feat(proj): init

mobile/lib/features/budgets/budgets_controller.dart

@@ -0,0 +1,137 @@
+import 'package:flutter/foundation.dart';
+import 'package:please_pay_me/core/state/async_value.dart';
+import 'package:please_pay_me/data/api/api_client.dart';
+import 'package:please_pay_me/data/models/budget.dart';
+import 'package:please_pay_me/data/repositories/repositories.dart';
+
+/// Source of truth for budgets: the overview, the budget list and the expense
+/// form all read the selected envelope from here.
+class BudgetsController extends ChangeNotifier {
+  BudgetsController({
+    required BudgetRepository budgets,
+    required ExpenseRepository expenses,
+  })  : _budgets = budgets,
+        _expenses = expenses;
+
+  final BudgetRepository _budgets;
+  final ExpenseRepository _expenses;
+
+  AsyncValue<List<BudgetStatus>> _state = const AsyncValue.loading();
+  bool _mutating = false;
+
+  AsyncValue<List<BudgetStatus>> get state => _state;
+
+  /// True while a write is in flight — used to disable buttons.
+  bool get isMutating => _mutating;
+
+  List<BudgetStatus> get items => _state.valueOrNull ?? const [];
+
+  /// Currently selected envelope; `null` when the user has no budgets at all.
+  BudgetStatus? get selected {
+    final all = items;
+    if (all.isEmpty) return null;
+    for (final status in all) {
+      if (status.selected) return status;
+    }
+    return all.first;
+  }
+
+  bool get hasBudgets => items.isNotEmpty;
+
+  Future<void> load({bool silent = false}) async {
+    if (!silent) {
+      _state = const AsyncValue.loading();
+      notifyListeners();
+    }
+
+    try {
+      _state = AsyncValue.data(await _budgets.list());
+    } on ApiException catch (error) {
+      _state = AsyncValue.error(error.message);
+    }
+    notifyListeners();
+  }
+
+  Future<String?> select(int budgetId) {
+    return _mutate(() => _budgets.select(budgetId));
+  }
+
+  Future<String?> setActive(int budgetId, {required bool isActive}) {
+    return _mutate(() => _budgets.setActive(budgetId, isActive: isActive));
+  }
+
+  Future<String?> create({
+    required String name,
+    required double totalAmount,
+    required DateTime endDate,
+    DateTime? startDate,
+  }) {
+    return _mutate(
+      () => _budgets.create(
+        name: name,
+        totalAmount: totalAmount,
+        endDate: endDate,
+        startDate: startDate,
+      ),
+    );
+  }
+
+  Future<String?> update({
+    required int budgetId,
+    String? name,
+    double? totalAmount,
+    DateTime? endDate,
+    DateTime? startDate,
+    bool resetExpenses = false,
+  }) {
+    return _mutate(
+      () => _budgets.update(
+        budgetId: budgetId,
+        name: name,
+        totalAmount: totalAmount,
+        endDate: endDate,
+        startDate: startDate,
+        resetExpenses: resetExpenses,
+      ),
+    );
+  }
+
+  Future<String?> delete(int budgetId) => _mutate(() => _budgets.delete(budgetId));
+
+  Future<String?> addExpense({
+    required double amount,
+    String? note,
+    DateTime? spentAt,
+    int? budgetId,
+  }) {
+    return _mutate(
+      () => _expenses.create(
+        amount: amount,
+        note: note,
+        spentAt: spentAt,
+        budgetId: budgetId ?? selected?.budget.id,
+      ),
+    );
+  }
+
+  Future<String?> undoLastExpense() {
+    return _mutate(() => _expenses.undoLast(budgetId: selected?.budget.id));
+  }
+
+  /// Runs a write, reloads the list and returns an error message or `null`.
+  Future<String?> _mutate(Future<void> Function() action) async {
+    _mutating = true;
+    notifyListeners();
+
+    try {
+      await action();
+      await load(silent: true);
+      return null;
+    } on ApiException catch (error) {
+      return error.message;
+    } finally {
+      _mutating = false;
+      notifyListeners();
+    }
+  }
+}