package utils

import (
	"math/rand"
	"time"
)

func RandString(n int) string {
	var letter = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*()_+"

	var src = rand.NewSource(time.Now().UnixNano())

	const (
		letterIdxBits = 6
		letterIdxMask = 1<<letterIdxBits - 1
		letterIdxMax  = 63 / letterIdxBits
	)
	b := make([]byte, n)
	for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
		if remain == 0 {
			cache, remain = src.Int63(), letterIdxMax
		}
		if idx := int(cache & letterIdxMask); idx < len(letter) {
			b[i] = letter[idx]
			i--
		}
		cache >>= letterIdxBits
		remain--
	}
	return string(b)
}