SASS: Create custom functions with a SASS plugin

gistfile1

# A sass plugin to calculate colums width based on a 100% width, the colspan and the spacing amount.
# 
# Apply this plugin by passing it to the sass command as a require parameter:
# >> sass --require ts_sass_functions.rb
#
# @copyright triplesense
# @author Tom Raithel
# @version 1.0
# @package com.vorwerk.corporate
#
# last change: $Date: 2012-08-28 16:27:00 +0200 (Di, 28 Aug 2012) $
# last author: $Author: traithel $
# svn path: $URL: http://svn.dev.europe.triplesense.de/vorwerk/cd-relaunch/batch/ruby/lib/ts_sass_functions.rb $
# revision: $Rev: 6901 $
#
# $Id: ts_sass_functions.rb 6901 2012-08-28 14:27:00Z traithel $

require 'sass/plugin'

# Container module for extended functionality
module TS
  def self.column_width(total_width, columns, total_columns, spacing)
    total_no_spacing = total_width.minus(spacing.times(total_columns.minus(Sass::Script::Number.new(1))))
    one_column = total_no_spacing.div(total_columns)
    all_columns = one_column.times(columns)
    all_columns.plus(spacing.times(columns.minus(Sass::Script::Number.new(1))))
  end
end

# SASS proxy module
module Sass::Script::Functions

  # Returns the width of a column based on:
  # - total_width:      The width of a 100% column
  # - columns:          The number columns 
  # - total_columns:    The total number of columns in a row
  # - spacing:          Spacing between each column
  #
  # For example to get the width of a 33% column in a container width 100px width and a column
  # spacing of 5px you would call this function this way:
  # .col-33 {
  #     width: column_width(100px, 1, 3, 5px)
  # }
  def column_width(total_width, columns, total_columns, spacing)
    assert_type total_width, :Number
    assert_type columns, :Number
    assert_type total_columns, :Number
    assert_type spacing, :Number

    TS::column_width(total_width, columns, total_columns, spacing)
  end
  declare :column_width, :args => [:total_width,:columns, :total_columns, :spacing]
end