package encrypt

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"encoding/base64"
	"math/rand"
	"unsafe"
)

const lettersString = "0123456789abcdefghijkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ"

// 字符串长度
const number = 16

/*
16位码，前15位随机字符串，最后一位通过前15位字符串计算校验生成
*/

func LotteryEncryptEncode() string {
	b := make([]byte, number)
	var sum byte
	for i := 0; i < number-1; i++ {
		b[i] = lettersString[rand.Int63()%int64(len(lettersString))]
		sum += b[i]
	}
	b[number-1] = lettersString[sum%byte(len(lettersString))]
	return *(*string)(unsafe.Pointer(&b))
}

func LotteryEncryptDecode(str string) bool {
	var sum byte
	for i := 0; i < len(str)-1; i++ {
		sum += str[i]
	}
	if lettersString[sum%byte(len(lettersString))] != str[len(str)-1] {
		return false
	}
	return true
}

// =================== CBC ======================
func AesEncryptCBC(origData []byte, key []byte) (str string) {
	// 分组秘钥
	// NewCipher该函数限制了输入k的长度必须为16, 24或者32
	block, _ := aes.NewCipher(key)
	blockSize := block.BlockSize()                              // 获取秘钥块的长度
	origData = pkcs5Padding(origData, blockSize)                // 补全码
	blockMode := cipher.NewCBCEncrypter(block, key[:blockSize]) // 加密模式
	encrypted := make([]byte, len(origData))                    // 创建数组
	blockMode.CryptBlocks(encrypted, origData)                  // 加密

	return base64.StdEncoding.EncodeToString(encrypted)
}
func AesDecryptCBC(data string, key []byte) (decrypted []byte) {
	encrypted, err := base64.StdEncoding.DecodeString(data)
	if err != nil {
		return
	}

	block, _ := aes.NewCipher(key)                              // 分组秘钥
	blockSize := block.BlockSize()                              // 获取秘钥块的长度
	blockMode := cipher.NewCBCDecrypter(block, key[:blockSize]) // 加密模式
	decrypted = make([]byte, len(encrypted))                    // 创建数组
	blockMode.CryptBlocks(decrypted, encrypted)                 // 解密
	decrypted = pkcs5UnPadding(decrypted)                       // 去除补全码
	return decrypted
}
func pkcs5Padding(ciphertext []byte, blockSize int) []byte {
	padding := blockSize - len(ciphertext)%blockSize
	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(ciphertext, padtext...)
}
func pkcs5UnPadding(origData []byte) []byte {
	length := len(origData)
	unpadding := int(origData[length-1])
	return origData[:(length - unpadding)]
}