Structure of UCL Webhook API by Cloud Functions for Firebase

index.js

exports.UCL = functions.region(region).runWith(runtimeOpts)
  .https.onRequest(async (req, res) => {
  let event = req.body.events[0]
  switch (event.type) {
    case 'message':
      if (event.message.type === 'image') {
        // [8.3]
      } else if (event.message.type === 'text' && event.message.text === 'subscribe') {
        // [8.2]
      } else {
        // [8.1]
      }
      break;
    case 'postback': {
      // [8.4]
      break;
    }
  }
  return null;
});