//middleware
app.use('/', (req, res, next) => {
  if (req.method === 'GET' || req.method === 'POST') {
    return next(req, res);
  } else {
    return res.status(400).send('Only POST and GET method allowed');
  }
});

//GET endpoint
app.get('/', (req, res) => {
  const ua = req.headers['user-agent'];
  res.render('index', { //index is html template
    ua,
    time: Date.now()
  });
});

//POST endpoint
app.post('/', (req, res) => {
  const {echo} = req.body;
  if (echo) {
    const ua = req.headers['user-agent'];
    res.render('index', {
      ua,
      time: Date.now(),
      echo
    });
  } else {
    res.status(400).send('\"echo\" field is missing');
  }
})