//生成單號
//06123xxxxx
//sum 最少10位,sum 表示全部單號位數
func MakeYearDaysRand(sum int) string {
  //年
  strs := time.Now().Format("06")
  //一年中的第幾天
  days := strconv.Itoa(GetDaysInYearByThisYear())
  count := len(days)
  if count < 3 {
    //重復字符0
    days = strings.Repeat("0", 3-count) + days
  }
  //組合
  strs += days
  //剩余隨機數
  sum = sum - 5
  if sum < 1 {
    sum = 5
  }
  //0~9999999的隨機數
  ran := GetRand()
  pow := math.Pow(10, float64(sum)) - 1
  //fmt.Println("sum=>", sum)
  //fmt.Println("pow=>", pow)
  result := strconv.Itoa(ran.Intn(int(pow)))
  count = len(result)
  //fmt.Println("result=>", result)
  if count < sum {
    //重復字符0
    result = strings.Repeat("0", sum-count) + result
  }
  //組合
  strs += result
  return strs
}
//年中的第幾天
func GetDaysInYearByThisYear() int {
  now := time.Now()
  total := 0
  arr := []int{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
  y, month, d := now.Date()
  m := int(month)
  for i := 0; i < m-1; i++ {
    total = total + arr[i]
  }
  if (y%400 == 0 || (y%4 == 0 && y%100 != 0)) && m > 2 {
    total = total + d + 1
  } else {
    total = total + d
  }
  return total;
}

package ordernum 
import (
  "fmt"
  "github.com/w3liu/go-common/constant/timeformat"
  "os"
  "sync/atomic"
  "time"
)
 
var num int64 
//生成24位訂單號
//前面17位代表時間精確到毫秒，中間3位代表進程id，最后4位代表序號
func Generate(t time.Time) string {
  s := t.Format(timeformat.Continuity)
  m := t.UnixNano()/1e6 - t.UnixNano()/1e9*1e3
  ms := sup(m, 3)
  p := os.Getpid() % 1000
  ps := sup(int64(p), 3)
  i := atomic.AddInt64(&num, 1)
  r := i % 10000
  rs := sup(r, 4)
  n := fmt.Sprintf("%s%s%s%s", s, ms, ps, rs)
  return n
}
 
//對長度不足n的數字前面補0
func sup(i int64, n int) string {
  m := fmt.Sprintf("%d", i)
  for len(m) < n {
   m = fmt.Sprintf("0%s", m)
  }
  return m
}