CSS Spliter for IE's CSS rules limits

css_splitter.rb

# lib/css_splitter.rb

class CssSplitter

  CHARSET = '@charset "UTF-8"'

  def initialize(infile, outdir = File.dirname(infile))
    @infile = infile
    @outdir = outdir
    @filenames = []
  end

  def split(max_selectors = 4095)

    rules = IO.readlines(@infile, "}")
    return if rules.first.nil?

    id = 0
    selectors_count = 0
    file = open_file(id += 1)

    rules.each do |rule|

      rule_selectors_count = count_selectors_of_rule rule
      selectors_count += rule_selectors_count

      if selectors_count > max_selectors
        file.close() if file
        file = open_file(id += 1)
        file.write CHARSET
        selectors_count = rule_selectors_count
      end
      file.write rule if file

    end

    if @filenames.length > 0
      imports = IO.readlines(@infile).select { |line| line =~ /@import.*/ }
      open(File.new(@infile), "w") do |f|
        imports.each do |import|
          f.puts import
        end
        @filenames.each do |filename|
          f.puts "@import url(\"#{filename}\");"
        end
      end
    end

  end

  def count_selectors(path)

    rules = IO.readlines(path, '}')
    return if rules.first.nil?

    rules.inject(0) {|count, rule| count + count_selectors_of_rule(rule)}.tap do |result|
      puts File.basename(path) + " contains #{result} selectors."
    end

  end

  private

  def count_selectors_of_rule(rule)
    rule.partition(/\{/).first.scan(/,/).count.to_i + 1
  end

  def open_file(id)
    filename = File.basename(@infile, File.extname(@infile)) + "_#{id.to_s}" + File.extname(@infile)
    @filenames << filename
    File.new(File.join(@outdir, filename), "w")
  end


end

splitcss

# bin/splitcss

#!/usr/bin/env ruby
$LOAD_PATH.unshift File.dirname(__FILE__) + "/../lib"

require 'css_splitter'

infile = File.dirname(__FILE__) + "/../.tmp/styles/main.css"
outdir = File.dirname infile
max_selectors = 4000

CssSplitter.new(infile, outdir).split(max_selectors)