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/*
 * (c) Copyright 2018 Palantir Technologies Inc. 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
 *
 *     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 com.palantir.atlasdb.keyvalue.dbkvs.util;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public final class DbKvsPartitioners {
    private DbKvsPartitioners() {
        // Utility class
    }

    /**
     * Partitions the provided map into batches, where the total count of every batch except the last is {@code limit}.
     * Note this means that a single element may be split into multiple batches. The ordering of the provided map is
     * preserved, i.e. if x appears before y in {@code counts}, then no batch containing x will appear after a batch
     * containing y, and if a batch contains both, then x will appear before y in that batch.
     */
    public static  List> partitionByTotalCount(Map counts, int limit) {
        List> batches = new ArrayList<>();
        Map currentBatch = new LinkedHashMap<>();
        batches.add(currentBatch);
        int currentBatchColumns = 0;

        for (Map.Entry entry : counts.entrySet()) {
            T currentElement = entry.getKey();
            int remainingCountForCurrentElement = entry.getValue();

            while (currentBatchColumns + remainingCountForCurrentElement > limit) {
                int numColumnsToInclude = limit - currentBatchColumns;
                if (numColumnsToInclude > 0) {
                    currentBatch.put(currentElement, numColumnsToInclude);
                }
                remainingCountForCurrentElement -= numColumnsToInclude;

                // Create new batch. Note that since we have exceeded the limit, something will eventually get added to
                // this batch
                currentBatch = new LinkedHashMap<>();
                batches.add(currentBatch);
                currentBatchColumns = 0;
            }

            currentBatch.put(currentElement, remainingCountForCurrentElement);
            currentBatchColumns += remainingCountForCurrentElement;
        }
        return batches;
    }
}