package org.junior.utils;

/**
* @Description: 使用雪花算法生成唯一ID
* @Author: Junior
* @Date: 2026/1/3
*/
public class SnowFlakeUtil {
    // 起始时间戳（2026-01-01）
    private static final long START_TIMESTAMP = 1735689600000L;
    // 机器位（自定义，单机部署设为0）
    private static final long MACHINE_BIT = 5;
    // 序列号位
    private static final long SEQUENCE_BIT = 12;
    // 最大机器ID
    private static final long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    // 最大序列号
    private static final long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
    // 机器位偏移量
    private static final long MACHINE_LEFT = SEQUENCE_BIT;
    // 时间戳偏移量
    private static final long TIMESTAMP_LEFT = SEQUENCE_BIT + MACHINE_BIT;

    private long machineId;     // 机器ID
    private long sequence = 0L; // 序列号
    private long lastTimeStamp = -1L; // 上一次时间戳

    public SnowFlakeUtil(long machineId) {
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("机器ID超出范围");
        }
        this.machineId = machineId;
    }

    // 生成下一个ID
    public synchronized long nextId() {
        long currTimeStamp = getNewTimeStamp();
        if (currTimeStamp < lastTimeStamp) {
            throw new RuntimeException("时钟回拨，拒绝生成ID");
        }
        if (currTimeStamp == lastTimeStamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0L) {
                currTimeStamp = getNextMill();
            }
        } else {
            sequence = 0L;
        }
        lastTimeStamp = currTimeStamp;
        return (currTimeStamp - START_TIMESTAMP) << TIMESTAMP_LEFT
                | machineId << MACHINE_LEFT
                | sequence;
    }

    // 获取下一个毫秒数
    private long getNextMill() {
        long mill = getNewTimeStamp();
        while (mill <= lastTimeStamp) {
            mill = getNewTimeStamp();
        }
        return mill;
    }

    // 获取当前时间戳
    private long getNewTimeStamp() {
        return System.currentTimeMillis();
    }

    // 单例实例（单机部署）
    private static class SingletonHolder {
        private static final SnowFlakeUtil INSTANCE = new SnowFlakeUtil(0);
    }

    public static SnowFlakeUtil getInstance() {
        return SingletonHolder.INSTANCE;
    }
}