feat: 添加分类统计功能，支持获取月度和年度预算统计信息

Service/BudgetService.cs

@@ -7,6 +7,11 @@ public interface IBudgetService
     Task<BudgetResult?> GetStatisticsAsync(long id, DateTime? referenceDate = null);
 
     Task<string> ArchiveBudgetsAsync(int year, int month);
+
+    /// <summary>
+    /// 获取指定分类的统计信息（月度和年度）
+    /// </summary>
+    Task<BudgetCategoryStats> GetCategoryStatsAsync(BudgetCategory category, DateTime? referenceDate = null);
 }
 
 public class BudgetService(
@@ -64,6 +69,92 @@ public class BudgetService(
         return BudgetResult.FromEntity(budget, currentAmount, referenceDate);
     }
 
+    public async Task<BudgetCategoryStats> GetCategoryStatsAsync(BudgetCategory category, DateTime? referenceDate = null)
+    {
+        var budgets = (await budgetRepository.GetAllAsync()).ToList();
+        var refDate = referenceDate ?? DateTime.Now;
+
+        var result = new BudgetCategoryStats();
+
+        // 获取月度统计
+        result.Month = await CalculateCategoryStatsAsync(budgets, category, BudgetPeriodType.Month, refDate);
+
+        // 获取年度统计
+        result.Year = await CalculateCategoryStatsAsync(budgets, category, BudgetPeriodType.Year, refDate);
+
+        return result;
+    }
+
+    private async Task<BudgetStatsDto> CalculateCategoryStatsAsync(
+        List<BudgetRecord> budgets,
+        BudgetCategory category,
+        BudgetPeriodType statType,
+        DateTime referenceDate)
+    {
+        var result = new BudgetStatsDto
+        {
+            PeriodType = statType,
+            Rate = 0,
+            Current = 0,
+            Limit = 0,
+            Count = 0
+        };
+
+        // 获取当前分类下所有未停止的预算
+        var relevant = budgets
+            .Where(b => b.Category == category && !b.IsStopped)
+            .ToList();
+
+        if (relevant.Count == 0)
+        {
+            return result;
+        }
+
+        result.Count = relevant.Count;
+        decimal totalCurrent = 0;
+        decimal totalLimit = 0;
+
+        foreach (var budget in relevant)
+        {
+            // 限额折算
+            var itemLimit = budget.Limit;
+            if (statType == BudgetPeriodType.Month && budget.Type == BudgetPeriodType.Year)
+            {
+                // 月度视图下，年度预算不参与限额计算
+                itemLimit = 0;
+            }
+            else if (statType == BudgetPeriodType.Year && budget.Type == BudgetPeriodType.Month)
+            {
+                // 年度视图下，月度预算折算为年度
+                itemLimit = budget.Limit * 12;
+            }
+            totalLimit += itemLimit;
+
+            // 当前值累加
+            var currentAmount = await CalculateCurrentAmountAsync(budget, referenceDate);
+            if (budget.Type == statType)
+            {
+                totalCurrent += currentAmount;
+            }
+            else
+            {
+                // 如果周期不匹配
+                if (statType == BudgetPeriodType.Year && budget.Type == BudgetPeriodType.Month)
+                {
+                    // 在年度视图下，月度预算计入其当前值（作为对年度目前的贡献）
+                    totalCurrent += currentAmount;
+                }
+                // 月度视图下，年度预算的 current 不计入
+            }
+        }
+
+        result.Limit = totalLimit;
+        result.Current = totalCurrent;
+        result.Rate = totalLimit > 0 ? (totalCurrent / totalLimit) * 100 : 0;
+
+        return result;
+    }
+
     public async Task<string> ArchiveBudgetsAsync(int year, int month)
     {
         var referenceDate = new DateTime(year, month, 1);
@@ -393,18 +484,22 @@ public class BudgetService(
             Category = BudgetCategory.Savings,
             Type = periodType,
             Limit = incomeLimitAtPeriod - expenseLimitAtPeriod,
-            StartDate = periodType == BudgetPeriodType.Year ? new DateTime(date.Year, 1, 1) : new DateTime(date.Year, date.Month, 1),
+            StartDate = periodType == BudgetPeriodType.Year 
+                ? new DateTime(date.Year, 1, 1) 
+                : new DateTime(date.Year, date.Month, 1),
             SelectedCategories = savingsCategories
         };
 
         // 计算实际发生的 收入 - 支出
-        var incomeHelper = new BudgetRecord { Category = BudgetCategory.Income, Type = periodType, StartDate = virtualBudget.StartDate, SelectedCategories = savingsCategories };
-        var expenseHelper = new BudgetRecord { Category = BudgetCategory.Expense, Type = periodType, StartDate = virtualBudget.StartDate, SelectedCategories = savingsCategories };
+        var current = await CalculateCurrentAmountAsync(new BudgetRecord
+        {
+            Category = virtualBudget.Category,
+            Type = virtualBudget.Type,
+            SelectedCategories = virtualBudget.SelectedCategories,
+            StartDate = virtualBudget.StartDate,
+        }, date);
 
-        var actualIncome = await CalculateCurrentAmountAsync(incomeHelper, date);
-        var actualExpense = await CalculateCurrentAmountAsync(expenseHelper, date);
-
-        return BudgetResult.FromEntity(virtualBudget, actualIncome - actualExpense, date, description.ToString());
+        return BudgetResult.FromEntity(virtualBudget, current, date, description.ToString());
     }
 }
 
@@ -459,3 +554,49 @@ public record BudgetResult
         };
     }
 }
+/// <summary>
+/// 预算统计结果 DTO
+/// </summary>
+public class BudgetStatsDto
+{
+    /// <summary>
+    /// 统计周期类型（Month/Year）
+    /// </summary>
+    public BudgetPeriodType PeriodType { get; set; }
+
+    /// <summary>
+    /// 使用率百分比（0-100）
+    /// </summary>
+    public decimal Rate { get; set; }
+
+    /// <summary>
+    /// 实际金额
+    /// </summary>
+    public decimal Current { get; set; }
+
+    /// <summary>
+    /// 目标/限额金额
+    /// </summary>
+    public decimal Limit { get; set; }
+
+    /// <summary>
+    /// 预算项数量
+    /// </summary>
+    public int Count { get; set; }
+}
+
+/// <summary>
+/// 分类统计结果
+/// </summary>
+public class BudgetCategoryStats
+{
+    /// <summary>
+    /// 月度统计
+    /// </summary>
+    public BudgetStatsDto Month { get; set; } = new();
+
+    /// <summary>
+    /// 年度统计
+    /// </summary>
+    public BudgetStatsDto Year { get; set; } = new();
+}