package myth

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"errors"
)

var (
	aesKey string
	aesIV  string
)

// AesCrypto define
type AesCrypto struct {
	Key []byte
	IV  []byte
}

// SetAesCryptoKey set key,
// key/iv length：16, 24, 32 bytes to AES-128, AES-192, AES-256
func SetAesCryptoKey(password, iv string) {
	aesKey = password
	aesIV = iv
}

// GetAesCryptoKey get current key/iv
func GetAesCryptoKey() (string, string) {
	return aesKey, aesIV
}

// NewAesCrypto new AesCrypto
func NewAesCrypto() *AesCrypto {
	return &AesCrypto{Key: []byte(aesKey), IV: []byte(aesIV)}
}

// SetKey set key
func (a *AesCrypto) SetKey(key, iv string) {
	a.Key = []byte(key)
	a.IV = []byte(iv)
}

// Encrypt encrypt data
func (a *AesCrypto) Encrypt(data []byte) ([]byte, error) {
	block, err := aes.NewCipher(a.Key)
	if err != nil {
		return nil, err
	}
	blockSize := block.BlockSize()
	data = pkcs7Padding(data, blockSize)

	blockMode := cipher.NewCBCEncrypter(block, a.IV[:blockSize])
	crypted := make([]byte, len(data))

	blockMode.CryptBlocks(crypted, data)
	return crypted, nil
}

// Decrypt decrypt data
func (a *AesCrypto) Decrypt(crypted []byte) ([]byte, error) {
	block, err := aes.NewCipher(a.Key)
	if err != nil {
		return nil, err
	}
	n := len(crypted)
	blockSize := block.BlockSize()
	if n%blockSize != 0 {
		return nil, errors.New(`crypto/cipher: input not full blocks`)
	}
	blockMode := cipher.NewCBCDecrypter(block, a.IV[:blockSize])
	origData := make([]byte, n)
	blockMode.CryptBlocks(origData, crypted)
	origData = pkcs7UnPadding(origData)

	return origData, nil
}

func pkcs7Padding(cipherText []byte, blockSize int) []byte {
	padding := blockSize - len(cipherText)%blockSize
	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(cipherText, padtext...)
}

func pkcs7UnPadding(data []byte) []byte {
	length := len(data)
	unpadding := int(data[length-1])
	if unpadding >= length {
		return []byte(``)
	}
	return data[:(length - unpadding)]
}