const multer = require('multer');
const fs = require('fs');
const path = require('path');
const crypto = require('crypto'); // 用於生成隨機字串

const storage = multer.diskStorage({
    destination: (req, file, cb) => {
        const { dbname, typeid } = req.params;
        const uploadPath = path.join(__dirname, `../../public/upload/${dbname}/${typeid}`);
        fs.mkdirSync(uploadPath, { recursive: true });
        cb(null, uploadPath);
    },
    filename: (req, file, cb) => {
		//下行程式會自動加入日期 tag 在檔名前, 目前先取消 2026/01/10
        //const dateStr = new Date().toISOString().replace(/[:.]/g, '-');
        //cb(null, `${dateStr}-${file.originalname}`);
		
		// 解決中文亂碼問題：將 latin1 轉回 utf-8
		//const originalName = Buffer.from(file.originalname, 'latin1').toString('utf8');
		//cb(null, `${file.originalname}`);
		
		
		// 1. 取得原始檔名與副檔名
        const ext = path.extname(file.originalname); // 包含點，例如 .jpg
        const baseName = path.basename(file.originalname, ext); // 只有主檔名

        // 2. 正則表達式：判斷是否為純英數、底線、橫線
        // ^[a-zA-Z0-9_-]+$ 表示從頭到尾都是英數或底線橫線
        const isAlphaNumeric = /^[a-zA-Z0-9_-]+$/.test(baseName);

        let finalFileName = '';
        //const dateStr = new Date().toISOString().replace(/[:.]/g, '-');
		const dateStr = new Date().toISOString().replace(/\D/g, '');
		
        if (isAlphaNumeric) {
            // A. 如果是純英數，保持原樣，~~加上時間戳防止重複~~
            //finalFileName = `${dateStr}-${file.originalname}`;
			finalFileName = `${file.originalname}`;
        } else {
            // B. 如果包含中文或其他字元
            // 先修復 Multer 的編碼錯誤 (latin1 -> utf8)
            const decodedName = Buffer.from(file.originalname, 'latin1').toString('utf8');
            
            // 為了系統穩定，硬碟端存儲建議改用「隨機英數」防止 URL 編碼問題
            const uniqueSuffix = crypto.randomBytes(4).toString('hex');
            finalFileName = `${dateStr}-${uniqueSuffix}${ext}`;
            
            // 將正確的中文名稱掛載，供 Controller 存入資料庫使用
            file.decodedOriginalName = decodedName;
        }

        cb(null, finalFileName);
    }
});

const upload = multer({
    storage,
    limits: { fileSize: parseInt(process.env.MAX_FILE_SIZE) || 50 * 1024 * 1024 },
    fileFilter: (req, file, cb) => {
        // 禁止上傳危險副檔名
        const forbiddenExtensions = ['.exe', '.sh', '.php', '.js', '.bat'];
        const ext = path.extname(file.originalname).toLowerCase();
        if (forbiddenExtensions.includes(ext)) {
            return cb(new Error('File type not allowed'), false);
        }
        cb(null, true);
    }
});

module.exports = upload;