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 if user document exists
              future: _checkUserExists(),
              builder: (context, snapshot) {
                if (snapshot.connectionState == ConnectionState.waiting) {
                  return const CircularProgressIndicator();
                } else if (snapshot.hasData && snapshot.data == true) {
                  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 of (snapshot.hasError)
                        return const UserDataPage(isRegProcess: true);
                      }
                    },
                  );
                } else {
                  // should user entry not exist, recreate it and force logout
                  _createUserEntry();
                  FirebaseAuth.instance.signOut();
                  return const LoginOrRegister();
                }
              },
            );
          } else {
            return const LoginOrRegister();
          }
        },
      ),
    );
  }

  Future<bool> _checkUserExists() async {
    // return true to avoid unneeded read access to database
    return true;
    /* enable code to check for deleted users
    try {
      String currentUserId = AuthService().getCurrentUser()!.uid;
      final userDoc = await FirebaseFirestore.instance
          .collection(Constants.dbCollectionUsers)
          .doc(currentUserId)
          .get();
      return userDoc.exists;

    } catch (e) {
      print(e.toString());
      return false;
    }
    */
  }

  Future<void> _createUserEntry() async {
    try {
      var currentUser = AuthService().getCurrentUser();
      String currentUserId = currentUser!.uid;
      String email = currentUser.email!;

      await FirebaseFirestore.instance
          .collection(Constants.dbCollectionUsers)
          .doc(currentUserId)
          .set({
        'uid': currentUserId,
        'email': email,
      });
    } catch (e) {
      print("Error creating user document: $e");
    }
  }

  Future<bool> _checkCollectionsExist() async {
    try {
      bool languagesExist =
          await _checkUsersCollectionExists(Constants.dbCollectionLanguages);
      bool locationsExist =
          await _checkUsersCollectionExists(Constants.dbCollectionLocations);
      return languagesExist && locationsExist;
    } catch (e) {
      print(e.toString());
      return false;
    }
  }

  Future<bool> _checkUsersCollectionExists(String collectionName) async {
    try {
      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;
    } catch (e) {
      print(e.toString());
      return false;
    }
  }
}