feat: add coupon support to orders and create user_coupons model

- Added CouponID field to Order model to track used coupons.
- Updated order query generation to include CouponID.
- Introduced UserCoupon model to manage user coupon associations.
- Implemented query methods for UserCoupon to facilitate CRUD operations.
- Updated query context and default query setup to include UserCoupon.

backend/app/services/order.go

@@ -91,11 +91,30 @@ func (s *order) Create(ctx context.Context, form *transaction_dto.OrderCreateFor
 
 	price, err := models.ContentPriceQuery.WithContext(ctx).Where(models.ContentPriceQuery.ContentID.Eq(cid)).First()
 	if err != nil {
-		// If price missing, treat as error? Or maybe 0?
-		// Better to require price record.
 		return nil, errorx.ErrDataCorrupted.WithCause(err).WithMsg("价格信息缺失")
 	}
 
+	amountOriginal := price.PriceAmount
+	var amountDiscount int64 = 0
+	var couponID int64 = 0
+
+	// Validate Coupon
+	if form.UserCouponID != "" {
+		ucid := cast.ToInt64(form.UserCouponID)
+		discount, err := Coupon.Validate(ctx, uid, ucid, amountOriginal)
+		if err != nil {
+			return nil, err
+		}
+		amountDiscount = discount
+
+		uc, err := models.UserCouponQuery.WithContext(ctx).Where(models.UserCouponQuery.ID.Eq(ucid)).First()
+		if err == nil {
+			couponID = uc.CouponID
+		}
+	}
+
+	amountPaid := amountOriginal - amountDiscount
+
 	// 2. Create Order (Status: Created)
 	order := &models.Order{
 		TenantID:       content.TenantID,
@@ -103,27 +122,46 @@ func (s *order) Create(ctx context.Context, form *transaction_dto.OrderCreateFor
 		Type:           consts.OrderTypeContentPurchase,
 		Status:         consts.OrderStatusCreated,
 		Currency:       consts.Currency(price.Currency),
-		AmountOriginal: price.PriceAmount,
-		AmountDiscount: 0,
-		AmountPaid:     price.PriceAmount,
+		AmountOriginal: amountOriginal,
+		AmountDiscount: amountDiscount,
+		AmountPaid:     amountPaid,
+		CouponID:       couponID,
 		IdempotencyKey: uuid.NewString(),
 		Snapshot:       types.NewJSONType(fields.OrdersSnapshot{}),
 	}
 
-	if err := models.OrderQuery.WithContext(ctx).Create(order); err != nil {
-		return nil, errorx.ErrDatabaseError.WithCause(err)
-	}
+	err = models.Q.Transaction(func(tx *models.Query) error {
+		if err := tx.Order.WithContext(ctx).Create(order); err != nil {
+			return err
+		}
 
-	// 3. Create Order Item
-	item := &models.OrderItem{
-		TenantID:      content.TenantID,
-		UserID:        uid,
-		OrderID:       order.ID,
-		ContentID:     cid,
-		ContentUserID: content.UserID,
-		AmountPaid:    order.AmountPaid,
-	}
-	if err := models.OrderItemQuery.WithContext(ctx).Create(item); err != nil {
+		// 3. Create Order Item
+		item := &models.OrderItem{
+			TenantID:      content.TenantID,
+			UserID:        uid,
+			OrderID:       order.ID,
+			ContentID:     cid,
+			ContentUserID: content.UserID,
+			AmountPaid:    amountPaid,
+		}
+		if err := tx.OrderItem.WithContext(ctx).Create(item); err != nil {
+			return err
+		}
+
+		// Mark Coupon Used
+		if form.UserCouponID != "" {
+			if err := Coupon.MarkUsed(ctx, tx, cast.ToInt64(form.UserCouponID), order.ID); err != nil {
+				return err
+			}
+		}
+
+		return nil
+	})
+
+	if err != nil {
+		if _, ok := err.(*errorx.AppError); ok {
+			return nil, err
+		}
 		return nil, errorx.ErrDatabaseError.WithCause(err)
 	}