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Easy Redis Java client and Real-Time Data Platform. Valkey compatible. Sync/Async/RxJava3/Reactive API. Client side caching. Over 50 Redis based Java objects and services: JCache API, Apache Tomcat, Hibernate, Spring, Set, Multimap, SortedSet, Map, List, Queue, Deque, Semaphore, Lock, AtomicLong, Map Reduce, Bloom filter, Scheduler, RPC

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/*
 * Copyright (c) 2016-2023 VMware Inc. or its affiliates, All Rights Reserved.
 *
 * 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
 *
 *   https://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 reactor.core.publisher;

import java.util.Objects;
import java.util.function.BiFunction;
import java.util.function.Supplier;

import org.reactivestreams.Subscriber;
import reactor.core.CoreSubscriber;
import reactor.core.Fuseable;
import reactor.core.Scannable;
import reactor.util.annotation.Nullable;

/**
 * Reduce the sequence of values in each 'rail' to a single value.
 *
 * @param  the input value type
 * @param  the result value type
 */
final class ParallelReduceSeed extends ParallelFlux implements
                                                             Scannable, Fuseable {

	final ParallelFlux source;

	final Supplier initialSupplier;

	final BiFunction reducer;

	ParallelReduceSeed(ParallelFlux source,
			Supplier initialSupplier,
			BiFunction reducer) {
		this.source = ParallelFlux.from(source);
		this.initialSupplier = initialSupplier;
		this.reducer = reducer;
	}

	@Override
	@Nullable
	public Object scanUnsafe(Scannable.Attr key) {
		if (key == Attr.PARENT) return source;
		if (key == Attr.PREFETCH) return getPrefetch();
		if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
		if (key == InternalProducerAttr.INSTANCE) return true;

		return null;
	}

	@Override
	public int getPrefetch() {
		return Integer.MAX_VALUE;
	}

	@Override
	public void subscribe(CoreSubscriber[] subscribers) {
		if (!validate(subscribers)) {
			return;
		}

		int n = subscribers.length;
		@SuppressWarnings("unchecked") CoreSubscriber[] parents = new CoreSubscriber[n];

		for (int i = 0; i < n; i++) {

			R initialValue;

			try {
				initialValue = Objects.requireNonNull(initialSupplier.get(),
						"The initialSupplier returned a null value");
			}
			catch (Throwable ex) {
				reportError(subscribers, Operators.onOperatorError(ex,
						subscribers[i].currentContext()));
				return;
			}
			parents[i] =
					new ParallelReduceSeedSubscriber<>(subscribers[i], initialValue, reducer);
		}

		source.subscribe(parents);
	}

	void reportError(Subscriber[] subscribers, Throwable ex) {
		for (Subscriber s : subscribers) {
			Operators.error(s, ex);
		}
	}

	@Override
	public int parallelism() {
		return source.parallelism();
	}


	static final class ParallelReduceSeedSubscriber
			extends Operators.BaseFluxToMonoOperator {

		final BiFunction reducer;

		R accumulator;

		boolean done;

		ParallelReduceSeedSubscriber(CoreSubscriber subscriber,
				R initialValue,
				BiFunction reducer) {
			super(subscriber);
			this.accumulator = initialValue;
			this.reducer = reducer;
		}

		@Override
		public void onNext(T t) {
			if (done) {
				Operators.onNextDropped(t, actual.currentContext());
				return;
			}

			synchronized (this) {
				R v;
				try {
					if (accumulator == null) {
						return;
					}

					v = Objects.requireNonNull(reducer.apply(accumulator, t),
							"The reducer returned a null value");
				}
				catch (Throwable ex) {
					onError(Operators.onOperatorError(this.s, ex, t, actual.currentContext()));
					return;
				}

				accumulator = v;
			}
		}

		@Override
		public void onError(Throwable t) {
			if (done) {
				Operators.onErrorDropped(t, actual.currentContext());
				return;
			}
			done = true;

			final R a;
			synchronized (this) {
				a = accumulator;
				if (a != null) {
					accumulator = null;
				}
			}

			if (a == null) {
				return;
			}

			Operators.onDiscard(a, currentContext());

			actual.onError(t);
		}

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

			completePossiblyEmpty();
		}

		@Override
		R accumulatedValue() {
			final R a;
			synchronized (this) {
				a = accumulator;
				if (a != null) {
					accumulator = null;
				}
			}
			return a;
		}

		@Override
		public void cancel() {
			s.cancel();

			final R a;
			synchronized (this) {
				a = accumulator;
				if (a != null) {
					accumulator = null;
				}
			}

			if (a == null) {
				return;
			}

			Operators.onDiscard(a, currentContext());
		}

		@Override
		public Object scanUnsafe(Attr key) {
			if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
			if (key == Attr.TERMINATED) return done;
			if (key == Attr.CANCELLED) return !done && accumulator == null;
			return super.scanUnsafe(key);
		}
	}
}