package com.hj.lock.alg;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.*;

public class ConsistentHash<T> {
    /**
     * Hash計算對象，用于自定義hash算法
     */
    HashFunc hashFunc;
    /**
     * 復制的節(jié)點個數(shù)
     */
    private final int numberOfReplicas;
    /**
     * 一致性Hash環(huán)
     */
    private final TreeMap<Long, T> hashCircle = new TreeMap<>();

    /**
     * 構造，使用Java默認的Hash算法
     *
     * @param numberOfReplicas 復制的節(jié)點個數(shù)，增加每個節(jié)點的復制節(jié)點有利于負載均衡
     * @param
    public ConsistentHash(int numberOfReplicas, Collection<T> nodes){
        this.numberOfReplicas = numberOfReplicas;
        this.hashFunc = ConsistentHash::md5HashingAlg;
        //初始化節(jié)點
        nodes.forEach(node -> add(node));
    }

    /**
     * 增加節(jié)點<br>
     * 每增加一個節(jié)點，就會在閉環(huán)上增加給定復制節(jié)點數(shù)<br>
     * 例如復制節(jié)點數(shù)是2，則每調用此方法一次，增加兩個虛擬節(jié)點，這兩個節(jié)點指向同一Node
     * 由于hash算法會調用node的toString方法，故按照toString去重
     *
     * @param
    public void add(T node){
        for (int i = 0; i < numberOfReplicas; i++) {
            hashCircle.put(hashFunc.hash(node.toString() + i), node);
        }
    }

    /**
     * 移除節(jié)點的同時移除相應的虛擬節(jié)點
     *
     * @param
    public void remove(T node){
        for (int i = 0; i < numberOfReplicas; i++) {
            hashCircle.remove(hashFunc.hash(node.toString() + i));
        }
    }

    /**
     * 獲得一個最近的順時針節(jié)點
     *
     * @param key 為給定鍵取Hash，取得順時針方向上最近的一個虛擬節(jié)點對應的實際節(jié)點
     * @return
    public T get(Object key){
        if (hashCircle.isEmpty()) {
            return null;
        }
        long hash = hashFunc.hash(key);
        hash = nextHash(hash);
        //正好命中
        return hashCircle.get(hash);
    }

    public Long nextHash(Long hash){
        if (!hashCircle.containsKey(hash)) {
            Long next = hashCircle.higherKey(hash + 1);//返回下一個hash值
            hash = next == null ? hashCircle.firstKey() : next;
        }
        return hash;
    }

    /**
     * 使用MD5算法
     *
     * @param key
     * @return
    private static long md5HashingAlg(Object key){
        MessageDigest md5 = null;
        try {
            md5 = MessageDigest.getInstance("MD5");
            md5.reset();
            String str = key.toString();
            md5.update(str.getBytes());
            byte[] bKey = md5.digest();
            long res = ((long) (bKey[3] & 0xFF) << 24) | ((long) (bKey[2] & 0xFF) << 16) | ((long) (bKey[1] & 0xFF) << 8) | (long) (bKey[0] & 0xFF);
            return res;
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        return 0l;
    }

    /**
     * 使用FNV1hash算法
     *
     * @param key
     * @return
    private static long fnv1HashingAlg(Object key){
        final int p = 16777619;
        int hash = (int) 2166136261L;
        String str = key.toString();
        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;
        return hash;
    }

    /**
     * Hash算法對象，用于自定義hash算法
     */
    public interface HashFunc {
        public Long hash(Object key);
    }

    public static void main(String[] args){
        List<String> nodes = new ArrayList<>();
        System.out.println("--添加節(jié)點 ABC");
        nodes.add("A");
        nodes.add("B");
        nodes.add("C");
        ConsistentHash<String> chash = new ConsistentHash(1, nodes);
        System.out.println(chash.get("test1"));
        System.out.println(chash.get("aest2"));
        System.out.println(chash.get("dest3"));
        System.out.println("--添加節(jié)點 D");
        chash.add("D");
        System.out.println(chash.get("test1"));
        System.out.println(chash.get("aest2"));
        System.out.println(chash.get("dest3"));

        for (Iterator<Map.Entry<Long, String>> it = chash.hashCircle.entrySet().iterator(); it.hasNext(); ) {
            Map.Entry<Long, String> entry = it.next();
            Long k = entry.getKey();
            System.out.println(k + ":" + entry.getValue());
            System.out.println(Math.abs(chash.nextHash(k + 1) - k));
        }
    }

}

--添加節(jié)點 ABC
C
C
A
--添加節(jié)點 D
D
C
A
748451404:B
1081611916
1830063320:A
1542566198
3372629518:D
491985806
3864615324:C
3116163920