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

const port = Number(process.env.PORT || 8080);
const publicDir = path.join(__dirname, 'public');
const publicRoot = publicDir + path.sep;
const dataDir = process.env.CALORIE_AI_DATA_DIR || path.join(__dirname, 'data');
const authFile = path.join(dataDir, 'auth.json');
const sessionCookieName = 'calorie_ai_session';
const sessionSeconds = 60 * 60 * 24 * 7;
const auth = loadAuthConfig();

const types = {
  '.html': 'text/html; charset=utf-8',
  '.css': 'text/css; charset=utf-8',
  '.js': 'application/javascript; charset=utf-8',
  '.json': 'application/json; charset=utf-8',
  '.svg': 'image/svg+xml',
};

function readBody(req) {
  return new Promise((resolve, reject) => {
    let body = '';
    req.on('data', chunk => {
      body += chunk;
      if (body.length > 12 * 1024 * 1024) {
        req.destroy();
        reject(new Error('Request body is too large'));
      }
    });
    req.on('end', () => resolve(body));
    req.on('error', reject);
  });
}

function loadAuthConfig() {
  let stored = {};
  try {
    stored = JSON.parse(fs.readFileSync(authFile, 'utf8'));
  } catch {
    stored = {};
  }

  const user = process.env.CALORIE_AI_WEB_USER || stored.user || 'admin';
  const password = process.env.CALORIE_AI_WEB_PASSWORD || stored.password || crypto.randomBytes(18).toString('base64url');
  const sessionSecret = process.env.CALORIE_AI_SESSION_SECRET || stored.sessionSecret || crypto.randomBytes(32).toString('hex');

  if (!process.env.CALORIE_AI_WEB_PASSWORD || !process.env.CALORIE_AI_SESSION_SECRET) {
    fs.mkdirSync(dataDir, { recursive: true });
    fs.writeFileSync(authFile, JSON.stringify({ user, password, sessionSecret, createdAt: new Date().toISOString() }, null, 2));
    fs.chmodSync(authFile, 0o600);
    console.log(`Calorie AI auth is stored at ${authFile}`);
  }

  return { user, password, sessionSecret };
}

function send(res, status, body, contentType = 'application/json; charset=utf-8', headOnly = false, headers = {}) {
  res.writeHead(status, {
    'content-type': contentType,
    'cache-control': 'no-store',
    'x-content-type-options': 'nosniff',
    'referrer-policy': 'same-origin',
    'x-frame-options': 'DENY',
    'content-security-policy': "default-src 'self'; img-src 'self' data: blob:; script-src 'self'; style-src 'self'; connect-src 'self'; base-uri 'self'; frame-ancestors 'none'",
    ...headers,
  });
  res.end(headOnly ? '' : body);
}

function redirect(res, location) {
  res.writeHead(302, {
    location,
    'cache-control': 'no-store',
    'referrer-policy': 'same-origin',
    'x-frame-options': 'DENY',
  });
  res.end();
}

function parseCookies(req) {
  return Object.fromEntries(String(req.headers.cookie || '').split(';').map(part => {
    const index = part.indexOf('=');
    if (index < 0) return ['', ''];
    return [part.slice(0, index).trim(), decodeURIComponent(part.slice(index + 1).trim())];
  }).filter(([key]) => key));
}

function safeEqual(left, right) {
  const leftBuffer = Buffer.from(String(left));
  const rightBuffer = Buffer.from(String(right));
  return leftBuffer.length === rightBuffer.length && crypto.timingSafeEqual(leftBuffer, rightBuffer);
}

function sign(value) {
  return crypto.createHmac('sha256', auth.sessionSecret).update(value).digest('base64url');
}

function createSession() {
  const payload = Buffer.from(JSON.stringify({ user: auth.user, exp: Date.now() + sessionSeconds * 1000 })).toString('base64url');
  return `${payload}.${sign(payload)}`;
}

function isAuthenticated(req) {
  const token = parseCookies(req)[sessionCookieName];
  if (!token) return false;
  const [payload, signature] = token.split('.');
  if (!payload || !signature || !safeEqual(sign(payload), signature)) return false;
  try {
    const decoded = JSON.parse(Buffer.from(payload, 'base64url').toString('utf8'));
    return decoded.user === auth.user && decoded.exp > Date.now();
  } catch {
    return false;
  }
}

function cookieOptions(req, maxAge = sessionSeconds) {
  const secure = req.headers['x-forwarded-proto'] === 'https' || process.env.CALORIE_AI_COOKIE_SECURE === 'true';
  return `HttpOnly; SameSite=Lax; Path=/; Max-Age=${maxAge}${secure ? '; Secure' : ''}`;
}

function publicRequest(req) {
  const url = req.url.split('?')[0];
  return (req.method === 'POST' && url === '/api/login')
    || ((req.method === 'GET' || req.method === 'HEAD') && ['/login.html', '/login.js', '/styles.css', '/favicon.svg'].includes(url));
}

function serveStatic(req, res) {
  const cleanUrl = decodeURIComponent(req.url.split('?')[0]);
  const file = cleanUrl === '/' ? '/index.html' : cleanUrl;
  const target = path.normalize(path.join(publicDir, file));
  if (!target.startsWith(publicRoot)) return send(res, 403, 'Forbidden', 'text/plain; charset=utf-8');

  fs.readFile(target, (err, data) => {
    if (err) return send(res, 404, 'Not found', 'text/plain; charset=utf-8');
    send(res, 200, data, types[path.extname(target)] || 'application/octet-stream', req.method === 'HEAD');
  });
}

async function proxyChat(req, res) {
  try {
    const payload = JSON.parse(await readBody(req));
    const baseUrl = String(payload.baseUrl || '').replace(/\/+$/, '');
    if (!/^https?:\/\//.test(baseUrl)) throw new Error('A valid API base URL is required');
    if (!payload.body || typeof payload.body !== 'object') throw new Error('Missing chat completion body');

    const headers = { 'content-type': 'application/json' };
    if (payload.apiKey) headers.authorization = `Bearer ${payload.apiKey}`;

    const upstream = await fetch(`${baseUrl}/chat/completions`, {
      method: 'POST',
      headers,
      body: JSON.stringify(payload.body),
    });
    const text = await upstream.text();
    send(res, upstream.status, text);
  } catch (error) {
    send(res, 400, JSON.stringify({ error: error.message }));
  }
}

async function login(req, res) {
  try {
    const payload = JSON.parse(await readBody(req));
    if (!safeEqual(payload.username || '', auth.user) || !safeEqual(payload.password || '', auth.password)) {
      return send(res, 401, JSON.stringify({ error: 'Invalid username or password' }));
    }

    send(res, 200, JSON.stringify({ ok: true, user: auth.user }), undefined, false, {
      'set-cookie': `${sessionCookieName}=${encodeURIComponent(createSession())}; ${cookieOptions(req)}`,
    });
  } catch (error) {
    send(res, 400, JSON.stringify({ error: error.message }));
  }
}

function logout(req, res) {
  send(res, 200, JSON.stringify({ ok: true }), undefined, false, {
    'set-cookie': `${sessionCookieName}=; ${cookieOptions(req, 0)}`,
  });
}

http.createServer((req, res) => {
  const url = req.url.split('?')[0];
  const authenticated = isAuthenticated(req);

  if (!authenticated && !publicRequest(req)) {
    if (url.startsWith('/api/')) return send(res, 401, JSON.stringify({ error: 'Authentication required' }));
    return redirect(res, '/login.html');
  }

  if (authenticated && (req.method === 'GET' || req.method === 'HEAD') && url === '/login.html') return redirect(res, '/');
  if (req.method === 'POST' && url === '/api/login') return login(req, res);
  if (req.method === 'POST' && url === '/api/logout') return logout(req, res);
  if (req.method === 'GET' && url === '/api/session') return send(res, 200, JSON.stringify({ user: auth.user }));
  if (req.method === 'POST' && req.url === '/api/chat') return proxyChat(req, res);
  if (req.method === 'GET' || req.method === 'HEAD') return serveStatic(req, res);
  send(res, 405, 'Method not allowed', 'text/plain; charset=utf-8');
}).listen(port, () => {
  console.log(`Calorie AI web listening on ${port}`);
});