Parse CSS 3 Media Queries

mqparse.rb

#!/usr/bin/env ruby
#
# mqparse - Media Query parser
# Copyright 2008 Apple, Inc. All Rights Reserved.
# http://gist.github.com/6863
#
# cf. http://www.w3.org/TR/css3-mediaqueries

require 'pp'

TOKEN = '([\w\-]+)' # letters, numbers, or "-"
#  Match against strings of form: key, (key), or (key: value)
KEYVALUE = Regexp.new("\\(#{TOKEN}(: #{TOKEN})?\\)", Regexp::IGNORECASE)
COMPARATOR = Regexp.new("(min|max)-#{TOKEN}", Regexp::IGNORECASE)
COMPARE = {"min" => ">=", "max" => "<="}

def mq_parse(mq_string)
  mq_string.split(",").collect do |query|
    query.split(" and ").collect do |expr|
      
      matched,key,_,value = *KEYVALUE.match(expr)
      next ["media-type", "==", expr] if not matched
      next [key, "!=", "0"] if value.nil?
      
      comparison, side, root = *COMPARATOR.match(key)
      next [key, "==", value] if not comparison
      [root, COMPARE[side], value]

    end     # expr
  end       # query
end         # mq_parse

parse_string = "screen "+
               "and (min-device-height: 640) "+
               "and (width: 720) "+
               "and (device-type: ipod) "+
               "and (color: rgb),"+
               " (color)"

puts "\n\tParsing:\n#{parse_string}"
qs = mq_parse(parse_string)
qs.each_index do |i|
  puts "\n\tQuery #{i}:"
  pp *qs[i]
end