package model

import (
	"crypto/md5"
	"crypto/rand"
	"fmt"
	"io"
	"strings"
)

// standard characters allowed in token string.
var chars = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789")

// default token length
var length = 40

// generateToken generates random strings good for use in URIs to
// identify unique objects.
func generateToken() string {
	b := make([]byte, length)
	r := make([]byte, length+(length/4)) // storage for random bytes.
	clen := byte(len(chars))
	maxrb := byte(256 - (256 % len(chars)))
	i := 0
	for {
		io.ReadFull(rand.Reader, r)
		for _, c := range r {
			if c >= maxrb {
				// Skip this number to avoid modulo bias.
				continue
			}
			b[i] = chars[c%clen]
			i++
			if i == length {
				return string(b)
			}
		}
	}
}

// helper function to create a Gravatar Hash
// for the given Email address.
func createGravatar(email string) string {
	email = strings.ToLower(strings.TrimSpace(email))
	hash := md5.New()
	hash.Write([]byte(email))
	return fmt.Sprintf("%x", hash.Sum(nil))
}