package crypt

import (
	"crypto/rand"
	"encoding/base64"
	"fmt"
	"math/big"
)

func Nonce() (string, error) {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(b), nil
}

func VerificationCode() (string, error) {
	max := big.NewInt(1000000)
	n, err := rand.Int(rand.Reader, max)
	if err != nil {
		return "", err
	}
	return fmt.Sprintf("%06d", n.Int64()), nil
}

const charset = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

func RID(length int) (string, error) {
	return RandomString(charset, length)
}

// RandomString draws length characters uniformly from alphabet.
func RandomString(alphabet string, length int) (string, error) {
	max := big.NewInt(int64(len(alphabet)))
	b := make([]byte, length)
	for i := range b {
		n, err := rand.Int(rand.Reader, max)
		if err != nil {
			return "", err
		}
		b[i] = alphabet[n.Int64()]
	}
	return string(b), nil
}