frontend compliant with backend

frontend/lib/structs/preferences.dart

@@ -3,80 +3,102 @@ import 'package:shared_preferences/shared_preferences.dart';
 
 
 class SinglePreference {
+  String slug;
   String name;
   String description;
   int value;
+  int minVal;
+  int maxVal;
   Icon icon;
-  String key;
 
   SinglePreference({
+    required this.slug,
     required this.name,
     required this.description,
     required this.value,
     required this.icon,
-    required this.key,
+    this.minVal = 0,
+    this.maxVal = 5,
   });
-}
-
-
-class UserPreferences {
-  List<SinglePreference> preferences = [
-    SinglePreference(
-      name: "Sightseeing",
-      description: "How much do you like sightseeing?",
-      value: 0,
-      icon: Icon(Icons.church),
-      key: "sightseeing",
-    ),
-    SinglePreference(
-      name: "Shopping",
-      description: "How much do you like shopping?",
-      value: 0,
-      icon: Icon(Icons.shopping_bag),
-      key: "shopping",
-    ),
-    SinglePreference(
-      name: "Foods & Drinks",
-      description: "How much do you like eating?",
-      value: 0,
-      icon: Icon(Icons.restaurant),
-      key: "eating",
-    ),
-    SinglePreference(
-      name: "Nightlife",
-      description: "How much do you like nightlife?",
-      value: 0,
-      icon: Icon(Icons.wine_bar),
-      key: "nightlife",
-    ),
-    SinglePreference(
-      name: "Nature",
-      description: "How much do you like nature?",
-      value: 0,
-      icon: Icon(Icons.landscape),
-      key: "nature",
-    ),
-    SinglePreference(
-      name: "Culture",
-      description: "How much do you like culture?",
-      value: 0,
-      icon: Icon(Icons.palette),
-      key: "culture",
-    ),
-  ];
-
 
   void save() async {
     SharedPreferences sharedPrefs = await SharedPreferences.getInstance();
-    for (SinglePreference pref in preferences) {
-      sharedPrefs.setInt(pref.key, pref.value);
-    }
+      sharedPrefs.setInt('pref_$slug', value);
   }
 
   void load() async {
     SharedPreferences sharedPrefs = await SharedPreferences.getInstance();
-    for (SinglePreference pref in preferences) {
-      pref.value = sharedPrefs.getInt(pref.key) ?? 0;
+      value = sharedPrefs.getInt('pref_$slug') ?? minVal;
+  }
+}
+
+
+class UserPreferences {
+  SinglePreference sightseeing = SinglePreference(
+    name: "Sightseeing",
+    slug: "sightseeing",
+    description: "How much do you like sightseeing?",
+    value: 0,
+    icon: Icon(Icons.church),
+  );
+  SinglePreference shopping = SinglePreference(
+    name: "Shopping",
+    slug: "shopping",
+    description: "How much do you like shopping?",
+    value: 0,
+    icon: Icon(Icons.shopping_bag),
+  );
+  SinglePreference nature = SinglePreference(
+    name: "Nature",
+    slug: "nature",
+    description: "How much do you like nature?",
+    value: 0,
+    icon: Icon(Icons.landscape),
+  );
+
+  SinglePreference maxTime = SinglePreference(
+    name: "Trip duration",
+    slug: "duration",
+    description: "How long do you want your trip to be?",
+    value: 30,
+    minVal: 30,
+    maxVal: 720,
+    icon: Icon(Icons.timer),
+  );
+  SinglePreference maxDetour = SinglePreference(
+    name: "Trip detours",
+    slug: "detours",
+    description: "Are you okay with roaming even if makes the trip longer?",
+    value: 0,
+    maxVal: 30,
+    icon: Icon(Icons.loupe_sharp),
+  );
+
+
+
+  Future<void> load() async {
+    for (SinglePreference pref in [sightseeing, shopping, nature, maxTime, maxDetour]) {
+      pref.load();
     }
   }
+
+  String toJson() {
+    // This is "opinionated" JSON, corresponding to the backend's expectations
+    return '''
+    {
+      "sightseeing": {"type": "sightseeing", "score": ${sightseeing.value}},
+      "shopping": {"type": "shopping", "score": ${shopping.value}},
+      "nature": {"type": "nature", "score": ${nature.value}},
+      "max_time_minutes": ${maxTime.value},
+      "detour_tolerance_minute": ${maxDetour.value}
+    }
+    ''';
+  }
+}
+
+
+Future<UserPreferences> loadUserPreferences() async {
+  UserPreferences prefs = UserPreferences();
+  await prefs.load();
+  return prefs;
 }