'use strict';

const coap = require('coap');

const PORT = Number(process.env.COAP_PORT) || 5683;
const HOST = process.env.COAP_HOST || '0.0.0.0';

// --- helpers ---------------------------------------------------------------

const TEXT = 'text/plain';
const JSON_FMT = 'application/json';

/** Split "/hello?name=Bob" into ["/hello", "name=Bob"]. */
function splitUrl(url) {
  const i = url.indexOf('?');
  const path = (i === -1 ? url : url.slice(0, i)).replace(/\/+$/, '') || '/';
  return [path, i === -1 ? '' : url.slice(i + 1)];
}

/** Pull a name out of "?name=Bob" style queries. */
function nameFromQuery(query) {
  return new URLSearchParams(query || '').get('name');
}

/** Pull a name out of a POST body: raw text or {"name":"Bob"}. */
function nameFromBody(buf) {
  const body = buf.toString('utf8').trim();
  if (!body) return null;
  if (body.startsWith('{')) {
    try {
      const parsed = JSON.parse(body);
      return typeof parsed.name === 'string' ? parsed.name.trim() : null;
    } catch {
      return null;
    }
  }
  return body;
}

function greet(name) {
  return `Hello, ${name && name.length ? name : 'World'}!`;
}

function send(res, code, payload, format = TEXT) {
  res.code = code;
  res.setOption('Content-Format', format);
  res.end(typeof payload === 'string' ? payload : JSON.stringify(payload));
}

// --- routes ----------------------------------------------------------------
// key: "METHOD /path"

const routes = {
  'GET /hello': (req, res) => {
    send(res, '2.05', greet(nameFromQuery(req.query)));
  },

  'POST /hello': (req, res) => {
    const name = nameFromBody(req.payload) || nameFromQuery(req.query);
    if (!name) {
      return send(res, '4.00', 'Bad Request: send a name as the payload');
    }
    send(res, '2.01', greet(name));
  },

  'GET /health': (_req, res) => {
    send(res, '2.05', { status: 'ok', uptime: Math.round(process.uptime()) }, JSON_FMT);
  },
};

// --- server ----------------------------------------------------------------

const server = coap.createServer({ type: 'udp4' });

server.on('request', (req, res) => {
  const [path, query] = splitUrl(req.url);
  req.query = query; // node-coap only gives us req.url on the server side
  const key = `${req.method} ${path}`;
  const handler = routes[key];

  console.log(`${req.method} ${req.url} from ${req.rsinfo.address}:${req.rsinfo.port}`);

  if (!handler) return send(res, '4.04', `Not Found: ${path}`);

  try {
    handler(req, res);
  } catch (err) {
    console.error('handler error:', err);
    send(res, '5.00', 'Internal Server Error');
  }
});

server.on('error', (err) => console.error('server error:', err));

server.listen(PORT, HOST, () => {
  console.log(`CoAP server (UDP) listening on coap://${HOST}:${PORT}`);
  console.log('  GET  /hello?name=Imran');
  console.log('  POST /hello   (payload: Imran  |  {"name":"Imran"})');
  console.log('  GET  /health');
});

process.on('SIGINT', () => server.close(() => process.exit(0)));