Flutter Cloud Messaging: how to send notification from the app (not from firebase console) - flutter

Question

Is it possible to send the notification from within the app instead of a cloud function on firebase?
The reason is, I want to do something similar to: FCM Push Notifications for Flutter, where they have this function that will be deployed to firebase:
export const sendToTopic = functions.firestore
.document('puppies/{puppyId}')
.onCreate(async snapshot => {
const puppy = snapshot.data();
const payload: admin.messaging.MessagingPayload = {
notification: {
title: 'New Puppy!',
body: `${puppy.name} is ready for adoption`,
icon: 'your-icon-url',
click_action: 'FLUTTER_NOTIFICATION_CLICK' // required only for onResume or onLaunch callbacks
}
};
return fcm.sendToTopic('puppies', payload);
});
this method works as intended on firebase cloud functions, however I need the path
.document('puppies/{puppyId}')
to be dynamic depending on which chatroom a user is in, so he would get a notification everytime i new message is send, so the 'chatroom22' would be a variable:
.document('chatroom22/{roomId}')
So is it possible to do this in the app-code, or can this be done in the deployed function?
In response to Doug Stevensons answer
Okay, that makes sence, and works. However, now everybody get the notifications. I want only the people in a given chatroom to receive the notification. I've tried something like this, where the users device token is saved for a given chat-room, then I want to notiffy all those tokens:
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().functions);
var newData;
exports.myTrigger = functions.firestore.document('messages/{messageId}/room/{roomId}/message/{messageId2}').onCreate(async (snapshot, context) => {
//
if (snapshot.empty) {
console.log('No Devices');
return;
}
newData = snapshot.data();
const deviceIdTokens = await admin
.firestore()
.collection('messages/{messageId}/room/{roomId}/tokens/{tokenId}')
.get();
var tokens = [];
for (var token of deviceIdTokens.docs) {
tokens.push(token.data().device_token);
}
var payload = {
notification: {
title: `${newData.sender}`,
body: `${newData.message}`,
sound: 'default',
},
data: {
push_key: 'Push Key Value',
key1: newData.message,
},
};
try {
const response = await admin.messaging().sendToDevice(tokens, payload);
console.log('Notification sent successfully');
} catch (err) {
console.log(err);
}
});
But it doesnt seem to work with wildcards.. how can I get the specific destination for each chatroom?

Answer 1

You can use a wildcard for the collection in the path:
functions.firestore.document('{collectionId}/{documentId}')
But this will trigger for all documents in all top-level collecitons, which is probably not what you want.
In fact, using variable names for top-level collections is actually not the preferred way to model data in Firestore. Consider instead having a top-level collection for all rooms, then use subcollections to contain their messages. If you do that, then you function becomes more more clearly defined as:
functions.firestore.document('rooms/{roomId}/messages/{messageId}')
Cloud Fuctions only allows wildcards for full path segments like this. There are no other patterns or regular expressions.