package cryptojs

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/md5"
	"encoding/base64"
	"errors"
	"math/rand"

	"bytes"
	"paste.ee/go/evpkdf"
)

const (
	keySize = 32
)

func Encrypt(data, passphrase string) (string, error) {
	salt := make([]byte, 8)

	if _, err := rand.Read(salt); err != nil {
		return "", err
	}

	key := make([]byte, keySize)
	iv := make([]byte, aes.BlockSize)

	keymat := evpkdf.New(md5.New, []byte(passphrase), salt, keySize + aes.BlockSize, 1)
	keymatbuf := bytes.NewReader(keymat)

	n, err := keymatbuf.Read(key)

	if n != keySize || err != nil {
		return "", err
	}

	n, err = keymatbuf.Read(iv)

	if n != aes.BlockSize || err != nil {
		return "", err
	}

	block, err := aes.NewCipher(key)

	if err != nil {
		return "", err
	}

	padded, err := pkcs7Pad([]byte(data), block.BlockSize())

	if err != nil {
		return "", err
	}

	ciphertext := make([]byte, len(padded))

	cbc := cipher.NewCBCEncrypter(block, iv)
	cbc.CryptBlocks(ciphertext, padded)

	return encode(ciphertext, salt), nil
}

func Decrypt(b64, passphrase string) ([]byte, error) {
	salt, ct, err := decode(b64)

	if err != nil {
		return nil, err
	}

	key := make([]byte, keySize)
	iv := make([]byte, aes.BlockSize)

	keymat := evpkdf.New(md5.New, []byte(passphrase), salt, keySize + aes.BlockSize, 1)
	keymatbuf := bytes.NewReader(keymat)

	n, err := keymatbuf.Read(key)

	if n != keySize || err != nil {
		return nil, err
	}

	n, err = keymatbuf.Read(iv)

	if n != aes.BlockSize || err != nil {
		return nil, err
	}

	block, err := aes.NewCipher(key)

	if err != nil {
		return nil, err
	}

	cbc := cipher.NewCBCDecrypter(block, iv)
	cbc.CryptBlocks(ct, ct)

	plain, err := pkcs7Unpad(ct, block.BlockSize())

	if err != nil {
		return nil, err
	}

	return plain, nil
}

func encode(ct []byte, salt []byte) string {
	b := []byte("Salted__")
	b = append(b, salt...)
	b = append(b, ct...)
	return base64.StdEncoding.EncodeToString(b)
}

func decode(b64 string) ([]byte, []byte, error) {
	decoded, err := base64.StdEncoding.DecodeString(b64)

	if err != nil {
		return nil, nil, err
	}

	if string(decoded[0:8]) != "Salted__" {
		return nil, nil, errors.New("invalid data")
	}

	return decoded[8:16], decoded[16:], nil
}