package aesx

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
)

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(origData []byte) []byte {
	length := len(origData)
	unpadding := int(origData[length-1])
	return origData[:(length - unpadding)]
}

// AES加密,CBC
func AesEncrypt(origData, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	blockSize := block.BlockSize()
	origData = PKCS7Padding(origData, blockSize)
	blockMode := cipher.NewCBCEncrypter(block, key[:blockSize])
	crypted := make([]byte, len(origData))
	blockMode.CryptBlocks(crypted, origData)
	return crypted, nil
}

// AES解密
func AesDecrypt(crypted, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	blockSize := block.BlockSize()
	blockMode := cipher.NewCBCDecrypter(block, key[:blockSize])
	origData := make([]byte, len(crypted))
	blockMode.CryptBlocks(origData, crypted)
	origData = PKCS7UnPadding(origData)
	return origData, nil
}

/*
AES  CBC 加密
key:加密key
plaintext：加密明文
ciphertext:解密返回字节字符串[ 整型以十六进制方式显示]
*/
func AESCBCEncrypt(key, plaintext string) (ciphertext string,err error) {
	plainbyte := []byte(plaintext)
	keybyte := []byte(key)
	if len(plainbyte)%aes.BlockSize != 0 {
		return "",errors.New ("plaintext is not a multiple of the block size")
	}
	block, err := aes.NewCipher(keybyte)
	if err != nil {
		return "",err
	}

	cipherbyte := make([]byte, aes.BlockSize+len(plainbyte))
	iv := cipherbyte[:aes.BlockSize]
	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
		return "",err
	}

	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(cipherbyte[aes.BlockSize:], plainbyte)

	ciphertext = fmt.Sprintf("%x\n", cipherbyte)
	return
}

/*
AES  CBC 解码
key:解密key
ciphertext:加密返回的串
plaintext：解密后的字符串
*/
func AESCBCDecrypter(key, ciphertext string) (plaintext string,err error) {
	cipherbyte, _ := hex.DecodeString(ciphertext)
	keybyte := []byte(key)
	block, err := aes.NewCipher(keybyte)
	if err != nil {
		return "",err
	}
	if len(cipherbyte) < aes.BlockSize {
		return "", errors.New("ciphertext too short")
	}

	iv := cipherbyte[:aes.BlockSize]
	cipherbyte = cipherbyte[aes.BlockSize:]
	if len(cipherbyte)%aes.BlockSize != 0 {
		return "", errors.New("ciphertext is not a multiple of the block size")
	}

	mode := cipher.NewCBCDecrypter(block, iv)
	mode.CryptBlocks(cipherbyte, cipherbyte)

	//fmt.Printf("%s\n", ciphertext)
	plaintext = string(cipherbyte[:])
	return
}

/*
AES  GCM 加密
key:加密key
plaintext：加密明文
ciphertext:解密返回字节字符串[ 整型以十六进制方式显示]
*/
func AESGCMEncrypt(key, plaintext string) (ciphertext, noncetext string, err error) {
	plainbyte := []byte(plaintext)
	keybyte := []byte(key)
	block, err := aes.NewCipher(keybyte)
	if err != nil {
		return "", "", err
	}

	// 由于存在重复的风险，请勿使用给定密钥使用超过2^32个随机值。
	nonce := make([]byte, 12)
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", "", err
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", "", err
	}

	cipherbyte := aesgcm.Seal(nil, nonce, plainbyte, nil)
	ciphertext = fmt.Sprintf("%x\n", cipherbyte)
	noncetext = fmt.Sprintf("%x\n", nonce)
	return
}

/*
AES  CBC 解码
key:解密key
ciphertext:加密返回的串
plaintext：解密后的字符串
*/
func AESGCMDecrypter(key, ciphertext, noncetext string) (plaintext string, err error) {
	cipherbyte, _ := hex.DecodeString(ciphertext)
	nonce, _ := hex.DecodeString(noncetext)
	keybyte := []byte(key)
	block, err := aes.NewCipher(keybyte)
	if err != nil {
		return "", err
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	plainbyte, err := aesgcm.Open(nil, nonce, cipherbyte, nil)
	if err != nil {
		return "", err
	}

	//fmt.Printf("%s\n", ciphertext)
	plaintext = string(plainbyte[:])
	return
}