package main

import (
 "fmt"
 "sync"
 "time"
)

const (
 workerBits     = 10
 sequenceBits   = 12
 workerMax      = -1 ^ (-1 << workerBits)
 sequenceMask   = -1 ^ (-1 << sequenceBits)
 timeShift      = workerBits + sequenceBits
 workerShift    = sequenceBits
 epoch          = 1609459200000
)

type Snowflake struct {
 mu          sync.Mutex
 lastTime    int64
 workerID    int64
 sequence    int64
}

func NewSnowflake(workerID int64) *Snowflake {
 if workerID < 0 || workerID > workerMax {
  panic(fmt.Sprintf("worker ID must be between 0 and %d", workerMax))
 }
 return &Snowflake{
  lastTime: time.Now().UnixNano() / 1e6,
  workerID: workerID,
  sequence: 0,
 }
}

func (sf *Snowflake) NextID() int64 {
 sf.mu.Lock()
 defer sf.mu.Unlock()

 currentTime := time.Now().UnixNano() / 1e6

 if currentTime < sf.lastTime {
  panic(fmt.Sprintf("clock moved backwards, refusing to generate ID for %d milliseconds", sf.lastTime-currentTime))
 }

 if currentTime == sf.lastTime {
  sf.sequence = (sf.sequence + 1) & sequenceMask
  if sf.sequence == 0 {
   for currentTime <= sf.lastTime {
    currentTime = time.Now().UnixNano() / 1e6
   }
  }
 } else {
  sf.sequence = 0
 }

 sf.lastTime = currentTime

 id := (currentTime-epoch)<<timeShift | (sf.workerID << workerShift) | sf.sequence
 return id
}

func main() {
 sf := NewSnowflake(1) // 假設(shè)工作節(jié)點(diǎn)ID為1

 for i := 0; i < 10; i++ {
  id := sf.NextID()
  fmt.Println(id)
  time.Sleep(time.Millisecond)
 }
}