import { applyCors, isAllowedOrigin } from './_cors.js';

const DEFAULT_DROPBOX_SHARED_URL = 'https://www.dropbox.com/scl/fi/usa8me7ywgylrij2bt6hj/Data-Matrix.xlsx?rlkey=tsec8csrhye54u1fdvk15ped1&st=qbxxs4cn&dl=0';

function getDropboxConfig() {
  return {
    appKey: process.env.DROPBOX_APP_KEY,
    appSecret: process.env.DROPBOX_APP_SECRET,
    refreshToken: process.env.DROPBOX_REFRESH_TOKEN,
    sharedUrl: process.env.DROPBOX_SHARED_URL || DEFAULT_DROPBOX_SHARED_URL,
  };
}

function normalizeDropboxSharedUrl(sharedUrl) {
  const url = new URL(sharedUrl);
  url.searchParams.delete('dl');
  url.searchParams.delete('raw');
  url.searchParams.delete('st');
  return url.toString();
}

function buildDropboxDownloadUrl(sharedUrl) {
  const url = new URL(normalizeDropboxSharedUrl(sharedUrl));
  url.searchParams.set('raw', '1');
  return url.toString();
}

function setCors(req, res) {
  applyCors(req, res, 'GET, OPTIONS');
}

async function getAccessToken() {
  const { appKey, appSecret, refreshToken } = getDropboxConfig();
  if (!appKey || !appSecret || !refreshToken) {
    throw new Error('Dropbox auth env vars are not configured.');
  }
  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: refreshToken,
      client_id: appKey,
      client_secret: appSecret,
    })
  });
  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 && !isAllowedOrigin(origin)) {
    return res.status(403).json({ error: 'Forbidden' });
  }

  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() });
  }

  const { sharedUrl } = getDropboxConfig();
  const sharingUrlForApi = normalizeDropboxSharedUrl(sharedUrl);
  const downloadUrl = buildDropboxDownloadUrl(sharedUrl);

  // Try authenticated Dropbox API first — bypasses CDN cache so we always get the latest version.
  // Falls back to the shared URL if credentials are not configured.
  let upstream = null;
  let usedAuth = false;

  try {
    const accessToken = await getAccessToken();
    const apiRes = await fetch('https://content.dropboxapi.com/2/sharing/get_shared_link_file', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${accessToken}`,
        'Dropbox-API-Arg': JSON.stringify({ url: sharingUrlForApi }),
        'Content-Type': 'text/plain; charset=utf-8',
      },
    });
    if (apiRes.ok) {
      upstream = apiRes;
      usedAuth = true;
      console.log('Dropbox: downloaded via authenticated API (no CDN cache)');
    } else {
      const errText = await apiRes.text();
      console.warn('Dropbox API download failed, falling back to sharing link:', apiRes.status, errText.substring(0, 200));
    }
  } catch (authErr) {
    console.warn('Dropbox auth unavailable, falling back to sharing link:', authErr?.message || String(authErr));
  }

  try {
    if (!upstream) {
      upstream = await fetch(downloadUrl, {
        method: 'GET',
        headers: {
          'Cache-Control': 'no-cache',
          'Pragma': '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 (!usedAuth && 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 +
          '\n\nSet DROPBOX_SHARED_URL in Vercel if the sharing link changed.'
      );
    }

    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 || String(err)));
  }
}