package password

import "golang.org/x/crypto/pbkdf2"
import "hash"
import "strconv"
import "encoding/base64"
import "crypto/sha1"
import "crypto/sha256"
import "crypto/sha512"
import "crypto/rand"
import "fmt"
import "strings"

const (
	saltLength         = 8
	hashLength         = 20
	interations        = 10000
	hashfunc    string = "sha256"
)

var hashlib = map[string]func() hash.Hash{
	"sha1":   sha1.New,
	"sha256": sha256.New,
	"sha512": sha512.New,
}

// Validate a password and a hash
func Validate(hash, password string) (output, replace bool) {
	parts := strings.Split(hash, "$")
	if len(parts) != 4 {
		return false, false
	}
	curIter, err := strconv.Atoi(parts[1])
	if err != nil {
		return false, false
	}
	hashfuncC := strings.Split(parts[0], "_")[1]
	replace = (hashfuncC != hashfunc)

	dk := pbkdf2.Key([]byte(password), []byte(parts[2]), curIter, len(parts[3])-8, hashlib[hashfuncC])
	x := fmt.Sprintf("pbkdf2_%s$%s$%s$%s", hashfuncC, parts[1], parts[2], base64.StdEncoding.EncodeToString(dk))
	output = (x == hash)
	return
}

// GenerateRandomString by length for key
func GenerateRandomString(n int) (string, error) {
	b := make([]byte, n)
	_, err := rand.Read(b)
	if err != nil {
		return "", err
	}
	return base64.URLEncoding.EncodeToString(b), nil
}

// NewHash of given password
func NewHash(password string) string {
	salt, _ := GenerateRandomString(saltLength)
	dk := pbkdf2.Key([]byte(password), []byte(salt), interations, hashLength, hashlib[hashfunc])
	return fmt.Sprintf("pbkdf2_%s$%d$%s$%s", hashfunc, interations, salt, base64.StdEncoding.EncodeToString(dk))
}