package keymgr

import (
	"crypto/rand"
	"math/big"
)

// charset avoids visually ambiguous characters (0/O, 1/l/I) since this
// password is normally read aloud or typed by hand on the recipient side.
const passwordCharset = "23456789ABCDEFGHJKMNPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz"

// GenerateBatchPassword returns a cryptographically random password shared
// by every archive produced in one export batch. It is shown to the admin
// exactly once (see the export result screen) and must be relayed to each
// recipient over a channel separate from the archive itself.
func GenerateBatchPassword(length int) (string, error) {
	if length <= 0 {
		length = 20
	}
	out := make([]byte, length)
	max := big.NewInt(int64(len(passwordCharset)))
	for i := range out {
		n, err := rand.Int(rand.Reader, max)
		if err != nil {
			return "", err
		}
		out[i] = passwordCharset[n.Int64()]
	}
	return string(out), nil
}