So, here's the deal with Firebase Firestore: it doesn't come with built-in full-text search. This means you can't just ask it to "find all documents where field 'x' contains 'y'". Instead, Firestore is great for exact-match and range queries. But don't worry! You can still get full-text search working by teaming up with third-party services.

Algolia is a fantastic full-text search engine that plays nicely with Firestore. The basic idea is to store your data in Firestore and then sync it with Algolia, which will handle all your search needs. Let's break it down:

Step 1: Create an Algolia Account and Install Required Libraries

First things first, sign up for an Algolia account. Then, in your Firebase Cloud functions folder, install these libraries:

npm install algoliasearch@3.35.1
npm install firebase-functions@3.14.1
npm install firebase-admin@9.5.0

Step 2: Sync Firestore data with Algolia

Next, set up a Cloud Function in Firestore to listen to the documents you want to make searchable:

const algoliasearch = require('algoliasearch');
const admin = require('firebase-admin');

admin.initializeApp();
const db = admin.firestore();

const algoliaClient = algoliasearch(ALGOLIA_ID, ALGOLIA_ADMIN_KEY);
const collectionIndex = algoliaClient.initIndex('collection');

exports.addToIndex = functions.firestore.document('collection/{docId}')
    .onCreate(snapshot => {
        const data = snapshot.data();
        const objectID = snapshot.id;

        return collectionIndex.saveObject({ ...data, objectID });
});

exports.updateIndex = functions.firestore.document('collection/{docId}')
    .onUpdate((change) => {
        const newData = change.after.data();
        const objectID = change.after.id;
        return collectionIndex.saveObject({ ...newData, objectID });
});

exports.removeFromIndex = functions.firestore.document('collection/{docId}')
    .onDelete(snapshot =>
        collectionIndex.deleteObject(snapshot.id));

Step 3: Implementing Search

Now that your Firestore data is synced with Algolia, you can use Algolia's search function to do the actual searching:

const algoliaClient = algoliasearch(ALGOLIA_ID, ALGOLIA_ADMIN_KEY);
const collectionIndex = algoliaClient.initIndex('collection');

collectionIndex.search('query')
    .then(({ hits }) => {
        console.log(hits);
    })
    .catch(err => {
        console.log(err);
    });

Remember to replace 'collection' with the name of your collection.

So, while Firebase Firestore doesn't natively support full-text search, you can still get it done by using services like Algolia. The trick is to sync your Firestore data with Algolia and let Algolia handle the search queries. Just keep in mind that Algolia has a free tier, but if you use it a lot, you might need to look into their paid plans.