package randomutil

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

func GenerateRandomBytes(n int) ([]byte, error) {
	result := make([]byte, n)

	_, err := rand.Read(result)
	if err != nil {
		return nil, fmt.Errorf("error generating random bytes: %w", err)
	}

	return result, nil
}

func GenerateFromCharset(charset string, n int) string {
	result := make([]byte, n)
	charsetBigLen := big.NewInt(int64(len(charset)))

	for i := 0; i < n; i++ {
		num, err := rand.Int(rand.Reader, charsetBigLen)
		if err != nil {
			panic(fmt.Errorf("error generating random string: %w", err))
		}

		result[i] = charset[num.Int64()]
	}

	return string(result)
}

const (
	SecureTokenCharset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	ShortCharset       = "abcdefghijklmnopqrstuvwxyz0123456789"
)

func GenerateSecureToken(length int) string {
	return GenerateFromCharset(SecureTokenCharset, length)
}

func GenerateRandomShort(n int) string {
	return GenerateFromCharset(ShortCharset, n)
}