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);
+}
+

frontend/lib/structs/linked_landmarks.dart

@@ -0,0 +1,46 @@
+// import "package:fast_network_navigation/structs/landmark.dart";
+
+// class Linked<Landmark> {
+//   Landmark? head;
+  
+//   Linked();
+
+//   // class methods
+//   bool get isEmpty => head == null;
+
+//   // Add a new node to the end of the list
+//   void add(Landmark value) {
+//     if (isEmpty) {
+//       // If the list is empty, set the new node as the head
+//       head = value;
+//     } else {
+//       Landmark? current = head;
+//       while (current!.next != null) {
+//         // Traverse the list to find the last node
+//         current = current.next;
+//       }
+//       current.next = value; // Set the new node as the next node of the last node
+//     }
+//   }
+
+//   // Remove the first node with the given value
+//   void remove(Landmark value) {
+//     if (isEmpty) return;
+
+//     // If the value is in the head node, update the head to the next node
+//     if (head! == value) {
+//       head = head.next;
+//       return;
+//     }
+
+//     var current = head;
+//     while (current!.next != null) {
+//       if (current.next! == value) {
+//         // If the value is found in the next node, skip the next node
+//         current.next = current.next.next;
+//         return;
+//       }
+//       current = current.next;
+//     }
+//   }
+// }

frontend/lib/structs/preferences.dart

@@ -67,16 +67,16 @@ class UserPreferences {
 
 
   void save() async {
-    SharedPreferences prefs = await SharedPreferences.getInstance();
+    SharedPreferences sharedPrefs = await SharedPreferences.getInstance();
     for (SinglePreference pref in preferences) {
-      prefs.setInt(pref.key, pref.value);
+      sharedPrefs.setInt(pref.key, pref.value);
     }
   }
 
   void load() async {
-    SharedPreferences prefs = await SharedPreferences.getInstance();
+    SharedPreferences sharedPrefs = await SharedPreferences.getInstance();
     for (SinglePreference pref in preferences) {
-      pref.value = prefs.getInt(pref.key) ?? 0;
+      pref.value = sharedPrefs.getInt(pref.key) ?? 0;
     }
   }
 }

frontend/lib/structs/route.dart

@@ -5,7 +5,7 @@ class Route {
   final String name;
   final Duration duration;
   final List<Landmark> landmarks;
-  
+
   Route({
     required this.name,
     required this.duration,

frontend/lib/structs/trip.dart

@@ -1,25 +1,49 @@
 // Represents a collection of landmarks that represent a journey
 // Different instances of a Trip can be saved and loaded by the user
 
+import 'dart:collection';
+import 'dart:convert';
+
 import 'package:fast_network_navigation/structs/landmark.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 
 class Trip {
   final String uuid;
   final String cityName;
-  final List<Landmark> landmarks;
+  // TODO: cityName should be inferred from coordinates of the Landmarks
+  final LinkedList<Landmark> landmarks;
+  // could be empty as well
 
-
-  Trip({required this.uuid, required this.cityName, required this.landmarks});
+  Trip({
+    required this.uuid,
+    required this.cityName,
+    required this.landmarks,
+    });
 
   factory Trip.fromJson(Map<String, dynamic> json) {
-    List<Landmark> landmarks = [];
-    for (var landmark in json['landmarks']) {
-      landmarks.add(Landmark.fromJson(landmark));
-    }
     return Trip(
       uuid: json['uuid'],
       cityName: json['cityName'],
-      landmarks: landmarks,
+      landmarks: LinkedList()
     );
   }
-}
+
+  factory Trip.fromPrefs(SharedPreferences prefs, String uuid) {
+    String? content = prefs.getString('trip_$uuid');
+    Map<String, dynamic> json = jsonDecode(content!);
+    Trip trip = Trip.fromJson(json);
+    String? firstUUID = json['entry_uuid'];
+    appendLandmarks(trip.landmarks, prefs, firstUUID);
+    return trip;
+  }
+}
+
+// Helper
+
+appendLandmarks(LinkedList<Landmark> landmarks, SharedPreferences prefs, String? firstUUID) {
+  while (firstUUID != null) {
+    var (head, nextUUID) = getLandmarkFromPrefs(prefs, firstUUID);
+    landmarks.add(head);
+    firstUUID = nextUUID;
+  }
+}