Split CSS files so that there are no more than a given number of selectors in one style sheet. This is a tool to cope with Internet Explorer's limitation of max. 4095 selectors per stylesheet. Fix bug when there is no charset. Always write first partial o

css_splitter.rake

require 'rake'
require Compass::AppIntegration::Rails.root.to_s + '/lib/compass/css_splitter'

namespace :css do  
  desc 'split css files'
  task :split do
    infile = ENV['infile'] || raise("missing infile")
    outdir = ENV['outdir'] || File.dirname(infile)
    max_selectors = ENV['max_selectors'] || 4095

    CssSplitter.split(infile, outdir, max_selectors)
  end
  
  desc 'count css files'
  task :count_selectors do
    css_file = ENV['css_file'] || raise("missing css file")

    CssSplitter.count_selectors(css_file)
  end
end

css_splitter.rb

module CssSplitter
  def self.split(infile, outdir = File.dirname(infile), max_selectors = 4095)

    raise "infile could not be found" unless File.exists? infile

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

    charset_statement, new_rule_0 = rules.first.partition(/^\@charset[^;]+;/)[1,2]
    rules[0] = new_rule_0 if new_rule_0 > ''
    return if rules.nil?
    
    filename = File.join(outdir, File.basename(infile, File.extname(infile)) + "_*" + File.extname(infile))
    FileUtils.rm(Dir.glob(filename))

    file_id = 1
    selectors_count = 0
    output = next_file(file_id, infile, outdir, charset_statement)

    rules.each do |rule|
      rule_selectors_count = count_selectors_of_rule rule
      selectors_count += rule_selectors_count

      # Nothing happens until the selectors limit is reached for the first time
      if selectors_count > max_selectors
        # Close current file if there is already one
        output.close if output

        # Prepare next file
        file_id += 1
        output = next_file(file_id, infile, outdir, charset_statement)

        # Reset count with current rule count
        selectors_count = rule_selectors_count
      end

      output.write rule if output
    end
  end
  
  def self.next_file(file_id, infile, outdir, charset_statement)
    filename = File.join(outdir, File.basename(infile, File.extname(infile)) + "_#{file_id.to_s}" + File.extname(infile))
    output = File.new(filename, "w")
    output.write charset_statement
    output
  end

  def self.count_selectors(css_file)
    raise "file could not be found" unless File.exists? css_file

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

    charset_statement, rules[0] = rules.first.partition(/^\@charset[^;]+;/)[1,2]
    return if rules.first.nil?

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

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