working save and load functionality with custom datastructures

frontend/lib/structs/landmark.dart

@@ -21,6 +21,7 @@ final class Landmark extends LinkedListEntry<Landmark>{
   // final Landmark? next;
   final Duration? tripTime;
 
+
   Landmark({
     required this.uuid,
     required this.name,
@@ -37,23 +38,28 @@ final class Landmark extends LinkedListEntry<Landmark>{
     this.tripTime,
   });
 
+
   factory Landmark.fromJson(Map<String, dynamic> json) {
     if (json
       case { // automatically match all the non-optionals and cast them to the right type
         'uuid': String uuid,
         'name': String name,
-        'location': List<double> location,
-        'type': LandmarkType type,
+        'location': List<dynamic> location,
+        'type': String type,
       }) {
-        // parse the rest separately, they could be missing
-        final isSecondary = json['is_secondary'] as bool?;
-        final imageURL = json['image_url'] as String?;
-        final description = json['description'] as String?;
-        final duration = json['duration'] as Duration?;
-        final visited = json['visited'] as bool?;
-        
-        return Landmark(
-          uuid: uuid, name: name, location: location, type: type, isSecondary: isSecondary, imageURL: imageURL, description: description, duration: duration, visited: visited);
+      // refine the parsing on a few
+      List<double> locationFixed = List<double>.from(location);
+      // parse the rest separately, they could be missing
+      LandmarkType typeFixed = LandmarkType(name: type);
+      final isSecondary = json['is_secondary'] as bool?;
+      final imageURL = json['image_url'] as String?;
+      final description = json['description'] as String?;
+      var duration = Duration(minutes: json['duration'] ?? 0) as Duration?;
+      if (duration == const Duration()) {duration = null;};
+      final visited = json['visited'] as bool?;
+      
+      return Landmark(
+        uuid: uuid, name: name, location: locationFixed, type: typeFixed, isSecondary: isSecondary, imageURL: imageURL, description: description, duration: duration, visited: visited);
     } else {
       throw FormatException('Invalid JSON: $json');
     }
@@ -64,6 +70,19 @@ final class Landmark extends LinkedListEntry<Landmark>{
   bool operator ==(Object other) {
     return other is Landmark && uuid == other.uuid;
   }
+
+
+  Map<String, dynamic> toJson() => {
+    'uuid': uuid,
+    'name': name,
+    'location': location,
+    'type': type.name,
+    'is_secondary': isSecondary,
+    'image_url': imageURL,
+    'description': description,
+    'duration': duration?.inMinutes,
+    'visited': visited
+  };
 }
 
 
@@ -80,8 +99,8 @@ class LandmarkType {
 }
 
 
-
-// Helper
+// Helpers
+// Handling the landmarks requires a little bit of special care because the linked list is not directly representable in json
 (Landmark, String?) getLandmarkFromPrefs(SharedPreferences prefs, String uuid) {
   String? content = prefs.getString('landmark_$uuid');
   Map<String, dynamic> json = jsonDecode(content!);
@@ -89,3 +108,9 @@ class LandmarkType {
   return (Landmark.fromJson(json), nextUUID);
 }
 
+
+void landmarkToPrefs(SharedPreferences prefs, Landmark current, Landmark? next) {
+  Map<String, dynamic> json = current.toJson();
+  json['next_uuid'] = next?.uuid;
+  prefs.setString('landmark_${current.uuid}', jsonEncode(json));
+}