module RubyXL::WorkbookConvenienceMethods

def modify_border(style_index, direction, weight)
  old_xf = cell_xfs[style_index].dup
  new_border = borders[old_xf.border_id].dup
  new_border.set_edge_style(direction, weight)
  new_xf = old_xf.dup
  new_xf.apply_border = true
  new_xf.border_id = borders.find_index { |x| x == new_border } # Use existing border, if it exists
  new_xf.border_id ||= borders.size # If this border has never existed before, add it to collection.
  borders[new_xf.border_id] = new_border
  register_new_xf(new_xf, style_index)
end