module RubyXL::WorkbookConvenienceMethods

def modify_border(style_index, direction, weight)
  xf = cell_xfs[style_index || 0].dup
  new_border = borders[xf.border_id || 0].dup
  edge = new_border.send(direction)
  new_border.send("#{direction}=", edge.dup) if edge
  new_border.set_edge_style(direction, weight)
  xf.border_id = borders.find_index { |x| x == new_border } # Reuse existing border, if it exists
  xf.border_id ||= borders.size # If this border has never existed before, add it to collection.
  borders[xf.border_id] = new_border
  xf.apply_border = true
  register_new_xf(xf)
end