add uuid lib and use it

Frontend-user/lib/sample_data.dart

@@ -1,3 +1,5 @@
+import 'package:uuid/uuid.dart';
+
 final now = DateTime.now();
 
 enum TransaktionArt { monatlBeitrag, aufladung, einkauf, korrektur }
@@ -27,7 +29,7 @@ class Product {
   final int id = 0;
   final String name;
   final Unit unit;
-  final double price; //pro Kilogramm oder Stück
+  final double price; //pro Kilogramm oder Stück, d.h. pro unit
   final double vat;
   final Category category;
   const Product(this.name, this.unit, this.price, this.vat, this.category);
@@ -42,8 +44,9 @@ class Purchase {
 class Basket {
   Map<Product, int> purchases;
   double price;
+  String guid;
 
-  Basket(this.purchases, this.price);
+  Basket(this.purchases, this.price): guid = const Uuid().v4();
 
   void addItem(Product product, int quantity) {
     if (purchases.containsKey(product)) {

Frontend-user/pubspec.lock

@@ -41,6 +41,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.17.1"
+  crypto:
+    dependency: transitive
+    description:
+      name: crypto
+      sha256: ff625774173754681d66daaf4a448684fb04b78f902da9cb3d308c19cc5e8bab
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.3"
   cupertino_icons:
     dependency: "direct main"
     description:
@@ -184,6 +192,22 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.5.1"
+  typed_data:
+    dependency: transitive
+    description:
+      name: typed_data
+      sha256: facc8d6582f16042dd49f2463ff1bd6e2c9ef9f3d5da3d9b087e244a7b564b3c
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.3.2"
+  uuid:
+    dependency: "direct main"
+    description:
+      name: uuid
+      sha256: "648e103079f7c64a36dc7d39369cabb358d377078a051d6ae2ad3aa539519313"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.7"
   vector_math:
     dependency: transitive
     description:

Frontend-user/pubspec.yaml

@@ -28,6 +28,7 @@ environment:
 # the latest version available on pub.dev. To see which dependencies have newer
 # versions available, run `flutter pub outdated`.
 dependencies:
+  uuid: ^3.0.4
   flutter:
     sdk: flutter