Added central user credentials management

lib/model/accountData.dart

@@ -0,0 +1,78 @@
+import 'dart:async';
+
+import 'package:flutter/cupertino.dart';
+import 'package:provider/provider.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'accountModel.dart';
+
+class AccountData {
+  static const _usernameField = "username";
+  static const _passwordField = "password";
+  
+  static final AccountData _instance = AccountData._construct();
+  final Future<SharedPreferences> _storage = SharedPreferences.getInstance();
+  Completer<void> _populated = Completer();
+
+  factory AccountData() {
+    return _instance;
+  }
+
+  AccountData._construct() {
+    _updateFromStorage();
+  }
+
+  String? _username;
+  String? _password;
+
+  String getUsername() {
+    if(_username == null) throw Exception("Username not initialized");
+    return _username!;
+  }
+
+  String getPassword() {
+    if(_password == null) throw Exception("Password not initialized");
+    return _password!;
+  }
+
+  Future<void> setData(BuildContext context, String username, String password) async {
+    SharedPreferences storage = await _storage;
+
+    storage.setString(_usernameField, username);
+    storage.setString(_passwordField, password);
+    await _updateFromStorage();
+  }
+
+  void removeData(BuildContext context) async {
+    _populated = Completer();
+    Provider.of<AccountModel>(context, listen: false).setState(AccountModelState.loggedOut);
+
+    SharedPreferences storage = await _storage;
+    storage.remove(_usernameField);
+    storage.remove(_passwordField);
+  }
+
+  Future<void> _updateFromStorage() async {
+    SharedPreferences storage = await _storage;
+    await storage.reload();
+    if(storage.containsKey(_usernameField) && storage.containsKey(_passwordField)) {
+      _username = storage.getString(_usernameField);
+      _password = storage.getString(_passwordField);
+      _populated.complete();
+    }
+  }
+
+  Future<bool> waitForPopulation() async {
+    await _populated.future;
+    return isPopulated();
+  }
+
+  bool isPopulated() {
+    return _username != null && _password != null;
+  }
+
+  String buildHttpAuthString() {
+    if(!isPopulated()) throw Exception("AccountData (e.g. username or password) is not initialized!");
+    return "$_username:$_password";
+  }
+}

lib/model/accountModel.dart

@@ -1,17 +1,17 @@
 import 'package:flutter/cupertino.dart';
 
 class AccountModel extends ChangeNotifier {
-  bool _isLoggedIn = false;
+  AccountModelState _accountState = AccountModelState.undefined;
+  AccountModelState get state => _accountState;
 
-  bool get isLoggedIn => _isLoggedIn;
-
-  void logout() {
-    _isLoggedIn = false;
+  void setState(AccountModelState state) {
+    _accountState = state;
     notifyListeners();
   }
+}
 
-  void login() {
-    _isLoggedIn = true;
-    notifyListeners();
-  }
+enum AccountModelState {
+  undefined,
+  loggedIn,
+  loggedOut,
 }