package utils

import (
	"crypto/aes"
	"encoding/base64"
	"fmt"
	"regexp"
)

// 解密函数
func Decrypt(ciphertext string, key []byte) (string, error) {
	// Base64 解码
	cipherTextDecoded, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		return "", err
	}

	// 创建 AES 密码块
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}

	// 检查密文长度是否为块大小的倍数
	if len(cipherTextDecoded)%aes.BlockSize != 0 {
		return "", fmt.Errorf("密文长度不是块大小的倍数")
	}

	// 解密密文
	decrypted := make([]byte, len(cipherTextDecoded))
	for bs := 0; bs < len(cipherTextDecoded); bs += aes.BlockSize {
		block.Decrypt(decrypted[bs:], cipherTextDecoded[bs:bs+aes.BlockSize])
	}

	// 移除填充
	decrypted = pkcs7Unpad(decrypted)

	// 移除不需要的字符
	re := regexp.MustCompile("[\\x00-\\x08\\x0b-\\x0c\\x0e-\\x1f\n\r\t]")
	cleanedString := re.ReplaceAllString(string(decrypted), "")

	return cleanedString, nil
}

// 移除PKCS7填充
func pkcs7Unpad(src []byte) []byte {
	length := len(src)
	unpadding := int(src[length-1])
	if unpadding > length {
		return src
	}
	return src[:(length - unpadding)]
}