package rand

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

var chars []byte = []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789~`!@#$%^&*()_+-=[]{}\\|;:'\",./<>?")
var letters []byte = chars[0:52]
var digits []byte = chars[52:62]
var symbols []byte = chars[62:94]

func gen(s []byte) (byte,error) {
	nBig, err := crand.Int(crand.Reader, big.NewInt(int64(len(s))))
	if err != nil {
		return 0, fmt.Errorf("Error in crypto/rand: %s",err)
	}
	x := nBig.Int64()
	return s[x], nil
}

func Letter() (byte,error) {
	return gen(letters)
}

func Digit() (byte,error) {
	return gen(digits)
}

func Symbol() (byte,error) {
	return gen(symbols)
}

func Char() (byte,error) {
	return gen(chars)
}

func Slice(f func() (byte,error), n int) ([]byte,error) {
	ret := make([]byte,0)
	for i := 0; i < n; i++ {
		x,err := f()
		if err != nil {
			return ret, err
		}
		ret = append(ret,x)
	}
	return ret, nil
}