// coding: utf-8
// @Author : lryself
// @Date : 2021/5/13 1:29
// @Software: GoLand

package snowflake

import (
	"errors"
	"sync"
	"time"
)

const (
	workerIDBits =  uint64(5)  // 10bit 工作机器ID中的 5bit workerID
	dataCenterIDBits = uint64(5) // 10 bit 工作机器ID中的 5bit dataCenterID
	sequenceBits = uint64(12)

	maxWorkerID = int64(-1) ^ (int64(-1) << workerIDBits) //节点ID的最大值 用于防止溢出
	maxDataCenterID = int64(-1) ^ (int64(-1) << dataCenterIDBits)
	maxSequence = int64(-1) ^ (int64(-1) << sequenceBits)

	timeLeft = uint8(22)  // timeLeft = workerIDBits + sequenceBits // 时间戳向左偏移量
	dataLeft = uint8(17)  // dataLeft = dataCenterIDBits + sequenceBits
	workLeft = uint8(12)  // workLeft = sequenceBits // 节点IDx向左偏移量
	// 2020-05-20 08:00:00 +0800 CST
	epoch = int64(1589923200000) // 常量时间戳(毫秒)
)

type Worker struct {
	mu sync.Mutex
	LastStamp int64 // 记录上一次ID的时间戳
	WorkerID int64 // 该节点的ID
	DataCenterID int64 // 该节点的 数据中心ID
	Sequence int64 // 当前毫秒已经生成的ID序列号(从0 开始累加) 1毫秒内最多生成4096个ID
}

func (w *Worker) getMilliSeconds() int64 {
	return time.Now().UnixNano() / 1e6
}

func (w *Worker) NextID() (uint64,error) {
	w.mu.Lock()
	defer w.mu.Unlock()

	return w.nextID()
}

func (w *Worker) nextID() (uint64,error) {
	timeStamp := w.getMilliSeconds()

	if timeStamp < w.LastStamp{
		return 0,errors.New("time is moving backwards,waiting until")
	}

	if w.LastStamp == timeStamp{
		w.Sequence = (w.Sequence + 1) & maxSequence
		if w.Sequence == 0 {
			for timeStamp <= w.LastStamp {
				timeStamp = w.getMilliSeconds()
			}
		}
	}else {
		w.Sequence = 0
	}

	w.LastStamp = timeStamp
	id := ((timeStamp - epoch) << timeLeft) |
		(w.DataCenterID << dataLeft)  |
		(w.WorkerID << workLeft) |
		w.Sequence

	return uint64(id),nil
}

func NewWorker(workerID,dataCenterID int64) *Worker {
	return &Worker{
		WorkerID: workerID,
		LastStamp: 0,
		Sequence: 0,
		DataCenterID: dataCenterID,
	}
}