提取修改猪群数量逻辑

internal/domain/pig/pig_batch.go

@@ -24,6 +24,8 @@ var (
 	ErrPenNotFound = errors.New("指定的猪栏不存在")
 	// ErrPenNotAssociatedWithBatch 表示猪栏未与该批次关联
 	ErrPenNotAssociatedWithBatch = errors.New("猪栏未与该批次关联")
+	// ErrInvalidOperation 非法操作
+	ErrInvalidOperation = errors.New("非法操作")
 )
 
 // --- 领域服务接口 ---
@@ -51,4 +53,6 @@ type PigBatchService interface {
 	SellPigs(batchID uint, quantity int, unitPrice float64, tatalPrice float64, traderName string, tradeDate time.Time, remarks string, operatorID uint) error
 	// BuyPigs 处理买猪的业务逻辑。
 	BuyPigs(batchID uint, quantity int, unitPrice float64, tatalPrice float64, traderName string, tradeDate time.Time, remarks string, operatorID uint) error
+
+	UpdatePigBatchQuantity(operatorID uint, batchID uint, changeType models.LogChangeType, changeAmount int, changeReason string, happenedAt time.Time) error
 }