package com.ruoyi.payment.infrastructure.util;

/**
 * 雪花算法ID生成器
 * 
 * @author ruoyi
 */
public class SnowflakeIdGenerator {

    // 起始时间戳 (2020-01-01)
    private static final long START_TIMESTAMP = 1577808000000L;

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

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

    // 每部分向左的位移
    private static final long MACHINE_LEFT = SEQUENCE_BIT;
    private static final long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private static final long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private static long datacenterId = 1;  // 数据中心ID
    private static long machineId = 1;     // 机器ID
    private static long sequence = 0L;     // 序列号
    private static long lastTimestamp = -1L;  // 上一次时间戳

    private SnowflakeIdGenerator() {}

    /**
     * 生成唯一ID
     */
    public static synchronized long generateId() {
        long currTimestamp = getCurrentTimestamp();

        if (currTimestamp < lastTimestamp) {
            throw new RuntimeException("时钟回拨，拒绝生成ID");
        }

        if (currTimestamp == lastTimestamp) {
            // 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) {
                currTimestamp = getNextTimestamp();
            }
        } else {
            // 不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastTimestamp = currTimestamp;

        return (currTimestamp - START_TIMESTAMP) << TIMESTAMP_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
    }

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

    /**
     * 获取下一个时间戳
     */
    private static long getNextTimestamp() {
        long timestamp = getCurrentTimestamp();
        while (timestamp <= lastTimestamp) {
            timestamp = getCurrentTimestamp();
        }
        return timestamp;
    }

    /**
     * 设置数据中心ID和机器ID
     */
    public static void setWorker(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId 不能大于 " + MAX_DATACENTER_NUM + " 或小于 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId 不能大于 " + MAX_MACHINE_NUM + " 或小于 0");
        }
        SnowflakeIdGenerator.datacenterId = datacenterId;
        SnowflakeIdGenerator.machineId = machineId;
    }
}