functional datastructure. Needs to be able to write to storage as well

frontend/lib/structs/landmark.dart

@@ -1,56 +1,69 @@
-class Landmark {
-  final String name;
-  final List location;
-  final LandmarkType type;
-  final String imageURL;
-  // final String description;
-  // final Duration duration;
-  // final bool visited;
+import 'dart:collection';
+import 'dart:convert';
 
-  const Landmark({
+import 'package:shared_preferences/shared_preferences.dart';
+
+final class Landmark extends LinkedListEntry<Landmark>{
+  // A linked node of a list of Landmarks
+  final String uuid;
+  final String name;
+  final List<double> location;
+  final LandmarkType type;
+  final bool? isSecondary;
+
+  // description to be shown in the overview
+  final String? imageURL;
+  final String? description;
+  final Duration? duration;
+  final bool? visited;
+
+  // Next node
+  // final Landmark? next;
+  final Duration? tripTime;
+
+  Landmark({
+    required this.uuid,
     required this.name,
     required this.location,
     required this.type,
-    this.imageURL = 'https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Tour_Eiffel_Wikimedia_Commons.jpg/1037px-Tour_Eiffel_Wikimedia_Commons.jpg',
-    // required this.description,
-    // required this.duration,
-    // required this.visited,
+    this.isSecondary,
+
+    this.imageURL,
+    this.description,
+    this.duration,
+    this.visited,
+
+    // this.next,
+    this.tripTime,
   });
 
   factory Landmark.fromJson(Map<String, dynamic> json) {
-    return switch (json) {
-      {
-        'loc': List location,
+    if (json
+      case { // automatically match all the non-optionals and cast them to the right type
+        'uuid': String uuid,
         'name': String name,
-        'type': String type,
-        // 'description': String description,
-        // 'duration': int duration,
-        // 'visited': bool visited
-
-      } =>
-        Landmark(
-          name: name,
-          location: location,
-          type: LandmarkType(name: type)
-          // description: description,
-          // duration: Duration(minutes: duration),
-          // visited: visited
-        ),
-      _ => throw const FormatException('Failed to load destination.'),
-    };
+        'location': List<double> location,
+        'type': LandmarkType 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);
+    } else {
+      throw FormatException('Invalid JSON: $json');
+    }
   }
 
 
-    Map<String, dynamic> toJson() {
-      return {
-        'name': name,
-        'location': location,
-        'type': type.name,
-        // 'description': description,
-        // 'duration': duration.inMinutes,
-        // 'visited': visited
-      };
-    }
+  @override
+  bool operator ==(Object other) {
+    return other is Landmark && uuid == other.uuid;
+  }
 }
 
 
@@ -67,3 +80,12 @@ class LandmarkType {
 }
 
 
+
+// Helper
+(Landmark, String?) getLandmarkFromPrefs(SharedPreferences prefs, String uuid) {
+  String? content = prefs.getString('landmark_$uuid');
+  Map<String, dynamic> json = jsonDecode(content!);
+  String? nextUUID = json['next_uuid'];
+  return (Landmark.fromJson(json), nextUUID);
+}
+