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

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.BiFunction;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.fuseable.SimplePlainQueue;
import io.reactivex.internal.queue.SpscArrayQueue;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.internal.util.BackpressureHelper;
import io.reactivex.plugins.RxJavaPlugins;

public final class FlowableScanSeed<T, R> extends AbstractFlowableWithUpstream<T, R> {
    final BiFunction<R, ? super T, R> accumulator;
    final Callable<R> seedSupplier;

    public FlowableScanSeed(Flowable<T> source, Callable<R> seedSupplier, BiFunction<R, ? super T, R> accumulator) {
        super(source);
        this.accumulator = accumulator;
        this.seedSupplier = seedSupplier;
    }

    @Override
    protected void subscribeActual(Subscriber<? super R> s) {
        R r;

        try {
            r = ObjectHelper.requireNonNull(seedSupplier.call(), "The seed supplied is null");
        } catch (Throwable e) {
            Exceptions.throwIfFatal(e);
            EmptySubscription.error(e, s);
            return;
        }

        source.subscribe(new ScanSeedSubscriber<T, R>(s, accumulator, r, bufferSize()));
    }

    static final class ScanSeedSubscriber<T, R>
    extends AtomicInteger
    implements FlowableSubscriber<T>, Subscription {
        private static final long serialVersionUID = -1776795561228106469L;

        final Subscriber<? super R> downstream;

        final BiFunction<R, ? super T, R> accumulator;

        final SimplePlainQueue<R> queue;

        final AtomicLong requested;

        final int prefetch;

        final int limit;

        volatile boolean cancelled;

        volatile boolean done;
        Throwable error;

        Subscription upstream;

        R value;

        int consumed;

        ScanSeedSubscriber(Subscriber<? super R> actual, BiFunction<R, ? super T, R> accumulator, R value, int prefetch) {
            this.downstream = actual;
            this.accumulator = accumulator;
            this.value = value;
            this.prefetch = prefetch;
            this.limit = prefetch - (prefetch >> 2);
            this.queue = new SpscArrayQueue<R>(prefetch);
            this.queue.offer(value);
            this.requested = new AtomicLong();
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(this.upstream, s)) {
                this.upstream = s;

                downstream.onSubscribe(this);

                s.request(prefetch - 1);
            }
        }

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }

            R v = value;
            try {
                v = ObjectHelper.requireNonNull(accumulator.apply(v, t), "The accumulator returned a null value");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                upstream.cancel();
                onError(ex);
                return;
            }

            value = v;
            queue.offer(v);
            drain();
        }

        @Override
        public void onError(Throwable t) {
            if (done) {
                RxJavaPlugins.onError(t);
                return;
            }
            error = t;
            done = true;
            drain();
        }

        @Override
        public void onComplete() {
            if (done) {
                return;
            }
            done = true;
            drain();
        }

        @Override
        public void cancel() {
            cancelled = true;
            upstream.cancel();
            if (getAndIncrement() == 0) {
                queue.clear();
            }
        }

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

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

            int missed = 1;
            Subscriber<? super R> a = downstream;
            SimplePlainQueue<R> q = queue;
            int lim = limit;
            int c = consumed;

            for (;;) {

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

                while (e != r) {
                    if (cancelled) {
                        q.clear();
                        return;
                    }
                    boolean d = done;

                    if (d) {
                        Throwable ex = error;
                        if (ex != null) {
                            q.clear();
                            a.onError(ex);
                            return;
                        }
                    }

                    R v = q.poll();
                    boolean empty = v == null;

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

                    if (empty) {
                        break;
                    }

                    a.onNext(v);

                    e++;
                    if (++c == lim) {
                        c = 0;
                        upstream.request(lim);
                    }
                }

                if (e == r) {
                    if (done) {
                        Throwable ex = error;
                        if (ex != null) {
                            q.clear();
                            a.onError(ex);
                            return;
                        }
                        if (q.isEmpty()) {
                            a.onComplete();
                            return;
                        }
                    }
                }

                if (e != 0L) {
                    BackpressureHelper.produced(requested, e);
                }

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