<?php
/**
 * QR Code 產生 API
 * 
 * 功能：
 * 1. 產生 QR Code 圖片
 * 2. 寫入資料庫
 * 3. 上傳到 Server 資料夾
 * 
 * 安裝依賴：
 * composer require endroid/qr-code
 */

header('Content-Type: application/json; charset=utf-8');
header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Methods: POST, OPTIONS');
header('Access-Control-Allow-Headers: Content-Type');

// 處理 OPTIONS 請求（CORS preflight）
if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
    http_response_code(200);
    exit;
}

// 只接受 POST 請求
if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
    sendError('METHOD_NOT_ALLOWED', '只接受 POST 請求', 'validation', 405);
}

// ============ 設定 ============
define('ENC_TABLE_64', 'rFuWWAcPSqEhPF9nn8jfqStVE4nZxRJrhMGUKLFWb2uGgSx65KvfjdeF3CVsvd69');
define('QRCODE_BASE_URL', 'https://class.aiacademy.tw/student/');
define('QRCODE_ASSET_PATH', 'class.aiacademy.tw/assets/qrcode/');
define('QRCODE_SAVE_DIR', __DIR__ . '/../../../assets/qrcode/'); // 根據實際路徑調整

// 資料庫設定
define('DB_HOST', 'localhost');
define('DB_NAME', 'your_database');
define('DB_USER', 'your_username');
define('DB_PASS', 'your_password');

// ============ 主程式 ============

try {
    // 解析輸入
    $input = json_decode(file_get_contents('php://input'), true);
    
    if (!$input) {
        sendError('INVALID_JSON', '無效的 JSON 輸入', 'validation');
    }
    
    // 檢查是否為測試模式
    if (!empty($input['test_mode'])) {
        sendSuccess([
            'message' => 'API 連線正常',
            'version' => '1.0.0'
        ]);
    }
    
    // 檢查是否為批次處理
    if (!empty($input['batch']) && !empty($input['students'])) {
        $results = processBatch($input['students'], $input['actions'] ?? []);
        echo json_encode(['success' => true, 'results' => $results]);
        exit;
    }
    
    // 單筆處理
    $result = processSingleStudent($input);
    sendSuccess($result);
    
} catch (Exception $e) {
    sendError('EXCEPTION', $e->getMessage(), 'unknown');
}

// ============ 處理函數 ============

/**
 * 處理單筆學員
 */
function processSingleStudent($input) {
    // 驗證必要欄位
    $required = ['class_prefix', 'student_no', 'name', 'email'];
    foreach ($required as $field) {
        if (empty($input[$field])) {
            throw new Exception("缺少必要欄位: {$field}");
        }
    }
    
    $classPrefix = trim($input['class_prefix']);
    $studentNo = trim($input['student_no']);
    $name = trim($input['name']);
    $email = trim($input['email']);
    $phone = trim($input['phone'] ?? '');
    $actions = $input['actions'] ?? [];
    
    // 1. 計算 Hash
    $qrcodeId = hashClassPrefixEmail($classPrefix, $email);
    $hashParameter = shortStr($name . $studentNo, 8);
    $hashFilename = shortStrEnc($hashParameter, 8, ENC_TABLE_64);
    
    // 2. 產生 QR Code
    $qrcodeUrl = QRCODE_BASE_URL . $qrcodeId;
    $filename = "{$studentNo}_{$hashFilename}.jpg";
    $qrcodeImage = generateQRCode($qrcodeUrl);
    
    // 3. 儲存到 Server（如果啟用）
    if (!empty($actions['upload_to_server'])) {
        saveQRCodeToServer($qrcodeImage, $filename);
    }
    
    // 4. 寫入資料庫（如果啟用）
    if (!empty($actions['save_to_db'])) {
        saveToDatabase([
            'class_prefix' => $classPrefix,
            'student_no' => $studentNo,
            'name' => $name,
            'email' => $email,
            'phone' => $phone,
            'qrcode_id' => $qrcodeId,
            'filename' => $filename
        ]);
    }
    
    return [
        'qrcode_id' => $qrcodeId,
        'qrcode_url' => $qrcodeUrl,
        'qrcode_image_base64' => base64_encode($qrcodeImage),
        'filename' => $filename,
        'file_link' => QRCODE_ASSET_PATH . $filename
    ];
}

/**
 * 批次處理
 */
function processBatch($students, $actions) {
    $results = [];
    
    foreach ($students as $student) {
        try {
            $student['actions'] = $actions;
            $result = processSingleStudent($student);
            $results[] = [
                'success' => true,
                'student_no' => $student['student_no'],
                'data' => $result
            ];
        } catch (Exception $e) {
            $results[] = [
                'success' => false,
                'student_no' => $student['student_no'] ?? 'unknown',
                'error' => [
                    'code' => 'PROCESS_ERROR',
                    'message' => $e->getMessage()
                ]
            ];
        }
    }
    
    return $results;
}

// ============ Hash 函數（與 Python 版本一致）============

/**
 * 計算 QR Code ID
 */
function hashClassPrefixEmail($classPrefix, $email) {
    $salt = 'newQRCODE' . $classPrefix . $email . 'from20201118byBaoYunIdea';
    return md5($salt);
}

/**
 * 短 Hash（SHA512 前 N 字元）
 */
function shortStr($s, $charLength = 8) {
    if ($charLength > 128) {
        throw new Exception("char_length {$charLength} exceeds 128");
    }
    $hashHex = hash('sha512', $s);
    return substr($hashHex, 0, $charLength);
}

/**
 * 自訂編碼的短 Hash
 */
function shortStrEnc($s, $charLength = 8, $encTable = ENC_TABLE_64) {
    if ($charLength > 128) {
        throw new Exception("char_length {$charLength} exceeds 128");
    }
    $hashHex = hash('sha512', $s);
    $hashEnc = intToEnc(hexToInt($hashHex), $encTable);
    return substr($hashEnc, 0, $charLength);
}

/**
 * 十六進位轉大整數（使用 BCMath）
 */
function hexToInt($hex) {
    $dec = '0';
    $len = strlen($hex);
    for ($i = 0; $i < $len; $i++) {
        $dec = bcadd(bcmul($dec, '16'), hexdec($hex[$i]));
    }
    return $dec;
}

/**
 * 大整數轉自訂編碼
 */
function intToEnc($n, $encTable) {
    if ($n === '0') {
        return $encTable[0];
    }
    
    $base = strlen($encTable);
    $digits = '';
    
    while (bccomp($n, '0') > 0) {
        $remainder = bcmod($n, $base);
        $digits .= $encTable[(int)$remainder];
        $n = bcdiv($n, $base, 0);
    }
    
    return strrev($digits);
}

// ============ QR Code 產生 ============

/**
 * 產生 QR Code 圖片
 */
function generateQRCode($data) {
    // 方法 1：使用 endroid/qr-code（推薦，需要 composer 安裝）
    if (class_exists('Endroid\QrCode\QrCode')) {
        return generateQRCodeEndroid($data);
    }
    
    // 方法 2：使用 Google Charts API（備用）
    return generateQRCodeGoogleCharts($data);
}

/**
 * 使用 endroid/qr-code 產生
 */
function generateQRCodeEndroid($data) {
    // 需要先安裝：composer require endroid/qr-code
    
    use Endroid\QrCode\QrCode;
    use Endroid\QrCode\Writer\PngWriter;
    use Endroid\QrCode\ErrorCorrectionLevel;
    
    $qrCode = new QrCode($data);
    $qrCode->setSize(300);
    $qrCode->setMargin(10);
    $qrCode->setErrorCorrectionLevel(ErrorCorrectionLevel::Low);
    
    $writer = new PngWriter();
    $result = $writer->write($qrCode);
    
    return $result->getString();
}

/**
 * 使用 Google Charts API 產生（備用方案）
 */
function generateQRCodeGoogleCharts($data) {
    $url = 'https://chart.googleapis.com/chart?' . http_build_query([
        'cht' => 'qr',
        'chs' => '300x300',
        'chl' => $data,
        'choe' => 'UTF-8'
    ]);
    
    $context = stream_context_create([
        'http' => [
            'timeout' => 10
        ]
    ]);
    
    $image = file_get_contents($url, false, $context);
    
    if ($image === false) {
        throw new Exception('無法從 Google Charts API 取得 QR Code');
    }
    
    return $image;
}

// ============ 檔案儲存 ============

/**
 * 儲存 QR Code 到 Server
 */
function saveQRCodeToServer($imageData, $filename) {
    $savePath = QRCODE_SAVE_DIR . $filename;
    
    // 確保目錄存在
    $dir = dirname($savePath);
    if (!is_dir($dir)) {
        mkdir($dir, 0755, true);
    }
    
    // 儲存檔案
    $result = file_put_contents($savePath, $imageData);
    
    if ($result === false) {
        throw new Exception('無法儲存 QR Code 檔案');
    }
    
    return true;
}

// ============ 資料庫操作 ============

/**
 * 取得資料庫連線
 */
function getDbConnection() {
    static $pdo = null;
    
    if ($pdo === null) {
        try {
            $dsn = 'mysql:host=' . DB_HOST . ';dbname=' . DB_NAME . ';charset=utf8mb4';
            $pdo = new PDO($dsn, DB_USER, DB_PASS, [
                PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
                PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
            ]);
        } catch (PDOException $e) {
            throw new Exception('資料庫連線失敗: ' . $e->getMessage());
        }
    }
    
    return $pdo;
}

/**
 * 寫入資料庫
 */
function saveToDatabase($data) {
    $pdo = getDbConnection();
    
    // 檢查是否已存在
    $stmt = $pdo->prepare('SELECT id FROM students WHERE student_no = ?');
    $stmt->execute([$data['student_no']]);
    $existing = $stmt->fetch();
    
    if ($existing) {
        // 更新
        $sql = 'UPDATE students SET 
                class_prefix = ?, name = ?, email = ?, phone = ?,
                qrcode_id = ?, qrcode_filename = ?, updated_at = NOW()
                WHERE student_no = ?';
        $params = [
            $data['class_prefix'],
            $data['name'],
            $data['email'],
            $data['phone'],
            $data['qrcode_id'],
            $data['filename'],
            $data['student_no']
        ];
    } else {
        // 新增
        $sql = 'INSERT INTO students 
                (class_prefix, student_no, name, email, phone, qrcode_id, qrcode_filename, created_at)
                VALUES (?, ?, ?, ?, ?, ?, ?, NOW())';
        $params = [
            $data['class_prefix'],
            $data['student_no'],
            $data['name'],
            $data['email'],
            $data['phone'],
            $data['qrcode_id'],
            $data['filename']
        ];
    }
    
    $stmt = $pdo->prepare($sql);
    $stmt->execute($params);
    
    return true;
}

// ============ 回應函數 ============

/**
 * 送出成功回應
 */
function sendSuccess($data) {
    echo json_encode([
        'success' => true,
        'data' => $data
    ], JSON_UNESCAPED_UNICODE);
    exit;
}

/**
 * 送出錯誤回應
 */
function sendError($code, $message, $stage, $httpCode = 400) {
    http_response_code($httpCode);
    echo json_encode([
        'success' => false,
        'error' => [
            'code' => $code,
            'message' => $message,
            'stage' => $stage
        ]
    ], JSON_UNESCAPED_UNICODE);
    exit;
}