package random

import (

cryptoRand "crypto/rand"

"encoding/base64"

"fmt"

"math/rand"

mathRand "math/rand"

"net"

"time"

)

type Randomizer struct {

mathRand.Rand

}

// Bytes returns securely generated random bytes.

// It will return an error if the system's secure random

// number generator fails to function correctly, in which

// case the caller should not continue.

func (r *Randomizer) Bytes(n int) ([]byte, error) {

b := make([]byte, n)

_, err := cryptoRand.Read(b)

// Note that err == nil only if we read len(b) bytes.

if err != nil {

return nil, err

}

return b, nil

}

// String returns a URL-safe, base64 encoded

// securely generated random string.

func (r *Randomizer) String(s int) (string, error) {

b, err := r.Bytes(s)

return base64.URLEncoding.EncodeToString(b), err

}

// Number generates a number between 0 and n

func (r *Randomizer) Number(n int) int {

return mathRand.Intn(n)

}

// NumberBetween returns a random number between n and m

func (r *Randomizer) NumberBetween(n int, m int) int {

return mathRand.Intn(m-n) + n

}

// Port asks the kernel for an available port

func (r *Randomizer) Port() (int, error) {

addr, err := net.ResolveTCPAddr("tcp", "localhost:0")

if err != nil {

return 0, err

}

l, err := net.ListenTCP("tcp", addr)

if err != nil {

return 0, err

}

defer l.Close()

return l.Addr().(*net.TCPAddr).Port, nil

}

// Code returns a random code

func (r *Randomizer) Code() string {

return fmt.Sprintf("%016d", rand.Int63n(1e16))

}

// New returns a preseeded randomizer

func New() *Randomizer {

randomizer := mathRand.New(mathRand.NewSource(time.Now().UTC().UnixNano()))

if randomizer == nil {

panic("Failed to start random number generator")

}

return &Randomizer{

*randomizer,

}

}