Added function to split stock

- Specify the quantity to move into the NEW stock item
- The left over quantity will remain in the current stock item

InvenTree/stock/models.py

@@ -281,7 +281,47 @@ class StockItem(models.Model):
         track.save()
 
     @transaction.atomic
-    def move(self, location, notes, user):
+    def splitStock(self, quantity, user):
+        """ Split this stock item into two items, in the same location.
+        Stock tracking notes for this StockItem will be duplicated,
+        and added to the new StockItem.
+
+        Args:
+            quantity: Number of stock items to remove from this entity, and pass to the next
+
+        Notes:
+            The provided quantity will be subtracted from this item and given to the new one.
+            The new item will have a different StockItem ID, while this will remain the same.
+        """
+
+        # Doesn't make sense for a zero quantity
+        if quantity <= 0:
+            return
+
+        # Also doesn't make sense to split the full amount
+        if quantity >= self.quantity:
+            return
+
+        # Create a new StockItem object, duplicating relevant fields
+        new_stock = StockItem.objects.create(
+            part=self.part,
+            quantity=quantity,
+            supplier_part=self.supplier_part,
+            location=self.location,
+            batch=self.batch,
+            delete_on_deplete=self.delete_on_deplete
+        )
+
+        new_stock.save()
+
+        # Add a new tracking item for the new stock item
+        new_stock.addTransactionNote(
+            "Split from existing stock",
+            user,
+            "Split {n} from existing stock item".format(n=quantity))
+
+        # Remove the specified quantity from THIS stock item
+        self.take_stock(quantity, user, 'Split {n} items into new stock item'.format(n=quantity))
 
         if location is None:
             # TODO - Raise appropriate error (cannot move to blank location)