// Passkey (WebAuthn) sign-in that gates the whole app.
// First passkey: enrolled with a setup code (HUB_SETUP_CODE, or a random one printed to the server log).
// After that, further passkeys can only be added from an already signed-in session.
const crypto = require('crypto');
const fs = require('fs');
const path = require('path');
const {
  generateRegistrationOptions, verifyRegistrationResponse,
  generateAuthenticationOptions, verifyAuthenticationResponse,
} = require('@simplewebauthn/server');

const DATA_DIR = process.env.DATA_DIR || path.join(__dirname, 'data');
fs.mkdirSync(DATA_DIR, { recursive: true });
const readJson = (f, d) => { try { return JSON.parse(fs.readFileSync(path.join(DATA_DIR, f), 'utf8')); } catch { return d; } };
const writeJson = (f, v) => fs.writeFileSync(path.join(DATA_DIR, f), JSON.stringify(v, null, 2), { mode: 0o600 });

// Signing secret for cookies: env wins, otherwise generated once and kept so sessions survive restarts.
let secret = process.env.COOKIE_SECRET;
if (!secret) {
  secret = readJson('secret.json', {}).secret;
  if (!secret) { secret = crypto.randomBytes(32).toString('hex'); writeJson('secret.json', { secret }); }
}

const store = readJson('passkeys.json', { userId: crypto.randomBytes(32).toString('base64url'), creds: [] });
const save = () => writeJson('passkeys.json', store);

const SETUP_CODE = process.env.HUB_SETUP_CODE || crypto.randomBytes(4).toString('hex');
if (!store.creds.length) console.log(`[auth] No passkeys yet. Setup code: ${SETUP_CODE}`);

const SESSION_DAYS = 30;
const mac = v => crypto.createHmac('sha256', secret).update(v).digest('base64url');
const cookies = req => Object.fromEntries((req.headers.cookie || '').split(/; */).filter(Boolean).map(c => { const i = c.indexOf('='); return [c.slice(0, i), decodeURIComponent(c.slice(i + 1))]; }));
const isHttps = req => (req.headers['x-forwarded-proto'] || '') === 'https';

function isAuthed(req) {
  const [exp, sig] = String(cookies(req).hub_session || '').split('.');
  if (!exp || !sig) return false;
  const want = mac('s' + exp);
  return sig.length === want.length && crypto.timingSafeEqual(Buffer.from(sig), Buffer.from(want)) && Number(exp) > Date.now();
}
function startSession(req, res) {
  const exp = Date.now() + SESSION_DAYS * 864e5;
  res.setHeader('Set-Cookie', `hub_session=${exp}.${mac('s' + exp)}; Path=/; HttpOnly; SameSite=Lax; Max-Age=${SESSION_DAYS * 86400}${isHttps(req) ? '; Secure' : ''}`);
}

const challenges = new Map(); // cid -> { challenge, kind, exp }
const newChallenge = (challenge, kind) => {
  for (const [k, v] of challenges) if (v.exp < Date.now()) challenges.delete(k);
  const cid = crypto.randomBytes(16).toString('base64url');
  challenges.set(cid, { challenge, kind, exp: Date.now() + 5 * 60e3 });
  return cid;
};
const takeChallenge = (cid, kind) => {
  const c = challenges.get(cid); challenges.delete(cid);
  return c && c.kind === kind && c.exp > Date.now() ? c.challenge : null;
};

const hits = new Map(); // crude per-IP throttle on anything that checks a secret
const throttled = req => {
  const ip = (req.headers['x-forwarded-for'] || req.socket.remoteAddress || '').split(',')[0].trim();
  const h = hits.get(ip) || { n: 0, t: Date.now() };
  if (Date.now() - h.t > 60e3) { h.n = 0; h.t = Date.now(); }
  h.n++; hits.set(ip, h);
  return h.n > 10;
};

const rp = req => {
  const host = req.headers['x-forwarded-host'] || req.headers.host || 'localhost';
  const proto = req.headers['x-forwarded-proto'] || 'http';
  return { rpID: host.split(':')[0], origin: `${proto}://${host}` };
};
const equalStr = (a, b) => { const x = Buffer.from(String(a)), y = Buffer.from(String(b)); return x.length === y.length && crypto.timingSafeEqual(x, y); };

const readBody = req => new Promise((ok, no) => { const c = []; req.on('data', d => c.push(d)); req.on('end', () => ok(Buffer.concat(c).toString())); req.on('error', no); });
const send = (res, code, obj) => { res.writeHead(code, { 'content-type': 'application/json', ...(res.getHeader('Set-Cookie') ? { 'Set-Cookie': res.getHeader('Set-Cookie') } : {}) }); res.end(JSON.stringify(obj)); };

async function handle(req, res) {
  const url = new URL(req.url, 'http://x'), p = url.pathname;
  try {
    if (p === '/api/auth/state') return send(res, 200, { registered: store.creds.length > 0, authed: isAuthed(req) });
    if (p === '/api/auth/logout' && req.method === 'POST') {
      res.setHeader('Set-Cookie', 'hub_session=; Path=/; HttpOnly; SameSite=Lax; Max-Age=0');
      return send(res, 200, { ok: true });
    }
    const body = req.method === 'POST' || req.method === 'DELETE' ? JSON.parse((await readBody(req)) || '{}') : {};
    const { rpID, origin } = rp(req);

    if (p === '/api/auth/register/options' && req.method === 'POST') {
      const authed = isAuthed(req);
      if (!authed) {
        if (throttled(req)) return send(res, 429, { error: 'Too many attempts. Wait a minute.' });
        if (store.creds.length || !equalStr(body.setupCode || '', SETUP_CODE)) return send(res, 403, { error: 'Wrong setup code' });
      }
      const options = await generateRegistrationOptions({
        rpName: 'NE Hub', rpID, userName: 'NE Hub owner', userID: Buffer.from(store.userId, 'base64url'),
        attestationType: 'none',
        excludeCredentials: store.creds.map(c => ({ id: c.id, transports: c.transports })),
        authenticatorSelection: { residentKey: 'required', userVerification: 'preferred' },
      });
      return send(res, 200, { cid: newChallenge(options.challenge, authed ? 'reg-authed' : 'reg-setup'), options });
    }
    if (p === '/api/auth/register/verify' && req.method === 'POST') {
      const authed = isAuthed(req);
      if (!authed && throttled(req)) return send(res, 429, { error: 'Too many attempts. Wait a minute.' });
      const challenge = takeChallenge(body.cid, authed ? 'reg-authed' : 'reg-setup');
      if (!challenge) return send(res, 400, { error: 'Request expired, try again' });
      if (!authed && store.creds.length) return send(res, 403, { error: 'Not allowed' });
      const v = await verifyRegistrationResponse({ response: body.response, expectedChallenge: challenge, expectedOrigin: origin, expectedRPID: rpID });
      if (!v.verified) return send(res, 400, { error: 'Could not verify passkey' });
      const c = v.registrationInfo.credential;
      store.creds.push({ id: c.id, publicKey: Buffer.from(c.publicKey).toString('base64url'), counter: c.counter, transports: c.transports || [],
        name: String(body.name || 'Passkey').slice(0, 40), created: Date.now() });
      save();
      if (!authed) startSession(req, res);
      return send(res, 200, { ok: true });
    }
    if (p === '/api/auth/login/options' && req.method === 'POST') {
      if (!store.creds.length) return send(res, 400, { error: 'No passkeys set up yet' });
      const options = await generateAuthenticationOptions({ rpID, userVerification: 'preferred' });
      return send(res, 200, { cid: newChallenge(options.challenge, 'login'), options });
    }
    if (p === '/api/auth/login/verify' && req.method === 'POST') {
      if (throttled(req)) return send(res, 429, { error: 'Too many attempts. Wait a minute.' });
      const challenge = takeChallenge(body.cid, 'login');
      const cred = store.creds.find(c => c.id === body.response?.id);
      if (!challenge || !cred) return send(res, 400, { error: 'Passkey not recognised' });
      const v = await verifyAuthenticationResponse({
        response: body.response, expectedChallenge: challenge, expectedOrigin: origin, expectedRPID: rpID,
        credential: { id: cred.id, publicKey: Buffer.from(cred.publicKey, 'base64url'), counter: cred.counter, transports: cred.transports },
      });
      if (!v.verified) return send(res, 401, { error: 'Sign-in failed' });
      cred.counter = v.authenticationInfo.newCounter; cred.lastUsed = Date.now(); save();
      startSession(req, res);
      return send(res, 200, { ok: true });
    }
    // Everything below needs a signed-in session.
    if (!isAuthed(req)) return send(res, 401, { error: 'Not signed in' });
    if (p === '/api/auth/passkeys' && req.method === 'GET') {
      return send(res, 200, store.creds.map(c => ({ id: c.id, name: c.name, created: c.created, lastUsed: c.lastUsed || null })));
    }
    if (p === '/api/auth/passkeys' && req.method === 'DELETE') {
      store.creds = store.creds.filter(c => c.id !== body.id); save();
      return send(res, 200, { ok: true, remaining: store.creds.length });
    }
    send(res, 404, { error: 'Not found' });
  } catch (e) { send(res, 400, { error: e.message }); }
}

module.exports = { handle, isAuthed, secret };