package oidc

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

const base62Alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

// randomNonce returns an n-character base62 string from crypto/rand, used
// for client_nonce. Deliberately not a dependency on
// github.com/hashicorp/go-secure-stdlib/base62 — this is the same
// crypto/rand-backed generation in about ten lines.
func randomNonce(n int) string {
	b := make([]byte, n)
	max := big.NewInt(int64(len(base62Alphabet)))
	for i := range b {
		idx, err := rand.Int(rand.Reader, max)
		if err != nil {
			panic(fmt.Sprintf("oidc: crypto/rand unavailable: %v", err))
		}
		b[i] = base62Alphabet[idx.Int64()]
	}
	return string(b)
}