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Composable asynchronous/reactive streams with powerful data processing capabilities.
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/*
 * Copyright (C) 2015 SoftIndex LLC.
 *
 * 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.datakernel.stream.processor;

import com.google.common.base.Function;
import io.datakernel.eventloop.Eventloop;
import io.datakernel.stream.StreamConsumer;

import java.util.Comparator;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Merges sorted by keys streams and streams its sorted union. It is simple
 * {@link AbstractStreamReducer} which do nothing with data and only streams it
 * sorted by keys.
 *
 * @param  type of key for mapping
 * @param  type of output data
 */
public final class StreamMerger extends AbstractStreamReducer {

	private final Function keyFunction;
	private final StreamReducers.Reducer reducer;

	/**
	 * Returns new instance of StreamMerger
	 *
	 * @param eventloop     eventloop in which runs reducer
	 * @param keyComparator comparator for compare keys
	 * @param keyFunction   function for counting key
	 * @param deduplicate   if it is true it means that in result will be not objects with same key
	 * @param            type of key for mapping
	 * @param            type of output data
	 */
	public static  StreamMerger streamMerger(Eventloop eventloop, Function keyFunction, Comparator keyComparator,
	                                                     boolean deduplicate) {
		return new StreamMerger<>(eventloop, keyFunction, keyComparator, deduplicate);
	}

	/**
	 * Creates a new instance of StreamMerger
	 *
	 * @param eventloop     eventloop in which runs reducer
	 * @param keyComparator comparator for compare keys
	 * @param keyFunction   function for counting key
	 * @param deduplicate   if it is true it means that in result will be not objects with same key
	 */
	public StreamMerger(Eventloop eventloop, Function keyFunction, Comparator keyComparator,
	                    boolean deduplicate) {
		super(eventloop, keyComparator);
		this.keyFunction = checkNotNull(keyFunction);
		this.reducer = deduplicate ? StreamReducers.mergeDeduplicateReducer() : StreamReducers.mergeSortReducer();
	}

	/**
	 * Adds new consumer to  StreamMerger
	 *
	 * @return this consumer
	 */
	public StreamConsumer newInput() {
		return super.newInput(keyFunction, reducer);
	}

}