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OptaPlanner solves planning problems. This lightweight, embeddable planning engine implements powerful and scalable algorithms to optimize business resource scheduling and planning. This module contains the examples which demonstrate how to use it in a normal Java application.

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/*
 * Copyright 2018 Red Hat, Inc. and/or its affiliates.
 *
 * 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 org.optaplanner.examples.common.solver.drools.functions;

import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;

import org.kie.api.runtime.rule.AccumulateFunction;

public class LoadBalanceByCountAccumulateFunction
        implements AccumulateFunction {

    protected static class LoadBalanceByCountData implements Serializable {

        private Map groupCountMap;
        // the sum of squared deviation from zero
        private long squaredSum;

    }

    @Override
    public LoadBalanceByCountData createContext() {
        return new LoadBalanceByCountData();
    }

    @Override
    public void init(LoadBalanceByCountData data) {
        data.groupCountMap = new HashMap<>();
        data.squaredSum = 0L;
    }

    @Override
    public void accumulate(LoadBalanceByCountData data, Object groupBy) {
        long count = data.groupCountMap.compute(groupBy,
                (key, value) -> (value == null) ? 1L : value + 1L);
        // squaredZeroDeviation = squaredZeroDeviation - (count - 1)² + count²
        // <=> squaredZeroDeviation = squaredZeroDeviation + (2 * count - 1)
        data.squaredSum += (2 * count - 1);
    }

    @Override
    public boolean supportsReverse() {
        return true;
    }

    @Override
    public void reverse(LoadBalanceByCountData data, Object groupBy) {
        Long count = data.groupCountMap.compute(groupBy,
                (key, value) -> (value.longValue() == 1L) ? null : value - 1L);
        data.squaredSum -= (count == null) ? 1L : (2 * count + 1);
    }

    @Override
    public Class getResultType() {
        return LoadBalanceByCountResult.class;
    }

    @Override
    public LoadBalanceByCountResult getResult(LoadBalanceByCountData data) {
        return new LoadBalanceByCountResult(data.squaredSum);
    }

    @Override
    public void writeExternal(ObjectOutput out) {
    }

    @Override
    public void readExternal(ObjectInput in) {
    }

    public static class LoadBalanceByCountResult implements Serializable {

        private final long squaredSum;

        public LoadBalanceByCountResult(long squaredSum) {
            this.squaredSum = squaredSum;
        }

        public long getZeroDeviationSquaredSum() {
            return squaredSum;
        }

        /**
         * @return {@link #getZeroDeviationSquaredSumRoot(double)} multiplied by {@literal 1 000}
         */
        public long getZeroDeviationSquaredSumRootMillis() {
            return getZeroDeviationSquaredSumRoot(1_000.0);
        }

        /**
         * @return {@link #getZeroDeviationSquaredSumRoot(double)} multiplied by {@literal 1 000 000}
         */
        public long getZeroDeviationSquaredSumRootMicros() {
            return getZeroDeviationSquaredSumRoot(1_000_000.0);
        }

        /**
         * @param scaleMultiplier {@code > 0}
         * @return {@code >= 0}, {@code latexmath:[f(n) = \sqrt{\sum_{i=1}^{n} (x_i - 0)^2}]} multiplied by scaleMultiplier
         */
        public long getZeroDeviationSquaredSumRoot(double scaleMultiplier) {
            return (long) (Math.sqrt((double) squaredSum) * scaleMultiplier);
        }

    }

}