code: func (w *WALWatcher) findSegmentForIndex(index int) (int, error) {
  	refs, err := w.segments(w.walDir)
  	if err != nil {
  		return -1, nil
  	}
  
  	for _, r := range refs {
  		if r >= index {
  			return r, nil
  		}
  	}
  
  	return -1, errors.New("failed to find segment for index")
  }
docs: // findSegmentForIndex finds the first segment greater than or equal to index.