The token that ran out

import express from 'express';

// Glass Garden gives every instance its own PORT, because they all share one machine here.
// In a real deployment they would each be on their own machine, and could all listen on the same port.
const port = Number(process.env.PORT);
if (!port) {
  throw new Error('PORT is not set');
}

// Named for the node it comes from, so connecting something else here would not change it.
// The Config tab lists every variable this instance is launched with
const carrier = process.env.CARRIER_URL;
if (!carrier) {
  throw new Error('CARRIER_URL is not set. Connect this instance group to Carrier.');
}

// The Carrier answers a rate request only when it carries an access token
async function accessToken() {
  const response = await fetch(`${carrier}/token`, { method: 'POST' });
  if (!response.ok) {
    throw new Error(`The Carrier answered ${response.status} to a token request`);
  }
  const { access_token } = await response.json();
  return access_token;
}

const app = express();
app.use(express.json());

app.post('/quotes', async (req, res) => {
  const { parcel } = req.body;

  const token = await accessToken();
  const response = await fetch(`${carrier}/rates?parcel=${parcel}`, {
    headers: { authorization: `Bearer ${token}` }
  });
  if (!response.ok) {
    throw new Error(`The Carrier answered ${response.status} for parcel ${parcel}`);
  }

  const { rate } = await response.json();
  res.json({ parcel, shipping: rate });
});

// Express hands a rejected handler here. A parcel that could not be priced is this server
// failing its caller, whoever was at fault behind it
app.use((error, req, res, next) => {
  console.error(error.message);
  res.status(502).type('text/plain').send(`${error.message}\n`);
});

app.listen(port, () => {
  console.log(`Server running on http://localhost:${port}`);
});