscribe(new MapSubscriber<T, R>(s, new SingletonArrayFunc()));
            return;
        }

        CombineLatestCoordinator<T, R> coordinator =
                new CombineLatestCoordinator<T, R>(s, combiner, n, bufferSize, delayErrors);

        s.onSubscribe(coordinator);

        coordinator.subscribe(a, n);
    }

    static final class CombineLatestCoordinator<T, R>
    extends BasicIntQueueSubscription<R> {

        private static final long serialVersionUID = -5082275438355852221L;

        final Subscriber<? super R> downstream;

        final Function<? super Object[], ? extends R> combiner;

        final CombineLatestInnerSubscriber<T>[] subscribers;

        final SpscLinkedArrayQueue<Object> queue;

        final Object[] latest;

        final boolean delayErrors;

        boolean outputFused;

        int nonEmptySources;

        int completedSources;

        volatile boolean cancelled;

        final AtomicLong requested;

        volatile boolean done;

        final AtomicReference<Throwable> error;

        CombineLatestCoordinator(Subscriber<? super R> actual,
                Function<? super Object[], ? extends R> combiner, int n,
                int bufferSize, boolean delayErrors) {
            this.downstream = actual;
            this.combiner = combiner;
            @SuppressWarnings("unchecked")
            CombineLatestInnerSubscriber<T>[] a = new CombineLatestInnerSubscriber[n];
            for (int i = 0; i < n; i++) {
                a[i] = new CombineLatestInnerSubscriber<T>(this, i, bufferSize);
            }
            this.subscribers = a;
            this.latest = new Object[n];
            this.queue = new SpscLinkedArrayQueue<Object>(bufferSize);
            this.requested = new AtomicLong();
            this.error = new  AtomicReference<Throwable>();
            this.delayErrors = delayErrors;
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                BackpressureHelper.add(requested, n);
                drain();
            }
        }

        @Override
        public void cancel() {
            cancelled = true;
            cancelAll();
        }

        void subscribe(Publisher<? extends T>[] sources, int n) {
            CombineLatestInnerSubscriber<T>[] a = subscribers;

            for (int i = 0; i < n; i++) {
                if (done || cancelled) {
                    return;
                }
                sources[i].subscribe(a[i]);
            }
        }

        void innerValue(int index, T value) {

            boolean replenishInsteadOfDrain;

            synchronized (this) {
                Object[] os = latest;

                int localNonEmptySources = nonEmptySources;

                if (os[index] == null) {
                    localNonEmptySources++;
                    nonEmptySources = localNonEmptySources;
                }

                os[index] = value;

                if (os.length == localNonEmptySources) {

                    queue.offer(subscribers[index], os.clone());

                    replenishInsteadOfDrain = false;
                } else {
                    replenishInsteadOfDrain = true;
                }
            }

            if (replenishInsteadOfDrain) {
                subscribers[index].requestOne();
            } else {
                drain();
            }
        }

        void innerComplete(int index) {
            synchronized (this) {
                Object[] os = latest;

                if (os[index] != null) {
                    int localCompletedSources = completedSources + 1;

                    if (localCompletedSources == os.length) {
                        done = true;
                    } else {
                        completedSources = localCompletedSources;
                        return;
                    }
                } else {
                    done = true;
                }
            }
            drain();
        }

        void innerError(int index, Throwable e) {

            if (ExceptionHelper.addThrowable(error, e)) {
                if (!delayErrors) {
                    cancelAll();
                    done = true;
                    drain();
                } else {
                    innerComplete(index);
                }
            } else {
                RxJavaPlugins.onError(e);
            }
        }

        void drainOutput() {
            final Subscriber<? super R> a = downstream;
            final SpscLinkedArrayQueue<Object> q = queue;

            int missed = 1;

            for (;;) {

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

                Throwable ex = error.get();
                if (ex != null) {
                    q.clear();

                    a.onError(ex);
                    return;
                }

                boolean d = done;

                boolean empty = q.isEmpty();

                if (!empty) {
                    a.onNext(null);
                }

                if (d && empty) {
                    a.onComplete();
                    return;
                }

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

        @SuppressWarnings("unchecked")
        void drainAsync() {
            final Subscriber<? super R> a = downstream;
            final SpscLinkedArrayQueue<Object> q = queue;

            int missed = 1;

            for (;;) {

                long r = requested.get();
                long e = 0L;

                while (e != r) {
                    boolean d = done;

                    Object v = q.poll();

                    boolean empty = v == null;

                    if (checkTerminated(d, empty, a, q)) {
                        return;
                    }

                    if (empty) {
                        break;
                    }

                    T[] va = (T[])q.poll();

                    R w;

                    try {
                        w = ObjectHelper.requireNonNull(combiner.apply(va), "The combiner returned a null value");
                    } catch (Throwable ex) {
                        Exceptions.throwIfFatal(ex);

                        cancelAll();
                        ExceptionHelper.addThrowable(error, ex);
                        ex = ExceptionHelper.terminate(error);

                        a.onError(ex);
                        return;
                    }

                    a.onNext(w);

                    ((CombineLatestInnerSubscriber<T>)v).requestOne();

                    e++;
                }

                if (e == r) {
                    if (checkTerminated(done, q.isEmpty(), a, q)) {
                        return;
                    }
                }

                if (e != 0L && r != Long.MAX_VALUE) {
                    requested.addAndGet(-e);
                }

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

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

            if (outputFused) {
                drainOutput();
            } else {
                drainAsync();
            }
        }

        boolean checkTerminated(boolean d, boolean empty, Subscriber<?> a, SpscLinkedArrayQueue<?> q) {
            if (cancelled) {
                cancelAll();
                q.clear();
                return true;
            }

            if (d) {
                if (delayErrors) {
                    if (empty) {
                        cancelAll();
                        Throwable e = ExceptionHelper.terminate(error);

                        if (e != null && e != ExceptionHelper.TERMINATED) {
                            a.onError(e);
                        } else {
                            a.onComplete();
                        }
                        return true;
                    }
                } else {
                    Throwable e = ExceptionHelper.terminate(error);

                    if (e != null && e != ExceptionHelper.TERMINATED) {
                        cancelAll();
                        q.clear();
                        a.onError(e);
                        return true;
                    } else
                    if (empty) {
                        cancelAll();

                        a.onComplete();
                        return true;
                    }
                }
            }
            return false;
        }

        void cancelAll() {
            for (CombineLatestInnerSubscriber<T> inner : subscribers) {
                inner.cancel();
            }
        }

        @Override
        public int requestFusion(int requestedMode) {
            if ((requestedMode & BOUNDARY) != 0) {
                return NONE;
            }
            int m = requestedMode & ASYNC;
            outputFused = m != 0;
            return m;
        }

        @Nullable
        @SuppressWarnings("unchecked")
        @Override
        public R poll() throws Exception {
            Object e = queue.poll();
            if (e == null) {
                return null;
            }
            T[] a = (T[])queue.poll();
            R r = ObjectHelper.requireNonNull(combiner.apply(a), "The combiner returned a null value");
            ((CombineLatestInnerSubscriber<T>)e).requestOne();
            return r;
        }

        @Override
        public void clear() {
            queue.clear();
        }

        @Override
        public boolean isEmpty() {
            return queue.isEmpty();
        }
    }

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

        private static final long serialVersionUID = -8730235182291002949L;

        final CombineLatestCoordinator<T, ?> parent;

        final int index;

        final int prefetch;

        final int limit;

        int produced;

        CombineLatestInnerSubscriber(CombineLatestCoordinator<T, ?> parent, int index, int prefetch) {
            this.parent = parent;
            this.index = index;
            this.prefetch = prefetch;
            this.limit = prefetch - (prefetch >> 2);
        }

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

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

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

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

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

        public void requestOne() {

            int p = produced + 1;
            if (p == limit) {
                produced = 0;
                get().request(p);
            } else {
                produced = p;
            }

        }
    }

    final class SingletonArrayFunc implements Function<T, R> {
        @Override
        public R apply(T t) throws Exception {
            return combiner.apply(new Object[] { t });
        }
    }
}