part1.md

Part 1 - A basic project setup

• Create a project in the Firebase console

https://console.firebase.google.com/

• Put the rates node into the database:

"rates" : {
   "usd" : 1.175,
   "czk" : 25.88,
   "pln" : 4.303,
   "rub" : 68.52
}

• Install and set up the Firebase CLI tools (if not yet done):

npm install -g firebase-tools
firebase login

• Initialize the Firebase project:

firebase init functions

• Open index.js (this is where functions are added) and write testPush function for later use:

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

exports.testPush = functions.https.onRequest((req, res) => {
   admin.database().ref('/conversions')
       .push({ eur: parseFloat(req.query.eur) })
       .then(snap => { res.status(200).send("done") })
})

• Deploy this function with the CLI tools:

firebase deploy --only function

• Trigger the test function to check if it works by calling:

https://<project-link>/testPush?eur=100

• Add the function that does the conversion:

exports.convert = functions.database.ref('/conversions/{conversionID}').onWrite(event => {
    const conversion = event.data.val()
    // Do not handle already converted values
    if (conversion.timestamp !== undefined) return

    const eur = conversion.eur
    admin.database().ref('/rates').once('value').then(ratesSnapshot => {
        const rates = ratesSnapshot.val()
        const result = {
            eur: eur,
            usd: eur * rates.usd,
            czk: eur * rates.czk,
            pln: eur * rates.pln,
            rub: eur * rates.rub,
            timestamp: Date.now()
        }
        admin.database().ref('/conversions').child(event.params.conversionID).set(result)
    })
})

Links:

• https://firebase.google.com/docs/functions/get-started
• https://firebase.google.com/docs/functions/http-events
• https://firebase.google.com/docs/functions/database-events
• https://github.com/firebase/functions-samples