feat: Refactor account handling and improve group creation logic

lib/models/account.dart

@@ -1,53 +1,61 @@
+import 'dart:convert';
 import 'group_member.dart';
 
 class Account {
   final String id;
   final String tripId;
-  final String groupId;
   final String name;
+  final DateTime createdAt;
+  final DateTime updatedAt;
   final List<GroupMember> members;
 
   Account({
     required this.id,
     required this.tripId,
-    required this.groupId,
     required this.name,
+    DateTime? createdAt,
+    DateTime? updatedAt,
     List<GroupMember>? members,
-  }) : members = members ?? [];
+  })  : createdAt = createdAt ?? DateTime.now(),
+        updatedAt = updatedAt ?? DateTime.now(),
+        members = members ?? [];
 
-
-  factory Account.fromMap(Map<String, dynamic> map) {
+  factory Account.fromMap(Map<String, dynamic> map, String id) {
     return Account(
-      id: map['id'] as String,
-      tripId: map['tripId'] as String,
-      groupId: map['groupId'] as String,
-      name: map['name'] as String,
+      id: id,
+      tripId: map['tripId'] ?? '',
+      name: map['name'] ?? '',
+      createdAt: DateTime.fromMillisecondsSinceEpoch(map['createdAt'] ?? 0),
+      updatedAt: DateTime.fromMillisecondsSinceEpoch(map['updatedAt'] ?? 0),
       members: [],
     );
   }
 
   Map<String, dynamic> toMap() {
     return {
-      'id': id,
       'tripId': tripId,
-      'groupId': groupId,
       'name': name,
-      'members': members.map((member) => member.toMap()).toList(),
+      'createdAt': createdAt.millisecondsSinceEpoch,
+      'updatedAt': updatedAt.millisecondsSinceEpoch,
     };
   }
 
+  String toJson() => json.encode(toMap());
+
   Account copyWith({
     String? id,
     String? tripId,
-    String? groupId,
     String? name,
+    DateTime? createdAt,
+    DateTime? updatedAt,
     List<GroupMember>? members,
   }) {
     return Account(
       id: id ?? this.id,
       tripId: tripId ?? this.tripId,
-      groupId: groupId ?? this.groupId,
       name: name ?? this.name,
+      createdAt: createdAt ?? this.createdAt,
+      updatedAt: updatedAt ?? this.updatedAt,
       members: members ?? this.members,
     );
   }