feat: 添加预算管理功能，包括预算的创建、查询、更新、删除及进度计算。

internal/service/budget_service.go

@@ -13,12 +13,11 @@ import (
 
 // Service layer errors for budgets
 var (
-	ErrBudgetNotFound            = errors.New("budget not found")
-	ErrBudgetInUse               = errors.New("budget is in use and cannot be deleted")
-	ErrInvalidBudgetAmount       = errors.New("budget amount must be positive")
-	ErrInvalidDateRange          = errors.New("end date must be after start date")
-	ErrInvalidPeriodType         = errors.New("invalid period type")
-	ErrCategoryOrAccountRequired = errors.New("either category or account must be specified")
+	ErrBudgetNotFound      = errors.New("budget not found")
+	ErrBudgetInUse         = errors.New("budget is in use and cannot be deleted")
+	ErrInvalidBudgetAmount = errors.New("budget amount must be positive")
+	ErrInvalidDateRange    = errors.New("end date must be after start date")
+	ErrInvalidPeriodType   = errors.New("invalid period type")
 )
 
 // BudgetInput represents the input data for creating or updating a budget
@@ -72,10 +71,7 @@ func (s *BudgetService) CreateBudget(input BudgetInput) (*models.Budget, error)
 		return nil, ErrInvalidBudgetAmount
 	}
 
-	// Validate that at least category or account is specified
-	if input.CategoryID == nil && input.AccountID == nil {
-		return nil, ErrCategoryOrAccountRequired
-	}
+	// 分类和账户都可选，支持全局预算
 
 	// Validate date range
 	if input.EndDate != nil && input.EndDate.Before(input.StartDate) {
@@ -147,10 +143,7 @@ func (s *BudgetService) UpdateBudget(userID, id uint, input BudgetInput) (*model
 		return nil, ErrInvalidBudgetAmount
 	}
 
-	// Validate that at least category or account is specified
-	if input.CategoryID == nil && input.AccountID == nil {
-		return nil, ErrCategoryOrAccountRequired
-	}
+	// 分类和账户都可选，支持全局预算
 
 	// Validate date range
 	if input.EndDate != nil && input.EndDate.Before(input.StartDate) {
@@ -222,41 +215,55 @@ func (s *BudgetService) GetBudgetProgress(userID, id uint) (*BudgetProgress, err
 	startDate, endDate := s.calculateCurrentPeriod(budget, now)
 
 	// Get spent amount for the current period
-	spent, err := s.repo.GetSpentAmount(budget, startDate, endDate)
+	currentSpent, err := s.repo.GetSpentAmount(budget, startDate, endDate)
 	if err != nil {
 		return nil, fmt.Errorf("failed to calculate spent amount: %w", err)
 	}
 
-	// Calculate effective budget amount (considering rolling budget)
+	// Calculate effective budget amount
 	effectiveAmount := budget.Amount
+	totalSpent := currentSpent
+
 	if budget.IsRolling {
-		// For rolling budgets, add the previous period's remaining balance
-		prevStartDate, prevEndDate := s.calculatePreviousPeriod(budget, now)
-		prevSpent, err := s.repo.GetSpentAmount(budget, prevStartDate, prevEndDate)
-		if err != nil {
-			return nil, fmt.Errorf("failed to calculate previous period spent: %w", err)
-		}
-		prevRemaining := budget.Amount - prevSpent
-		if prevRemaining > 0 {
-			effectiveAmount += prevRemaining
+		// 滚动预算：结余自动累加到下一周期
+		// 当期可用额度 = 总额度 - 历史支出
+
+		// 计算已过的完整周期数（不含当期）
+		periodsElapsed := s.calculatePeriodsElapsed(budget, startDate)
+
+		// 总额度 = (已过周期数 + 当期) × 单期额度
+		totalBudget := budget.Amount * float64(periodsElapsed+1)
+
+		// 获取历史支出（从预算开始到当期开始前一秒）
+		historyEnd := startDate.Add(-time.Second)
+		historySpent := 0.0
+		if historyEnd.After(budget.StartDate) {
+			historySpent, err = s.repo.GetSpentAmount(budget, budget.StartDate, historyEnd)
+			if err != nil {
+				return nil, fmt.Errorf("failed to calculate history spent: %w", err)
+			}
 		}
+
+		// 当期可用额度 = 总额度 - 历史支出
+		effectiveAmount = totalBudget - historySpent
+		totalSpent = currentSpent
 	}
 
 	// Calculate progress metrics
-	remaining := effectiveAmount - spent
+	remaining := effectiveAmount - totalSpent
 	progress := 0.0
 	if effectiveAmount > 0 {
-		progress = (spent / effectiveAmount) * 100
+		progress = (totalSpent / effectiveAmount) * 100
 	}
 
-	isOverBudget := spent > effectiveAmount
+	isOverBudget := totalSpent > effectiveAmount
 	isNearLimit := progress >= 80.0 && !isOverBudget
 
 	return &BudgetProgress{
 		BudgetID:      budget.ID,
 		Name:          budget.Name,
 		Amount:        effectiveAmount,
-		Spent:         spent,
+		Spent:         totalSpent,
 		Remaining:     remaining,
 		Progress:      progress,
 		PeriodType:    budget.PeriodType,
@@ -353,6 +360,41 @@ func (s *BudgetService) calculatePreviousPeriod(budget *models.Budget, reference
 	}
 }
 
+// calculatePeriodsElapsed 计算从预算开始日期到当前周期开始日期之间的完整周期数
+func (s *BudgetService) calculatePeriodsElapsed(budget *models.Budget, currentPeriodStart time.Time) int {
+	if currentPeriodStart.Before(budget.StartDate) || currentPeriodStart.Equal(budget.StartDate) {
+		return 0
+	}
+
+	var periods int
+	switch budget.PeriodType {
+	case models.PeriodTypeDaily:
+		periods = int(currentPeriodStart.Sub(budget.StartDate).Hours() / 24)
+
+	case models.PeriodTypeWeekly:
+		periods = int(currentPeriodStart.Sub(budget.StartDate).Hours() / (24 * 7))
+
+	case models.PeriodTypeMonthly:
+		yearDiff := currentPeriodStart.Year() - budget.StartDate.Year()
+		monthDiff := int(currentPeriodStart.Month()) - int(budget.StartDate.Month())
+		periods = yearDiff*12 + monthDiff
+
+	case models.PeriodTypeYearly:
+		periods = currentPeriodStart.Year() - budget.StartDate.Year()
+
+	default:
+		yearDiff := currentPeriodStart.Year() - budget.StartDate.Year()
+		monthDiff := int(currentPeriodStart.Month()) - int(budget.StartDate.Month())
+		periods = yearDiff*12 + monthDiff
+	}
+
+	// 确保返回非负数
+	if periods < 0 {
+		return 0
+	}
+	return periods
+}
+
 // isValidPeriodType checks if a period type is valid
 func isValidPeriodType(periodType models.PeriodType) bool {
 	switch periodType {