package utils

import (
	"bytes"
	"crypto/des"
	"encoding/hex"
	"errors"
	"fmt"
)

const (
	DES_CRYPT_KEY = "w$D5%8x@"
)

func DesEcbDecrypt(src string, key ...string) (result string, err error) {
	if len(key) == 0 {
		return DES_ECB{}.DecryptDES_ECB(src, DES_CRYPT_KEY)
	} else {
		return DES_ECB{}.DecryptDES_ECB(src, key[0])
	}
}

type DES_ECB struct {
}

//DecryptDES_ECB ECB解密
func (d DES_ECB) DecryptDES_ECB(src, key string) (result string, err error) {
	defer func() {
		if defErr := recover(); defErr != nil {
			fmt.Printf("DecryptDES_ECB_V2 panic info:%v\n", defErr)
			result = ""
			err = errors.New("DecryptDES_ECB_V2 err")
		}
	}()
	data, err := hex.DecodeString(src)
	if err != nil {
		return "", err
	}
	keyByte := []byte(key)
	block, err := des.NewCipher(keyByte)
	if err != nil {
		return "", err
	}
	bs := block.BlockSize()
	if len(data)%bs != 0 {
		return "", errors.New("crypto/cipher: input not full blocks")
	}
	out := make([]byte, len(data))
	dst := out
	for len(data) > 0 {
		block.Decrypt(dst, data[:bs])
		data = data[bs:]
		dst = dst[bs:]
	}
	out = d.PKCS5UnPadding(out)
	return string(out), nil
}

//明文补码算法
func (d DES_ECB) PKCS5Padding(ciphertext []byte, blockSize int) []byte {
	padding := blockSize - len(ciphertext)%blockSize
	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(ciphertext, padtext...)
}

//明文减码算法
func (d DES_ECB) PKCS5UnPadding(origData []byte) []byte {
	length := len(origData)
	unpadding := int(origData[length-1])
	return origData[:(length - unpadding)]
}