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lib/api/budget_api.dart

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+import 'package:dio/dio.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../core/network/api_exception.dart';
+import '../core/network/dio_client.dart';
+import '../models/budget.dart';
+
+final budgetApiProvider = Provider<BudgetApi>((ref) => BudgetApi(ref.watch(dioProvider)));
+
+/// 预算接口（后端只提供当月预算）
+class BudgetApi {
+  final Dio _dio;
+
+  BudgetApi(this._dio);
+
+  /// 获取当月预算。
+  ///
+  /// 未设置预算时后端可能返回 204 / 空 body，此时返回 [BudgetInfo.empty]
+  /// 而不是抛错——否则首页会因为"没设预算"而进入错误态。
+  Future<BudgetInfo> getBudget() async {
+    try {
+      final res = await _dio.get('/budgets');
+      return _parse(res.data);
+    } on DioException catch (e) {
+      final err = e.error;
+      throw err is ApiException ? err : ApiException(-1, '预算加载失败');
+    }
+  }
+
+  /// 设置/修改当月预算（每月生效，可随时修改）。
+  /// 后端自动填充年月，amount 必须 >= 0。
+  Future<BudgetInfo> setCurrentBudget(double amount) async {
+    try {
+      final res = await _dio.put('/budgets/current', data: {'amount': amount});
+      return _parse(res.data);
+    } on DioException catch (e) {
+      final err = e.error;
+      throw err is ApiException ? err : ApiException(-1, '预算保存失败');
+    }
+  }
+
+  BudgetInfo _parse(Object? data) {
+    if (data == null) return BudgetInfo.empty;
+    if (data is Map<String, dynamic>) return BudgetInfo.fromJson(data);
+    if (data is Map && data['data'] is Map) {
+      return BudgetInfo.fromJson(Map<String, dynamic>.from(data['data'] as Map));
+    }
+    return BudgetInfo.empty;
+  }
+}