const jwt = require('jsonwebtoken');

// Langkah 3-5 OAuth2: tukar code dengan access token, ambil profil, terbitkan JWT sendiri.
module.exports = async function handler(req, res) {
  const { GITHUB_CLIENT_ID, GITHUB_CLIENT_SECRET, JWT_SECRET } = process.env;
  if (!GITHUB_CLIENT_ID || !GITHUB_CLIENT_SECRET || !JWT_SECRET) {
    res.status(500).json({ error: 'GITHUB_CLIENT_ID / GITHUB_CLIENT_SECRET / JWT_SECRET belum diatur di environment' });
    return;
  }

  const { code, state } = req.query;

  // state sekali pakai: hapus cookie apa pun hasilnya.
  const expectedState = req.cookies.oauth_state;
  res.setHeader('Set-Cookie', 'oauth_state=; HttpOnly; SameSite=Lax; Path=/; Max-Age=0');

  if (!code) {
    res.status(400).json({ error: 'Parameter code tidak ada' });
    return;
  }
  if (!state || !expectedState || state !== expectedState) {
    res.status(400).json({ error: 'State tidak valid, ulangi login lewat /auth/login' });
    return;
  }

  try {
    const tokenRes = await fetch('https://github.com/login/oauth/access_token', {
      method: 'POST',
      headers: { Accept: 'application/json', 'Content-Type': 'application/json' },
      body: JSON.stringify({
        client_id: GITHUB_CLIENT_ID,
        client_secret: GITHUB_CLIENT_SECRET,
        code,
      }),
    });
    const { access_token, error_description } = await tokenRes.json();
    if (!access_token) {
      res.status(401).json({ error: error_description || 'Gagal menukar code dengan access token' });
      return;
    }

    const userRes = await fetch('https://api.github.com/user', {
      headers: { Authorization: `Bearer ${access_token}`, Accept: 'application/json' },
    });
    if (!userRes.ok) {
      res.status(502).json({ error: 'Gagal mengambil profil dari GitHub' });
      return;
    }
    const githubUser = await userRes.json();

    const token = jwt.sign({ username: githubUser.login }, JWT_SECRET, { expiresIn: '1h' });
    res.json({ token });
  } catch (err) {
    console.error('[OAuth error] /auth/callback:', err);
    res.status(500).json({ error: 'Terjadi kesalahan pada server, silakan coba lagi' });
  }
};