Update TaskViewModel to Use TaskService and Task API Integration

This commit includes a significant overhaul of the TaskViewModel to use the newly created TaskService and integrate it with the task API. Specifically:

- Removed dependency on mock data for tasks.
- Added real API calls through the TaskService for task operations like creating and fetching tasks.
- Updated createTask to return the ID of the newly created task.
- Updated fetchTasks method to fetch tasks from the API and update the local list.
- Updated selectTask to handle selection based on string IDs.

These changes make the TaskViewModel ready for real-world usage and remove dependencies on mock data.

lib/viewmodels/task_viewmodel.dart

@@ -1,37 +1,41 @@
 import 'package:auto_gpt_flutter_client/models/task.dart';
-import 'package:auto_gpt_flutter_client/viewmodels/mock_data.dart';
 import 'package:flutter/foundation.dart';
 import 'package:collection/collection.dart';
+import 'package:auto_gpt_flutter_client/services/task_service.dart';
+import 'package:auto_gpt_flutter_client/models/task_request_body.dart';
 
-// TODO: Update whole class once we have created TaskService
 class TaskViewModel with ChangeNotifier {
+  final TaskService _taskService;
   List<Task> _tasks = [];
   Task? _selectedTask; // This will store the currently selected task
 
+  TaskViewModel(this._taskService);
+
   /// Returns the list of tasks.
   List<Task> get tasks => _tasks;
 
   /// Returns the currently selected task.
   Task? get selectedTask => _selectedTask;
 
-  /// Adds a task.
-  void createTask(String title) {
-    // Generate an ID (This is a simplistic approach for mock data)
-    final id = _tasks.length + 1;
-    final newTask = Task(id: id, title: title);
-
+  /// Adds a task and returns its ID.
+  Future<String> createTask(String title) async {
+    final newTask = TaskRequestBody(input: title);
     // Add to data source
-    addTask(newTask);
+    final createdTask = await _taskService.createTask(newTask);
+    // Create a Task object from the created task response
+    final newTaskObject =
+        Task(id: createdTask['task_id'], title: createdTask['input']);
 
     // Update local tasks list and notify listeners
-    _tasks.add(newTask);
+    _tasks.add(newTaskObject);
     notifyListeners();
+
+    return newTaskObject.id; // Return the ID of the new task
   }
 
   /// Deletes a task.
-  void deleteTask(int id) {
-    // Remove from data source
-    removeTask(id);
+  void deleteTask(String id) async {
+    // TODO: Protocol doesn't support deleting tasks, we need to manually manage this list
 
     // Update local tasks list and notify listeners
     _tasks.removeWhere((task) => task.id == id);
@@ -39,19 +43,24 @@ class TaskViewModel with ChangeNotifier {
   }
 
   /// Fetches tasks from the data source.
-  void fetchTasks() {
+  void fetchTasks() async {
     try {
-      _tasks = mockTasks;
-      notifyListeners(); // Notify listeners to rebuild UI
+      final fetchedTasks = await _taskService.listAllTasks();
+      _tasks = fetchedTasks.map((taskMap) {
+        return Task(
+          id: taskMap['task_id'].toString(),
+          title: taskMap['output'].toString(),
+        );
+      }).toList();
+      notifyListeners();
       print("Tasks fetched successfully!");
     } catch (error) {
       print("Error fetching tasks: $error");
-      // TODO: Handle additional error scenarios or log them as required
     }
   }
 
   /// Handles the selection of a task by its ID.
-  void selectTask(int id) {
+  void selectTask(String id) {
     final task = _tasks.firstWhereOrNull((t) => t.id == id);
 
     if (task != null) {