quite a few UX improvements

frontend/lib/structs/agreement.dart

@@ -0,0 +1,17 @@
+import 'package:shared_preferences/shared_preferences.dart';
+
+final class Agreement{
+  bool agreed;
+
+  Agreement({required this.agreed});
+}
+
+void saveAgreement(bool agreed) async {
+  SharedPreferences prefs = await SharedPreferences.getInstance();
+  prefs.setBool('agreed_to_terms_and_conditions', agreed);
+}
+
+Future<Agreement> getAgreement() async {
+  SharedPreferences prefs = await SharedPreferences.getInstance();
+  return Agreement(agreed: prefs.getBool('agreed_to_terms_and_conditions') ?? false);
+}

frontend/lib/structs/trip.dart

@@ -12,7 +12,7 @@ import 'package:shared_preferences/shared_preferences.dart';
 
 class Trip with ChangeNotifier {
   String uuid;
-  int totalTime;
+  Duration totalTime;
   LinkedList<Landmark> landmarks;
   // could be empty as well
   String? errorDescription;
@@ -44,7 +44,7 @@ class Trip with ChangeNotifier {
 
   Trip({
     this.uuid = 'pending',
-    this.totalTime = 0,
+    this.totalTime = Duration.zero,
     LinkedList<Landmark>? landmarks
     // a trip can be created with no landmarks, but the list should be initialized anyway
   }) : landmarks = landmarks ?? LinkedList<Landmark>();
@@ -53,7 +53,7 @@ class Trip with ChangeNotifier {
   factory Trip.fromJson(Map<String, dynamic> json) {
     Trip trip = Trip(
       uuid: json['uuid'],
-      totalTime: json['total_time'],
+      totalTime: Duration(minutes: json['total_time']),
     );
 
     return trip;
@@ -61,7 +61,7 @@ class Trip with ChangeNotifier {
 
   void loadFromJson(Map<String, dynamic> json) {
     uuid = json['uuid'];
-    totalTime = json['total_time'];
+    totalTime = Duration(minutes: json['total_time']);
     notifyListeners();
   }
 
@@ -82,9 +82,12 @@ class Trip with ChangeNotifier {
     // removing the landmark means we need to recompute the time between the two adjoined landmarks
     if (previous != null && next != null) {
       // previous.next = next happens automatically since we are using a LinkedList
+      this.totalTime -= previous.tripTime ?? Duration.zero;
       previous.tripTime = null;
       // TODO
     }
+    this.totalTime -= landmark.tripTime ?? Duration.zero;
+
     notifyListeners();
   }
 
@@ -111,7 +114,7 @@ class Trip with ChangeNotifier {
 
   Map<String, dynamic> toJson() => {
     'uuid': uuid,
-    'total_time': totalTime,
+    'total_time': totalTime.inMinutes,
     'first_landmark_uuid': landmarks.first.uuid
   };