module Haml::Version

def revision_number
  if File.exists?(scope('REVISION'))
    rev = File.read(scope('REVISION')).strip
    return rev unless rev =~ /^([a-f0-9]+|\(.*\))$/ || rev == '(unknown)'
  end
  return unless File.exists?(scope('.git/HEAD'))
  rev = File.read(scope('.git/HEAD')).strip
  return rev unless rev =~ /^ref: (.*)$/
  ref_name = $1
  ref_file = scope(".git/#{ref_name}")
  info_file = scope(".git/info/refs")
  return File.read(ref_file).strip if File.exists?(ref_file)
  return unless File.exists?(info_file)
  File.open(info_file) do |f|
    f.each do |l|
      sha, ref = l.strip.split("\t", 2)
      next unless ref == ref_name
      return sha
    end
  end
  return nil
end