package com.usky.cdi.service.util;

import lombok.extern.slf4j.Slf4j;

/**
 * 雪花算法ID生成器
 * 用于生成15位不重复的数据包ID
 * 
 * @author han
 * @date 2025/03/20
 */
@Slf4j
public class SnowflakeIdGenerator {
    
    // 起始时间戳 (2025-01-01 00:00:00)
    private static final long START_TIMESTAMP = 1735689600000L;
    
    // 机器ID所占的位数
    private static final long WORKER_ID_BITS = 5L;
    
    // 数据标识ID所占的位数
    private static final long DATACENTER_ID_BITS = 5L;
    
    // 支持的最大机器ID，结果是31
    private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
    
    // 支持的最大数据标识ID，结果是31
    private static final long MAX_DATACENTER_ID = ~(-1L << DATACENTER_ID_BITS);
    
    // 序列在ID中占的位数
    private static final long SEQUENCE_BITS = 12L;
    
    // 机器ID向左移12位
    private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;
    
    // 数据标识ID向左移17位(12+5)
    private static final long DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
    
    // 时间戳向左移22位(5+5+12)
    private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTER_ID_BITS;
    
    // 生成序列的掩码，这里为4095 (0b111111111111=0xfff=4095)
    private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);
    
    // 工作机器ID(0~31)
    private long workerId;
    
    // 数据中心ID(0~31)
    private long datacenterId;
    
    // 毫秒内序列(0~4095)
    private long sequence = 0L;
    
    // 上次生成ID的时间戳
    private long lastTimestamp = -1L;
    
    /**
     * 构造函数
     * 
     * @param workerId 工作ID (0~31)
     * @param datacenterId 数据中心ID (0~31)
     */
    public SnowflakeIdGenerator(long workerId, long datacenterId) {
        if (workerId > MAX_WORKER_ID || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", MAX_WORKER_ID));
        }
        if (datacenterId > MAX_DATACENTER_ID || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", MAX_DATACENTER_ID));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }
    
    /**
     * 获得下一个ID (该方法是线程安全的)
     * 
     * @return SnowflakeId
     */
    public synchronized long nextId() {
        long timestamp = timeGen();
        
        // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
        if (timestamp < lastTimestamp) {
            log.error("时钟回退，拒绝生成ID。当前时间戳: {}, 上次时间戳: {}", timestamp, lastTimestamp);
            throw new RuntimeException(String.format("时钟回退，拒绝生成ID。当前时间戳: %d, 上次时间戳: %d", timestamp, lastTimestamp));
        }
        
        // 如果是同一时间生成的，则进行毫秒内序列
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & SEQUENCE_MASK;
            // 毫秒内序列溢出
            if (sequence == 0) {
                // 阻塞到下一个毫秒,获得新的时间戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 时间戳改变，毫秒内序列重置
            sequence = 0L;
        }
        
        // 上次生成ID的时间戳
        lastTimestamp = timestamp;
        
        // 移位并通过或运算拼到一起组成64位的ID
        return ((timestamp - START_TIMESTAMP) << TIMESTAMP_LEFT_SHIFT)
                | (datacenterId << DATACENTER_ID_SHIFT)
                | (workerId << WORKER_ID_SHIFT)
                | sequence;
    }
    
    /**
     * 阻塞到下一个毫秒，直到获得新的时间戳
     * 
     * @param lastTimestamp 上次生成ID的时间戳
     * @return 当前时间戳
     */
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }
    
    /**
     * 返回以毫秒为单位的当前时间
     * 
     * @return 当前时间(毫秒)
     */
    protected long timeGen() {
        return System.currentTimeMillis();
    }
    
    /**
     * 生成15位数据包ID（取后15位）
     * 
     * @return 15位数据包ID
     */
    public long nextPacketId() {
        long id = nextId();
        // 取后15位，确保不超过15位
        return id % 1000000000000000L;
    }

    /**
     * 生成10位数据包ID（取后10位）
     * */

    public long nextPacketId10() {
        long id = nextId();
        // 取后10位，确保不超过10位
        return id % 10000000000L;
    }
}

