feat: add task and habit reordering

backend/main.py

@@ -45,6 +45,7 @@ from .schemas import (
     TaskDetailOut,
     TaskOut,
     TaskPage,
+    TaskReorder,
     TaskUpdate,
     UserOut,
 )
@@ -434,16 +435,16 @@ async def restore_list(
 
 
 
-def _encode_cursor(created_at: datetime, task_id: UUID) -> str:
-    raw = json.dumps([created_at.isoformat(), str(task_id)]).encode()
+def _encode_cursor(position: int, created_at: datetime, task_id: UUID) -> str:
+    raw = json.dumps([position, created_at.isoformat(), str(task_id)]).encode()
     return base64.urlsafe_b64encode(raw).decode().rstrip("=")
 
 
-def _decode_cursor(cursor: str) -> tuple[datetime, UUID]:
+def _decode_cursor(cursor: str) -> tuple[int, datetime, UUID]:
     try:
         raw = base64.urlsafe_b64decode(cursor + "=" * (-len(cursor) % 4))
-        timestamp, task_id = json.loads(raw)
-        return datetime.fromisoformat(timestamp), UUID(task_id)
+        position, timestamp, task_id = json.loads(raw)
+        return int(position), datetime.fromisoformat(timestamp), UUID(task_id)
     except (ValueError, TypeError, json.JSONDecodeError) as exc:
         raise HTTPException(status_code=422, detail="无效的游标") from exc
 
@@ -468,7 +469,14 @@ async def create_task(
         if parent is None:
             raise HTTPException(status_code=400, detail="父任务必须是同一清单的顶层任务")
     data = payload.model_dump()
-    task = Task(user_id=user.id, **data)
+    parent_filter = Task.parent_id == payload.parent_id if payload.parent_id else Task.parent_id.is_(None)
+    max_position = await db.scalar(select(func.max(Task.position)).where(
+        Task.user_id == user.id,
+        Task.list_id == payload.list_id,
+        parent_filter,
+        Task.deleted_at.is_(None),
+    ))
+    task = Task(user_id=user.id, position=(max_position if max_position is not None else -1) + 1, **data)
     db.add(task)
     await db.flush()
     audit(db, user.id, "create", "task", task.id)
@@ -516,20 +524,24 @@ async def list_tasks(
             or_(Task.title.ilike(pattern), Task.description.ilike(pattern), list_match)
         )
     total = await db.scalar(select(func.count()).select_from(query.order_by(None).subquery())) or 0
-    ordering = (Task.created_at, Task.id)
+    ordering = (Task.position, Task.created_at, Task.id)
     if page is not None:
         size = page_size or limit
         items = list((await db.scalars(query.order_by(*ordering).offset((page - 1) * size).limit(size))).all())
         return TaskPage(items=await _task_details(db, items), total=total, page=page, page_size=size)
     if cursor:
-        created_at, task_id = _decode_cursor(cursor)
+        position, created_at, task_id = _decode_cursor(cursor)
         query = query.where(
-            or_(Task.created_at > created_at, (Task.created_at == created_at) & (Task.id > task_id))
+            or_(
+                Task.position > position,
+                (Task.position == position) & (Task.created_at > created_at),
+                (Task.position == position) & (Task.created_at == created_at) & (Task.id > task_id),
+            )
         )
     rows = list((await db.scalars(query.order_by(*ordering).limit(limit + 1))).all())
     has_more = len(rows) > limit
     items = rows[:limit]
-    next_cursor = _encode_cursor(items[-1].created_at, items[-1].id) if has_more else None
+    next_cursor = _encode_cursor(items[-1].position, items[-1].created_at, items[-1].id) if has_more else None
     return TaskPage(items=await _task_details(db, items), next_cursor=next_cursor, total=total, page=1, page_size=limit)
 
 
@@ -561,6 +573,36 @@ async def _task_detail(db: AsyncSession, task: Task) -> TaskDetailOut:
     return (await _task_details(db, [task]))[0]
 
 
+@app.put("/api/v1/tasks/reorder", status_code=204)
+async def reorder_tasks(
+    payload: TaskReorder,
+    user: User = Depends(current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    rows = list((await db.scalars(select(Task).where(
+        Task.id.in_(payload.task_ids), Task.user_id == user.id, Task.deleted_at.is_(None)
+    ))).all())
+    if len(rows) != len(payload.task_ids):
+        raise HTTPException(status_code=404, detail="任务不存在")
+    parent_scopes = {row.parent_id for row in rows}
+    if len(parent_scopes) != 1:
+        raise HTTPException(status_code=400, detail="只能调整同一层级任务的顺序")
+    parent_id = next(iter(parent_scopes))
+    scope_query = select(Task).where(
+        Task.user_id == user.id,
+        Task.deleted_at.is_(None),
+        Task.parent_id.is_(None) if parent_id is None else Task.parent_id == parent_id,
+    ).order_by(Task.position, Task.created_at, Task.id)
+    scope_rows = list((await db.scalars(scope_query)).all())
+    requested = set(payload.task_ids)
+    ordered_rows = iter([next(row for row in rows if row.id == task_id) for task_id in payload.task_ids])
+    merged = [next(ordered_rows) if row.id in requested else row for row in scope_rows]
+    for position, row in enumerate(merged):
+        row.position = position
+    await db.commit()
+    return Response(status_code=204)
+
+
 @app.get("/api/v1/tasks/{task_id}", response_model=TaskDetailOut)
 async def get_task(
     task_id: UUID,