package cmdline

import (
	"math/rand"
	"time"
)

var (
	randsrc = rand.New(rand.NewSource(time.Now().UnixNano()))
)

// copy of "utils", but avoiding import cycle
func RandomString(n int) string {
	const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
	const (
		letterIdxBits = 6                    // 6 bits to represent a letter index
		letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
		letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits

	)

	b := make([]byte, n)
	// A randsrc.Int63() generates 63 random bits, enough for letterIdxMax characters!
	for i, cache, remain := n-1, randsrc.Int63(), letterIdxMax; i >= 0; {
		if remain == 0 {
			cache, remain = randsrc.Int63(), letterIdxMax
		}
		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
			b[i] = letterBytes[idx]
			i--
		}
		cache >>= letterIdxBits
		remain--
	}

	return string(b)
}