handle some edge cases

internal/file_store.go

@@ -50,6 +50,9 @@ func (fs *FileStore) Load(ctx context.Context) (map[string]*FillerQueue, error)
 		}
 		return nil, fmt.Errorf("reading state file: %w", err)
 	}
+	if len(data) == 0 {
+		return make(map[string]*FillerQueue), nil
+	}
 
 	var s State
 	if err := json.Unmarshal(data, &s); err != nil {
@@ -74,7 +77,7 @@ func (fs *FileStore) Load(ctx context.Context) (map[string]*FillerQueue, error)
 	for symbol, persisted := range s.Queues {
 		q := new(FillerQueue)
 		for _, pf := range persisted {
-			rec, err := fs.serializer.UnmarshalRecord(ctx, pf.ReaderData)
+			rec, err := fs.serializer.UnmarshalRecord(ctx, pf.RecordData)
 			if err != nil {
 				return nil, fmt.Errorf(
 					"unmarshalling record for symbol %q: %w", symbol, err,
@@ -98,7 +101,7 @@ func (fs *FileStore) Save(ctx context.Context, queue map[string]*FillerQueue) er
 	}
 
 	for symbol, q := range queue {
-		if q == nil {
+		if q == nil || q.Len() == 0 {
 			continue
 		}
 		var persisted []persistedFiller
@@ -109,7 +112,7 @@ func (fs *FileStore) Save(ctx context.Context, queue map[string]*FillerQueue) er
 				return fmt.Errorf("marshalling record for symbol %q: %w", symbol, err)
 			}
 			persisted = append(persisted, persistedFiller{
-				ReaderData: data,
+				RecordData: data,
 				Quantity:   f.Quantity(),
 				Price:      f.Price(),
 				Filled:     f.Filled(),