/**
 * Copyright 2016 Netflix, Inc.
 *
 * 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 org.reactivestreams.*;

import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.BiFunction;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscribers.SinglePostCompleteSubscriber;
import io.reactivex.internal.subscriptions.EmptySubscription;

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

    public FlowableScanSeed(Publisher<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));
    }

    static final class ScanSeedSubscriber<T, R> extends SinglePostCompleteSubscriber<T, R> {
        private static final long serialVersionUID = -1776795561228106469L;

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

        ScanSeedSubscriber(Subscriber<? super R> actual, BiFunction<R, ? super T, R> accumulator, R value) {
            super(actual);
            this.accumulator = accumulator;
            this.value = value;
        }

        @Override
        public void onNext(T t) {
            R v = value;

            R u;

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

            value = u;
            produced++;
            actual.onNext(v);
        }

        @Override
        public void onError(Throwable t) {
            value = null;
            actual.onError(t);
        }

        @Override
        public void onComplete() {
            complete(value);
        }
    }
}
