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 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.subscriptions.SubscriptionHelper;
import io.reactivex.plugins.RxJavaPlugins;

public final class FlowableScan<T> extends AbstractFlowableWithUpstream<T, T> {
    final BiFunction<T, T, T> accumulator;
    public FlowableScan(Flowable<T> source, BiFunction<T, T, T> accumulator) {
        super(source);
        this.accumulator = accumulator;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {
        source.subscribe(new ScanSubscriber<T>(s, accumulator));
    }

    static final class ScanSubscriber<T> implements FlowableSubscriber<T>, Subscription {
        final Subscriber<? super T> downstream;
        final BiFunction<T, T, T> accumulator;

        Subscription upstream;

        T value;

        boolean done;

        ScanSubscriber(Subscriber<? super T> actual, BiFunction<T, T, T> accumulator) {
            this.downstream = actual;
            this.accumulator = accumulator;
        }

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

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }
            final Subscriber<? super T> a = downstream;
            T v = value;
            if (v == null) {
                value = t;
                a.onNext(t);
            } else {
                T u;

                try {
                    u = ObjectHelper.requireNonNull(accumulator.apply(v, t), "The value returned by the accumulator is null");
                } catch (Throwable e) {
                    Exceptions.throwIfFatal(e);
                    upstream.cancel();
                    onError(e);
                    return;
                }

                value = u;
                a.onNext(u);
            }
        }

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

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

        @Override
        public void request(long n) {
            upstream.request(n);
        }

        @Override
        public void cancel() {
            upstream.cancel();
        }
    }
}