parser logic added

lib/models/line_item.dart

@@ -8,20 +8,27 @@ class LineItem {
     required this.price,
     this.quantity,
     this.unitPrice,
+    this.discount = 0,
   });
 
   final String id;
   final String name;
+
+  /// Line total after any discount.
   final double price;
   final int? quantity;
   final double? unitPrice;
 
+  /// Negative amount when a discount was folded into [price].
+  final double discount;
+
   LineItem copyWith({
     String? id,
     String? name,
     double? price,
     int? quantity,
     double? unitPrice,
+    double? discount,
     bool clearQuantity = false,
   }) {
     return LineItem(
@@ -30,6 +37,7 @@ class LineItem {
       price: price ?? this.price,
       quantity: clearQuantity ? null : (quantity ?? this.quantity),
       unitPrice: clearQuantity ? null : (unitPrice ?? this.unitPrice),
+      discount: discount ?? this.discount,
     );
   }
 }