const multer = require('multer');
const path = require('path');
const crypto = require('crypto');
const fs = require('fs');

const UPLOAD_DIR = path.join(__dirname, '..', '..', 'data', 'uploads');
if (!fs.existsSync(UPLOAD_DIR)) fs.mkdirSync(UPLOAD_DIR, { recursive: true });

const ALLOWED_MIME = {
  'image/jpeg': ['.jpg', '.jpeg'],
  'image/png': ['.png'],
  'image/gif': ['.gif'],
  'image/webp': ['.webp'],
  'video/mp4': ['.mp4'],
  'video/webm': ['.webm'],
};

const ALLOWED_EXT = ['.jpg', '.jpeg', '.png', '.gif', '.webp', '.mp4', '.webm'];

function validateMagicBytes(buffer, mime) {
  const head = buffer.slice(0, 12);
  const sigs = {
    'image/jpeg': () => head[0] === 0xFF && head[1] === 0xD8,
    'image/png': () => head[0] === 0x89 && head[1] === 0x50 && head[2] === 0x4E && head[3] === 0x47,
    'image/gif': () => head.toString('ascii', 0, 6) === 'GIF89a' || head.toString('ascii', 0, 6) === 'GIF87a',
    'image/webp': () => head.toString('ascii', 0, 4) === 'RIFF' && head.toString('ascii', 8, 12) === 'WEBP',
    'video/mp4': () => buffer.includes(Buffer.from('ftyp')),
    'video/webm': () => head[0] === 0x1A && head[1] === 0x45 && head[2] === 0xDF && head[3] === 0xA3,
  };
  if (!sigs[mime]) return false;
  try { return sigs[mime](); } catch { return false; }
}

const storage = multer.diskStorage({
  destination: (req, file, cb) => cb(null, UPLOAD_DIR),
  filename: (req, file, cb) => {
    const ext = path.extname(file.originalname).toLowerCase();
    cb(null, crypto.randomUUID() + ext);
  },
});

function fileFilter(req, file, cb) {
  const ext = path.extname(file.originalname).toLowerCase();
  if (!ALLOWED_EXT.includes(ext)) {
    return cb(new Error('不支持的文件类型，仅允许: ' + ALLOWED_EXT.join(', ')));
  }
  cb(null, true);
}

const upload = multer({
  storage,
  fileFilter,
  limits: {
    fileSize: 50 * 1024 * 1024,
    files: 5,
  },
});

function finalizeUpload(req, res, next) {
  if (!req.files || req.files.length === 0) return next();
  for (const file of req.files) {
    const buf = fs.readFileSync(file.path);
    if (!ALLOWED_MIME[file.mimetype]) {
      fs.unlinkSync(file.path);
      return res.status(400).json({ error: `不支持的文件类型: ${file.mimetype}` });
    }
    if (!validateMagicBytes(buf, file.mimetype)) {
      fs.unlinkSync(file.path);
      return res.status(400).json({ error: '文件内容与声明类型不符，可能是恶意文件' });
    }
  }
  next();
}

module.exports = { upload, finalizeUpload, validateMagicBytes, UPLOAD_DIR, ALLOWED_MIME };