code: def tag(context: click.Context, file_id: int, tags: List[str]):
      
      file_obj = context.obj['db'].file_(file_id)
      if file_obj is None:
          print(click.style('unable to find file', fg='red'))
          context.abort()
      for tag_name in tags:
          tag_obj = context.obj['db'].tag(tag_name)
          if tag_obj is None:
              tag_obj = context.obj['db'].new_tag(tag_name)
          elif tag_obj in file_obj.tags:
              print(click.style(f"{tag_name}: tag already added", fg='yellow'))
              continue
          file_obj.tags.append(tag_obj)
      context.obj['db'].commit()
      all_tags = (tag.name for tag in file_obj.tags)
      print(click.style(f"file tags: {', '.join(all_tags)}", fg='blue'))
docs: Add tags to an existing file.