byte text[len] = {0};
int textIndex = 0;
for (int i = 0; i < data.length(); i += 4) {
  byte base64_bit_6[4];
  for (int j = 0; j < 4; j++) {
    base64_bit_6[j] = base64_chars.find(data[i + j]);
  }
  text[textIndex] =
    ((base64_bit_6[0] & 0x3f) << 2) | ((base64_bit_6[1] & 0x30) >> 4);
  text[textIndex + 1] =
    ((base64_bit_6[1] & 0xf) << 4) | ((base64_bit_6[2] & 0x3c) >> 2);
  text[textIndex + 2] =
    ((base64_bit_6[2] & 0x3) << 6) | (base64_bit_6[3] & 0x3f);
  textIndex += 3;
}

String title = "";
oiFirst = data[i] & 0x7f;
oiIndex = min(oiFirst / 40, 2);
title.append(to_string(min(oiFirst / 40, 2)));
title.append(".");
title.append(to_string(oiFirst - 40 * oiIndex));
title.append(".");
oiIndex = 2;
oiFirst = 0;
for (int t = 1; t < lens.len; t++) {
  oiFirst <<= 7;
  oiFirst += data[i + t] & 0x7f;
  if (!(data[i + t] & 0x80)) {
    title.append(to_string(oiFirst));
    title.append(".");
    oiIndex++;
    oiFirst = 0;
  }
}
// title 为OID字符串

// main.cpp
string fileName;
string base64Str = "";
fileName = string(argv[1]);
ifstream in(fileName);
if (!in.is_open()) {
  cout << "Error opening file";
  exit(1);
}
cout << fileName << endl;
char buffer[1024];
while (!in.eof()) {
  in.getline(buffer, 1024);
  if (string(buffer).find("BEGIN CERTIFICATE") != -1) {
    cout << "Begin" << endl;
  } else if (string(buffer).find("END CERTIFICATE") != -1) {
    parseX509(base64Str);
    cout << "End" << endl << endl;
    base64Str = "";
  } else {
    base64Str.append(buffer);
  }
}

// x509.cpp

static const string base64_chars =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "abcdefghijklmnopqrstuvwxyz"
    "0123456789+/";

while (data.length() % 4 != 0) {
  cout << "Error" << endl;
  data.append("=");
}
int len = (data.length() / 4) * 3;
cout << "证书长度：" << len << endl;
byte text[len] = {0};
int textIndex = 0;
for (int i = 0; i < data.length(); i += 4) {
  byte base64_bit_6[4];
  for (int j = 0; j < 4; j++) {
    base64_bit_6[j] = base64_chars.find(data[i + j]);
  }
  text[textIndex] =
    ((base64_bit_6[0] & 0x3f) << 2) | ((base64_bit_6[1] & 0x30) >> 4);
  text[textIndex + 1] =
    ((base64_bit_6[1] & 0xf) << 4) | ((base64_bit_6[2] & 0x3c) >> 2);
  text[textIndex + 2] =
    ((base64_bit_6[2] & 0x3) << 6) | (base64_bit_6[3] & 0x3f);
  textIndex += 3;
}

parseANS(text, 0, len);

typedef struct {
  int len;     // 长度
  int lenLen;  // 长度所占的长度
} lenData;     // 长度信息

typedef struct {
  string title;
  int len;
  byte* data;
  int type;
} Item;  // 解析项目

vector<Item> ansData;

// 长度、长度占用
lenData getLen(byte* data, int i) {
  lenData res;
  res.lenLen = 1;
  if (data[i] & 0x80) {
    int len_len = data[i] & 0x7f;
    int len = 0;
    i++;
    for (int j = 0; j < len_len; j++) {
      len <<= 8;
      len += data[i + j];
    }
    res.len = len;
    res.lenLen += len_len;
  } else {
    res.len = data[i] & 0x7f;
  }
  return res;
}

void parseANS(byte* data, int begin, int end) {
  int i = begin;
  lenData lens;
  byte* text;
  int oiFirst;
  int oiIndex;
  string title;
  int type;
  while (i < end) {
    int type = data[i];
    i++;
    lens = getLen(data, i);
    if (i + lens.lenLen <= end) {
      i += lens.lenLen;
    }
    if (lens.len <0 || i + lens.len > end) {
      break;
    }
    title = "";
    switch (type) {
      case 0x30:  // 结构体序列
        parseANS(data, i, i + lens.len);
        break;
      case 0x31:  // Set序列
        parseANS(data, i, i + lens.len);
        break;
      case 0xa3:  // 扩展字段
        title = "Extension";
        ansData.push_back({title, lens.len, NULL, type});
        parseANS(data, i, i + lens.len);
        break;
      case 0xa0:  // 证书版本
        title = "Version";
        ansData.push_back({title, lens.len, NULL, type});
        parseANS(data, i, i + lens.len);
        break;
      case 0x04:  // OCTET STRING
        // title = "Octet";
        // ansData.push_back({title, lens.len, NULL, type});
        parseANS(data, i, i + lens.len);
      case 0x05:
        break;
      case 0x06:  // Object Identifier
        title = "";
        oiFirst = data[i] & 0x7f;
        oiIndex = min(oiFirst / 40, 2);
        title.append(to_string(min(oiFirst / 40, 2)));
        title.append(".");
        title.append(to_string(oiFirst - 40 * oiIndex));
        title.append(".");
        oiIndex = 2;
        oiFirst = 0;
        for (int t = 1; t < lens.len; t++) {
          oiFirst <<= 7;
          oiFirst += data[i + t] & 0x7f;
          if (!(data[i + t] & 0x80)) {
            title.append(to_string(oiFirst));
            title.append(".");
            oiIndex++;
            oiFirst = 0;
          }
        }
        ansData.push_back(
            {title.substr(0, title.length() - 1), lens.len, NULL, type});
        break;
      case 0x17:  // 时间戳
        title = "UTCTime";
      case 0x13:  // 字符串
      case 0x82:  // subjectUniqueID
      case 0x16:  // IA5String类型
      case 0x0c:  // UTF8String类型
      case 0x86:  // 特殊IA5String类型
        for (int t = 0; t < lens.len; t++) {
          title += (char)data[i + t];
        }
        ansData.push_back({title, lens.len, NULL, type});
        break;
      case 0x01:  // 布尔类型
        oiFirst = 0xff;
        for (int t = 0; t < lens.len; t++) {
          oiFirst &= data[i + t];
        }
        ansData.push_back(
            {oiFirst == 0 ? "False" : "True", lens.len, NULL, type});
        break;
      case 0x02:  // 整数类型
      case 0x80:  // 直接输出
        text = new byte[lens.len];
        for (int t = 0; t < lens.len; t++) {
          text[t] = data[i + t];
        }
        ansData.push_back({title, lens.len, text, type});
        break;
      case 0x03:  // Bit String 类型
        text = new byte[lens.len - 1];
        for (int t = 0; t < lens.len - 1; t++) {
          text[t] = data[i + t + 1];
        }
        ansData.push_back({"", lens.len - 1, text, type});
        break;
      case 0x00:
        text = new byte[end - begin];
        for (int t = begin + 1; t < end; t++) {
          text[t - begin - 1] = data[t];
        }
        ansData.push_back({"0x00", end - begin - 1, text, type});
        break;
      default:
        i--;
        if (i + lens.len > end) {
          text = new byte[end - begin];
          for (int t = 0; t < end - begin; t++) {
            text[t] = data[i + t];
          }
          ansData.push_back({"", end - begin, text, type});
        } else {
          text = new byte[lens.len];
          for (int t = 0; t < lens.len; t++) {
            text[t] = data[i + t];
          }
          ansData.push_back({"", lens.len, text, type});
        }
        i = end;
    }
    i += lens.len;
  }
}

void printTime(string timeStr) {
  cout << "20" << timeStr[0] << timeStr[1] << "年";
  cout << timeStr[2] << timeStr[3] << "月";
  cout << timeStr[4] << timeStr[5] << "日";
  cout << timeStr[6] << timeStr[7] << ":";
  cout << timeStr[8] << timeStr[9] << ":";
  cout << timeStr[10] << timeStr[11];
}

void printHex(byte* data, int len) {
  cout << hex;
  for (int t = 0; t < len; t++) {
    cout << ((data[t] & 0xf0) >> 4) << (data[t] & 0xf);
  }
  cout << dec << endl;
}

void printHexLimit(byte* data, int len) {
  cout << hex;
  for (int t = 0; t < len; t++) {
    cout << ((data[t] & 0xf0) >> 4) << (data[t] & 0xf);
    if (t % 30 == 29) cout << endl;
  }
  cout << dec << endl;
}

void printRes() {
  std::map<string, string> titleToString = {
      {"1.3.6.1.5.5.7.3.1", "服务器身份验证(id_kp_serverAuth): True"},
      {"1.3.6.1.5.5.7.3.2", "客户端身份验证(id_kp_clientAuth): True"},
      {"2.5.29.37", "扩展密钥用法(Extended key usage):"},
      {"2.5.29.31", "CRL Distribution Points:"},
      {"1.2.840.10045.2.1", "EC Public Key:"},
      {"Extension", "扩展字段:"},
      {"2.23.140.1.2.2","组织验证(organization-validated):"},
      {"1.3.6.1.5.5.7.1.1", "AuthorityInfoAccess:"},
      {"2.5.29.19", "基本约束(Basic Constraints):"},
      {"1.3.6.1.5.5.7.3.2", "客户端身份验证(id_kp_clientAuth): True"}};
  std::map<string, string> titleToHex = {
      {"1.2.840.10045.3.1.7",
       "推荐椭圆曲线域(SEC 2 recommended elliptic curve domain): \n"},
      {"2.5.29.35", "授权密钥标识符(Authority Key Identifier): "},
      {"2.5.29.14", "主体密钥标识符(Subject Key Identifier): "}};
  std::map<string, string> titleToNext = {
      {"1.3.6.1.5.5.7.2.1", "OID for CPS qualifier: "},
      {"1.3.6.1.5.5.7.48.1", "OCSP: "},
      {"1.3.6.1.5.5.7.48.2", "id-ad-caIssuers: "},
      {"1.3.6.1.4.1.311.60.2.1.1", "所在地(Locality): "},
      {"1.3.6.1.4.1.311.60.2.1.3", "国家(Country): "},
      {"1.3.6.1.4.1.311.60.2.1.2", "州或省(State or province): "},
      {"2.5.4.3", "通用名称(id-at-commonName): "},
      {"2.5.4.5", "颁发者序列号(id-at-serialNumber): "},
      {"2.5.4.6", "颁发者国家名(id-at-countryName): "},
      {"2.5.4.7", "颁发者位置名(id-at-localityName): "},
      {"2.5.4.8", "颁发者州省名(id-at-stateOrProvinceName): "},
      {"2.5.4.9", "颁发者街区地址(id-at-streetAddress): "},
      {"2.5.4.10", "颁发者组织名(id-at-organizationName): "},
      {"2.5.4.11", "颁发者组织单位名(id-at-organizationalUnitName): "},
      {"2.5.4.12", "颁发者标题(id-at-title): "},
      {"2.5.4.13", "颁发者描述(id-at-description): "},
      {"2.5.4.15", "颁发者业务类别(id-at-businessCategory): "},
      {"2.5.29.32", "证书策略(Certificate Policies): "},
      {"2.5.29.15", "使用密钥(Key Usage): "}};

    std::map<string, string> algorithmObject = {
      {"1.2.840.10040.4.1", "DSA"},
      {"1.2.840.10040.4.3" , "sha1DSA"},
      {"1.2.840.113549.1.1.1" ,"RSA"},
      {"1.2.840.113549.1.1.2" , "md2RSA"},
      {"1.2.840.113549.1.1.3" , "md4RSA"},
      {"1.2.840.113549.1.1.4" , "md5RSA"},
      {"1.2.840.113549.1.1.5" , "sha1RSA"},
      {"1.3.14.3.2.29", "sha1RSA"},
      {"1.2.840.113549.1.1.13", "sha512RSA"},
      {"1.2.840.113549.1.1.11","sha256RSA"}};

  for (int i = 0; i < ansData.size(); i++) {
    Item item = ansData[i];
    if (!strcmp(item.title.c_str(), "Version")) {
      item = ansData[++i];
      if (item.type == 0x02) {
        cout << "证书版本: ";
        cout << "V" << item.data[0] + 1 << endl;
        item = ansData[++i];
        cout << "序列号: ";
        printHex(item.data, item.len);
      } else {
        i--;
      }
    } else if (titleToString.find(item.title) != titleToString.end()) {
      cout << titleToString[item.title] << endl;
    } else if (titleToHex.find(item.title) != titleToHex.end()) {
      string title = titleToHex[item.title];
      item = ansData[++i];
      if (item.data != NULL) {
        cout << title;
        printHex(item.data, item.len);
      } else {
        i--;
      }
    } else if (titleToNext.find(item.title) != titleToNext.end()) {
      cout << titleToNext[item.title];
      item = ansData[++i];
      cout << item.title << endl;
    } else if (algorithmObject.find(item.title) != algorithmObject.end()) {
      cout << "加密算法: " << algorithmObject[item.title];
      item = ansData[++i];
      if (item.type == 0x03) {
        cout << "\n公钥：" << endl;
        printHexLimit(item.data, item.len);
      } else {
        i--;
      }
    } else if (!strcmp(item.title.c_str(), "0x00")) {
      cout << "Public Key: " << endl;
      printHexLimit(item.data, item.len);
    } else if (!strcmp(item.title.c_str(), "2.5.29.17")) {
      cout << "主体别名(Subject Alternative Name): ";
      item = ansData[++i];
      cout << item.title;
      item = ansData[++i];
      while (item.type == 0x82) {
        cout << ", " << item.title;
        item = ansData[++i];
      }
      i--;
      cout << endl;
    } else if (item.title.length() > 7 &&
               !strcmp(item.title.substr(0, 7).c_str(), "UTCTime")) {
      cout << "有效期: ";
      string beginTime = item.title.substr(7, item.title.length() - 8);
      printTime(beginTime);
      cout << " - ";
      item = ansData[++i];
      string endTime = item.title.substr(7, item.title.length() - 8);
      printTime(endTime);
      cout << endl;
    }
  }
}