SHA1 cache buster extension for Middleman 2.x

sha1_cache_buster.rb

module Middleman::Features
  # modeled after built-in CacheBuster extension
  # appends truncated SHA1 hashes to the querystring of asset_url'd files.
  module Sha1CacheBuster
    require 'digest/sha1'

    class << self
      def registered(app)
        app.set :sha1_asset_paths, []
        app.send :include, InstanceMethods

        app.after_build do
          puts "   Appending SHA1 cache busters…"
          app.sha1_asset_paths.uniq!

          # build the SHA1 digests
          digests = app.sha1_asset_paths.map do |f|
            build_path = File.expand_path(File.join(app.build_dir, f))
            Digest::SHA1.hexdigest(File.read(build_path))[7..16]
          end

          Dir[File.join(app.build_dir, '**/*.{html,js,css}')].each do |f|
            contents = File.read(f)
            app.sha1_asset_paths.each_with_index do |path, i|
              contents.gsub!(path, path + "?#{digests[i]}")
            end
            File.open(f, 'w') {|f| f.puts(contents) }
          end
        end
      end
      alias :included :registered
    end

    module InstanceMethods
      def asset_url(path, prefix="")
        settings.sha1_asset_paths << super 
        super
      end
    end
  end
end