check stock lookup methods

Distribution/Features/Stock/IStockRepository.cs

@@ -6,6 +6,7 @@ public interface IStockRepository
 {
     // Balance
     Task<StockBalance?> GetBalanceAsync(Guid itemId, Guid locationId);
+    Task<StockBalance?> GetBalanceAsync(Guid itemId, Guid locationId, Guid? itemBatchId, Guid? itemSerialNumberId);
     Task<List<StockBalance>> GetBalancesByLocationAsync(Guid locationId, LocationType locationType);
     Task<List<StockBalance>> GetBalancesAsync(Guid? locationId, LocationType? locationType, Guid? itemId, int page, int pageSize);
     Task<int> GetBalancesCountAsync(Guid? locationId, LocationType? locationType, Guid? itemId);
@@ -20,4 +21,12 @@ public interface IStockRepository
     void UpdateMovement(StockMovement movement);
     Task<List<StockMovement>> GetMovementsAsync(Guid? locationId, Guid? itemId, MovementType? type, DateTime? from, DateTime? to, int page, int pageSize);
     Task<int> GetMovementsCountAsync(Guid? locationId, Guid? itemId, MovementType? type, DateTime? from, DateTime? to);
+
+    // Batches — a null batchNumber always creates a fresh expiry-only lot (no dedup possible on null).
+    Task<ItemBatch?> FindBatchAsync(Guid itemId, string batchNumber);
+    Task AddItemBatchAsync(ItemBatch batch);
+
+    // Serial numbers
+    Task<bool> SerialNumberExistsAsync(Guid itemId, string serialNumber);
+    Task AddItemSerialNumberAsync(ItemSerialNumber serial);
 }

Distribution/Features/Stock/StockRepository.cs

@@ -9,7 +9,14 @@ public class StockRepository(AppDBContext db) : IStockRepository
     public Task<StockBalance?> GetBalanceAsync(Guid itemId, Guid locationId) =>
         db.StockBalances
             .Include(b => b.Item)
-            .FirstOrDefaultAsync(b => b.FK_ItemId == itemId && b.LocationId == locationId);
+            .FirstOrDefaultAsync(b => b.FK_ItemId == itemId && b.LocationId == locationId
+                && b.FK_ItemBatchId == null && b.FK_ItemSerialNumberId == null);
+
+    public Task<StockBalance?> GetBalanceAsync(Guid itemId, Guid locationId, Guid? itemBatchId, Guid? itemSerialNumberId) =>
+        db.StockBalances
+            .Include(b => b.Item)
+            .FirstOrDefaultAsync(b => b.FK_ItemId == itemId && b.LocationId == locationId
+                && b.FK_ItemBatchId == itemBatchId && b.FK_ItemSerialNumberId == itemSerialNumberId);
 
     public Task<List<StockBalance>> GetBalancesByLocationAsync(Guid locationId, LocationType locationType) =>
         db.StockBalances
@@ -90,4 +97,16 @@ public class StockRepository(AppDBContext db) : IStockRepository
         if (to.HasValue) query = query.Where(m => m.CreatedAt <= to.Value);
         return query.CountAsync();
     }
+
+    public Task<ItemBatch?> FindBatchAsync(Guid itemId, string batchNumber) =>
+        db.ItemBatches.FirstOrDefaultAsync(b => b.FK_ItemId == itemId && b.BatchNumber == batchNumber);
+
+    public async Task AddItemBatchAsync(ItemBatch batch) =>
+        await db.ItemBatches.AddAsync(batch);
+
+    public Task<bool> SerialNumberExistsAsync(Guid itemId, string serialNumber) =>
+        db.ItemSerialNumbers.AnyAsync(s => s.FK_ItemId == itemId && s.SerialNumber == serialNumber);
+
+    public async Task AddItemSerialNumberAsync(ItemSerialNumber serial) =>
+        await db.ItemSerialNumbers.AddAsync(serial);
 }