package crypto

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
)

func paddingPKCS7(ciphertext []byte, blockSize int) []byte {
	padding := blockSize - len(ciphertext)%blockSize
	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(ciphertext, padtext...)
}

func unpaddingPKCS7(origData []byte) []byte {
	length := len(origData)
	unpadding := int(origData[length-1])
	return origData[:(length - unpadding)]
}

//EncryptAES 加密函式
func EncryptAES(plaintext, key, iv []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	blockSize := block.BlockSize()
	plaintext = paddingPKCS7(plaintext, blockSize)
	blockMode := cipher.NewCBCEncrypter(block, iv)
	crypted := make([]byte, len(plaintext))
	blockMode.CryptBlocks(crypted, plaintext)
	return crypted, nil
}

// DecryptAES 解密函式
func DecryptAES(ciphertext, key, iv []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	blockSize := block.BlockSize()
	blockMode := cipher.NewCBCDecrypter(block, iv[:blockSize])
	origData := make([]byte, len(ciphertext))
	blockMode.CryptBlocks(origData, ciphertext)
	origData = unpaddingPKCS7(origData)
	return origData, nil
}