const DROPBOX_APP_KEY = process.env.DROPBOX_APP_KEY;
const DROPBOX_APP_SECRET = process.env.DROPBOX_APP_SECRET;
const DROPBOX_REFRESH_TOKEN = process.env.DROPBOX_REFRESH_TOKEN;

const ALLOWED_ORIGIN = 'https://craze-data-check.vercel.app';

function setCors(req, res) {
  const origin = req.headers.origin;
  if (origin === ALLOWED_ORIGIN) {
    res.setHeader('Access-Control-Allow-Origin', ALLOWED_ORIGIN);
  }
  res.setHeader('Access-Control-Allow-Methods', 'GET, OPTIONS');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type');
  res.setHeader('Vary', 'Origin');
}

async function getAccessToken() {
  const response = await fetch('https://api.dropboxapi.com/oauth2/token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      grant_type: 'refresh_token',
      refresh_token: DROPBOX_REFRESH_TOKEN,
      client_id: DROPBOX_APP_KEY,
      client_secret: DROPBOX_APP_SECRET,
    })
  });
  const data = await response.json();
  if (!data.access_token) {
    throw new Error('Failed to get access token: ' + JSON.stringify(data));
  }
  return data.access_token;
}

export default async function handler(req, res) {
  setCors(req, res);

  if (req.method === 'OPTIONS') {
    return res.status(204).end();
  }

  const origin = req.headers.origin;
  if (origin && origin !== ALLOWED_ORIGIN) {
    return res.status(403).json({ error: 'Forbidden' });
  }

  try {
    await getAccessToken();
  } catch (err) {
    console.warn('Token refresh optional failure (sharing link might still work):', err.message);
  }

  if (req.method === 'GET' && req.query.info === '1') {
    res.setHeader('Cache-Control', 'no-store, no-cache, must-revalidate, proxy-revalidate');
    res.setHeader('Pragma', 'no-cache');
    res.setHeader('Expires', '0');
    return res.json({ rev: 'new-url-v1', size: 0, server_modified: new Date().toISOString() });
  }

  try {
    const sharingUrl = 'https://www.dropbox.com/scl/fi/usa8me7ywgylrij2bt6hj/Data-Matrix.xlsx?rlkey=tsec8csrhye54u1fdvk15ped1&dl=1';
    const upstream = await fetch(sharingUrl, {
      method: 'GET',
      headers: {
        'Cache-Control': 'no-cache',
        'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36'
      }
    });

    const contentType = upstream.headers.get('content-type');
    if (contentType && contentType.includes('text/html')) {
      console.error('Dropbox returned HTML instead of file');
      return res.status(500).send('Error: El enlace de Dropbox ha devuelto una página HTML en lugar del archivo. Es probable que el enlace haya caducado o necesite ser renovado.');
    }

    if (!upstream.ok) {
      const errText = await upstream.text();
      console.error('Dropbox URL error:', upstream.status, errText);
      return res.status(upstream.status).send('Dropbox error: ' + errText);
    }

    const buffer = await upstream.arrayBuffer();
    res.setHeader('Content-Type', 'application/octet-stream');
    res.setHeader('Cache-Control', 'no-store');
    res.send(Buffer.from(buffer));
  } catch (err) {
    console.error('Dropbox proxy error:', err);
    res.status(500).send('Proxy error: ' + err.message);
  }
}