Filer: Refactor deletion processors for better readability

Extract large callback functions into dedicated private methods to
improve code organization and maintainability.

Changes:
1. Extract processDeletionBatch method
   - Handles deletion of a batch of file IDs
   - Classifies errors (success, not found, retryable, permanent)
   - Manages retry queue additions
   - Consolidates logging logic

2. Extract processRetryBatch method
   - Handles retry attempts for previously failed deletions
   - Processes retry results and updates queue
   - Symmetric to processDeletionBatch for consistency

Benefits:
- Main loop functions (loopProcessingDeletion, loopProcessingDeletionRetry)
  are now concise and focused on orchestration
- Business logic is separated into testable methods
- Reduced nesting depth improves readability
- Easier to understand control flow at a glance
- Better separation of concerns

The refactored methods follow the single responsibility principle,
making the codebase more maintainable and easier to extend.

weed/filer/filer_deletion.go

@@ -218,6 +218,17 @@ func (f *Filer) loopProcessingDeletion() {
 						toDeleteFileIds = fileIds
 						fileIds = fileIds[:0]
 					}
+					f.processDeletionBatch(toDeleteFileIds, lookupFunc, retryQueue)
+				}
+			})
+		}
+	}
+}
+
+// processDeletionBatch handles deletion of a batch of file IDs and processes results.
+// It classifies errors into retryable and permanent categories, adds retryable failures
+// to the retry queue, and logs appropriate messages.
+func (f *Filer) processDeletionBatch(toDeleteFileIds []string, lookupFunc func([]string) (map[string]*operation.LookupResult, error), retryQueue *DeletionRetryQueue) {
 	results := operation.DeleteFileIdsWithLookupVolumeId(f.GrpcDialOption, toDeleteFileIds, lookupFunc)
 
 	// Process individual results for better error tracking
@@ -264,10 +275,6 @@ func (f *Filer) loopProcessingDeletion() {
 		glog.V(2).Infof("retry queue size: %d", retryQueue.Size())
 	}
 }
-			})
-		}
-	}
-}
 
 // isRetryableError determines if an error is retryable based on its message.
 //
@@ -327,7 +334,15 @@ func (f *Filer) loopProcessingDeletionRetry(lookupFunc func([]string) (map[strin
 			}
 
 			glog.V(1).Infof("retrying deletion of %d files", len(readyItems))
+			f.processRetryBatch(readyItems, lookupFunc, retryQueue)
+		}
+	}
+}
 
+// processRetryBatch attempts to retry deletion of files and processes results.
+// Successfully deleted items are removed from tracking, retryable failures are
+// re-queued with updated retry counts, and permanent errors are logged and discarded.
+func (f *Filer) processRetryBatch(readyItems []*DeletionRetryItem, lookupFunc func([]string) (map[string]*operation.LookupResult, error), retryQueue *DeletionRetryQueue) {
 	// Extract file IDs from retry items
 	var fileIds []string
 	itemsByFileId := make(map[string]*DeletionRetryItem)
@@ -367,8 +382,6 @@ func (f *Filer) loopProcessingDeletionRetry(lookupFunc func([]string) (map[strin
 		glog.V(1).Infof("retry: %d files still failing, will retry again later", retryCount)
 	}
 }
-	}
-}
 
 func (f *Filer) DeleteUncommittedChunks(ctx context.Context, chunks []*filer_pb.FileChunk) {
 	f.doDeleteChunks(ctx, chunks)