module Middleman::Features::CacheBuster

def registered(app)
  app.register_asset_handler :cache_buster do |path, prefix, request|
    http_path = app.before_asset_handler(:cache_buster, path, prefix, request)
    if http_path.include?("://") || !%w(.css .png .jpg .js .gif).include?(File.extname(http_path))
      http_path
    else
      begin
        prefix = app.images_dir if prefix == app.http_images_path
      rescue
      end
      real_path_static  = File.join(app.views, prefix, path)
      if File.readable?(real_path_static)
        http_path << "?" + File.mtime(real_path_static).strftime("%s") 
      elsif app.build?
        real_path_dynamic = File.join(app.root, app.build_dir, prefix, path)
        http_path << "?" + File.mtime(real_path_dynamic).strftime("%s") if File.readable?(real_path_dynamic)
      end
      http_path
    end
  end
  app.compass_config do |config|
    config.asset_cache_buster do |path, real_path|
      real_path = real_path.path if real_path.is_a? File
      real_path = real_path.gsub(File.join(app.root, app.build_dir), app.views)
      if File.readable?(real_path)
        File.mtime(real_path).strftime("%s") 
      else
        $stderr.puts "WARNING: '#{File.basename(path)}' was not found (or cannot be read) in #{File.dirname(real_path)}"
      end
    end
  end
end