merge ?3

lib/ui/sell_page/view_model/sell_view_model.dart

@@ -52,6 +52,47 @@ class SellViewModel extends ChangeNotifier {
     notifyListeners();
   }
 
+  Future<void> scanBook(BarcodeCapture barcode) async {
+    int ean = int.parse(barcode.barcodes.first.rawValue!);
+    Bal? bal = await _balRepository.ongoingBal();
+    _scannedBooks.clear();
+
+    final result = await _bookInstanceRepository.getByEan(bal!.id, ean);
+    switch (result) {
+      case Ok():
+        for (BookInstance instance in result.value) {
+          Book book;
+          final result2 = await _bookRepository.getBookById(instance.bookId);
+          switch (result2) {
+            case Ok():
+              book = result2.value;
+              break;
+            case Error():
+              continue;
+          }
+          Owner owner;
+          final result3 = await _ownerRepository.getOwnerById(instance.ownerId);
+          switch (result3) {
+            case Ok():
+              owner = result3.value;
+              break;
+            case Error():
+              continue;
+          }
+          _scannedBooks.add(
+            BookStack(instance: instance, book: book, owner: owner),
+          );
+        }
+        break;
+      case Error():
+        break;
+    }
+
+    isScanLoaded = true;
+    notifyListeners();
+    return;
+  }
+
   /*
  * =================
  * =====[ BAL ]=====