package utils

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


// AesDecrypt 解密函数
// encryptedStr：base64后的密文
// secret：appid/client_key对应的client_secret
// return: []byte 明文
func AesDecrypt(encryptedStr string, secret string) ([]byte, error) {
   // 加密字符串进行base64解码
   decodeBytes, err := base64.StdEncoding.DecodeString(encryptedStr)
   if err != nil {
      return nil, err
   }

   key, iv := parseSecret(secret)

   block, err := aes.NewCipher(key)
   if err != nil {
      return nil, err
   }

   blockSize := block.BlockSize()
   blockMode := cipher.NewCBCDecrypter(block, iv[:blockSize])
   origData := make([]byte, len(decodeBytes))
   blockMode.CryptBlocks(origData, decodeBytes)
   origData = PKCS5UnPadding(origData)
   return origData, nil
}

// parseSecret 将secret解析为key和iv
func parseSecret(secret string) ([]byte, []byte) {
   // secret对齐为32位
   secret = cutSecret(secret)
   secret = fillSecret(secret)

   key, iv := secret, secret[16:]

   return []byte(key), []byte(iv)
}

func fillSecret(secret string) string {
   if len(secret) >= 32 {
      return secret
   }
   rightCnt := (32 - len(secret)) / 2
   leftCnt := 32 - len(secret) - rightCnt

   var byt bytes.Buffer
   byt.Write(bytes.Repeat([]byte("#"), leftCnt))
   byt.WriteString(secret)
   byt.Write(bytes.Repeat([]byte("#"), rightCnt))
   return byt.String()
}

func cutSecret(secret string) string {
   if len(secret) <= 32 {
      return secret
   }

   rightCnt := (len(secret) - 32) / 2
   leftCnt := len(secret) - 32 - rightCnt

   return secret[leftCnt: 32+leftCnt]
}

func PKCS5UnPadding(origData []byte) []byte {
   length := len(origData)
   unpadding := int(origData[length-1])
   return origData[:(length - unpadding)]
}

package com.douyin.open.goodlife;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.util.Base64;

public class SignUtil {
    /*
     * appid/client_key对应的client_secret TODO 这里换成服务商的appsecret
     */
    private static final String secret = "12345678901234566543210987654321";
    private static final String key;

    private static final String iv;

    static {
        key = parseSecret(secret);
        iv = key.substring(16);
    }

    /**
     * @Description AES解密
     * @param data base64后的密文
     * @return 明文
     */
    public static String decryptAES(String data) throws Exception {
        try
        {
            byte[] encrypted1 = decode(data);//先用base64解密

            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
            SecretKeySpec keyspec = new SecretKeySpec(key.getBytes(), "AES");
            IvParameterSpec ivspec = new IvParameterSpec(iv.getBytes());

            cipher.init(Cipher.DECRYPT_MODE, keyspec, ivspec);

            byte[] original = cipher.doFinal(encrypted1);
            String originalString = new String(original);
            return originalString.trim();
        }
        catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }
    /**
     * base64编码
     */
    public static String encode(byte[] byteArray) {
        return new String(Base64.getEncoder().encode(byteArray));
    }

    /**
     * base64解码
     */
    public static byte[] decode(String base64EncodedString) {
        return Base64.getDecoder().decode(base64EncodedString);
    }

    private static String parseSecret(String secret) {
        secret = fillSecret(secret);
        secret = cutSecret(secret);
        return secret;
    }

    private static String cutSecret(String secret) {
        if (secret.length() <= 32) {
            return secret;
        }

        int rightCnt = (secret.length() - 32) / 2;
        int leftCnt = secret.length() - 32 - rightCnt;

        return secret.substring(leftCnt, 32 + leftCnt);
    }

    private static String fillSecret(String secret) {
        if (secret.length() >= 32) {
            return secret;
        }
        int rightCnt = (32 - secret.length()) / 2;
        int leftCnt = 32 - secret.length() - rightCnt;

        StringBuilder sb = new StringBuilder("");
        for (int i = 0; i < leftCnt; i++) {
            sb.append('#');
        }
        sb.append(secret);
        for (int i = 0; i < rightCnt; i++) {
            sb.append('#');
        }
        return sb.toString();
    }
}