package aes

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

const defaultKey = "gkit"

func PadKey(s string) string {
	if s == "" {
		s = defaultKey
	}
	ps := []byte(s)
	ls := len(ps)

	if ls > 32 {
		return string(ps[:32])
	}
	idx := 0
	for i := ls; !(i == 16 || i == 24 || i == 32); i++ {
		ps = append(ps, s[idx])
		idx = (idx + 1) % ls
	}

	return string(ps)
}

func Encrypt(orig string, key string) string {
	defer func() {
		if err := recover(); err != nil {
			//fmt.Println("Encrypt Err", orig, err)
			return
		}
	}()
	// 转成字节数组
	origData := []byte(orig)
	k := []byte(key)
	// 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(k)
	// 获取秘钥块的长度
	blockSize := block.BlockSize()
	// 补全码
	origData = PKCS7Padding(origData, blockSize)
	// 加密模式
	blockMode := cipher.NewCBCEncrypter(block, k[:blockSize])
	// 创建数组
	cryted := make([]byte, len(origData))
	// 加密
	blockMode.CryptBlocks(cryted, origData)
	return base64.StdEncoding.EncodeToString(cryted)
}

func Decrypt(cryted string, key string) string {
	defer func() {
		if err := recover(); err != nil {
			//fmt.Println("Decrypt Err", cryted, err)
			return
		}
	}()
	// 转成字节数组
	crytedByte, _ := base64.StdEncoding.DecodeString(cryted)
	k := []byte(key)
	// 分组秘钥
	block, _ := aes.NewCipher(k)
	// 获取秘钥块的长度
	blockSize := block.BlockSize()
	// 加密模式
	blockMode := cipher.NewCBCDecrypter(block, k[:blockSize])
	// 创建数组
	orig := make([]byte, len(crytedByte))
	// 解密
	if len(crytedByte)%block.BlockSize() != 0 {
		return ""
	}
	if len(orig) < len(crytedByte) {
		return ""
	}
	if InexactOverlap(orig[:len(crytedByte)], crytedByte) {
		return ""
	}

	blockMode.CryptBlocks(orig, crytedByte)
	// 去补全码
	orig = PKCS7UnPadding(orig)
	return string(orig)
}

// PKCS7Padding 补码
// AES加密数据块分组长度必须为128bit(byte[16])，密钥长度可以是128bit(byte[16])、192bit(byte[24])、256bit(byte[32])中的任意一个。
func PKCS7Padding(ciphertext []byte, blocksize int) []byte {
	padding := blocksize - len(ciphertext)%blocksize
	padText := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(ciphertext, padText...)
}

// PKCS7UnPadding 去码
func PKCS7UnPadding(origData []byte) []byte {
	length := len(origData)
	unPadding := int(origData[length-1])
	return origData[:(length - unPadding)]
}

func InexactOverlap(x, y []byte) bool {
	if len(x) == 0 || len(y) == 0 || &x[0] == &y[0] {
		return false
	}
	return AnyOverlap(x, y)
}

func AnyOverlap(x, y []byte) bool {
	return len(x) > 0 && len(y) > 0 &&
		uintptr(unsafe.Pointer(&x[0])) <= uintptr(unsafe.Pointer(&y[len(y)-1])) &&
		uintptr(unsafe.Pointer(&y[0])) <= uintptr(unsafe.Pointer(&x[len(x)-1]))
}