package crypter

import (
	"crypto/md5"
	"encoding/base64"
	"fmt"
	"io"
	"strconv"
	"strings"
	"time"
)

// SSO gxytoken authcode
// btype 加密or解密 bool true：加密 false：解密 默认false
// skey 秘钥
// text 加/解密内容

func AuthCode(text, skey string, btype bool) string {

	isEncode := btype
	key := skey
	expiry := 0
	cKeyLen := 4

	timestamp := time.Now().Unix()
	// md5加密key
	mKey := Md5Sum(key)
	// 参与加密的
	keyA := Md5Sum(mKey[0:16])
	// 用于验证数据有效性的
	keyB := Md5Sum(mKey[16:])
	// 动态部分
	var keyC string
	if cKeyLen > 0 {
		if isEncode {
			// 加密的时候，动态获取一个秘钥
			keyC = Md5Sum(fmt.Sprint(timestamp))[32-cKeyLen:]
		} else {
			// 解密的时候从头部获取动态秘钥部分
			keyC = text[0:cKeyLen]
		}
	}
	// 加入了动态的秘钥
	cryptKey := keyA + Md5Sum(keyA+keyC)
	// 秘钥长度
	keyLen := len(cryptKey)
	if isEncode {
		// 加密 前10位是过期验证字符串 10-26位字符串验证
		var d int64
		if expiry > 0 {
			d = timestamp + int64(expiry)
		}
		text = fmt.Sprintf("%010d%s%s", d, Md5Sum(text + keyB)[0:16], text)
	} else {
		// 解密
		//res, _ := base64.StdEncoding.DecodeString(text[cKeyLen:])
		res := Base64Decode(text[cKeyLen:])
		text = string(res)
	}
	// 字符串长度
	textLen := len(text)
	if textLen <= 0 {
		return ""
	}

	// 密匙簿(0-256)
	box := make([]int, 0)
	for i := 0; i < 256; i++ {
		box = append(box, i)
	}

	// 对称算法
	var rndKey []int
	cryptKeyB := []byte(cryptKey)
	for i := 0; i < 256; i++ {
		pos := i % keyLen
		rndKey = append(rndKey, int(cryptKeyB[pos]))
	}

	j := 0
	for i := 0; i < 256; i++ {
		j = (j + box[i] + rndKey[i]) % 256
		box[i], box[j] = box[j], box[i]
	}

	textB := []byte(text)
	a := 0
	j = 0
	var result []byte
	for i := 0; i < textLen; i++ {
		a = (a + 1) % 256
		j = (j + box[a]) % 256
		box[a], box[j] = box[j], box[a]
		result = append(result, byte(int(textB[i])^(box[(box[a]+box[j])%256])))
	}

	if isEncode {
		return keyC + strings.Replace(base64.StdEncoding.EncodeToString(result), "=", "", -1)
	}

	// 获取前10位，判断过期时间
	d, err := strconv.ParseInt(string(result[0:10]), 10, 64)
	if err != nil {
		d = 0
	}
	fmt.Println(string(result[10:26]), Md5Sum(string(result[26:]) + keyB)[0:16])
	if (d == 0 || d-timestamp > 0) && string(result[10:26]) == Md5Sum(string(result[26:]) + keyB)[0:16] {
		return string(result[26:])
	}

	fmt.Println(string(result[26:]))

	return ""
}

//MD5SUm
func Md5Sum(str string) string {
	h := md5.New()
	io.WriteString(h, str)
	return fmt.Sprintf("%x", h.Sum(nil))
}

//Base64Decode
func Base64Decode(str string) []byte {
	var sdec []byte
	var err error
	x := len(str) * 3 % 4
	fmt.Println(x)
	switch {
	case x == 2:
		str += "=="
	case x == 1:
		str += "="
	}
	if sdec, err = base64.StdEncoding.DecodeString(str); err != nil {
		return sdec
	}
	return sdec
}