cofounderella/lib/services/auth/auth_gate.dart

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'auth_service.dart';
import 'login_or_register.dart';
import '../../constants.dart';
import '../../pages/home_page.dart';
import '../../pages/user_data_page.dart';

class AuthGate extends StatelessWidget {
  const AuthGate({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: StreamBuilder(
        stream: FirebaseAuth.instance.authStateChanges(),
        builder: (context, snapshot) {
          // check if user is logged in or not
          if (snapshot.hasData) {
            return FutureBuilder(
              // check database entries, if data is missing
              // then complete registration process
              // else go to HomePage
              future: _checkCollectionsExist(),
              builder: (context, snapshot) {
                if (snapshot.connectionState == ConnectionState.waiting) {
                  return const CircularProgressIndicator();
                } else if (snapshot.hasData && snapshot.data == true) {
                  return HomePage();
                } else {
                  // also in case (snapshot.hasError)
                  return const UserDataPage(isRegProcess: true);
                }
              },
            );
          } else {
            return const LoginOrRegister();
          }
        },
      ),
    );
  }

  Future<bool> _checkCollectionsExist() async {
    bool languagesExist =
        await _checkUsersCollectionExists(Constants.dbCollectionLanguages);
    bool locationsExist =
        await _checkUsersCollectionExists(Constants.dbCollectionLocations);
    return languagesExist && locationsExist;
  }

  Future<bool> _checkUsersCollectionExists(String collectionName) async {
    String currentUserId = AuthService().getCurrentUser()!.uid;
    final collection = FirebaseFirestore.instance
        .collection(Constants.dbCollectionUsers)
        .doc(currentUserId)
        .collection(collectionName);
    final snapshot = await collection.limit(1).get();
    return snapshot.docs.isNotEmpty;
  }
}