package tools

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

// AesCBCDecrypt AEC解密（CBC模式）
func AesCBCDecrypt(encryptData, key, iv []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	blockSize := block.BlockSize()
	if len(encryptData) < blockSize {
		return nil, errors.New("ciphertext too short")
	}
	if len(encryptData)%blockSize != 0 {
		return nil, errors.New("ciphertext is not a multiple of the block size")
	}
	mode := cipher.NewCBCDecrypter(block, iv)
	mode.CryptBlocks(encryptData, encryptData)
	// 解填充
	encryptData = PKCS7UnPadding(encryptData)
	return encryptData, nil
}

// PKCS7UnPadding 对密文删除填充
func PKCS7UnPadding(origData []byte) []byte {
	length := len(origData)
	unpadding := int(origData[length-1])
	return origData[:(length - unpadding)]
}