module LessCompiler
  class Middleware
    def initialize(app)
      @app = Rack::Static.new(app, :urls => %w(/stylesheets), :root => 'tmp')
      @compiler = Compiler.instance
    end

    def call(env)
      maybe_compile_less(env)
      @app.call(env)
    end

    private

    def maybe_compile_less(env)
      path = env['PATH_INFO']
      return unless path =~ %r(^/stylesheets/(.*)\.css$)
      @compiler.maybe_compile($1)
    end
  end

  class Compiler
    include Singleton

    #
    # path should be something like "global/nav" for "/global/nav.css"
    #
    def maybe_compile(path)
      less_path = File.join(Rails.root, 'app', 'stylesheets', "#{path}.less")
      css_path = File.join(Rails.root, 'tmp', 'stylesheets', "#{path}.css")
      unless !File.exist?(less_path) || File.exist?(css_path) && File.mtime(less_path) <= File.mtime(css_path)
        Rails.logger.debug "Recompiling #{less_path} => #{css_path}"
        FileUtils.mkdir_p(File.dirname(css_path))
        Less::Command.new(:source => less_path, :destination => css_path).run!
      end
    end
  end
end