package flrstring

import (
	"math/rand"
	"time"
)

// Constants and variables for random string generation
const (
	letterBytes   = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
	letterIdxBits = 6
	letterIdxMask = 1<<letterIdxBits - 1
	letterIdxMax  = 63 / letterIdxBits
)

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

// createRandString creates a random string with the size of n
// See: http://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-golang
func CreateRandString(n int) string {
	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(letterBytes) {
			b[i] = letterBytes[idx]
			i--
		}
		cache >>= letterIdxBits
		remain--
	}

	return string(b)
}