Chart widget fetching data from Firebase

Hi, Community!

In the past few days i'm having troubles in undestanding how can i fetch data from Firebase to plot in a chart widget. I asked chatGPT to build a sample function, but the result put me in more doubts.

I know the data needs to be in a list format in order to be read by the chart, but... how?

The chatGPT sample code uses the "map" to return a list of 2 types. I've tried this in a custom function but doesnt worked.

Can someone help me understand how can i fetch data from Firebase to be proted in a chart widget? As a example, imagine that i need to build a bar chart that displays [X] the count of users (from Users collection) by the [Y] "created_date" field.

The chatGPT's sample code:

import 'package:cloud_firestore/cloud_firestore.dart';

Future<Map<DateTime, int>> getUserData() async {
  Map<DateTime, int> userCountByDate = {};
  QuerySnapshot snapshot = await FirebaseFirestore.instance.collection('users').get();

  snapshot.docs.forEach((doc) {
    DateTime createdTime = (doc['created_time'] as Timestamp).toDate();
    DateTime dateOnly = DateTime(createdTime.year, createdTime.month, createdTime.day);

    if (userCountByDate.containsKey(dateOnly)) {
      userCountByDate[dateOnly] = userCountByDate[dateOnly]! + 1;
    } else {
      userCountByDate[dateOnly] = 1;
    }
  });

  return userCountByDate;
}