Implement post /tasks/{task id}/labels/ api to add a label to a task

README.md

@@ -93,4 +93,32 @@
 5. To fix lint issues
     ```
     ruff check --fix
-    ```
+    ```
+
+## API Documentation
+
+### Tasks
+
+#### Add Label to Task
+```
+POST /v1/tasks/{task_id}/labels
+
+Add a label to an existing task.
+
+Request Body:
+{
+    "label_id": "string"  // ID of the label to add
+}
+
+Responses:
+200 OK - Label added successfully
+400 Bad Request - Invalid input (e.g., invalid label ID format)
+404 Not Found - Task or label not found
+500 Internal Server Error - Unexpected server error
+
+Example:
+POST /v1/tasks/123/labels
+{
+    "label_id": "456"
+}
+```

todo/serializers/add_label_serializer.py

@@ -0,0 +1,12 @@
+from rest_framework import serializers
+from todo.models.common.pyobjectid import PyObjectId
+
+
+class AddLabelSerializer(serializers.Serializer):
+    label_id = serializers.CharField(required=True)
+
+    def validate_label_id(self, value):
+        try:
+            return PyObjectId(value)
+        except Exception:
+            raise serializers.ValidationError("Invalid label ID format") 

todo/services/task_service.py

@@ -221,3 +221,45 @@ def create_task(cls, dto: CreateTaskDTO) -> CreateTaskResponse:
                     ],
                 )
             )
+
+    @staticmethod
+    def add_label_to_task(task_id: PyObjectId, label_id: PyObjectId) -> None:
+        """
+        Add a label to a task.
+
+        Args:
+            task_id: The ID of the task
+            label_id: The ID of the label to add
+
+        Raises:
+            ValueError: If the task or label doesn't exist
+        """
+        from todo.repositories.task_repository import TaskRepository
+        from todo.repositories.label_repository import LabelRepository
+
+        # Check if task exists
+        task = TaskRepository.get_by_id(task_id)
+        if not task:
+            raise ValueError(ApiErrorResponse(
+                statusCode=404,
+                message="Task not found",
+                errors=[{"detail": f"Task with ID {task_id} does not exist"}]
+            ))
+
+        # Check if label exists
+        label = LabelRepository.get_by_id(label_id)
+        if not label:
+            raise ValueError(ApiErrorResponse(
+                statusCode=404,
+                message="Label not found",
+                errors=[{"detail": f"Label with ID {label_id} does not exist"}]
+            ))
+
+        # Initialize labels list if None
+        if task.labels is None:
+            task.labels = []
+
+        # Add label if not already present
+        if label_id not in task.labels:
+            task.labels.append(label_id)
+            TaskRepository.update(task)

todo/urls.py

@@ -5,5 +5,6 @@
 
 urlpatterns = [
     path("tasks", TaskView.as_view(), name="tasks"),
+    path("tasks/<str:task_id>/labels", TaskView.as_view({"post": "post_label"}), name="task_labels"),
     path("health", HealthView.as_view(), name="health"),
 ]

todo/views/task.py

@@ -6,11 +6,13 @@
 
 from todo.serializers.get_tasks_serializer import GetTaskQueryParamsSerializer
 from todo.serializers.create_task_serializer import CreateTaskSerializer
+from todo.serializers.add_label_serializer import AddLabelSerializer
 from todo.services.task_service import TaskService
 from todo.dto.task_dto import CreateTaskDTO
 from todo.dto.responses.error_response import ApiErrorResponse, ApiErrorDetail, ApiErrorSource
 from todo.dto.responses.create_task_response import CreateTaskResponse
 from todo.constants.messages import ApiErrors
+from todo.models.common.pyobjectid import PyObjectId
 
 class TaskView(APIView):
     def get(self, request: Request):
@@ -59,6 +61,51 @@ def post(self, request: Request):
                 data=fallback_response.model_dump(mode="json"), status=status.HTTP_500_INTERNAL_SERVER_ERROR
             )
 
+    def post_label(self, request: Request, task_id: str):
+        """
+        Add a label to a task.
+
+        Args:
+            request: HTTP request containing label data
+            task_id: ID of the task to add the label to
+
+        Returns:
+            Response: HTTP response with success or error details
+        """
+        try:
+            task_id = PyObjectId(task_id)
+        except Exception:
+            return Response(
+                data=ApiErrorResponse(
+                    statusCode=400,
+                    message="Invalid task ID format",
+                    errors=[{"detail": "The provided task ID is not valid"}]
+                ).model_dump(mode="json"),
+                status=status.HTTP_400_BAD_REQUEST
+            )
+
+        serializer = AddLabelSerializer(data=request.data)
+        if not serializer.is_valid():
+            return self._handle_validation_errors(serializer.errors)
+
+        try:
+            TaskService.add_label_to_task(task_id, serializer.validated_data["label_id"])
+            return Response(status=status.HTTP_200_OK)
+
+        except ValueError as e:
+            if isinstance(e.args[0], ApiErrorResponse):
+                error_response = e.args[0]
+                return Response(data=error_response.model_dump(mode="json"), status=error_response.statusCode)
+
+            fallback_response = ApiErrorResponse(
+                statusCode=500,
+                message=ApiErrors.UNEXPECTED_ERROR_OCCURRED,
+                errors=[{"detail": str(e) if settings.DEBUG else ApiErrors.INTERNAL_SERVER_ERROR}],
+            )
+            return Response(
+                data=fallback_response.model_dump(mode="json"), status=status.HTTP_500_INTERNAL_SERVER_ERROR
+            )
+
     def _handle_validation_errors(self, errors):
         formatted_errors = []
         for field, messages in errors.items():