module RubyXL::LegacyWorkbook

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
  unless borders[old_xf.border_id].count == 1 && old_xf.border_id > 0 # If the old border not used anymore, just replace it
    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.
  end
  borders[old_xf.border_id].count -= 1
  new_border.count += 1
  borders[new_xf.border_id] = new_border
  new_xf.apply_border = true
  register_new_xf(new_xf, style_index)
end