package cryptorand

import (

"crypto/rand"

"encoding/binary"

"strings"

)

// Charsets

const (

// Numeric includes decimal numbers (0-9)

Numeric = "0123456789"

// Upper is uppercase characters in the Latin alphabet

Upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"

// Lower is lowercase characters in the Latin alphabet

Lower = "abcdefghijklmnopqrstuvwxyz"

// Alpha is upper or lowercase alphabetic characters

Alpha = Upper + Lower

// Default is uppercase, lowercase, or numeric characters

Default = Numeric + Alpha

// Hex is hexadecimal lowercase characters

Hex = "0123456789abcdef"

// Human creates strings which are easily distinguishable from

// others created with the same charset. It contains most lowercase

// alphanumeric characters without 0,o,i,1,l.

Human = "23456789abcdefghjkmnpqrstuvwxyz"

)

// StringCharset generates a random string using the provided charset and size

func StringCharset(charSetStr string, size int) (string, error) {

charSet := []rune(charSetStr)

if len(charSet) == 0 || size == 0 {

return "", nil

}

// This buffer facilitates pre-emptively creation of random uint32s

// to reduce syscall overhead.

ibuf := make([]byte, 4*size)

_, err := rand.Read(ibuf)

if err != nil {

return "", err

}

var buf strings.Builder

buf.Grow(size)

for i := 0; i < size; i++ {

count, err := UnbiasedModulo32(

binary.BigEndian.Uint32(ibuf[i*4:(i+1)*4]),

int32(len(charSet)),

)

if err != nil {

return "", err

}

_, _ = buf.WriteRune(charSet[count])

}

return buf.String(), nil

}

// String returns a random string using Default.

func String(size int) (string, error) {

return StringCharset(Default, size)

}

// HexString returns a hexadecimal string of given length.

func HexString(size int) (string, error) {

return StringCharset(Hex, size)

}

// Sha1String returns a 40-character hexadecimal string, which matches

// the length of a SHA-1 hash (160 bits).

func Sha1String() (string, error) {

return StringCharset(Hex, 40)

}