package com.java4all.grouth.consistent;

import java.util.LinkedList;
import java.util.List;
import java.util.SortedMap;
import java.util.TreeMap;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 一致性hash算法java簡易實現(xiàn)
 * @author IT云清
 * 參考：https://blog.csdn.net/zhanglu0223/article/details/100579254
 */
public class ConsistentHash {

 private static final Logger LOGGER = LoggerFactory.getLogger(ConsistentHash.class);

 /**
  * 虛擬節(jié)點個數(shù)
  * 每個真實節(jié)點對應(yīng)的虛擬節(jié)點個數(shù)
  */
 private static final int VIRTUAL_NUM = 5;

 /**
  * 虛擬節(jié)點
  * eg:<656715414,192.168.1.1&&VN3>
  * 真實節(jié)點數(shù)量一般偏少，引入虛擬節(jié)點來平衡
  * 每個真實節(jié)點對應(yīng)多個虛擬節(jié)點，這樣每個節(jié)點盡可能在hash環(huán)上均勻分布，可以根據(jù)虛擬節(jié)點找到真實節(jié)點
  */
 private static SortedMap<Integer,String> shards = new TreeMap<>();

 /**
  * 真實節(jié)點
  */
 private static List<String> realNodes = new LinkedList<>();

 /**
  * 模擬初始節(jié)點
  */
 private static String[] servers = {"116.116.1.1", "116.116.1.2", "116.116.1.3", "116.116.1.5", "116.116.1.6"};


 /**
  * 初始化虛擬節(jié)點
  */
 static {
  for (String server : servers) {
   realNodes.add(server);
   LOGGER.info("添加真實節(jié)點{}",server);
   for(int i = 0;i < VIRTUAL_NUM; i ++){
    String virtualNode = server + "&&VN" + i;
    int hash = getHash(virtualNode);
    shards.put(hash,virtualNode);
    LOGGER.info("添加虛擬節(jié)點{}，hash為{}",virtualNode,hash);
   }
  }
 }


 public static void main(String[]args){
  test2();
 }

 public static void test2(){
  //測試定位node
  LOGGER.info(getSever("aa"));
  LOGGER.info(getSever("漲三"));
  LOGGER.info(getSever("num_19120000"));
  LOGGER.info(getSever("num_19120000"));
  LOGGER.info("------------------");
  //測試添加節(jié)點
  addNode("192.192.116.1");
  addNode("192.192.116.2");
  LOGGER.info("------------------");
  //測試刪除節(jié)點
  delNode("116.116.1.1");
 }
 /**
  * 獲取真實節(jié)點ip
  * @param str 字符串
  * @return
  */
 public static String getSever(String str){
  //計算hash
  int hash = getHash(str);
  Integer key = null;
  //尋找最近的虛擬node
  SortedMap<Integer, String> tailMap = shards.tailMap(hash);
  //獲取在hash環(huán)上 右側(cè)最近的虛擬節(jié)點的key
  key = tailMap.isEmpty() ? shards.lastKey() : tailMap.firstKey();
  //根據(jù)hash獲取虛擬節(jié)點
  String virtualNode = shards.get(key);
  //返回虛擬節(jié)點的真實ip
  return virtualNode.substring(0,virtualNode.indexOf("&&"));
 }



 /**
  * 添加節(jié)點
  * @param node
  */
 public static void addNode(String node){
  if(!realNodes.contains(node)){
   realNodes.add(node);
   LOGGER.info("新增真實節(jié)點上線，{}",node);
   for(int i = 0;i < VIRTUAL_NUM;i ++){
    String virtualNode = node + "&&VN" + i;
    int hash = getHash(virtualNode);
    shards.put(hash,virtualNode);
    LOGGER.info("新增虛擬節(jié)點{}，hash為{}",virtualNode,hash);
   }
  }

 }

 /**
  * 刪除節(jié)點
  * @param node
  */
 public static void delNode(String node){
  if(realNodes.contains(node)){
   //下線真實節(jié)點
   realNodes.remove(node);
   LOGGER.info("真實節(jié)點下線，{}",node);
   for(int i = 0;i < VIRTUAL_NUM; i++){
    String virtualNode = node + "&&VN" + i;
    int hash = getHash(virtualNode);
    //移除虛擬節(jié)點
    shards.remove(hash);
    LOGGER.info("下線虛擬節(jié)點{}，hash為{}",virtualNode,hash);
   }
  }
 }

 /**
  * FNV1_32_HASH算法
  * @param str 任意字符串
  * @return 返回int類型的hash值
  */
 private static int getHash(String str) {
  final int p = 16777619;
  int hash = (int) 2166136261L;
  for (int i = 0; i < str.length(); i++) {
   hash = (hash ^ str.charAt(i)) * p;
  }
  hash += hash << 13;
  hash ^= hash >> 7;
  hash += hash << 3;
  hash ^= hash >> 17;
  hash += hash << 5;
  // 如果算出來的值為負(fù)數(shù)則取其絕對值
  if (hash < 0) {
   hash = Math.abs(hash);
  }
  return hash;
 }
}