package crypt

import (
	"errors"
	"math/rand"
	"strings"
	"time"
	"unsafe"
)

// #cgo LDFLAGS: -lcrypt
// #define _GNU_SOURCE
// #include <crypt.h>
// #include <stdlib.h>
// #include <errno.h>
import "C"

// EPasswordIncorrect is a password verification failure error
var EPasswordIncorrect = errors.New("passwords do not match")
var EBadPasswordFormat = errors.New("bad password format")

// Crypt wraps C library crypt_r
func Crypt(Password, Salt string) (*string, error) {
	data := C.struct_crypt_data{}
	ckey := C.CString(Password)
	csalt := C.CString(Salt)
	cpass, err := C.crypt_r(ckey, csalt, &data)
	if err != nil {
		return nil, err
	}
	out := C.GoString(cpass)
	C.free(unsafe.Pointer(ckey))
	C.free(unsafe.Pointer(csalt))
	return &out, nil
}

// MakeSaltSHA512 generates a random salt for SHA512
// encrypted password hash.
func MakeSaltSHA512() string {
	var LetterRunes = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789./")
	salt := make([]rune, 8)

	for i := range salt {
		salt[i] = LetterRunes[rand.Intn(len(LetterRunes))]
	}

	return "$6$" + string(salt) + "$"
}

// Verify checks key against previously crypted hash
func CompareHashAndPassword(Hash, Password string) error {
	// ignore empty hashes
	if len(Hash) == 0 {
		return EPasswordIncorrect
	}
	// Split salt from password
	HashItems := strings.SplitN(Hash, "$", 4)
	if len(HashItems) < 3 {
		return EBadPasswordFormat
	}
	Salt := "$" + HashItems[1] + "$" + HashItems[2] + "$"

	hash, err := Crypt(Password, Salt)
	if err != nil {
		// Crypt error
		return err
	}

	if *hash == Hash {
		// Passwords match
		return nil
	}

	return EPasswordIncorrect
}

func init() {
	// Initialize RNG seed
	rand.Seed(time.Now().UnixNano())
}