fix(journey): correct calculation of duration

lib/transport_helper.dart

@@ -1,4 +1,5 @@
 import 'package:sqflite/sqflite.dart';
+import 'utilities.dart';
 // import './state_helper.dart';
 // import './db_helper.dart';
 
@@ -94,13 +95,15 @@ class Journey {
     Map<String, Object?> journeyMaps,
     List<Segment> segmentMaps,
   ) {
-    return Journey(
+    Journey journey = Journey(
       id: journeyMaps["id"] as int,
       startStation: journeyMaps["startstation"] as String?,
       endStation: journeyMaps["endstation"] as String?,
       segments: segmentMaps,
       duration: Duration(minutes: 0),
     );
+    journey.sync();
+    return journey;
   }
 
   // from trip API request
@@ -134,8 +137,8 @@ class Journey {
     if (segments.isNotEmpty) {
       startStation = segments.first.start.stationName;
       endStation = segments.last.end.stationName;
-      duration = segments.first.start.departureTime.difference(
-        segments.last.end.arrivalTime,
+      duration = segments.last.end.arrivalTime.difference(
+        segments.first.start.departureTime,
       );
     } else {
       // if the journey has no segments yet, at least the startStation should remain,
@@ -223,7 +226,6 @@ class Journey {
   static Future<Journey> fromMapWrapper(Map<String, Object?> journeyMap) async {
     Future<List<Segment>> segs = _dbGetJourneySegments(journeyMap["id"] as int);
     Journey res = Journey.fromMap(journeyMap, await segs);
-    res.sync();
     return res;
   }