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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.eventmesh.common.loadbalance;

import org.apache.eventmesh.common.exception.EventMeshException;

import org.apache.commons.collections4.CollectionUtils;

import java.util.List;
import java.util.concurrent.ThreadLocalRandom;

/**
 * This selector use the weighted random strategy to select from list. If all the weights are same, it will randomly select one from list. If the
 * weights are different, it will select one by using RandomUtils.nextInt(0, w0 + w1 ... + wn)
 *
 * @param  Target type
 */
public class WeightRandomLoadBalanceSelector implements LoadBalanceSelector {

    private final transient List> clusterGroup;

    private final transient int totalWeight;

    private transient boolean sameWeightGroup = true;

    public WeightRandomLoadBalanceSelector(List> clusterGroup) throws EventMeshException {
        if (CollectionUtils.isEmpty(clusterGroup)) {
            throw new EventMeshException("clusterGroup can not be empty");
        }
        int totalWeight = 0;
        int firstWeight = clusterGroup.get(0).getValue();
        for (Weight weight : clusterGroup) {
            totalWeight += weight.getValue();
            if (sameWeightGroup && firstWeight != weight.getValue()) {
                sameWeightGroup = false;
            }
        }
        this.clusterGroup = clusterGroup;
        this.totalWeight = totalWeight;
    }

    @Override
    public T select() {
        if (!sameWeightGroup) {
            int targetWeight = ThreadLocalRandom.current().nextInt(totalWeight);
            for (Weight weight : clusterGroup) {
                targetWeight -= weight.getValue();
                if (targetWeight < 0) {
                    return weight.getTarget();
                }
            }
        }

        int length = clusterGroup.size();
        return clusterGroup.get(ThreadLocalRandom.current().nextInt(length)).getTarget();
    }

    @Override
    public LoadBalanceType getType() {
        return LoadBalanceType.WEIGHT_RANDOM;
    }
}