package com.ynxbd.common.helper.common;

/**
 * @author wsq
 * @description 雪花算法
 * @date 2019/8/14 下午8:22
 */
public class SnowHelper {
    /**
     * 起始的时间戳
     */
    private final static long START_STAMP = 3500522218L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12;  // 序列号占用的位数
    private final static long MACHINE_BIT = 5;    // 机器标识占用的位数
    private final static long DATACENTER_BIT = 5; // 数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIME_STAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId;    // 数据中心
    private long machineId;       // 机器标识
    private long sequence = 0L;   // 序列号
    private long lastStamp = -1L; // 上一次时间戳

    public SnowHelper(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     *
     */
    public synchronized long nextId() {
        long curTimeStamp = getCurTime();
        if (curTimeStamp < lastStamp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (curTimeStamp == lastStamp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                curTimeStamp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStamp = curTimeStamp;

        return (curTimeStamp - START_STAMP) << TIME_STAMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
    }

    private long getNextMill() {
        long mill = getCurTime();
        while (mill <= lastStamp) {
            mill = getCurTime();
        }
        return mill;
    }

    private long getCurTime() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        SnowHelper snowFlake = new SnowHelper(2, 3);
        for (int i = 0; i < (1 << 12); i++) {
            System.out.println(snowFlake.nextId());
        }
    }


}