implemented undo button and proper sorting

lib/models/todo.dart

@@ -1,7 +1,5 @@
 import 'package:isar/isar.dart';
 
-import '../services/dbhelper.dart';
-
 part 'todo.g.dart';
 
 @collection
@@ -13,11 +11,10 @@ class Todo {
   bool done;
 
   Todo({
-    int? index,
+    required this.id,
     required this.title,
+    required this.createdAt,
     this.description = '',
-    DateTime? createdTime,
     this.done = false,
-  })  : createdAt = createdTime ?? DateTime.now(),
-        id = index ?? DbHelper.nextTodoId;
+  });
 }

lib/pages/todo_create_page.dart

@@ -56,7 +56,12 @@ class _CreateTodoPageState extends State<CreateTodoPage> {
   }
 
   void _onSubmitted() {
-    DbHelper.addOrUpdateTodo(Todo(title: _title, description: _description));
+    DbHelper.addOrUpdateTodo(Todo(
+      id: DbHelper.nextTodoId,
+      title: _title,
+      description: _description,
+      createdAt: DateTime.now(),
+    ));
     Navigator.of(context).pop();
   }
 }

lib/services/dbhelper.dart

@@ -17,7 +17,7 @@ class DbHelper {
   }
 
   static List<Todo> fetchTodos() =>
-      _isar.todos.where().doneEqualTo(false).findAll();
+      _isar.todos.where().doneEqualTo(false).sortByCreatedAtDesc().findAll();
 
   static void addOrUpdateTodo(Todo todo) =>
       _isar.write((isar) => isar.todos.put(todo));

lib/widgets/todo_list.dart

@@ -39,7 +39,11 @@ class _TodoListState extends State<TodoList> {
       tileColor: Theme.of(context).colorScheme.primaryContainer,
       title: Text(todo.title),
       trailing: IconButton(
-        onPressed: () {},
+        onPressed: () {
+          todo.done = true;
+          DbHelper.addOrUpdateTodo(todo);
+          _showSnackbar(todo);
+        },
         icon: Icon(
           Icons.check_box,
           color: Theme.of(context).colorScheme.primary,
@@ -47,4 +51,18 @@ class _TodoListState extends State<TodoList> {
       ),
     );
   }
+
+  void _showSnackbar(Todo todo) {
+    ScaffoldMessenger.of(context).showSnackBar(
+      SnackBar(
+        content: const Text('Todo done'),
+        action: SnackBarAction(
+            label: 'Undo',
+            onPressed: () {
+              todo.done = false;
+              DbHelper.addOrUpdateTodo(todo);
+            }),
+      ),
+    );
+  }
 }