Firebase_Algolia_Functions.ts

// ABOUT:  This is how you import and sync your Firestore data in Algolia via Firebase functions. 
// You need NodeJS and NPM installed prior on your dev PC and have created your Algolia and firebase project(s).

// Open terminal/cmd type in (NOTE: Use TypeScript):
// npm install -g firebase-tools
// firebase login
// firebase init
// npm install algoliasearch --save
// firebase functions:config:set algolia.appid="YOUR_APP_ID" algolia.apikey="YOUR_API_KEY"
// Open 'functions/src/index.ts' with VSCode/Atom/NotePad and put this code in it.
// In terminal/cmd type in 'firebase deploy' to make it go live. This process can be kinda slow at times.

import * as functions from 'firebase-functions';
import * as admin from 'firebase-admin';
import algoliasearch from 'algoliasearch';

// Set up Firestore.
admin.initializeApp();
const db = admin.firestore();

// Set up Algolia.
// The app id and API key are coming from the cloud functions environment, as we set up in Part 1, Step 3.
const algoliaClient = algoliasearch(functions.config().algolia.appid, functions.config().algolia.apikey);
const collectionIndex = algoliaClient.initIndex('ALGOLIA_INDEX_NAME_HERE');

// HTTP request to manually add index to Algolia
export const sendCollectionToAlgolia = functions.https.onRequest(async (req, res) => {
	// This array will contain all records to be indexed in Algolia.
	const algoliaRecords : any[] = [];

	// Retrieve all documents from the COLLECTION collection.
	const querySnapshot = await db.collection('FIRESTORE_COLLECTION_NAME_HERE').get();

	querySnapshot.docs.forEach(doc => {
		const document = doc.data();
        // Essentially, you want your records to contain any information that facilitates search, 
        // display, filtering, or relevance. Otherwise, you can leave it out.
        const record = {
            objectID: doc.id,
            title: document.title,
			content: document.content
        };

        algoliaRecords.push(record);
    });

    collectionIndex.saveObjects(algoliaRecords).wait().then(() => {
        res.status(200).send("topics was indexed to Algolia successfully.");
    });
	
});

// Automatic request on firebase doc update
export const algoliaTopicsSync = functions
  .firestore.document(`FIRESTORE_COLLECTION_NAME_HERE/{docId}`).onWrite(async (change, _context) => {
    const oldData = change.before
    const newData = change.after
    const data = newData.data()
    const objectID = newData.id

    if (!oldData.exists && newData.exists) {
        // creating
        return collectionIndex.saveObject(Object.assign({}, {
          objectID
        }, data))
      } else if (!newData.exists && oldData.exists) {
        // deleting
        return collectionIndex.deleteObject(objectID)
      } else  {
        // updating
        return collectionIndex.saveObject(Object.assign({}, {
          objectID
        }, data))
    }
})