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/*
 * Copyright (c) 2020-2030, Shuigedeng ([email protected] & https://blog.taotaocloud.top/).
 *
 * 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 com.taotao.boot.sms.common.loadbalancer;

import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * smooth weight round robin Load Balancer
 *
 * @author shuigedeng
 * @version 2022.04
 * @since 2022-04-27 17:53:07
 */
public class SmoothWeightRoundRobinLoadBalancer extends AbstractLoadBalancer {

    private final Map originWeightMap = new ConcurrentHashMap<>();

    private final Map currentWeightMap = new ConcurrentHashMap<>();

    private final Lock lock = new ReentrantLock();

    /** instantiation Load Balancer with CopyOnWriteArrayList */
    public SmoothWeightRoundRobinLoadBalancer() {
        super();
    }

    /**
     * instantiation Load Balancer with appoint list
     *
     * @param targetList target object list
     */
    public SmoothWeightRoundRobinLoadBalancer(List> targetList) {
        super(targetList);
    }

    @Override
    protected void afterAdd(TargetWrapper wrapper) {
        originWeightMap.put(wrapper.getTarget(), MIN_WEIGHT);
        currentWeightMap.put(wrapper.getTarget(), MIN_WEIGHT);
    }

    @Override
    protected void afterRemove(TargetWrapper wrapper) {
        originWeightMap.remove(wrapper.getTarget());
        currentWeightMap.remove(wrapper.getTarget());
    }

    @Override
    public void setWeight(T target, int weight) {
        if (target == null) {
            return;
        }

        originWeightMap.put(target, Math.max(weight, MIN_WEIGHT));
    }

    @Override
    protected T choose0(List> activeTargetList, C chooseReferenceObject) {
        lock.lock();
        try {
            int originWeightSum = 0;
            int currentMaxWeight = Integer.MIN_VALUE;
            TargetWrapper currentMaxWeightWrapper = null;

            for (TargetWrapper wrapper : activeTargetList) {
                int originWeight = originWeightMap.getOrDefault(wrapper.getTarget(), MIN_WEIGHT);
                int currentWeight = currentWeightMap.getOrDefault(wrapper.getTarget(), originWeight);
                originWeightSum += originWeight;
                if (currentWeight > currentMaxWeight) {
                    currentMaxWeight = currentWeight;
                    currentMaxWeightWrapper = wrapper;
                }
            }

            if (currentMaxWeightWrapper == null) {
                return null;
            }

            currentWeightMap.put(currentMaxWeightWrapper.getTarget(), currentMaxWeight - originWeightSum);

            for (TargetWrapper wrapper : activeTargetList) {
                int originWeight = originWeightMap.getOrDefault(wrapper.getTarget(), MIN_WEIGHT);
                int currentWeight = currentWeightMap.getOrDefault(wrapper.getTarget(), MIN_WEIGHT);
                currentWeightMap.put(wrapper.getTarget(), currentWeight + originWeight);
            }

            return currentMaxWeightWrapper.getTarget();
        } finally {
            lock.unlock();
        }
    }
}