package util

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
)

// RandomHexString returns byteLength random bytes from the operating system's
// random source, written as lowercase hexadecimal, so the returned string is
// twice as long as byteLength. The bytes come from crypto/rand, which means the
// result is fit for session tokens, temporary filenames and anything else a
// stranger should not be able to guess.
//
// An error comes back only for a negative length or if the random source
// itself fails, which does not happen on a working system.
func RandomHexString(byteLength int) (string, error) {
	if byteLength < 0 {
		return "", errors.New("byte length cannot be negative")
	}

	buffer := make([]byte, byteLength)
	if _, err := rand.Read(buffer); err != nil {
		return "", err
	}

	return hex.EncodeToString(buffer), nil
}