/*
 * 增强版考勤服务器 - 支持AES加密数据
 *
 * 功能：
 * 1. HTTP端口8082 - 接收STM32加密签到数据
 * 2. HTTP API - 提供Qt客户端接口
 * 3. AES-128-CBC解密支持
 *
 * 编译：g++ -o server_encrypted.exe server_encrypted.cpp -lws2_32 -lcrypto -lssl -lsqlite3 -std=c++11
 */

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <thread>
#include <vector>
#include <map>
#include <set>
#include <ctime>
#include <algorithm>
#include <cctype>
#include <cstdlib>
#include <cstdio>

#ifdef _WIN32
    #include <winsock2.h>
    #include <ws2tcpip.h>
    #include <direct.h>
    #pragma comment(lib, "ws2_32.lib")
    typedef int socklen_t;
#else
    #include <sys/socket.h>
    #include <netinet/in.h>
    #include <unistd.h>
    #include <arpa/inet.h>
    #include <cstring>
    #include <sys/stat.h>
    #define SOCKET int
    #define INVALID_SOCKET -1
    #define SOCKET_ERROR -1
    #define closesocket(s) close(s)
    #define _mkdir(d) mkdir(d, 0755)
#endif

// OpenSSL库用于AES解密和Base64
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/buffer.h>
#include <openssl/aes.h>
#include <sqlite3.h>

const int HTTP_PORT = 8082;
const int BUFFER_SIZE = 4096;
const std::string SQLITE_DB_FILE = "attendance.db";
const std::string LOG_FILE = "attendance.log";
const std::string FACES_DIR = "faces";  // 人脸照片目录
const std::string DB_BACKUP_DIR = "backups";
const size_t MAX_JSON_BODY_SIZE = 64 * 1024;
const size_t MAX_PHOTO_BODY_SIZE = 512 * 1024;
const size_t MAX_ENCRYPTED_JSON_BODY_SIZE = ((MAX_JSON_BODY_SIZE + 16) * 4 / 3) + 32;
const size_t MAX_ENCRYPTED_PHOTO_BODY_SIZE = ((MAX_PHOTO_BODY_SIZE + 16) * 4 / 3) + 32;
const char* DEFAULT_API_TOKEN = "atk_nKfVWLhMjL0RGSfRll3R_sdJS6IrIjuV";
const char* DEFAULT_CORS_ORIGIN = "http://localhost";
const char* DEFAULT_TIMESLOTS_JSON =
    "{\"time_slots\":[]}";

std::string getEnvOrDefault(const char* name, const char* fallback) {
    const char* value = std::getenv(name);
    if (value && value[0] != '\0') {
        return std::string(value);
    }
    return std::string(fallback);
}

const std::string& apiToken() {
    static const std::string token = getEnvOrDefault("ATTENDANCE_API_TOKEN", DEFAULT_API_TOKEN);
    return token;
}

const std::string& allowedCorsOrigin() {
    static const std::string origin = getEnvOrDefault("ATTENDANCE_CORS_ORIGIN", DEFAULT_CORS_ORIGIN);
    return origin;
}

const std::string& bindAddress() {
    static const std::string address = getEnvOrDefault("ATTENDANCE_BIND_HOST", "0.0.0.0");
    return address;
}

std::string readStudents();
std::string readClasses();
std::string readFaceProfiles();
std::string getPendingDeleteList();
std::string getFacePhotosList();
bool setSyncRequest(bool sync);
bool removeFromPendingDelete(const std::string& face_id);
bool cancelPendingDeleteForFace(sqlite3* db, const std::string& face_id, const std::string& now);
bool updateDeviceSyncState(const std::string& client, unsigned long long seen_version, unsigned long long ack_version);
std::string getDeviceSyncSummary();
bool initializeSqliteStorage();
bool saveAttendanceRecord(const std::string& timestamp, const std::string& student_id,
                          const std::string& name, const std::string& confidence,
                          const std::string& status, const std::string& class_id);
bool saveStudents(const std::string& json_data);
bool saveClasses(const std::string& json_data);
bool saveFaceProfiles(const std::string& json_data);
unsigned long long bumpSyncVersion(const std::string& reason);
std::vector<std::map<std::string, std::string>> parseJsonObjectArray(const std::string& json_data, const std::string& key);
std::string extractJsonMemberValue(const std::string& json, const std::string& key, const std::string& fallback);

std::string jsonEscape(const std::string& value) {
    std::ostringstream out;
    for (unsigned char c : value) {
        switch (c) {
        case '\"': out << "\\\""; break;
        case '\\': out << "\\\\"; break;
        case '\b': out << "\\b"; break;
        case '\f': out << "\\f"; break;
        case '\n': out << "\\n"; break;
        case '\r': out << "\\r"; break;
        case '\t': out << "\\t"; break;
        default:
            if (c < 0x20) {
                const char* hex = "0123456789abcdef";
                out << "\\u00" << hex[(c >> 4) & 0x0f] << hex[c & 0x0f];
            } else {
                out << static_cast<char>(c);
            }
            break;
        }
    }
    return out.str();
}

std::string csvEscape(const std::string& value) {
    bool needs_quotes = false;
    for (char c : value) {
        if (c == ',' || c == '"' || c == '\r' || c == '\n') {
            needs_quotes = true;
            break;
        }
    }
    if (!needs_quotes) {
        return value;
    }

    std::string escaped = "\"";
    for (char c : value) {
        if (c == '"') {
            escaped += "\"\"";
        } else {
            escaped += c;
        }
    }
    escaped += "\"";
    return escaped;
}

bool parseIntInRange(const std::string& value, int min_value, int max_value, int& output) {
    if (value.empty()) {
        return false;
    }

    try {
        size_t pos = 0;
        int parsed = std::stoi(value, &pos);
        if (pos != value.size() || parsed < min_value || parsed > max_value) {
            return false;
        }
        output = parsed;
        return true;
    } catch (...) {
        return false;
    }
}

bool parseTimeParts(const std::string& value, int& hour, int& minute) {
    if (value.size() != 5 || value[2] != ':'
        || !std::isdigit(static_cast<unsigned char>(value[0]))
        || !std::isdigit(static_cast<unsigned char>(value[1]))
        || !std::isdigit(static_cast<unsigned char>(value[3]))
        || !std::isdigit(static_cast<unsigned char>(value[4]))) {
        return false;
    }

    int parsed_hour = (value[0] - '0') * 10 + (value[1] - '0');
    int parsed_minute = (value[3] - '0') * 10 + (value[4] - '0');
    if (parsed_hour < 0 || parsed_hour > 23 || parsed_minute < 0 || parsed_minute > 59) {
        return false;
    }
    hour = parsed_hour;
    minute = parsed_minute;
    return true;
}

bool isSafeId(const std::string& value) {
    if (value.empty() || value.size() > 64) {
        return false;
    }
    for (unsigned char c : value) {
        if (!(std::isalnum(c) || c == '_' || c == '-')) {
            return false;
        }
    }
    return true;
}

bool buildFacePhotoPath(const std::string& face_id, std::string& filepath) {
    if (!isSafeId(face_id)) {
        return false;
    }
    filepath = FACES_DIR + "/" + face_id + ".jpg";
    return true;
}

bool fileExistsAndNotEmpty(const std::string& filepath) {
    std::ifstream file(filepath.c_str(), std::ios::binary | std::ios::ate);
    return file.is_open() && file.tellg() > 0;
}

bool getHeaderValue(const std::string& request, const std::string& header_name, std::string& output) {
    size_t headers_end = request.find("\r\n\r\n");
    std::string headers = headers_end == std::string::npos ? request : request.substr(0, headers_end);
    std::istringstream stream(headers);
    std::string line;

    std::string expected_key = header_name;
    std::transform(expected_key.begin(), expected_key.end(), expected_key.begin(),
        [](unsigned char c) { return static_cast<char>(std::tolower(c)); });

    while (std::getline(stream, line)) {
        if (!line.empty() && line.back() == '\r') {
            line.pop_back();
        }

        size_t colon = line.find(':');
        if (colon == std::string::npos) {
            continue;
        }

        std::string key = line.substr(0, colon);
        std::string value = line.substr(colon + 1);
        key.erase(std::remove_if(key.begin(), key.end(),
            [](unsigned char c) { return std::isspace(c); }), key.end());
        std::transform(key.begin(), key.end(), key.begin(),
            [](unsigned char c) { return static_cast<char>(std::tolower(c)); });

        if (key != expected_key) {
            continue;
        }

        size_t first = value.find_first_not_of(" \t");
        if (first == std::string::npos) {
            output.clear();
        } else {
            value.erase(0, first);
            size_t last = value.find_last_not_of(" \t");
            if (last != std::string::npos) {
                value.erase(last + 1);
            }
            output = value;
        }
        return true;
    }

    return false;
}

bool hasHeaderToken(const std::string& request, const std::string& header_name, const std::string& expected) {
    size_t headers_end = request.find("\r\n\r\n");
    std::string headers = headers_end == std::string::npos ? request : request.substr(0, headers_end);
    std::istringstream stream(headers);
    std::string line;

    while (std::getline(stream, line)) {
        if (!line.empty() && line.back() == '\r') {
            line.pop_back();
        }
        size_t colon = line.find(':');
        if (colon == std::string::npos) {
            continue;
        }
        std::string key = line.substr(0, colon);
        std::string value = line.substr(colon + 1);
        key.erase(std::remove_if(key.begin(), key.end(),
            [](unsigned char c) { return std::isspace(c); }), key.end());
        size_t first = value.find_first_not_of(" \t");
        if (first == std::string::npos) {
            value.clear();
        } else {
            value.erase(0, first);
            size_t last = value.find_last_not_of(" \t");
            if (last != std::string::npos) {
                value.erase(last + 1);
            }
        }

        std::transform(key.begin(), key.end(), key.begin(),
            [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
        std::string expected_key = header_name;
        std::transform(expected_key.begin(), expected_key.end(), expected_key.begin(),
            [](unsigned char c) { return static_cast<char>(std::tolower(c)); });

        if (key == expected_key && value == expected) {
            return true;
        }
    }
    return false;
}

bool hasBearerToken(const std::string& request, const std::string& expected) {
    std::string authorization;
    if (!getHeaderValue(request, "Authorization", authorization)) {
        return false;
    }

    const std::string prefix = "Bearer ";
    if (authorization.size() <= prefix.size()) {
        return false;
    }

    std::string scheme = authorization.substr(0, prefix.size());
    std::transform(scheme.begin(), scheme.end(), scheme.begin(),
        [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
    if (scheme != "bearer ") {
        return false;
    }

    return authorization.substr(prefix.size()) == expected;
}

bool isPublicEndpoint(const std::string& method, const std::string& endpoint) {
    (void)endpoint;
    return method == "OPTIONS";
}

bool isAuthorizedRequest(const std::string& request, const std::string& method, const std::string& endpoint) {
    if (isPublicEndpoint(method, endpoint)) {
        return true;
    }
    return hasHeaderToken(request, "X-Api-Token", apiToken()) || hasBearerToken(request, apiToken());
}

std::string makeJsonError(const std::string& message) {
    return "{\"success\":false,\"message\":\"" + jsonEscape(message) + "\"}";
}

bool isEncryptedRequest(const std::string& request) {
    return hasHeaderToken(request, "X-Encrypted", "AES128-CBC");
}

bool isJsonLikeContentType(const std::string& content_type) {
    std::string lower = content_type;
    std::transform(lower.begin(), lower.end(), lower.begin(),
        [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
    return lower.find("application/json") != std::string::npos
        || lower.find("text/json") != std::string::npos
        || lower.find("+json") != std::string::npos;
}

// ⚠️ 重要：密钥和IV必须与STM32端完全一致！
static const unsigned char MY_AES_KEY[16] = {
    0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
    0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c
};

static const unsigned char MY_AES_IV[16] = {
    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
    0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
};

// ============= Base64解码 =============
std::string base64_decode(const std::string& encoded_string) {
    BIO *bio, *b64;
    int decode_len = static_cast<int>(encoded_string.length());
    if (decode_len <= 0) {
        return "";
    }
    char* buffer = new char[decode_len];

    bio = BIO_new_mem_buf(encoded_string.c_str(), -1);
    b64 = BIO_new(BIO_f_base64());
    bio = BIO_push(b64, bio);

    BIO_set_flags(bio, BIO_FLAGS_BASE64_NO_NL);
    int length = BIO_read(bio, buffer, decode_len);
    BIO_free_all(bio);
    if (length <= 0) {
        delete[] buffer;
        return "";
    }

    std::string result(buffer, length);
    delete[] buffer;

    return result;
}

// ============= 添加PKCS#7填充 =============
std::string add_pkcs7_padding(const std::string& data) {
    size_t padding_len = 16 - (data.length() % 16);
    std::string result = data;
    for (size_t i = 0; i < padding_len; i++) {
        result += (char)padding_len;
    }
    return result;
}

// ============= 手动移除PKCS#7填充 =============
std::string remove_pkcs7_padding(const std::string& data) {
    if (data.empty()) return "";

    // 获取最后一个字节（填充长度）
    unsigned char padding_len = (unsigned char)data[data.length() - 1];

    // 验证填充长度
    if (padding_len < 1 || padding_len > 16 || padding_len > data.length()) {
        std::cerr << "[CRYPTO] Invalid padding length: " << (int)padding_len << std::endl;
        return data; // 返回原数据
    }

    // 验证所有填充字节都相同
    for (size_t i = data.length() - padding_len; i < data.length(); i++) {
        if ((unsigned char)data[i] != padding_len) {
            std::cerr << "[CRYPTO] Invalid padding at position " << i << std::endl;
            return data; // 返回原数据
        }
    }

    // 移除填充
    return data.substr(0, data.length() - padding_len);
}

// ============= AES-CBC加密 (用于响应Qt客户端) =============
std::string aes_encrypt_cbc(const std::string& plaintext) {
    // 添加PKCS#7填充
    std::string padded = add_pkcs7_padding(plaintext);

    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    if (!ctx) {
        std::cerr << "[CRYPTO] Failed to create context" << std::endl;
        return "";
    }

    // 初始化加密
    if (EVP_EncryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, MY_AES_KEY, MY_AES_IV) != 1) {
        std::cerr << "[CRYPTO] EncryptInit failed" << std::endl;
        EVP_CIPHER_CTX_free(ctx);
        return "";
    }

    // 禁用自动填充（我们已手动添加）
    EVP_CIPHER_CTX_set_padding(ctx, 0);

    // 加密数据
    std::vector<unsigned char> ciphertext(padded.length() + 16);
    int len;
    int ciphertext_len = 0;

    if (EVP_EncryptUpdate(ctx, ciphertext.data(), &len,
                         (unsigned char*)padded.c_str(),
                         padded.length()) != 1) {
        std::cerr << "[CRYPTO] EncryptUpdate failed" << std::endl;
        EVP_CIPHER_CTX_free(ctx);
        return "";
    }
    ciphertext_len = len;

    // 完成加密
    if (EVP_EncryptFinal_ex(ctx, ciphertext.data() + len, &len) != 1) {
        std::cerr << "[CRYPTO] EncryptFinal failed" << std::endl;
        EVP_CIPHER_CTX_free(ctx);
        return "";
    }
    ciphertext_len += len;

    EVP_CIPHER_CTX_free(ctx);

    return std::string((char*)ciphertext.data(), ciphertext_len);
}

// ============= AES-CBC解密 (使用OpenSSL标准库) =============
std::string aes_decrypt_cbc(const std::string& encrypted_data) {
    if (encrypted_data.empty() || encrypted_data.length() % 16 != 0) {
        std::cerr << "[CRYPTO] Invalid encrypted data length: " << encrypted_data.length() << std::endl;
        return "";
    }

    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    if (!ctx) {
        std::cerr << "[CRYPTO] Failed to create context" << std::endl;
        return "";
    }

    // 初始化解密（使用标准AES-128-CBC）
    if (EVP_DecryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, MY_AES_KEY, MY_AES_IV) != 1) {
        std::cerr << "[CRYPTO] DecryptInit failed" << std::endl;
        EVP_CIPHER_CTX_free(ctx);
        return "";
    }

    // 禁用自动填充，我们手动处理PKCS#7
    EVP_CIPHER_CTX_set_padding(ctx, 0);

    // 解密数据
    std::vector<unsigned char> plaintext(encrypted_data.length() + 16);
    int len;
    int plaintext_len = 0;

    if (EVP_DecryptUpdate(ctx, plaintext.data(), &len,
                         (unsigned char*)encrypted_data.c_str(),
                         encrypted_data.length()) != 1) {
        std::cerr << "[CRYPTO] DecryptUpdate failed" << std::endl;
        EVP_CIPHER_CTX_free(ctx);
        return "";
    }
    plaintext_len = len;

    // 完成解密
    if (EVP_DecryptFinal_ex(ctx, plaintext.data() + len, &len) != 1) {
        std::cerr << "[CRYPTO] DecryptFinal failed" << std::endl;
        EVP_CIPHER_CTX_free(ctx);
        return "";
    }
    plaintext_len += len;

    EVP_CIPHER_CTX_free(ctx);

    std::string result((char*)plaintext.data(), plaintext_len);

    // 手动移除PKCS#7填充
    result = remove_pkcs7_padding(result);

    return result;
}

// ============= 十六进制输出辅助函数 =============
void print_hex(const std::string& label, const unsigned char* data, size_t len) {
    std::cout << label << " (" << len << " bytes): ";
    for (size_t i = 0; i < len && i < 32; i++) {
        printf("%02x ", data[i]);
    }
    if (len > 32) std::cout << "...";
    std::cout << std::endl;
}

// ============= Base64编码 =============
std::string base64_encode(const std::string& input) {
    BIO *bio, *b64;
    BUF_MEM *bufferPtr;

    b64 = BIO_new(BIO_f_base64());
    bio = BIO_new(BIO_s_mem());
    bio = BIO_push(b64, bio);

    BIO_set_flags(bio, BIO_FLAGS_BASE64_NO_NL);
    BIO_write(bio, input.c_str(), input.length());
    BIO_flush(bio);
    BIO_get_mem_ptr(bio, &bufferPtr);

    std::string result(bufferPtr->data, bufferPtr->length);
    BIO_free_all(bio);

    return result;
}

// ============= 加密传输数据 =============
std::string encryptPayload(const std::string& plain_data) {
    std::cout << "[CRYPTO] Encrypting payload (" << plain_data.size() << " bytes)..." << std::endl;

    // AES加密
    std::string encrypted = aes_encrypt_cbc(plain_data);
    if (encrypted.empty()) {
        std::cerr << "[CRYPTO] Encryption failed!" << std::endl;
        return "";
    }

    // Base64编码
    std::string encrypted_base64 = base64_encode(encrypted);

    std::cout << "[CRYPTO] ✓ Payload encrypted" << std::endl;
    return encrypted_base64;
}

std::string encryptJSON(const std::string& json_data) {
    return encryptPayload(json_data);
}

// ============= 解密传输数据 =============
std::string decryptPayload(const std::string& encrypted_base64) {
    try {
        std::cout << "[CRYPTO] Decrypting payload..." << std::endl;
        std::cout << "[CRYPTO] Base64 length: " << encrypted_base64.length() << std::endl;

        // 1. Base64解码
        std::string encrypted_binary = base64_decode(encrypted_base64);
        std::cout << "[CRYPTO] Binary length: " << encrypted_binary.length() << std::endl;
        print_hex("[CRYPTO] Encrypted binary", (unsigned char*)encrypted_binary.c_str(), encrypted_binary.length());

        // 调试：打印密钥和IV
        print_hex("[CRYPTO] Using KEY", MY_AES_KEY, 16);
        print_hex("[CRYPTO] Using IV", MY_AES_IV, 16);

        // 2. AES解密
        std::string decrypted = aes_decrypt_cbc(encrypted_binary);

        if (decrypted.empty()) {
            std::cerr << "[CRYPTO] Decryption failed!" << std::endl;
            return "";
        }

        std::cout << "[CRYPTO] ✓ Decryption successful" << std::endl;
        std::cout << "[CRYPTO] Decrypted length: " << decrypted.length() << std::endl;
        print_hex("[CRYPTO] Decrypted hex", (unsigned char*)decrypted.c_str(), decrypted.length());

        return decrypted;

    } catch (const std::exception& e) {
        std::cerr << "[CRYPTO] Exception: " << e.what() << std::endl;
        return "";
    }
}

std::string decryptJSON(const std::string& encrypted_base64) {
    return decryptPayload(encrypted_base64);
}

// ============= 工具函数 =============
std::string getCurrentTimestamp() {
    time_t now = time(0);
    tm ltm;
#ifdef _WIN32
    localtime_s(&ltm, &now);
#else
    localtime_r(&now, &ltm);
#endif
    char buffer[80];
    strftime(buffer, sizeof(buffer), "%Y-%m-%d %H:%M:%S", &ltm);
    return std::string(buffer);
}

// 清理字符串中的控制字符（\r, \n等）
std::string cleanString(const std::string& str) {
    std::string result;
    result.reserve(str.length());
    for (char c : str) {
        // 只保留可打印字符和空格，过滤掉\r\n\t等控制字符
        if (c >= 32 && c <= 126) {
            result += c;
        }
    }
    return result;
}

std::string urlDecode(const std::string& str) {
    std::string result;
    for (size_t i = 0; i < str.length(); ++i) {
        if (str[i] == '%' && i + 2 < str.length()) {
            int value;
            std::istringstream is(str.substr(i + 1, 2));
            if (is >> std::hex >> value) {
                result += static_cast<char>(value);
                i += 2;
            } else {
                result += str[i];
            }
        } else if (str[i] == '+') {
            result += ' ';
        } else {
            result += str[i];
        }
    }
    return result;
}

std::map<std::string, std::string> parseQueryParams(const std::string& query) {
    std::map<std::string, std::string> params;
    std::istringstream stream(query);
    std::string pair;

    while (std::getline(stream, pair, '&')) {
        size_t pos = pair.find('=');
        if (pos != std::string::npos) {
            std::string key = urlDecode(pair.substr(0, pos));
            std::string value = urlDecode(pair.substr(pos + 1));
            params[key] = value;
        }
    }
    return params;
}

bool parseJsonStringLiteral(const std::string& json, size_t& pos, std::string& output) {
    if (pos >= json.size() || json[pos] != '"') return false;
    pos++;
    output.clear();

    while (pos < json.size()) {
        char c = json[pos++];
        if (c == '"') {
            return true;
        }
        if (c != '\\') {
            output += c;
            continue;
        }
        if (pos >= json.size()) return false;
        char esc = json[pos++];
        switch (esc) {
        case '"': output += '"'; break;
        case '\\': output += '\\'; break;
        case '/': output += '/'; break;
        case 'b': output += '\b'; break;
        case 'f': output += '\f'; break;
        case 'n': output += '\n'; break;
        case 'r': output += '\r'; break;
        case 't': output += '\t'; break;
        case 'u':
            // 当前接口字段只需要保留UTF-8原文；遇到unicode转义时不执行错误拆分。
            output += "\\u";
            for (int i = 0; i < 4 && pos < json.size(); ++i) {
                output += json[pos++];
            }
            break;
        default:
            output += esc;
            break;
        }
    }

    return false;
}

// 解析签到接口使用的扁平JSON对象，支持字符串转义、逗号和冒号。
std::map<std::string, std::string> parseJSON(const std::string& json) {
    std::map<std::string, std::string> result;
    size_t pos = json.find('{');
    if (pos == std::string::npos) return result;
    pos++;

    while (pos < json.size()) {
        while (pos < json.size() && std::isspace(static_cast<unsigned char>(json[pos]))) pos++;
        if (pos >= json.size() || json[pos] == '}') break;

        std::string key;
        if (!parseJsonStringLiteral(json, pos, key)) {
            result.clear();
            return result;
        }

        while (pos < json.size() && std::isspace(static_cast<unsigned char>(json[pos]))) pos++;
        if (pos >= json.size() || json[pos] != ':') {
            result.clear();
            return result;
        }
        pos++;
        while (pos < json.size() && std::isspace(static_cast<unsigned char>(json[pos]))) pos++;

        std::string value;
        if (pos < json.size() && json[pos] == '"') {
            if (!parseJsonStringLiteral(json, pos, value)) {
                result.clear();
                return result;
            }
        } else {
            size_t start = pos;
            while (pos < json.size() && json[pos] != ',' && json[pos] != '}') pos++;
            value = json.substr(start, pos - start);
            size_t first = value.find_first_not_of(" \t\r\n");
            size_t last = value.find_last_not_of(" \t\r\n");
            value = first == std::string::npos ? "" : value.substr(first, last - first + 1);
        }

        result[key] = value;
        while (pos < json.size() && std::isspace(static_cast<unsigned char>(json[pos]))) pos++;
        if (pos < json.size() && json[pos] == ',') pos++;
    }

    return result;
}

// ============= SQLite存储层 =============
sqlite3* openSqliteDb() {
    sqlite3* db = nullptr;
    if (sqlite3_open(SQLITE_DB_FILE.c_str(), &db) != SQLITE_OK) {
        std::cerr << "[SQLITE] Open failed: " << (db ? sqlite3_errmsg(db) : "unknown") << std::endl;
        if (db) sqlite3_close(db);
        return nullptr;
    }
    sqlite3_busy_timeout(db, 3000);
    return db;
}

bool sqliteExec(sqlite3* db, const std::string& sql) {
    char* err = nullptr;
    if (sqlite3_exec(db, sql.c_str(), nullptr, nullptr, &err) != SQLITE_OK) {
        std::cerr << "[SQLITE] Exec failed: " << (err ? err : sqlite3_errmsg(db)) << std::endl;
        sqlite3_free(err);
        return false;
    }
    return true;
}

std::string sqliteColumnText(sqlite3_stmt* stmt, int col) {
    const unsigned char* text = sqlite3_column_text(stmt, col);
    return text ? reinterpret_cast<const char*>(text) : "";
}

bool sqliteBindText(sqlite3_stmt* stmt, int index, const std::string& value) {
    return sqlite3_bind_text(stmt, index, value.c_str(), -1, SQLITE_TRANSIENT) == SQLITE_OK;
}

bool copyFileBinary(const std::string& src, const std::string& dst) {
    std::ifstream in(src.c_str(), std::ios::binary);
    if (!in.is_open()) return false;
    std::ofstream out(dst.c_str(), std::ios::binary);
    if (!out.is_open()) return false;
    out << in.rdbuf();
    return out.good();
}

bool backupSqliteDatabaseOnStartup() {
    std::ifstream check(SQLITE_DB_FILE.c_str(), std::ios::binary);
    if (!check.is_open()) {
        return true;
    }
    check.close();

    _mkdir(DB_BACKUP_DIR.c_str());

    std::string ts = getCurrentTimestamp();
    std::replace(ts.begin(), ts.end(), ':', '-');
    std::replace(ts.begin(), ts.end(), ' ', '_');
    const std::string backup_path = DB_BACKUP_DIR + "/attendance_" + ts + ".db";

    if (!copyFileBinary(SQLITE_DB_FILE, backup_path)) {
        std::cerr << "[BACKUP] Failed to create SQLite backup: " << backup_path << std::endl;
        return false;
    }

    std::cout << "[BACKUP] SQLite backup created: " << backup_path << std::endl;
    return true;
}

bool sqliteSetKv(sqlite3* db, const std::string& key, const std::string& value) {
    sqlite3_stmt* stmt = nullptr;
    const char* sql = "REPLACE INTO kv_store(key,value) VALUES(?,?)";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) != SQLITE_OK) return false;
    sqliteBindText(stmt, 1, key);
    sqliteBindText(stmt, 2, value);
    bool ok = sqlite3_step(stmt) == SQLITE_DONE;
    sqlite3_finalize(stmt);
    return ok;
}

std::string sqliteGetKv(sqlite3* db, const std::string& key, const std::string& fallback) {
    sqlite3_stmt* stmt = nullptr;
    std::string value = fallback;
    const char* sql = "SELECT value FROM kv_store WHERE key=?";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, key);
        if (sqlite3_step(stmt) == SQLITE_ROW) {
            value = sqliteColumnText(stmt, 0);
        }
    }
    sqlite3_finalize(stmt);
    return value;
}

bool sqliteSetKvValue(const std::string& key, const std::string& value) {
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    bool ok = sqliteSetKv(db, key, value);
    sqlite3_close(db);
    return ok;
}

std::string sqliteGetKvValue(const std::string& key, const std::string& fallback) {
    sqlite3* db = openSqliteDb();
    if (!db) return fallback;
    std::string value = sqliteGetKv(db, key, fallback);
    sqlite3_close(db);
    return value;
}

int sqliteCountRows(sqlite3* db, const std::string& table) {
    sqlite3_stmt* stmt = nullptr;
    std::string sql = "SELECT COUNT(*) FROM " + table;
    int count = 0;
    if (sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr) == SQLITE_OK
        && sqlite3_step(stmt) == SQLITE_ROW) {
        count = sqlite3_column_int(stmt, 0);
    }
    sqlite3_finalize(stmt);
    return count;
}

std::string normalizedClassId(const std::string& class_id) {
    return class_id.empty() ? "0" : class_id;
}

std::string defaultClassName(const std::string& class_id) {
    return class_id == "0" ? "默认班级" : class_id;
}

bool upsertClass(sqlite3* db, const std::string& class_id, const std::string& class_name, const std::string& now) {
    if (!db) return false;
    const std::string normalized_id = normalizedClassId(class_id);
    const std::string normalized_name = class_name.empty() ? defaultClassName(normalized_id) : class_name;

    sqlite3_stmt* stmt = nullptr;
    const char* sql =
        "INSERT INTO classes(class_id,class_name,updated_at) VALUES(?,?,?) "
        "ON CONFLICT(class_id) DO UPDATE SET "
        "class_name=CASE WHEN excluded.class_name<>'' THEN excluded.class_name ELSE classes.class_name END,"
        "updated_at=excluded.updated_at";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) != SQLITE_OK) return false;
    sqliteBindText(stmt, 1, normalized_id);
    sqliteBindText(stmt, 2, normalized_name);
    sqliteBindText(stmt, 3, now);
    bool ok = sqlite3_step(stmt) == SQLITE_DONE;
    sqlite3_finalize(stmt);
    return ok;
}

bool ensureClassExists(sqlite3* db, const std::string& class_id, const std::string& now) {
    if (!db) return false;
    const std::string normalized_id = normalizedClassId(class_id);
    sqlite3_stmt* stmt = nullptr;
    const char* sql = "INSERT OR IGNORE INTO classes(class_id,class_name,updated_at) VALUES(?,?,?)";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) != SQLITE_OK) return false;
    sqliteBindText(stmt, 1, normalized_id);
    sqliteBindText(stmt, 2, defaultClassName(normalized_id));
    sqliteBindText(stmt, 3, now);
    bool ok = sqlite3_step(stmt) == SQLITE_DONE;
    sqlite3_finalize(stmt);
    return ok;
}

bool upsertStudent(sqlite3* db, const std::string& student_id, const std::string& student_name,
                   const std::string& class_id, const std::string& now) {
    if (!db || student_id.empty()) return false;
    const std::string insert_class_id = normalizedClassId(class_id);
    if (!class_id.empty() && !ensureClassExists(db, insert_class_id, now)) {
        return false;
    }

    sqlite3_stmt* stmt = nullptr;
    const char* sql =
        "INSERT INTO students(student_id,student_name,class_id,status,created_at,updated_at) "
        "VALUES(?,?,?,?,?,?) "
        "ON CONFLICT(student_id) DO UPDATE SET "
        "student_name=CASE WHEN excluded.student_name<>'' THEN excluded.student_name ELSE students.student_name END,"
        "class_id=CASE WHEN ?<>'' THEN excluded.class_id ELSE students.class_id END,"
        "status='active',"
        "updated_at=excluded.updated_at";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) != SQLITE_OK) return false;
    sqliteBindText(stmt, 1, student_id);
    sqliteBindText(stmt, 2, student_name);
    sqliteBindText(stmt, 3, insert_class_id);
    sqliteBindText(stmt, 4, "active");
    sqliteBindText(stmt, 5, now);
    sqliteBindText(stmt, 6, now);
    sqliteBindText(stmt, 7, class_id);
    bool ok = sqlite3_step(stmt) == SQLITE_DONE;
    sqlite3_finalize(stmt);
    return ok;
}

bool upsertFaceProfile(sqlite3* db, const std::string& face_id, const std::string& student_id,
                       const std::string& status, const std::string& now) {
    if (!db || face_id.empty()) return false;
    sqlite3_stmt* stmt = nullptr;
    const char* sql =
        "INSERT INTO face_profiles(face_id,student_id,device_id,status,created_at,updated_at) "
        "VALUES(?,?,?,?,?,?) "
        "ON CONFLICT(face_id) DO UPDATE SET "
        "student_id=CASE WHEN excluded.student_id<>'' THEN excluded.student_id ELSE face_profiles.student_id END,"
        "device_id=excluded.device_id,"
        "status=excluded.status,"
        "updated_at=excluded.updated_at";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) != SQLITE_OK) return false;
    sqliteBindText(stmt, 1, face_id);
    sqliteBindText(stmt, 2, student_id);
    sqliteBindText(stmt, 3, "k210-01");
    sqliteBindText(stmt, 4, status.empty() ? "active" : status);
    sqliteBindText(stmt, 5, now);
    sqliteBindText(stmt, 6, now);
    bool ok = sqlite3_step(stmt) == SQLITE_DONE;
    sqlite3_finalize(stmt);
    return ok;
}

bool clearFaceProfileBinding(sqlite3* db, const std::string& face_id, const std::string& now) {
    if (!db || face_id.empty()) return false;
    sqlite3_stmt* stmt = nullptr;
    bool ok = false;
    const char* sql =
        "UPDATE face_profiles SET "
        "student_id='',"
        "status=CASE WHEN EXISTS(SELECT 1 FROM face_photos WHERE face_photos.face_id=face_profiles.face_id) "
        "THEN 'active' ELSE 'inactive' END,"
        "updated_at=? "
        "WHERE face_id=?";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, now);
        sqliteBindText(stmt, 2, face_id);
        ok = sqlite3_step(stmt) == SQLITE_DONE;
    }
    sqlite3_finalize(stmt);
    return ok;
}

sqlite3_int64 getFileSize(const std::string& filepath) {
    std::ifstream file(filepath.c_str(), std::ios::binary | std::ios::ate);
    if (!file.is_open()) return 0;
    return static_cast<sqlite3_int64>(file.tellg());
}

bool facePhotoExists(sqlite3* db, const std::string& face_id) {
    if (!db || !isSafeId(face_id)) return false;

    sqlite3_stmt* stmt = nullptr;
    bool exists = false;
    if (sqlite3_prepare_v2(db,
        "SELECT file_path FROM face_photos WHERE face_id=?",
        -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, face_id);
        if (sqlite3_step(stmt) == SQLITE_ROW) {
            exists = getFileSize(sqliteColumnText(stmt, 0)) > 0;
        }
    }
    sqlite3_finalize(stmt);

    if (!exists) {
        std::string filepath;
        exists = buildFacePhotoPath(face_id, filepath) && fileExistsAndNotEmpty(filepath);
    }
    return exists;
}

bool faceProfileExists(sqlite3* db, const std::string& face_id) {
    if (!db || !isSafeId(face_id)) return false;
    sqlite3_stmt* stmt = nullptr;
    bool exists = false;
    if (sqlite3_prepare_v2(db,
        "SELECT 1 FROM face_profiles WHERE face_id=? LIMIT 1",
        -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, face_id);
        exists = sqlite3_step(stmt) == SQLITE_ROW;
    }
    sqlite3_finalize(stmt);
    return exists;
}

std::vector<std::string> unboundPhotoCandidates(sqlite3* db,
                                                const std::string& wrong_face_id,
                                                const std::string& student_id) {
    std::vector<std::string> candidates;
    if (!db || student_id.empty()) return candidates;

    sqlite3_stmt* stmt = nullptr;
    if (sqlite3_prepare_v2(db,
        "SELECT ph.face_id FROM face_photos ph "
        "LEFT JOIN face_profiles fp ON fp.face_id=ph.face_id "
        "WHERE ph.face_id<>? AND (COALESCE(fp.student_id,'')='' OR fp.student_id=?) "
        "ORDER BY ph.face_id",
        -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, wrong_face_id);
        sqliteBindText(stmt, 2, student_id);
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            const std::string candidate = sqliteColumnText(stmt, 0);
            if (isSafeId(candidate)) {
                candidates.push_back(candidate);
            }
        }
    }
    sqlite3_finalize(stmt);
    return candidates;
}

bool deleteFaceProfileOnly(sqlite3* db, const std::string& face_id) {
    if (!db || !isSafeId(face_id)) return false;
    sqlite3_stmt* stmt = nullptr;
    bool ok = false;
    if (sqlite3_prepare_v2(db,
        "DELETE FROM face_profiles WHERE face_id=?",
        -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, face_id);
        ok = sqlite3_step(stmt) == SQLITE_DONE;
    }
    sqlite3_finalize(stmt);
    return ok;
}

int reconcileFaceProfilesWithPhotos(sqlite3* db, const std::string& now) {
    if (!db) return 0;

    struct Row {
        std::string face_id;
        std::string student_id;
    };
    std::vector<Row> rows;
    sqlite3_stmt* stmt = nullptr;
    if (sqlite3_prepare_v2(db,
        "SELECT fp.face_id,COALESCE(fp.student_id,'') "
        "FROM face_profiles fp "
        "LEFT JOIN face_photos ph ON ph.face_id=fp.face_id "
        "WHERE COALESCE(fp.student_id,'')<>'' "
        "AND (ph.face_id IS NULL OR fp.face_id=fp.student_id)",
        -1, &stmt, nullptr) == SQLITE_OK) {
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            rows.push_back({sqliteColumnText(stmt, 0), sqliteColumnText(stmt, 1)});
        }
    }
    sqlite3_finalize(stmt);

    int fixed = 0;
    for (const Row& row : rows) {
        const std::vector<std::string> candidates = unboundPhotoCandidates(db, row.face_id, row.student_id);
        if (candidates.size() != 1) {
            continue;
        }
        const std::string& real_face_id = candidates.front();
        if (upsertFaceProfile(db, real_face_id, row.student_id, "active", now)
            && deleteFaceProfileOnly(db, row.face_id)) {
            fixed++;
            std::cout << "[FACE_PROFILE] Repaired mapping: wrong face_id "
                      << row.face_id << " -> real face_id " << real_face_id
                      << " for student " << row.student_id << std::endl;
        }
    }
    return fixed;
}

bool sqliteQuickCheck(std::string& message) {
    sqlite3* db = openSqliteDb();
    if (!db) {
        message = "open_failed";
        return false;
    }
    sqlite3_stmt* stmt = nullptr;
    bool ok = false;
    message = "unknown";
    if (sqlite3_prepare_v2(db, "PRAGMA quick_check", -1, &stmt, nullptr) == SQLITE_OK
        && sqlite3_step(stmt) == SQLITE_ROW) {
        message = sqliteColumnText(stmt, 0);
        ok = message == "ok";
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    return ok;
}

int countFacePhotoFiles() {
    sqlite3* db = openSqliteDb();
    if (!db) return 0;
    int count = sqliteCountRows(db, "face_photos");
    sqlite3_close(db);
    return count;
}

bool sqliteInsertRecord(sqlite3* db, const std::string& timestamp, const std::string& student_id,
                        const std::string& name, const std::string& confidence,
                        const std::string& status, const std::string& class_id) {
    sqlite3_stmt* stmt = nullptr;
    const char* sql =
        "INSERT INTO records(timestamp,student_id,name,confidence,status,class_id) "
        "VALUES(?,?,?,?,?,?)";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) != SQLITE_OK) return false;
    sqliteBindText(stmt, 1, timestamp);
    sqliteBindText(stmt, 2, student_id);
    sqliteBindText(stmt, 3, name);
    sqliteBindText(stmt, 4, confidence);
    sqliteBindText(stmt, 5, status);
    sqliteBindText(stmt, 6, class_id.empty() ? "0" : class_id);
    bool ok = sqlite3_step(stmt) == SQLITE_DONE;
    sqlite3_finalize(stmt);
    if (!ok) return false;

    upsertStudent(db, student_id, name, class_id, timestamp);

    return true;
}

bool saveAttendanceRecord(const std::string& timestamp, const std::string& student_id,
                          const std::string& name, const std::string& confidence,
                          const std::string& status, const std::string& class_id) {
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    bool ok = sqliteInsertRecord(db, timestamp, student_id, name, confidence, status, class_id);
    sqlite3_close(db);
    return ok;
}

bool initializeSqliteStorage() {
    sqlite3* db = openSqliteDb();
    if (!db) return false;

    bool ok = sqliteExec(db,
        "PRAGMA journal_mode=WAL;"
        "CREATE TABLE IF NOT EXISTS records("
        "id INTEGER PRIMARY KEY AUTOINCREMENT,"
        "timestamp TEXT NOT NULL,"
        "student_id TEXT NOT NULL,"
        "name TEXT,"
        "confidence TEXT,"
        "status TEXT,"
        "class_id TEXT DEFAULT '0'"
        ");"
        "CREATE INDEX IF NOT EXISTS idx_records_student_time ON records(student_id,timestamp);"
        "CREATE INDEX IF NOT EXISTS idx_records_timestamp ON records(timestamp);"
        "CREATE TABLE IF NOT EXISTS kv_store("
        "key TEXT PRIMARY KEY,"
        "value TEXT NOT NULL"
        ");"
        "CREATE TABLE IF NOT EXISTS classes("
        "class_id TEXT PRIMARY KEY,"
        "class_name TEXT NOT NULL,"
        "updated_at TEXT NOT NULL"
        ");"
        "CREATE TABLE IF NOT EXISTS students("
        "student_id TEXT PRIMARY KEY,"
        "student_name TEXT,"
        "class_id TEXT DEFAULT '0',"
        "status TEXT NOT NULL DEFAULT 'active',"
        "created_at TEXT NOT NULL,"
        "updated_at TEXT NOT NULL"
        ");"
        "CREATE INDEX IF NOT EXISTS idx_students_class ON students(class_id);"
        "CREATE TABLE IF NOT EXISTS face_profiles("
        "face_id TEXT PRIMARY KEY,"
        "student_id TEXT,"
        "device_id TEXT DEFAULT 'k210-01',"
        "status TEXT NOT NULL DEFAULT 'active',"
        "created_at TEXT NOT NULL,"
        "updated_at TEXT NOT NULL"
        ");"
        "CREATE INDEX IF NOT EXISTS idx_face_profiles_student ON face_profiles(student_id);"
        "CREATE TABLE IF NOT EXISTS face_photos("
        "face_id TEXT PRIMARY KEY,"
        "file_path TEXT NOT NULL,"
        "content_type TEXT DEFAULT 'image/jpeg',"
        "file_size INTEGER DEFAULT 0,"
        "uploaded_at TEXT NOT NULL"
        ");"
        "CREATE TABLE IF NOT EXISTS pending_delete("
        "task_id TEXT PRIMARY KEY,"
        "face_id TEXT NOT NULL,"
        "student_id TEXT,"
        "created_at TEXT NOT NULL,"
        "status TEXT NOT NULL DEFAULT 'pending',"
        "ack_at TEXT"
        ");"
        "CREATE INDEX IF NOT EXISTS idx_pending_delete_face ON pending_delete(face_id);"
        "CREATE TABLE IF NOT EXISTS device_sync_state("
        "client TEXT PRIMARY KEY,"
        "last_seen_version INTEGER NOT NULL DEFAULT 0,"
        "last_ack_version INTEGER NOT NULL DEFAULT 0,"
        "last_seen_at TEXT NOT NULL"
        ");");

    if (!ok) {
        sqlite3_close(db);
        return false;
    }

    if (sqliteGetKv(db, "time_slots", "").empty()) {
        sqliteSetKv(db, "time_slots", DEFAULT_TIMESLOTS_JSON);
    }
    if (sqliteGetKv(db, "sync_request", "").empty()) {
        sqliteSetKv(db, "sync_request", "{\"sync\":false}");
    }
    if (sqliteGetKv(db, "sync_version", "").empty()) {
        sqliteSetKv(db, "sync_version", "1");
    }

    const std::string now = getCurrentTimestamp();
    upsertClass(db, "0", "默认班级", now);

    _mkdir(FACES_DIR.c_str());
    sqlite3_close(db);
    std::cout << "[SQLITE] Storage ready: " << SQLITE_DB_FILE << std::endl;
    return true;
}

// ============= 数据库操作 =============
std::string readDatabase(int limit = -1, int offset = 0) {
    sqlite3* db = openSqliteDb();
    if (!db) return "[]";

    std::ostringstream json;
    json << "[";
    sqlite3_stmt* stmt = nullptr;
    std::string sql = "SELECT timestamp,student_id,name,confidence,status,class_id FROM records ORDER BY id DESC";
    if (limit > 0) {
        sql += " LIMIT ? OFFSET ?";
    }

    bool first = true;
    if (sqlite3_prepare_v2(db, sql.c_str(), -1, &stmt, nullptr) == SQLITE_OK) {
        if (limit > 0) {
            sqlite3_bind_int(stmt, 1, limit);
            sqlite3_bind_int(stmt, 2, offset);
        }
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            if (!first) json << ",";
            first = false;
            std::string conf = sqliteColumnText(stmt, 3);
            if (conf.empty()) conf = "0";
            std::string class_id = sqliteColumnText(stmt, 5);
            if (class_id.empty()) class_id = "0";
            json << "{"
                 << "\"timestamp\":\"" << jsonEscape(sqliteColumnText(stmt, 0)) << "\","
                 << "\"student_id\":\"" << jsonEscape(sqliteColumnText(stmt, 1)) << "\","
                 << "\"name\":\"" << jsonEscape(sqliteColumnText(stmt, 2)) << "\","
                 << "\"confidence\":" << conf << ","
                 << "\"status\":\"" << jsonEscape(sqliteColumnText(stmt, 4)) << "\","
                 << "\"class_id\":\"" << jsonEscape(class_id) << "\""
                 << "}";
        }
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);

    json << "]";
    return json.str();
}

std::string getStatistics() {
    sqlite3* db = openSqliteDb();
    if (!db) return "{\"total\":0,\"today\":0}";
    int total = 0;
    int today = 0;
    std::string todayDate = getCurrentTimestamp().substr(0, 10);
    sqlite3_stmt* stmt = nullptr;
    if (sqlite3_prepare_v2(db, "SELECT COUNT(*) FROM records", -1, &stmt, nullptr) == SQLITE_OK
        && sqlite3_step(stmt) == SQLITE_ROW) {
        total = sqlite3_column_int(stmt, 0);
    }
    sqlite3_finalize(stmt);
    stmt = nullptr;
    if (sqlite3_prepare_v2(db, "SELECT COUNT(*) FROM records WHERE substr(timestamp,1,10)=?", -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, todayDate);
        if (sqlite3_step(stmt) == SQLITE_ROW) {
            today = sqlite3_column_int(stmt, 0);
        }
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);

    std::ostringstream json;
    json << "{"
         << "\"total\":" << total << ","
         << "\"today\":" << today << ","
         << "\"server_time\":\"" << getCurrentTimestamp() << "\""
         << "}";
    return json.str();
}

bool clearDatabase() {
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    bool ok = sqliteExec(db, "DELETE FROM records");
    sqlite3_close(db);
    return ok;
}

// ============= 时间段配置管理 =============
bool saveTimeSlots(const std::string& json_data) {
    std::cout << "[TIMESLOTS] Attempting to save " << json_data.size() << " bytes" << std::endl;

    if (json_data.empty()) {
        std::cerr << "[TIMESLOTS] ERROR: json_data is empty!" << std::endl;
        return false;
    }

    if (!sqliteSetKvValue("time_slots", json_data)) {
        std::cerr << "[TIMESLOTS] Failed to save configuration to SQLite" << std::endl;
        return false;
    }
    std::cout << "[TIMESLOTS] ✓ Configuration saved successfully to SQLite" << std::endl;
    std::cout << "[TIMESLOTS] Preview: " << json_data.substr(0, 100) << "..." << std::endl;
    return true;
}

std::string readTimeSlots() {
    std::string content = sqliteGetKvValue("time_slots", DEFAULT_TIMESLOTS_JSON);
    std::cout << "[TIMESLOTS] Read " << content.size() << " bytes from SQLite" << std::endl;
    return content;
}

std::string readStudents() {
    std::ostringstream json;
    json << "{\"students\":[";
    sqlite3* db = openSqliteDb();
    bool first = true;
    if (db) {
        sqlite3_stmt* stmt = nullptr;
        if (sqlite3_prepare_v2(db,
            "SELECT student_id,COALESCE(student_name,''),COALESCE(class_id,'0'),COALESCE(status,'active') "
            "FROM students WHERE student_id<>'' AND COALESCE(status,'active')<>'deleted' ORDER BY student_id",
            -1, &stmt, nullptr) == SQLITE_OK) {
            while (sqlite3_step(stmt) == SQLITE_ROW) {
                if (!first) json << ",";
                json << "{\"student_id\":\"" << jsonEscape(sqliteColumnText(stmt, 0)) << "\","
                     << "\"student_name\":\"" << jsonEscape(sqliteColumnText(stmt, 1)) << "\","
                     << "\"class_id\":\"" << jsonEscape(sqliteColumnText(stmt, 2)) << "\","
                     << "\"status\":\"" << jsonEscape(sqliteColumnText(stmt, 3)) << "\"}";
                first = false;
            }
        }
        sqlite3_finalize(stmt);
        sqlite3_close(db);
    }
    json << "]}";
    return json.str();
}

std::string readClasses() {
    std::ostringstream json;
    json << "{\"classes\":[";
    sqlite3* db = openSqliteDb();
    bool first = true;
    if (db) {
        sqlite3_stmt* stmt = nullptr;
        if (sqlite3_prepare_v2(db,
            "SELECT class_id,COALESCE(class_name,'') FROM classes WHERE class_id<>'' ORDER BY class_id",
            -1, &stmt, nullptr) == SQLITE_OK) {
            while (sqlite3_step(stmt) == SQLITE_ROW) {
                if (!first) json << ",";
                json << "{\"class_id\":\"" << jsonEscape(sqliteColumnText(stmt, 0)) << "\","
                     << "\"class_name\":\"" << jsonEscape(sqliteColumnText(stmt, 1)) << "\"}";
                first = false;
            }
        }
        sqlite3_finalize(stmt);
        sqlite3_close(db);
    }
    json << "]}";
    return json.str();
}

std::string readFaceProfiles() {
    std::ostringstream json;
    json << "{\"face_profiles\":[";
    sqlite3* db = openSqliteDb();
    bool first = true;
    int repaired = 0;
    if (db) {
        repaired = reconcileFaceProfilesWithPhotos(db, getCurrentTimestamp());
        if (repaired > 0) {
            std::cout << "[FACE_PROFILE] Repaired " << repaired
                      << " profile/photo mismatches before listing" << std::endl;
        }
        sqlite3_stmt* stmt = nullptr;
        if (sqlite3_prepare_v2(db,
            "SELECT fp.face_id,COALESCE(fp.student_id,''),COALESCE(fp.device_id,'k210-01'),COALESCE(fp.status,'active'),"
            "CASE WHEN ph.face_id IS NULL THEN 0 ELSE 1 END "
            "FROM face_profiles fp "
            "LEFT JOIN face_photos ph ON ph.face_id=fp.face_id "
            "WHERE fp.face_id<>'' "
            "UNION "
            "SELECT ph.face_id,'','k210-01','photo_only',1 FROM face_photos ph "
            "LEFT JOIN face_profiles fp ON fp.face_id=ph.face_id "
            "WHERE ph.face_id<>'' AND fp.face_id IS NULL "
            "ORDER BY face_id",
            -1, &stmt, nullptr) == SQLITE_OK) {
            while (sqlite3_step(stmt) == SQLITE_ROW) {
                if (!first) json << ",";
                json << "{\"face_id\":\"" << jsonEscape(sqliteColumnText(stmt, 0)) << "\","
                     << "\"student_id\":\"" << jsonEscape(sqliteColumnText(stmt, 1)) << "\","
                     << "\"device_id\":\"" << jsonEscape(sqliteColumnText(stmt, 2)) << "\","
                     << "\"status\":\"" << jsonEscape(sqliteColumnText(stmt, 3)) << "\","
                     << "\"has_photo\":" << (sqlite3_column_int(stmt, 4) ? "true" : "false") << "}";
                first = false;
            }
        }
        sqlite3_finalize(stmt);
        sqlite3_close(db);
    }
    if (repaired > 0) {
        bumpSyncVersion("face_profile_repair");
    }
    json << "]}";
    return json.str();
}

bool saveStudents(const std::string& json_data) {
    const std::vector<std::map<std::string, std::string>> students = parseJsonObjectArray(json_data, "students");
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    const std::string now = getCurrentTimestamp();
    bool ok = sqliteExec(db, "BEGIN");

    if (ok) {
        for (const auto& student : students) {
            const auto id_it = student.find("student_id");
            const std::string student_id = id_it == student.end() ? "" : id_it->second;
            if (!isSafeId(student_id)) {
                ok = false;
                break;
            }
            const std::string name = student.count("student_name") ? student.at("student_name") : "";
            const std::string class_id = student.count("class_id") ? normalizedClassId(student.at("class_id")) : "0";
            if (!isSafeId(class_id) || name.size() > 64 || !upsertStudent(db, student_id, name, class_id, now)) {
                ok = false;
                break;
            }
        }
    }

    if (ok) {
        sqlite3_stmt* stmt = nullptr;
        if (sqlite3_prepare_v2(db,
            "UPDATE students SET status='deleted',updated_at=? WHERE student_id=?",
            -1, &stmt, nullptr) == SQLITE_OK) {
            sqlite3_stmt* clear_face_stmt = nullptr;
            const bool clear_face_ready = sqlite3_prepare_v2(db,
                "UPDATE face_profiles SET student_id='',status=CASE "
                "WHEN EXISTS(SELECT 1 FROM face_photos WHERE face_photos.face_id=face_profiles.face_id) "
                "THEN 'active' ELSE 'unbound' END,updated_at=? WHERE student_id=?",
                -1, &clear_face_stmt, nullptr) == SQLITE_OK;
            std::vector<std::string> existing_ids;
            sqlite3_stmt* select_stmt = nullptr;
            if (sqlite3_prepare_v2(db,
                "SELECT student_id FROM students WHERE COALESCE(status,'active')<>'deleted'",
                -1, &select_stmt, nullptr) == SQLITE_OK) {
                while (sqlite3_step(select_stmt) == SQLITE_ROW) {
                    existing_ids.push_back(sqliteColumnText(select_stmt, 0));
                }
            }
            sqlite3_finalize(select_stmt);

            std::set<std::string> incoming_ids;
            for (const auto& student : students) {
                auto it = student.find("student_id");
                if (it != student.end()) incoming_ids.insert(it->second);
            }
            for (const std::string& student_id : existing_ids) {
                if (student_id == "UNKNOWN" || incoming_ids.count(student_id)) continue;
                sqlite3_reset(stmt);
                sqlite3_clear_bindings(stmt);
                sqliteBindText(stmt, 1, now);
                sqliteBindText(stmt, 2, student_id);
                if (sqlite3_step(stmt) != SQLITE_DONE) {
                    ok = false;
                    break;
                }
                if (clear_face_ready) {
                    sqlite3_reset(clear_face_stmt);
                    sqlite3_clear_bindings(clear_face_stmt);
                    sqliteBindText(clear_face_stmt, 1, now);
                    sqliteBindText(clear_face_stmt, 2, student_id);
                    if (sqlite3_step(clear_face_stmt) != SQLITE_DONE) {
                        ok = false;
                        break;
                    }
                }
            }
            sqlite3_finalize(clear_face_stmt);
        } else {
            ok = false;
        }
        sqlite3_finalize(stmt);
    }

    sqliteExec(db, ok ? "COMMIT" : "ROLLBACK");
    sqlite3_close(db);
    return ok;
}

bool saveClasses(const std::string& json_data) {
    const std::vector<std::map<std::string, std::string>> classes = parseJsonObjectArray(json_data, "classes");
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    const std::string now = getCurrentTimestamp();
    bool ok = sqliteExec(db, "BEGIN");
    std::set<std::string> incoming_ids;

    if (ok) {
        for (const auto& row : classes) {
            const std::string class_id = row.count("class_id") ? normalizedClassId(row.at("class_id")) : "";
            const std::string class_name = row.count("class_name") ? row.at("class_name") : "";
            if (!isSafeId(class_id) || class_name.empty() || class_name.size() > 64) {
                ok = false;
                break;
            }
            incoming_ids.insert(class_id);
            if (!upsertClass(db, class_id, class_name, now)) {
                ok = false;
                break;
            }
        }
    }

    if (ok) {
        sqlite3_stmt* select_stmt = nullptr;
        sqlite3_stmt* count_stmt = nullptr;
        sqlite3_stmt* delete_stmt = nullptr;
        std::vector<std::string> existing_ids;
        if (sqlite3_prepare_v2(db, "SELECT class_id FROM classes WHERE class_id<>'0'", -1, &select_stmt, nullptr) == SQLITE_OK) {
            while (sqlite3_step(select_stmt) == SQLITE_ROW) {
                existing_ids.push_back(sqliteColumnText(select_stmt, 0));
            }
        }
        sqlite3_finalize(select_stmt);

        if (sqlite3_prepare_v2(db, "SELECT COUNT(*) FROM students WHERE class_id=? AND COALESCE(status,'active')<>'deleted'",
                               -1, &count_stmt, nullptr) != SQLITE_OK
            || sqlite3_prepare_v2(db, "DELETE FROM classes WHERE class_id=?", -1, &delete_stmt, nullptr) != SQLITE_OK) {
            ok = false;
        }

        for (const std::string& class_id : existing_ids) {
            if (!ok || incoming_ids.count(class_id)) continue;
            sqlite3_reset(count_stmt);
            sqlite3_clear_bindings(count_stmt);
            sqliteBindText(count_stmt, 1, class_id);
            int student_count = 0;
            if (sqlite3_step(count_stmt) == SQLITE_ROW) {
                student_count = sqlite3_column_int(count_stmt, 0);
            }
            if (student_count > 0) {
                ok = false;
                break;
            }
            sqlite3_reset(delete_stmt);
            sqlite3_clear_bindings(delete_stmt);
            sqliteBindText(delete_stmt, 1, class_id);
            if (sqlite3_step(delete_stmt) != SQLITE_DONE) {
                ok = false;
                break;
            }
        }
        sqlite3_finalize(count_stmt);
        sqlite3_finalize(delete_stmt);
    }

    sqliteExec(db, ok ? "COMMIT" : "ROLLBACK");
    sqlite3_close(db);
    return ok;
}

bool saveFaceProfiles(const std::string& json_data) {
    const std::vector<std::map<std::string, std::string>> profiles = parseJsonObjectArray(json_data, "face_profiles");
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    const std::string now = getCurrentTimestamp();
    bool ok = sqliteExec(db, "BEGIN");
    std::set<std::string> incoming_face_ids;
    std::set<std::string> bound_face_ids;

    if (ok) {
        for (const auto& profile : profiles) {
            const std::string face_id = profile.count("face_id") ? profile.at("face_id") : "";
            const std::string student_id = profile.count("student_id") ? profile.at("student_id") : "";
            const std::string status = profile.count("status") ? profile.at("status") : "active";
            if (!isSafeId(face_id) || (!student_id.empty() && !isSafeId(student_id))) {
                ok = false;
                break;
            }

            std::string effective_face_id = face_id;
            if (!student_id.empty() && !facePhotoExists(db, effective_face_id)) {
                const std::vector<std::string> candidates = unboundPhotoCandidates(db, effective_face_id, student_id);
                if (candidates.size() == 1) {
                    effective_face_id = candidates.front();
                    deleteFaceProfileOnly(db, face_id);
                    std::cout << "[FACE_PROFILE] Corrected submitted face_id " << face_id
                              << " -> " << effective_face_id
                              << " for student " << student_id << std::endl;
                } else {
                    std::cerr << "[FACE_PROFILE] Reject mapping without K210 photo: face_id="
                              << face_id << ", student_id=" << student_id << std::endl;
                    ok = false;
                    break;
                }
            }

            if (student_id.empty() && bound_face_ids.count(effective_face_id)) {
                incoming_face_ids.insert(effective_face_id);
                continue;
            }

            if (!student_id.empty()) {
                cancelPendingDeleteForFace(db, effective_face_id, now);
            }

            incoming_face_ids.insert(effective_face_id);
            if (!upsertFaceProfile(db, effective_face_id, student_id, status.empty() ? "active" : status, now)) {
                ok = false;
                break;
            }
            if (!student_id.empty()) {
                bound_face_ids.insert(effective_face_id);
            }
            if (student_id.empty()) {
                if (!clearFaceProfileBinding(db, effective_face_id, now)) {
                    ok = false;
                    break;
                }
            }
            if (!student_id.empty()) {
                if (!upsertStudent(db, student_id, "", "", now)) {
                    ok = false;
                    break;
                }
            }
        }
    }

    if (ok) {
        sqlite3_stmt* clear_stmt = nullptr;
        if (sqlite3_prepare_v2(db,
            "UPDATE face_profiles SET student_id='',status=CASE WHEN EXISTS(SELECT 1 FROM face_photos WHERE face_photos.face_id=face_profiles.face_id) THEN 'active' ELSE 'unbound' END,updated_at=? WHERE face_id=?",
            -1, &clear_stmt, nullptr) == SQLITE_OK) {
            sqlite3_stmt* select_stmt = nullptr;
            std::vector<std::string> existing_ids;
            if (sqlite3_prepare_v2(db, "SELECT face_id FROM face_profiles", -1, &select_stmt, nullptr) == SQLITE_OK) {
                while (sqlite3_step(select_stmt) == SQLITE_ROW) {
                    existing_ids.push_back(sqliteColumnText(select_stmt, 0));
                }
            }
            sqlite3_finalize(select_stmt);

            for (const std::string& face_id : existing_ids) {
                if (incoming_face_ids.count(face_id)) continue;
                sqlite3_reset(clear_stmt);
                sqlite3_clear_bindings(clear_stmt);
                sqliteBindText(clear_stmt, 1, now);
                sqliteBindText(clear_stmt, 2, face_id);
                if (sqlite3_step(clear_stmt) != SQLITE_DONE) {
                    ok = false;
                    break;
                }
            }
        } else {
            ok = false;
        }
        sqlite3_finalize(clear_stmt);
    }

    sqliteExec(db, ok ? "COMMIT" : "ROLLBACK");
    sqlite3_close(db);
    return ok;
}

unsigned long long readSyncVersion() {
    unsigned long long version = 1;
    std::string value = sqliteGetKvValue("sync_version", "1");
    std::istringstream ss(value);
    if (!(ss >> version)) {
        version = 1;
    }
    if (version == 0) version = 1;
    return version;
}

unsigned long long bumpSyncVersion(const std::string& reason) {
    unsigned long long version = readSyncVersion() + 1;
    sqliteSetKvValue("sync_version", std::to_string(version));
    std::cout << "[SYNC] Version bumped to " << version << " (" << reason << ")" << std::endl;
    return version;
}

unsigned long long parseVersionParam(const std::map<std::string, std::string>& params) {
    auto it = params.find("last_version");
    if (it == params.end()) return 0;
    unsigned long long value = 0;
    for (char c : it->second) {
        if (!std::isdigit(static_cast<unsigned char>(c))) return 0;
        value = value * 10 + static_cast<unsigned long long>(c - '0');
    }
    return value;
}

size_t findMatchingJsonEnd(const std::string& text, size_t start) {
    if (start >= text.size()) return std::string::npos;
    const char open = text[start];
    const char close = (open == '{') ? '}' : ']';
    int depth = 0;
    bool in_string = false;
    bool escape = false;

    for (size_t i = start; i < text.size(); ++i) {
        char c = text[i];
        if (escape) {
            escape = false;
            continue;
        }
        if (c == '\\' && in_string) {
            escape = true;
            continue;
        }
        if (c == '"') {
            in_string = !in_string;
            continue;
        }
        if (in_string) continue;
        if (c == open) depth++;
        if (c == close) {
            depth--;
            if (depth == 0) return i;
        }
    }
    return std::string::npos;
}

std::string extractJsonMemberValue(const std::string& json, const std::string& key, const std::string& fallback) {
    std::string marker = "\"" + key + "\":";
    size_t pos = json.find(marker);
    if (pos == std::string::npos) return fallback;
    pos += marker.size();
    while (pos < json.size() && std::isspace(static_cast<unsigned char>(json[pos]))) pos++;
    if (pos >= json.size()) return fallback;

    if (json[pos] == '{' || json[pos] == '[') {
        size_t end = findMatchingJsonEnd(json, pos);
        if (end != std::string::npos) {
            return json.substr(pos, end - pos + 1);
        }
    }

    size_t end = json.find_first_of(",}", pos);
    if (end != std::string::npos) {
        return json.substr(pos, end - pos);
    }
    return fallback;
}

std::string extractJsonStringValue(const std::string& json, const std::string& key, const std::string& fallback = "") {
    std::string marker = "\"" + key + "\":\"";
    size_t pos = json.find(marker);
    if (pos == std::string::npos) return fallback;
    pos += marker.size();
    size_t end = json.find("\"", pos);
    if (end == std::string::npos) return fallback;
    return json.substr(pos, end - pos);
}

std::vector<std::string> extractJsonStringArray(const std::string& json, const std::string& key) {
    std::vector<std::string> values;
    std::string arr = extractJsonMemberValue(json, key, "[]");
    if (arr.size() < 2) return values;
    size_t pos = 0;
    while (pos < arr.size()) {
        size_t start = arr.find("\"", pos);
        if (start == std::string::npos) break;
        size_t end = arr.find("\"", start + 1);
        if (end == std::string::npos) break;
        values.push_back(arr.substr(start + 1, end - start - 1));
        pos = end + 1;
    }
    return values;
}

std::vector<std::map<std::string, std::string>> parseJsonObjectArray(const std::string& json_data, const std::string& key) {
    std::vector<std::map<std::string, std::string>> rows;
    const std::string array = extractJsonMemberValue(json_data, key, "[]");
    size_t pos = 0;
    while (pos < array.size()) {
        size_t start = array.find('{', pos);
        if (start == std::string::npos) break;
        size_t end = findMatchingJsonEnd(array, start);
        if (end == std::string::npos) break;

        const std::string object = array.substr(start, end - start + 1);
        std::map<std::string, std::string> row;
        size_t item_pos = 1;
        while (item_pos < object.size()) {
            while (item_pos < object.size() && std::isspace(static_cast<unsigned char>(object[item_pos]))) item_pos++;
            if (item_pos >= object.size() || object[item_pos] == '}') break;

            std::string item_key;
            if (!parseJsonStringLiteral(object, item_pos, item_key)) break;
            while (item_pos < object.size() && std::isspace(static_cast<unsigned char>(object[item_pos]))) item_pos++;
            if (item_pos >= object.size() || object[item_pos] != ':') break;
            item_pos++;
            while (item_pos < object.size() && std::isspace(static_cast<unsigned char>(object[item_pos]))) item_pos++;

            std::string item_value;
            if (item_pos < object.size() && object[item_pos] == '"') {
                if (!parseJsonStringLiteral(object, item_pos, item_value)) break;
            } else {
                size_t value_start = item_pos;
                while (item_pos < object.size() && object[item_pos] != ',' && object[item_pos] != '}') item_pos++;
                item_value = object.substr(value_start, item_pos - value_start);
                size_t first = item_value.find_first_not_of(" \t\r\n");
                size_t last = item_value.find_last_not_of(" \t\r\n");
                item_value = first == std::string::npos ? "" : item_value.substr(first, last - first + 1);
            }
            row[item_key] = item_value;

            while (item_pos < object.size() && std::isspace(static_cast<unsigned char>(object[item_pos]))) item_pos++;
            if (item_pos < object.size() && object[item_pos] == ',') item_pos++;
        }

        rows.push_back(row);
        pos = end + 1;
    }
    return rows;
}

unsigned long long jsonNumberValue(const std::string& json, const std::string& key, unsigned long long fallback) {
    std::string marker = "\"" + key + "\":";
    size_t pos = json.find(marker);
    if (pos == std::string::npos) return fallback;
    pos += marker.size();
    while (pos < json.size() && std::isspace(static_cast<unsigned char>(json[pos]))) pos++;
    unsigned long long value = 0;
    bool has_digit = false;
    while (pos < json.size() && std::isdigit(static_cast<unsigned char>(json[pos]))) {
        has_digit = true;
        value = value * 10ULL + static_cast<unsigned long long>(json[pos] - '0');
        pos++;
    }
    return has_digit ? value : fallback;
}

std::string makeSyncStateResponse(const std::string& client, unsigned long long last_version) {
    const unsigned long long version = readSyncVersion();
    const bool changed = last_version < version;
    updateDeviceSyncState(client.empty() ? "all" : client, version, 0);

    std::ostringstream json;
    json << "{\"version\":" << version
         << ",\"changed\":" << (changed ? "true" : "false")
         << ",\"client\":\"" << jsonEscape(client) << "\""
         << ",\"server_time\":\"" << jsonEscape(getCurrentTimestamp()) << "\"";

    if (changed) {
        json << ",\"state\":{";
        bool first = true;
        bool emitted_face_profiles = false;

        if (client == "k210" || client == "all" || client.empty()) {
            const std::string profiles = extractJsonMemberValue(readFaceProfiles(), "face_profiles", "[]");
            const std::string pending_json = getPendingDeleteList();
            const std::string pending = extractJsonMemberValue(pending_json, "pending_delete", "[]");
            const std::string delete_tasks = extractJsonMemberValue(pending_json, "delete_tasks", "[]");
            json << "\"face_profiles\":" << profiles
                 << ",\"pending_delete\":" << pending
                 << ",\"delete_tasks\":" << delete_tasks;
            first = false;
            emitted_face_profiles = true;
        }

        if (client == "stm32" || client == "qt" || client == "all" || client.empty()) {
            if (!first) json << ",";
            const std::string slots = extractJsonMemberValue(readTimeSlots(), "time_slots", "[]");
            json << "\"time_slots\":" << slots;
            first = false;
        }

        if (client == "qt" || client == "all" || client.empty()) {
            if (!first) json << ",";
            json << "\"students\":" << extractJsonMemberValue(readStudents(), "students", "[]")
                 << ",\"classes\":" << extractJsonMemberValue(readClasses(), "classes", "[]");
            if (!emitted_face_profiles) {
                json << ",\"face_profiles\":" << extractJsonMemberValue(readFaceProfiles(), "face_profiles", "[]");
            }
            json << ",\"face_photos\":" << extractJsonMemberValue(getFacePhotosList(), "photos", "[]")
                 << ",\"records\":" << readDatabase(1000, 0)
                 << ",\"statistics\":" << getStatistics();
        }

        json << "}";
    }

    json << "}";
    return json.str();
}

std::string makeSyncAckResponse(const std::string& request_body) {
    const std::string client = extractJsonStringValue(request_body, "client", "unknown");
    const unsigned long long ack_version = static_cast<unsigned long long>(jsonNumberValue(request_body, "version", 0));
    const std::vector<std::string> deleted = extractJsonStringArray(request_body, "deleted");
    const std::vector<std::string> task_ids = extractJsonStringArray(request_body, "task_ids");
    int confirmed_delete_count = 0;

    for (const std::string& task_id : task_ids) {
        if (!task_id.empty() && removeFromPendingDelete(task_id)) {
            confirmed_delete_count++;
        }
    }

    for (const std::string& id : deleted) {
        if (!id.empty() && removeFromPendingDelete(id)) {
            confirmed_delete_count++;
        }
    }

    updateDeviceSyncState(client, readSyncVersion(), ack_version);

    if (confirmed_delete_count > 0) {
        bumpSyncVersion("sync_ack_delete");
    }

    std::ostringstream json;
    json << "{\"success\":true,"
         << "\"client\":\"" << jsonEscape(client) << "\","
         << "\"version\":" << readSyncVersion() << ","
         << "\"confirmed_delete_count\":" << confirmed_delete_count << "}";
    return json.str();
}

std::string makeSyncVersionResponse() {
    std::ostringstream json;
    json << "{"
         << "\"version\":" << readSyncVersion() << ","
         << "\"server_time\":\"" << jsonEscape(getCurrentTimestamp()) << "\""
         << "}";
    return json.str();
}

std::string makeStorageStatusResponse() {
    std::string quick_check_message;
    const bool quick_ok = sqliteQuickCheck(quick_check_message);
    sqlite3* db = openSqliteDb();

    int records = 0;
    int face_profiles = 0;
    int pending_deletes = 0;
    int face_photos = countFacePhotoFiles();
    if (db) {
        records = sqliteCountRows(db, "records");
        face_profiles = sqliteCountRows(db, "face_profiles");
        pending_deletes = sqliteCountRows(db, "pending_delete");
        sqlite3_close(db);
    }

    std::ostringstream json;
    json << "{"
         << "\"storage\":\"sqlite\","
         << "\"database\":\"" << jsonEscape(SQLITE_DB_FILE) << "\","
         << "\"ok\":" << (quick_ok ? "true" : "false") << ","
         << "\"quick_check\":\"" << jsonEscape(quick_check_message) << "\","
         << "\"records\":" << records << ","
         << "\"face_profiles\":" << face_profiles << ","
         << "\"face_photos\":" << face_photos << ","
         << "\"pending_deletes\":" << pending_deletes << ","
         << "\"sync_version\":" << readSyncVersion() << ","
         << "\"device_sync_state\":" << getDeviceSyncSummary() << ","
         << "\"server_time\":\"" << jsonEscape(getCurrentTimestamp()) << "\""
         << "}";
    return json.str();
}

std::string makeHealthResponse() {
    std::string quick_check_message;
    const bool quick_ok = sqliteQuickCheck(quick_check_message);
    std::ostringstream json;
    json << "{"
         << "\"status\":\"" << (quick_ok ? "healthy" : "degraded") << "\","
         << "\"time\":\"" << jsonEscape(getCurrentTimestamp()) << "\","
         << "\"storage\":\"sqlite\","
         << "\"database\":\"" << jsonEscape(SQLITE_DB_FILE) << "\","
         << "\"database_ok\":" << (quick_ok ? "true" : "false") << ","
         << "\"quick_check\":\"" << jsonEscape(quick_check_message) << "\","
         << "\"sync_version\":" << readSyncVersion()
         << "}";
    return json.str();
}

// ============= 检查重复签到 =============
// 参数: student_id - 学号, slot_start - 时段开始时间(HH:MM), slot_end - 时段结束时间(HH:MM)
// 返回: JSON格式 {"duplicate": true/false, "record_time": "..."}
std::string checkDuplicate(const std::string& student_id, const std::string& slot_start, const std::string& slot_end) {
    std::string todayDate = getCurrentTimestamp().substr(0, 10);
    int start_hour = 0, start_minute = 0, end_hour = 23, end_minute = 59;
    parseTimeParts(slot_start, start_hour, start_minute);
    parseTimeParts(slot_end, end_hour, end_minute);
    int start_total_minutes = start_hour * 60 + start_minute;
    int end_total_minutes = end_hour * 60 + end_minute;

    sqlite3* db = openSqliteDb();
    if (!db) return "{\"duplicate\":false}";
    sqlite3_stmt* stmt = nullptr;
    const char* sql = "SELECT timestamp FROM records WHERE student_id=? AND substr(timestamp,1,10)=? ORDER BY id DESC";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, student_id);
        sqliteBindText(stmt, 2, todayDate);
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            std::string timestamp = sqliteColumnText(stmt, 0);
            if (timestamp.length() < 16) continue;
            int record_hour = 0;
            int record_minute = 0;
            if (!parseIntInRange(timestamp.substr(11, 2), 0, 23, record_hour)
                || !parseIntInRange(timestamp.substr(14, 2), 0, 59, record_minute)) continue;
            int record_total_minutes = record_hour * 60 + record_minute;
            if (record_total_minutes >= start_total_minutes && record_total_minutes <= end_total_minutes) {
                sqlite3_finalize(stmt);
                sqlite3_close(db);
                std::cout << "[CHECK] Duplicate found: " << student_id << " at " << timestamp << std::endl;
                return "{\"duplicate\":true,\"record_time\":\"" + jsonEscape(timestamp) + "\"}";
            }
        }
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    return "{\"duplicate\":false}";
}

// ============= 删除记录 =============
bool deleteRecord(const std::string& timestamp, const std::string& student_id) {
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    sqlite3_stmt* stmt = nullptr;
    const char* sql = "DELETE FROM records WHERE timestamp=? AND student_id=?";
    bool ok = false;
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, timestamp);
        sqliteBindText(stmt, 2, student_id);
        ok = sqlite3_step(stmt) == SQLITE_DONE && sqlite3_changes(db) > 0;
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    return ok;
}

// ============= 人脸照片管理函数 =============

// 获取人脸照片列表
std::string getFacePhotosList() {
    std::ostringstream json;
    json << "{\"photos\":[";

    sqlite3* db = openSqliteDb();
    bool first = true;
    if (db) {
        sqlite3_stmt* stmt = nullptr;
        if (sqlite3_prepare_v2(db,
            "SELECT face_id,file_path FROM face_photos ORDER BY face_id",
            -1, &stmt, nullptr) == SQLITE_OK) {
            while (sqlite3_step(stmt) == SQLITE_ROW) {
                const std::string face_id = sqliteColumnText(stmt, 0);
                const std::string file_path = sqliteColumnText(stmt, 1);
                if (!isSafeId(face_id) || getFileSize(file_path) <= 0) {
                    continue;
                }
                if (!first) json << ",";
                json << "{\"id\":\"" << jsonEscape(face_id) << "\",\"filename\":\"" << jsonEscape(face_id + ".jpg") << "\"}";
                first = false;
            }
        }
        sqlite3_finalize(stmt);
        sqlite3_close(db);
    }

    json << "]}";
    return json.str();
}

// 保存人脸照片
bool saveFacePhoto(const std::string& face_id, const std::string& photo_data) {
    _mkdir(FACES_DIR.c_str());
    std::string filepath;
    if (!buildFacePhotoPath(face_id, filepath)) {
        std::cerr << "[FACE_PHOTO] Invalid face_id: " << face_id << std::endl;
        return false;
    }
    std::ofstream file(filepath, std::ios::binary);
    if (!file.is_open()) {
        std::cerr << "[FACE_PHOTO] Failed to create: " << filepath << std::endl;
        return false;
    }
    file.write(photo_data.c_str(), photo_data.size());
    file.close();
    sqlite3* db = openSqliteDb();
    if (db) {
        const std::string now = getCurrentTimestamp();
        cancelPendingDeleteForFace(db, face_id, now);
        sqlite3_stmt* stmt = nullptr;
        if (sqlite3_prepare_v2(db,
            "REPLACE INTO face_photos(face_id,file_path,content_type,file_size,uploaded_at) VALUES(?,?,?,?,?)",
            -1, &stmt, nullptr) == SQLITE_OK) {
            sqliteBindText(stmt, 1, face_id);
            sqliteBindText(stmt, 2, filepath);
            sqliteBindText(stmt, 3, "image/jpeg");
            sqlite3_bind_int64(stmt, 4, static_cast<sqlite3_int64>(photo_data.size()));
            sqliteBindText(stmt, 5, now);
            sqlite3_step(stmt);
        }
        sqlite3_finalize(stmt);

        upsertFaceProfile(db, face_id, "", "active", now);
        reconcileFaceProfilesWithPhotos(db, now);
        sqlite3_close(db);
    }
    std::cout << "[FACE_PHOTO] Saved: " << filepath << " (" << photo_data.size() << " bytes)" << std::endl;
    return true;
}

// 读取人脸照片
std::string readFacePhoto(const std::string& face_id) {
    std::string filepath;
    if (!buildFacePhotoPath(face_id, filepath)) return "";
    std::ifstream file(filepath, std::ios::binary);
    if (!file.is_open()) return "";
    std::string content((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());
    file.close();
    return content;
}

// 删除人脸照片
bool deleteFacePhoto(const std::string& face_id) {
    std::string filepath;
    if (!buildFacePhotoPath(face_id, filepath)) return false;
    sqlite3* db = openSqliteDb();
    if (db) {
        sqlite3_stmt* stmt = nullptr;
        if (sqlite3_prepare_v2(db, "DELETE FROM face_photos WHERE face_id=?", -1, &stmt, nullptr) == SQLITE_OK) {
            sqliteBindText(stmt, 1, face_id);
            sqlite3_step(stmt);
        }
        sqlite3_finalize(stmt);

        clearFaceProfileBinding(db, face_id, getCurrentTimestamp());
        sqlite3_close(db);
    }
    if (std::remove(filepath.c_str()) == 0) {
        std::cout << "[FACE_PHOTO] Deleted: " << filepath << std::endl;
        return true;
    }
    return false;
}

// 删除指定学生ID的所有考勤记录
int deleteRecordsByStudentId(const std::string& student_id) {
    sqlite3* db = openSqliteDb();
    if (!db) return 0;
    sqlite3_stmt* stmt = nullptr;
    int deleted_count = 0;
    if (sqlite3_prepare_v2(db, "DELETE FROM records WHERE student_id=?", -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, student_id);
        if (sqlite3_step(stmt) == SQLITE_DONE) {
            deleted_count = sqlite3_changes(db);
        }
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    return deleted_count;
}

std::vector<std::string> findFaceIdsForStudent(sqlite3* db, const std::string& student_id) {
    std::vector<std::string> face_ids;
    if (!db || student_id.empty()) return face_ids;
    sqlite3_stmt* stmt = nullptr;
    if (sqlite3_prepare_v2(db,
        "SELECT face_id FROM face_profiles WHERE student_id=? AND face_id<>'' ORDER BY face_id",
        -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, student_id);
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            face_ids.push_back(sqliteColumnText(stmt, 0));
        }
    }
    sqlite3_finalize(stmt);
    return face_ids;
}

bool updateDeviceSyncState(const std::string& client, unsigned long long seen_version, unsigned long long ack_version) {
    if (client.empty()) return false;
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    sqlite3_stmt* stmt = nullptr;
    bool ok = false;
    const char* sql =
        "INSERT INTO device_sync_state(client,last_seen_version,last_ack_version,last_seen_at) "
        "VALUES(?,?,?,?) "
        "ON CONFLICT(client) DO UPDATE SET "
        "last_seen_version=MAX(device_sync_state.last_seen_version, excluded.last_seen_version),"
        "last_ack_version=MAX(device_sync_state.last_ack_version, excluded.last_ack_version),"
        "last_seen_at=excluded.last_seen_at";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, client);
        sqlite3_bind_int64(stmt, 2, static_cast<sqlite3_int64>(seen_version));
        sqlite3_bind_int64(stmt, 3, static_cast<sqlite3_int64>(ack_version));
        sqliteBindText(stmt, 4, getCurrentTimestamp());
        ok = sqlite3_step(stmt) == SQLITE_DONE;
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    return ok;
}

std::string getDeviceSyncSummary() {
    sqlite3* db = openSqliteDb();
    if (!db) return "[]";
    sqlite3_stmt* stmt = nullptr;
    std::ostringstream json;
    json << "[";
    bool first = true;
    const char* sql = "SELECT client,last_seen_version,last_ack_version,last_seen_at FROM device_sync_state ORDER BY client";
    if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) == SQLITE_OK) {
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            if (!first) json << ",";
            json << "{"
                 << "\"client\":\"" << jsonEscape(sqliteColumnText(stmt, 0)) << "\","
                 << "\"last_seen_version\":" << sqlite3_column_int64(stmt, 1) << ","
                 << "\"last_ack_version\":" << sqlite3_column_int64(stmt, 2) << ","
                 << "\"last_seen_at\":\"" << jsonEscape(sqliteColumnText(stmt, 3)) << "\""
                 << "}";
            first = false;
        }
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    json << "]";
    return json.str();
}

// 添加人脸ID到待删除列表
bool addToPendingDelete(const std::string& face_id, const std::string& student_id) {
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    sqlite3_stmt* stmt = nullptr;
    bool ok = false;
    std::string task_id = face_id + "-" + std::to_string(static_cast<long long>(time(0)));
    if (sqlite3_prepare_v2(db,
        "REPLACE INTO pending_delete(task_id,face_id,student_id,created_at,status) VALUES(?,?,?,?,?)",
        -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, task_id);
        sqliteBindText(stmt, 2, face_id);
        sqliteBindText(stmt, 3, student_id);
        sqliteBindText(stmt, 4, getCurrentTimestamp());
        sqliteBindText(stmt, 5, "pending");
        ok = sqlite3_step(stmt) == SQLITE_DONE;
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    std::cout << "[PENDING_DELETE] Added: " << face_id << " task=" << task_id << std::endl;
    return ok;
}

// 获取待删除列表
std::string getPendingDeleteList() {
    sqlite3* db = openSqliteDb();
    if (!db) return "{\"pending_delete\":[],\"delete_tasks\":[]}";
    sqlite3_stmt* stmt = nullptr;
    std::vector<std::map<std::string, std::string>> tasks;
    if (sqlite3_prepare_v2(db,
        "SELECT task_id,face_id,student_id,created_at,status,COALESCE(ack_at,'') FROM pending_delete WHERE status<>'acked' ORDER BY created_at,face_id",
        -1, &stmt, nullptr) == SQLITE_OK) {
        while (sqlite3_step(stmt) == SQLITE_ROW) {
            std::map<std::string, std::string> row;
            row["task_id"] = sqliteColumnText(stmt, 0);
            row["face_id"] = sqliteColumnText(stmt, 1);
            row["student_id"] = sqliteColumnText(stmt, 2);
            row["created_at"] = sqliteColumnText(stmt, 3);
            row["status"] = sqliteColumnText(stmt, 4);
            row["ack_at"] = sqliteColumnText(stmt, 5);
            tasks.push_back(row);
        }
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);

    std::ostringstream json;
    json << "{\"pending_delete\":[";
    bool first = true;
    for (const auto& task : tasks) {
        if (!first) json << ",";
        json << "\"" << jsonEscape(task.at("face_id")) << "\"";
        first = false;
    }
    json << "],\"delete_tasks\":[";
    first = true;
    for (const auto& task : tasks) {
        if (!first) json << ",";
        json << "{"
             << "\"task_id\":\"" << jsonEscape(task.at("task_id")) << "\","
             << "\"face_id\":\"" << jsonEscape(task.at("face_id")) << "\","
             << "\"student_id\":\"" << jsonEscape(task.at("student_id")) << "\","
             << "\"created_at\":\"" << jsonEscape(task.at("created_at")) << "\","
             << "\"status\":\"" << jsonEscape(task.at("status")) << "\""
             << "}";
        first = false;
    }
    json << "]}";
    return json.str();
}

// 从待删除列表中移除指定ID（K210确认删除后调用）
bool removeFromPendingDelete(const std::string& face_id_or_task_id) {
    sqlite3* db = openSqliteDb();
    if (!db) return false;
    sqlite3_stmt* stmt = nullptr;
    bool ok = false;
    if (sqlite3_prepare_v2(db,
        "UPDATE pending_delete SET status='acked',ack_at=? WHERE (task_id=? OR face_id=?) AND status<>'acked'",
        -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, getCurrentTimestamp());
        sqliteBindText(stmt, 2, face_id_or_task_id);
        sqliteBindText(stmt, 3, face_id_or_task_id);
        ok = sqlite3_step(stmt) == SQLITE_DONE && sqlite3_changes(db) > 0;
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    std::cout << "[PENDING_DELETE] Acked: " << face_id_or_task_id << std::endl;
    return ok;
}

bool cancelPendingDeleteForFace(sqlite3* db, const std::string& face_id, const std::string& now) {
    if (!db || !isSafeId(face_id)) return false;
    sqlite3_stmt* stmt = nullptr;
    bool ok = false;
    if (sqlite3_prepare_v2(db,
        "UPDATE pending_delete SET status='acked',ack_at=? WHERE face_id=? AND status<>'acked'",
        -1, &stmt, nullptr) == SQLITE_OK) {
        sqliteBindText(stmt, 1, now);
        sqliteBindText(stmt, 2, face_id);
        ok = sqlite3_step(stmt) == SQLITE_DONE;
    }
    const int changed = sqlite3_changes(db);
    sqlite3_finalize(stmt);
    if (ok && changed > 0) {
        std::cout << "[PENDING_DELETE] Canceled stale delete for face_id: " << face_id << std::endl;
    }
    return ok;
}

// ============= K210同步请求管理 =============
// 设置同步请求标志（QT端调用）
bool setSyncRequest(bool sync) {
    if (!sqliteSetKvValue("sync_request", std::string("{\"sync\":") + (sync ? "true" : "false") + "}")) {
        return false;
    }
    std::cout << "[SYNC] Sync request set to: " << (sync ? "true" : "false") << std::endl;
    return true;
}

// 获取同步请求状态（K210轮询调用）
std::string getSyncRequest() {
    return sqliteGetKvValue("sync_request", "{\"sync\":false}");
}

// 清除同步请求标志（K210确认后调用）
bool clearSyncRequest() {
    return setSyncRequest(false);
}

// ============= HTTP请求处理 =============
void handleHttpRequest(SOCKET client_socket) {
    char buffer[BUFFER_SIZE] = {0};
    int bytes = recv(client_socket, buffer, BUFFER_SIZE - 1, 0);

    if (bytes <= 0) {
        closesocket(client_socket);
        return;
    }

    std::string request(buffer, bytes);
    std::istringstream stream(request);
    std::string method, path, version;
    stream >> method >> path >> version;

    std::cout << "[HTTP] " << method << " " << path << std::endl;

    std::string endpoint = path;
    std::string query;
    size_t q_pos = path.find('?');
    if (q_pos != std::string::npos) {
        endpoint = path.substr(0, q_pos);
        query = path.substr(q_pos + 1);
    }

    std::string response_body;
    std::string content_type = "application/json";
    int status_code = 200;
    std::string status_text = "OK";
    auto sendResponse = [&]() {
        bool response_encrypted = false;
        const bool can_encrypt_response = method != "OPTIONS" && endpoint.find("/api/v1/") == 0
            && !isPublicEndpoint(method, endpoint) && !response_body.empty()
            && isJsonLikeContentType(content_type);
        if (can_encrypt_response) {
            const std::string encrypted_body = encryptPayload(response_body);
            if (encrypted_body.empty()) {
                status_code = 500;
                status_text = "Internal Server Error";
                response_body = makeJsonError("Encryption failed");
                content_type = "application/json";
            } else {
                response_body = encrypted_body;
                content_type = "application/octet-stream";
                response_encrypted = true;
            }
        }

        if (can_encrypt_response && !response_encrypted) {
            const std::string fallback_body = encryptPayload(makeJsonError("Encryption failed"));
            if (!fallback_body.empty()) {
                response_body = fallback_body;
                content_type = "application/octet-stream";
                response_encrypted = true;
            }
        }

        std::ostringstream response;
        response << "HTTP/1.1 " << status_code << " " << status_text << "\r\n";
        response << "Content-Type: " << content_type;
        if (isJsonLikeContentType(content_type)) {
            response << "; charset=utf-8";
        }
        response << "\r\n";
        if (response_encrypted) {
            response << "X-Encrypted: AES128-CBC\r\n";
        }
        response << "Content-Length: " << response_body.length() << "\r\n";
        response << "Access-Control-Allow-Origin: " << allowedCorsOrigin() << "\r\n";
        response << "Access-Control-Allow-Headers: Content-Type, Authorization, X-Api-Token, X-Encrypted-Response, X-Encrypted\r\n";
        response << "Access-Control-Allow-Methods: GET, POST, DELETE, OPTIONS\r\n";
        response << "Connection: close\r\n";
        response << "\r\n";
        response << response_body;

        std::string resp_str = response.str();
        send(client_socket, resp_str.c_str(), resp_str.length(), 0);
        closesocket(client_socket);
    };

    if (method != "OPTIONS" && endpoint.find("/api/v1/") != 0) {
        response_body = "{\"error\":\"Not Found\"}";
        status_code = 404;
        status_text = "Not Found";
        sendResponse();
        return;
    }

    if (!isAuthorizedRequest(request, method, endpoint)) {
        response_body = makeJsonError("Unauthorized");
        status_code = 401;
        status_text = "Unauthorized";
        sendResponse();
        return;
    }

    // 提取请求体
    std::string request_body;
    if (method == "POST") {
        size_t content_length = 0;
        std::string cl_str;
        if (getHeaderValue(request, "Content-Length", cl_str)) {
            int parsed_content_length = 0;
            if (!parseIntInRange(cl_str, 0, static_cast<int>(MAX_ENCRYPTED_PHOTO_BODY_SIZE), parsed_content_length)) {
                response_body = makeJsonError("Invalid Content-Length");
                status_code = 400;
                status_text = "Bad Request";
                sendResponse();
                return;
            }
            content_length = static_cast<size_t>(parsed_content_length);
        }

        const bool is_photo_upload = endpoint.find("/api/v1/faces/photos/") == 0;
        const bool encrypted_body = isEncryptedRequest(request);
        const size_t max_body_size = encrypted_body
            ? (is_photo_upload ? MAX_ENCRYPTED_PHOTO_BODY_SIZE : MAX_ENCRYPTED_JSON_BODY_SIZE)
            : (is_photo_upload ? MAX_PHOTO_BODY_SIZE : MAX_JSON_BODY_SIZE);
        if (content_length > max_body_size) {
            response_body = makeJsonError("Request body too large");
            status_code = 413;
            status_text = "Payload Too Large";
            sendResponse();
            return;
        }

        size_t header_end = request.find("\r\n\r\n");
        if (header_end != std::string::npos) {
            size_t body_start = header_end + 4;
            size_t current_body_size = request.size() - body_start;

            if (current_body_size >= content_length) {
                request_body = request.substr(body_start, content_length);
            } else {
                request_body = request.substr(body_start);
                size_t remaining = content_length - current_body_size;

                while (remaining > 0) {
                    char extra_buffer[BUFFER_SIZE] = {0};
                    int extra_bytes = recv(client_socket, extra_buffer,
                                          static_cast<int>(std::min(remaining, (size_t)BUFFER_SIZE)), 0);
                    if (extra_bytes <= 0) break;

                    request_body.append(extra_buffer, extra_bytes);
                    remaining -= extra_bytes;
                }
            }
        }

        std::cout << "[HTTP] POST body size: " << request_body.size()
                  << " bytes (expected: " << content_length << ")" << std::endl;

        if (request_body.size() != content_length) {
            response_body = makeJsonError("Incomplete request body");
            status_code = 400;
            status_text = "Bad Request";
            sendResponse();
            return;
        }

        if (!is_photo_upload && !encrypted_body) {
            response_body = makeJsonError("Encrypted request body required");
            status_code = 400;
            status_text = "Bad Request";
            sendResponse();
            return;
        }

        if (encrypted_body) {
            const std::string decrypted_body = decryptPayload(request_body);
            if (decrypted_body.empty() && content_length > 0) {
                response_body = makeJsonError("Decrypt request body failed");
                status_code = 400;
                status_text = "Bad Request";
                sendResponse();
                return;
            }

            if (decrypted_body.size() > (is_photo_upload ? MAX_PHOTO_BODY_SIZE : MAX_JSON_BODY_SIZE)) {
                response_body = makeJsonError("Decrypted request body too large");
                status_code = 413;
                status_text = "Payload Too Large";
                sendResponse();
                return;
            }

            request_body = decrypted_body;
            std::cout << "[HTTP] Decrypted POST body size: " << request_body.size() << " bytes" << std::endl;
        }
    }

    // ============= 路由处理 =============

    if (method == "OPTIONS") {
        response_body = "{}";

    } else if (method == "GET" && endpoint == "/api/v1/sync/version") {
        response_body = makeSyncVersionResponse();
        std::cout << "[SYNC] Version fetched: " << readSyncVersion() << std::endl;

    } else if (method == "GET" && endpoint == "/api/v1/sync/state") {
        auto params = parseQueryParams(query);
        const std::string client = params.count("client") ? params["client"] : "all";
        const unsigned long long last_version = parseVersionParam(params);
        response_body = makeSyncStateResponse(client, last_version);
        std::cout << "[SYNC] State fetched: client=" << client
                  << ", last_version=" << last_version
                  << ", current_version=" << readSyncVersion() << std::endl;

    } else if (method == "POST" && endpoint == "/api/v1/sync/ack") {
        response_body = makeSyncAckResponse(request_body);
        std::cout << "[SYNC] Ack received: " << request_body << std::endl;

    } else if (method == "POST" && endpoint == "/api/v1/attendance/checkins") {
        std::cout << "[CHECKIN] Processing checkin data..." << std::endl;

        auto json_data = parseJSON(request_body);

        if (json_data.find("student_id") != json_data.end()) {
            std::string timestamp = getCurrentTimestamp();
            std::string student_id = json_data["student_id"];
            std::string name = json_data.count("name") ? json_data["name"] : "";
            std::string confidence = json_data.count("confidence") ? json_data["confidence"] : "0";
            std::string status = json_data.count("status") ? json_data["status"] : "success";
            std::string class_id = json_data.count("class_id") ? json_data["class_id"] : "0";
            char* conf_end = nullptr;
            const double conf_value = std::strtod(confidence.c_str(), &conf_end);

            if (!isSafeId(student_id) || student_id.size() > 32 || name.size() > 64 ||
                class_id.size() > 32 || conf_end == confidence.c_str() || *conf_end != '\0' ||
                conf_value < 0.0 || conf_value > 1.0 ||
                (status != "success" && status != "failed" && status != "late")) {
                response_body = makeJsonError("Invalid checkin fields");
                status_code = 400;
                status_text = "Bad Request";
                sendResponse();
                return;
            }

            std::cout << "[CHECKIN] Student ID: " << student_id << std::endl;

            if (saveAttendanceRecord(timestamp, student_id, name, confidence, status, class_id)) {
                response_body = "{\"success\":true,\"message\":\"签到成功\",\"timestamp\":\""
                              + jsonEscape(timestamp) + "\"}";
                bumpSyncVersion("checkin");
                std::cout << "[CHECKIN] ✓ " << name << " (ID:" << student_id << ", Class:" << class_id << ")" << std::endl;
            } else {
                response_body = "{\"success\":false,\"message\":\"数据库写入失败\"}";
                status_code = 500;
                status_text = "Internal Server Error";
            }
        } else {
            response_body = "{\"success\":false,\"message\":\"缺少必要字段\"}";
            status_code = 400;
            status_text = "Bad Request";
        }
    }
    else if (method == "GET" && endpoint == "/api/v1/attendance/records") {
        auto params = parseQueryParams(query);
        int limit = 100;
        int offset = 0;
        if (params.count("limit") && !parseIntInRange(params["limit"], 1, 5000, limit)) {
            response_body = makeJsonError("Invalid limit");
            status_code = 400;
            status_text = "Bad Request";
        } else if (params.count("offset") && !parseIntInRange(params["offset"], 0, 1000000, offset)) {
            response_body = makeJsonError("Invalid offset");
            status_code = 400;
            status_text = "Bad Request";
        } else {

            response_body = readDatabase(limit, offset);
        }

    } else if (method == "GET" && endpoint == "/api/v1/attendance/statistics") {
        response_body = getStatistics();

    } else if (method == "POST" && endpoint == "/api/v1/attendance/records/clear") {
        if (clearDatabase()) {
            response_body = "{\"success\":true,\"message\":\"Database cleared\"}";
            bumpSyncVersion("clear_records");
        } else {
            response_body = "{\"success\":false,\"message\":\"Failed to clear database\"}";
            status_code = 500;
            status_text = "Internal Server Error";
        }

    } else if (method == "DELETE" && endpoint == "/api/v1/attendance/records") {
        auto params = parseQueryParams(query);
        if (params.count("timestamp") && params.count("student_id")) {
            std::string timestamp = params["timestamp"];
            std::string student_id = params["student_id"];

            if (deleteRecord(timestamp, student_id)) {
                response_body = "{\"success\":true,\"message\":\"Record deleted\"}";
                bumpSyncVersion("delete_record");
            } else {
                response_body = "{\"success\":false,\"message\":\"Record not found\"}";
                status_code = 404;
                status_text = "Not Found";
            }
        } else {
            response_body = "{\"success\":false,\"message\":\"Missing parameters\"}";
            status_code = 400;
            status_text = "Bad Request";
        }

    } else if (method == "GET" && endpoint == "/api/v1/system/health") {
        response_body = makeHealthResponse();

    } else if (method == "GET" && endpoint == "/api/v1/system/storage") {
        response_body = makeStorageStatusResponse();

    } else if (method == "GET" && endpoint == "/api/v1/system/time") {
        // 返回服务器当前Unix时间戳（UTC秒）和可读时间
        std::ostringstream json;
        json << "{"
             << "\"epoch\":" << static_cast<long long>(time(0)) << ","
             << "\"server_time\":\"" << getCurrentTimestamp() << "\""
             << "}";
        response_body = json.str();

    } else if (method == "POST" && endpoint == "/api/v1/config/time-slots") {
        // 上传时间段配置: POST /api/v1/config/time-slots
        std::cout << "[TIMESLOTS] Received upload request, data size: " << request_body.size() << " bytes" << std::endl;

        if (saveTimeSlots(request_body)) {
            response_body = "{\"success\":true,\"message\":\"时间段配置已更新\"}";
            bumpSyncVersion("timeslots");
            std::cout << "[TIMESLOTS] ✓ Configuration uploaded successfully" << std::endl;
        } else {
            response_body = "{\"success\":false,\"message\":\"保存时间段配置失败\"}";
            status_code = 500;
            status_text = "Internal Server Error";
        }

    } else if (method == "GET" && endpoint == "/api/v1/config/time-slots") {
        // 获取时间段配置: GET /api/v1/config/time-slots
        std::cout << "[TIMESLOTS] Reading configuration" << std::endl;
        response_body = readTimeSlots();

    } else if (method == "GET" && endpoint == "/api/v1/attendance/duplicates") {
        // 检查重复签到: GET /api/v1/attendance/duplicates?student_id=xxx&slot_start=08:00&slot_end=09:30
        auto params = parseQueryParams(query);
        if (params.count("student_id") && params.count("slot_start") && params.count("slot_end")) {
            response_body = checkDuplicate(params["student_id"], params["slot_start"], params["slot_end"]);
            std::cout << "[CHECK] student_id=" << params["student_id"]
                      << ", slot=" << params["slot_start"] << "-" << params["slot_end"]
                      << ", result=" << response_body << std::endl;
        } else {
            response_body = "{\"error\":\"Missing parameters: student_id, slot_start, slot_end\"}";
            status_code = 400;
            status_text = "Bad Request";
        }

    } else if (method == "GET" && endpoint == "/api/v1/attendance/today") {
        // 获取今日已签到记录（供STM32开机下载）
        // GET /api/v1/attendance/today?slot_start=08:00&slot_end=09:30
        auto params = parseQueryParams(query);
        std::string slot_start = params.count("slot_start") ? params["slot_start"] : "00:00";
        std::string slot_end = params.count("slot_end") ? params["slot_end"] : "23:59";

        std::string todayDate = getCurrentTimestamp().substr(0, 10);

        int start_hour = 0, start_minute = 0, end_hour = 23, end_minute = 59;
        parseTimeParts(slot_start, start_hour, start_minute);
        parseTimeParts(slot_end, end_hour, end_minute);

        std::ostringstream json;
        json << "{\"date\":\"" << jsonEscape(todayDate) << "\",\"records\":[";

        sqlite3* db = openSqliteDb();
        if (db) {
            sqlite3_stmt* stmt = nullptr;
            bool first = true;
            const char* sql = "SELECT timestamp,student_id FROM records WHERE substr(timestamp,1,10)=? ORDER BY id ASC";
            if (sqlite3_prepare_v2(db, sql, -1, &stmt, nullptr) == SQLITE_OK) {
                sqliteBindText(stmt, 1, todayDate);
                while (sqlite3_step(stmt) == SQLITE_ROW) {
                    std::string timestamp = sqliteColumnText(stmt, 0);
                    if (timestamp.length() < 16) continue;
                    int record_hour = 0;
                    int record_minute = 0;
                    if (!parseIntInRange(timestamp.substr(11, 2), 0, 23, record_hour)
                        || !parseIntInRange(timestamp.substr(14, 2), 0, 59, record_minute)) continue;
                    int record_total = record_hour * 60 + record_minute;
                    int start_total = start_hour * 60 + start_minute;
                    int end_total = end_hour * 60 + end_minute;

                    if (record_total < start_total || record_total > end_total) continue;
                    if (!first) json << ",";
                    json << "\"" << jsonEscape(sqliteColumnText(stmt, 1)) << "\"";
                    first = false;
                }
            }
            sqlite3_finalize(stmt);
            sqlite3_close(db);
        }

        json << "]}";
        response_body = json.str();
        std::cout << "[TODAY] Returning today's records: " << response_body << std::endl;

    } else if (method == "GET" && endpoint == "/api/v1/students") {
        response_body = readStudents();
        std::cout << "[STUDENTS] List fetched" << std::endl;

    } else if (method == "POST" && endpoint == "/api/v1/students") {
        if (saveStudents(request_body)) {
            response_body = "{\"success\":true,\"message\":\"学生档案已保存\"}";
            bumpSyncVersion("students");
        } else {
            response_body = "{\"success\":false,\"message\":\"保存学生档案失败\"}";
            status_code = 400;
            status_text = "Bad Request";
        }

    } else if (method == "GET" && endpoint == "/api/v1/classes") {
        response_body = readClasses();
        std::cout << "[CLASSES] List fetched" << std::endl;

    } else if (method == "POST" && endpoint == "/api/v1/classes") {
        if (saveClasses(request_body)) {
            response_body = "{\"success\":true,\"message\":\"班级配置已保存\"}";
            bumpSyncVersion("classes");
        } else {
            response_body = "{\"success\":false,\"message\":\"保存班级失败，请确认被删除班级下没有学生\"}";
            status_code = 400;
            status_text = "Bad Request";
        }

    } else if (method == "GET" && endpoint == "/api/v1/face_profiles") {
        response_body = readFaceProfiles();
        std::cout << "[FACE_PROFILE] List fetched" << std::endl;

    } else if (method == "POST" && endpoint == "/api/v1/face_profiles") {
        if (saveFaceProfiles(request_body)) {
            response_body = "{\"success\":true,\"message\":\"人脸档案已保存，已触发 K210 同步\"}";
            bumpSyncVersion("face_profiles");
            setSyncRequest(true);
        } else {
            response_body = "{\"success\":false,\"message\":\"保存人脸档案失败\"}";
            status_code = 400;
            status_text = "Bad Request";
        }

    // ============= 人脸照片管理 API =============
    } else if (method == "GET" && endpoint == "/api/v1/faces/photos") {
        // 获取人脸照片列表
        _mkdir(FACES_DIR.c_str());
        response_body = getFacePhotosList();
        std::cout << "[FACE_PHOTO] Photos list fetched" << std::endl;

    } else if (method == "GET" && endpoint.find("/api/v1/faces/photos/") == 0) {
        // 获取指定人脸照片: GET /api/v1/faces/photos/<id>
        std::string face_id = urlDecode(endpoint.substr(std::string("/api/v1/faces/photos/").size()));
        std::string photo_data = readFacePhoto(face_id);

        if (!photo_data.empty()) {
            response_body = photo_data;
            content_type = "image/jpeg";
            std::cout << "[FACE_PHOTO] Photo fetched for id: " << face_id << std::endl;
        } else {
            response_body = "{\"error\":\"Photo not found\"}";
            status_code = 404;
            status_text = "Not Found";
        }

    } else if (method == "POST" && endpoint.find("/api/v1/faces/photos/") == 0) {
        // 人脸照片上传: POST /api/v1/faces/photos/<face_id>
        std::string face_id = urlDecode(endpoint.substr(std::string("/api/v1/faces/photos/").size()));
        std::cout << "[FACE_PHOTO] Simple upload for face_id: " << face_id << ", size: " << request_body.size() << " bytes" << std::endl;

        if (!isSafeId(face_id)) {
            response_body = "{\"success\":false,\"message\":\"Invalid face_id\"}";
            status_code = 400;
            status_text = "Bad Request";
        } else if (!request_body.empty()) {
            if (saveFacePhoto(face_id, request_body)) {
                response_body = "{\"success\":true,\"message\":\"Photo saved\",\"face_id\":\"" + jsonEscape(face_id) + "\"}";
                bumpSyncVersion("face_photo");
            } else {
                response_body = "{\"success\":false,\"message\":\"Failed to save photo\"}";
                status_code = 500;
                status_text = "Internal Server Error";
            }
        } else {
            response_body = "{\"success\":false,\"message\":\"Invalid face_id or empty data\"}";
            status_code = 400;
            status_text = "Bad Request";
        }

    } else if (method == "DELETE" && endpoint.find("/api/v1/faces/") == 0) {
        // 删除人脸信息: DELETE /api/v1/faces/<face_id_or_student_id>?delete_records=true
        std::string requested_id = urlDecode(endpoint.substr(std::string("/api/v1/faces/").size()));
        auto params = parseQueryParams(query);
        bool delete_records = (params.count("delete_records") && params["delete_records"] == "true");

        std::cout << "[DELETE_FACE] Deleting face for id: " << requested_id
                  << ", delete_records: " << (delete_records ? "yes" : "no") << std::endl;

        if (!isSafeId(requested_id)) {
            response_body = "{\"success\":false,\"message\":\"Invalid id\"}";
            status_code = 400;
            status_text = "Bad Request";
        } else {
            std::vector<std::string> face_ids;
            sqlite3* db = openSqliteDb();
            if (db) {
                if (facePhotoExists(db, requested_id) || faceProfileExists(db, requested_id)) {
                    face_ids.push_back(requested_id);
                } else {
                    face_ids = findFaceIdsForStudent(db, requested_id);
                }
                sqlite3_close(db);
            }
            if (face_ids.empty()) {
                face_ids.push_back(requested_id);
            }

            bool photo_deleted = false;
            int records_deleted = 0;

            if (delete_records) {
                records_deleted = deleteRecordsByStudentId(requested_id);
            }

            // 添加K210原始face_id到待删除列表，等待K210同步删除本地特征
            bool pending_added = false;
            for (const auto& face_id : face_ids) {
                photo_deleted = deleteFacePhoto(face_id) || photo_deleted;
                pending_added = addToPendingDelete(face_id, requested_id) || pending_added;
            }
            bumpSyncVersion("delete_face");
            setSyncRequest(true);

            std::ostringstream result;
            result << "{\"success\":true,"
                   << "\"photo_deleted\":" << (photo_deleted ? "true" : "false") << ","
                   << "\"profile_unbound\":true,"
                   << "\"records_deleted\":" << records_deleted << ","
                   << "\"k210_pending\":" << (pending_added ? "true" : "false") << ","
                   << "\"sync_requested\":true}";
            response_body = result.str();

            std::cout << "[DELETE_FACE] Result: " << response_body << std::endl;
        }

    // ============= K210同步请求 API =============
    } else if (method == "GET" && endpoint == "/api/v1/sync/request") {
        // K210查询是否需要同步
        response_body = getSyncRequest();
        std::cout << "[SYNC] K210 checking sync request: " << response_body << std::endl;

    } else if (method == "POST" && endpoint == "/api/v1/sync/request/ack") {
        // K210确认收到同步请求，清除标志
        if (clearSyncRequest()) {
            response_body = "{\"success\":true,\"message\":\"Sync acknowledged\"}";
            std::cout << "[SYNC] K210 acknowledged sync request" << std::endl;
        } else {
            response_body = "{\"success\":false,\"message\":\"Failed to clear sync request\"}";
            status_code = 500;
            status_text = "Internal Server Error";
        }

    } else {
        response_body = "{\"error\":\"Not Found\"}";
        status_code = 404;
        status_text = "Not Found";
    }

    sendResponse();
}

// ============= HTTP服务器线程 =============
void httpServerThread() {
    SOCKET server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket == INVALID_SOCKET) {
        std::cerr << "[HTTP] Failed to create socket" << std::endl;
        return;
    }

    int opt = 1;
    setsockopt(server_socket, SOL_SOCKET, SO_REUSEADDR, (char*)&opt, sizeof(opt));

    sockaddr_in server_addr;
    server_addr.sin_family = AF_INET;
    const std::string bind_host = bindAddress();
    if (bind_host == "0.0.0.0" || bind_host.empty()) {
        server_addr.sin_addr.s_addr = INADDR_ANY;
    } else {
        if (inet_pton(AF_INET, bind_host.c_str(), &server_addr.sin_addr) != 1) {
            std::cerr << "[HTTP] Invalid ATTENDANCE_BIND_HOST: " << bind_host << std::endl;
            closesocket(server_socket);
            return;
        }
    }
    server_addr.sin_port = htons(HTTP_PORT);

    if (bind(server_socket, (sockaddr*)&server_addr, sizeof(server_addr)) == SOCKET_ERROR) {
        std::cerr << "[HTTP] Bind failed" << std::endl;
        closesocket(server_socket);
        return;
    }

    listen(server_socket, 10);
    std::cout << "[HTTP] Server listening on " << bind_host << ":" << HTTP_PORT << std::endl;

    while (true) {
        sockaddr_in client_addr;
        socklen_t client_len = sizeof(client_addr);
        SOCKET client_socket = accept(server_socket, (sockaddr*)&client_addr, &client_len);

        if (client_socket != INVALID_SOCKET) {
            std::thread(handleHttpRequest, client_socket).detach();
        }
    }
}

int main() {
#ifdef _WIN32
    WSADATA wsa;
    WSAStartup(MAKEWORD(2, 2), &wsa);
#endif

    std::cout << "========================================" << std::endl;
    std::cout << "  Face Recognition Attendance Server" << std::endl;
    std::cout << "  with AES-128-CBC Encryption" << std::endl;
    std::cout << "========================================" << std::endl;
    std::cout << "HTTP Port " << HTTP_PORT << " - Encrypted API" << std::endl;
    std::cout << "Database: " << SQLITE_DB_FILE << std::endl;
    std::cout << "----------------------------------------" << std::endl;

    if (!backupSqliteDatabaseOnStartup()) {
        std::cerr << "[BACKUP] Startup backup failed, stop to avoid unsafe writes" << std::endl;
        return 1;
    }

    // 初始化SQLite，所有运行时数据统一写入 attendance.db
    if (!initializeSqliteStorage()) {
        std::cerr << "[SQLITE] Failed to initialize storage" << std::endl;
        return 1;
    }
    std::cout << "[SYNC] Current version: " << readSyncVersion() << std::endl;

    // 启动HTTP服务器
    std::thread http_thread(httpServerThread);
    http_thread.join();

#ifdef _WIN32
    WSACleanup();
#endif

    return 0;
}