cleanup

src/server/services/download_service.py

@@ -77,6 +77,8 @@ class DownloadService:
         
         # Queue storage by status
         self._pending_queue: deque[DownloadItem] = deque()
+        # Helper dict for O(1) lookup of pending items by ID
+        self._pending_items_by_id: Dict[str, DownloadItem] = {}
         self._active_downloads: Dict[str, DownloadItem] = {}
         self._completed_items: deque[DownloadItem] = deque(maxlen=100)
         self._failed_items: deque[DownloadItem] = deque(maxlen=50)
@@ -107,6 +109,46 @@ class DownloadService:
             max_retries=max_retries,
         )
 
+    def _add_to_pending_queue(
+        self, item: DownloadItem, front: bool = False
+    ) -> None:
+        """Add item to pending queue and update helper dict.
+        
+        Args:
+            item: Download item to add
+            front: If True, add to front of queue (higher priority)
+        """
+        if front:
+            self._pending_queue.appendleft(item)
+        else:
+            self._pending_queue.append(item)
+        self._pending_items_by_id[item.id] = item
+
+    def _remove_from_pending_queue(self, item_or_id: str) -> Optional[DownloadItem]:  # noqa: E501
+        """Remove item from pending queue and update helper dict.
+        
+        Args:
+            item_or_id: Item ID to remove
+            
+        Returns:
+            Removed item or None if not found
+        """
+        if isinstance(item_or_id, str):
+            item = self._pending_items_by_id.get(item_or_id)
+            if not item:
+                return None
+            item_id = item_or_id
+        else:
+            item = item_or_id
+            item_id = item.id
+        
+        try:
+            self._pending_queue.remove(item)
+            del self._pending_items_by_id[item_id]
+            return item
+        except (ValueError, KeyError):
+            return None
+
     def set_broadcast_callback(self, callback: Callable) -> None:
         """Set callback for broadcasting status updates via WebSocket."""
         self._broadcast_callback = callback
@@ -146,14 +188,14 @@ class DownloadService:
                     # Reset status if was downloading when saved
                     if item.status == DownloadStatus.DOWNLOADING:
                         item.status = DownloadStatus.PENDING
-                    self._pending_queue.append(item)
+                    self._add_to_pending_queue(item)
                 
                 # Restore failed items that can be retried
                 for item_dict in data.get("failed", []):
                     item = DownloadItem(**item_dict)
                     if item.retry_count < self._max_retries:
                         item.status = DownloadStatus.PENDING
-                        self._pending_queue.append(item)
+                        self._add_to_pending_queue(item)
                     else:
                         self._failed_items.append(item)
                 
@@ -231,10 +273,9 @@ class DownloadService:
                 # Insert based on priority. High-priority downloads jump the
                 # line via appendleft so they execute before existing work;
                 # everything else is appended to preserve FIFO order.
-                if priority == DownloadPriority.HIGH:
-                    self._pending_queue.appendleft(item)
-                else:
-                    self._pending_queue.append(item)
+                self._add_to_pending_queue(
+                    item, front=(priority == DownloadPriority.HIGH)
+                )
                 
                 created_ids.append(item.id)
                 
@@ -293,15 +334,15 @@ class DownloadService:
                     logger.info("Cancelled active download", item_id=item_id)
                     continue
                 
-                # Check pending queue
-                for item in list(self._pending_queue):
-                    if item.id == item_id:
-                        self._pending_queue.remove(item)
-                        removed_ids.append(item_id)
-                        logger.info(
-                            "Removed from pending queue", item_id=item_id
-                        )
-                        break
+                # Check pending queue - O(1) lookup using helper dict
+                if item_id in self._pending_items_by_id:
+                    item = self._pending_items_by_id[item_id]
+                    self._pending_queue.remove(item)
+                    del self._pending_items_by_id[item_id]
+                    removed_ids.append(item_id)
+                    logger.info(
+                        "Removed from pending queue", item_id=item_id
+                    )
             
             if removed_ids:
                 self._save_queue()
@@ -338,24 +379,25 @@ class DownloadService:
             DownloadServiceError: If reordering fails
         """
         try:
-            # Find and remove item
-            item_to_move = None
-            for item in list(self._pending_queue):
-                if item.id == item_id:
-                    self._pending_queue.remove(item)
-                    item_to_move = item
-                    break
+            # Find and remove item - O(1) lookup using helper dict
+            item_to_move = self._pending_items_by_id.get(item_id)
             
             if not item_to_move:
                 raise DownloadServiceError(
                     f"Item {item_id} not found in pending queue"
                 )
             
+            # Remove from current position
+            self._pending_queue.remove(item_to_move)
+            del self._pending_items_by_id[item_id]
+            
             # Insert at new position
             queue_list = list(self._pending_queue)
             new_position = max(0, min(new_position, len(queue_list)))
             queue_list.insert(new_position, item_to_move)
             self._pending_queue = deque(queue_list)
+            # Re-add to helper dict
+            self._pending_items_by_id[item_id] = item_to_move
             
             self._save_queue()
             
@@ -575,7 +617,7 @@ class DownloadService:
                 item.retry_count += 1
                 item.error = None
                 item.progress = None
-                self._pending_queue.append(item)
+                self._add_to_pending_queue(item)
                 retried_ids.append(item.id)
                 
                 logger.info(