package com.ruoyi.common.utils;

/**
 * https://blog.csdn.net/wanghao112956/article/details/102794497?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromBaidu-3.control&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromBaidu-3.control
 */

import com.ruoyi.common.config.RuoYiConfig;
import com.ruoyi.common.utils.spring.SpringUtils;
import com.ruoyi.common.utils.systemClock.SystemClock;
import lombok.extern.slf4j.Slf4j;

/**
 * 雪花算法分布式唯一ID生成器<br>
 * 每个机器号最高支持每秒‭65535个序列, 当秒序列不足时启用备份机器号, 若备份机器也不足时借用备份机器下一秒可用序列<br>
 * 53 bits 趋势自增ID结构如下:
 *
 * |00000000|00011111|11111111|11111111|11111111|11111111|11111111|11111111|
 * |-----------|##########32bit 秒级时间戳##########|-----|-----------------|
 * |--------------------------------------5bit机器位|xxxxx|-----------------|
 * |-----------------------------------------16bit自增序列|xxxxxxxx|xxxxxxxx|
 *
 **/
@Slf4j
public class SnowFlakeUtils {
    /** 初始偏移时间戳 */
    private static final long OFFSET = 1546300800L;

    /** 机器id (0~15 保留 16~31作为备份机器) */
    private static final long WORKER_ID;
    /** 机器id所占位数 (5bit, 支持最大机器数 2^5 = 32)*/
    private static final long WORKER_ID_BITS = 5L;
    /** 自增序列所占位数 (16bit, 支持最大每秒生成 2^16 = ‭65536‬) */
    private static final long SEQUENCE_ID_BITS = 16L;
    /** 机器id偏移位数 */
    private static final long WORKER_SHIFT_BITS = SEQUENCE_ID_BITS;
    /** 自增序列偏移位数 */
    private static final long OFFSET_SHIFT_BITS = SEQUENCE_ID_BITS + WORKER_ID_BITS;
    /** 机器标识最大值 (2^5 / 2 - 1 = 15) */
    private static final long WORKER_ID_MAX = ((1 << WORKER_ID_BITS) - 1) >> 1;
    /** 备份机器ID开始位置 (2^5 / 2 = 16) */
    private static final long BACK_WORKER_ID_BEGIN = (1 << WORKER_ID_BITS) >> 1;
    /** 自增序列最大值 (2^16 - 1 = ‭65535) */
    private static final long SEQUENCE_MAX = (1 << SEQUENCE_ID_BITS) - 1;
    /** 发生时间回拨时容忍的最大回拨时间 (秒) */
    private static final long BACK_TIME_MAX = 1L;

    /** 上次生成ID的时间戳 (秒) */
    private static long lastTimestamp = 0L;
    /** 当前秒内序列 (2^16)*/
    private static long sequence = 0L;
    /** 备份机器上次生成ID的时间戳 (秒) */
    private static long lastTimestampBak = 0L;
    /** 备份机器当前秒内序列 (2^16)*/
    private static long sequenceBak = 0L;

    static {
        // 初始化机器ID
        // 伪代码: 由你的配置文件获取节点ID
        RuoYiConfig erpConfig = SpringUtils.getBean(RuoYiConfig.class);
        long workerId = erpConfig.getWorkerId();
        if (workerId < 0 || workerId > WORKER_ID_MAX) {
            throw new IllegalArgumentException(String.format("cmallshop.workerId范围: 0 ~ %d 目前: %d", WORKER_ID_MAX, workerId));
        }
        WORKER_ID = workerId;
    }

    /** 私有构造函数禁止外部访问 */
    private SnowFlakeUtils() {}

    /**
     * 获取自增序列
     * @return long
     */
    public static long snowFlakeId() {
        return nextId(SystemClock.now() / 1000);
    }

    /**
     * 主机器自增序列
     * @param timestamp 当前Unix时间戳
     * @return long
     */
    private static synchronized long nextId(long timestamp) {
        // 时钟回拨检查
        if (timestamp < lastTimestamp) {
            // 发生时钟回拨
            log.warn("时钟回拨, 启用备份机器ID: now: [{}] last: [{}]", timestamp, lastTimestamp);
            return nextIdBackup(timestamp);
        }

        // 开始下一秒
        if (timestamp != lastTimestamp) {
            lastTimestamp = timestamp;
            sequence = 0L;
        }
        if (0L == (++sequence & SEQUENCE_MAX)) {
            // 秒内序列用尽
//            log.warn("秒内[{}]序列用尽, 启用备份机器ID序列", timestamp);
            sequence--;
            return nextIdBackup(timestamp);
        }

        return ((timestamp - OFFSET) << OFFSET_SHIFT_BITS) | (WORKER_ID << WORKER_SHIFT_BITS) | sequence;
    }

    /**
     * 备份机器自增序列
     * @param timestamp timestamp 当前Unix时间戳
     * @return long
     */
    private static long nextIdBackup(long timestamp) {
        if (timestamp < lastTimestampBak) {
            if (lastTimestampBak - SystemClock.now() / 1000 <= BACK_TIME_MAX) {
                timestamp = lastTimestampBak;
            } else {
                throw new RuntimeException(String.format("时钟回拨: now: [%d] last: [%d]", timestamp, lastTimestampBak));
            }
        }

        if (timestamp != lastTimestampBak) {
            lastTimestampBak = timestamp;
            sequenceBak = 0L;
        }

        if (0L == (++sequenceBak & SEQUENCE_MAX)) {
            // 秒内序列用尽
//            logger.warn("秒内[{}]序列用尽, 备份机器ID借取下一秒序列", timestamp);
            return nextIdBackup(timestamp + 1);
        }

        return ((timestamp - OFFSET) << OFFSET_SHIFT_BITS) | ((WORKER_ID ^ BACK_WORKER_ID_BEGIN) << WORKER_SHIFT_BITS) | sequenceBak;
    }

//    public static void main(String[] args){
//        Runnable r1 = new Runnable() {
//            @Override
//            public void run() {
//                for(int i=0;i<10000;i++){
//                    long l = nextId();
//                    System.out.println(String.format("线程1,第%d次获取主键结果为:%d",i+1,l));
//                }
//            }
//        };
//
//        Runnable r2 = new Runnable() {
//            @Override
//            public void run() {
//                for(int i=0;i<30000;i++){
//                    long l = nextId();
//                    System.out.println(String.format("线程2,第%d次获取主键结果为:%d",i+1,l));
//                }
//            }
//        };
//
//        Thread t1 = new Thread(r1);
//        Thread t2 = new Thread(r2);
//        t1.start();
//        t2.start();
//    }
}
