reworkでrails asset-url 問題をなんとかする

asset.coffee

fs = require('fs')

module.exports =
  manifest: ->
    JSON.parse(fs.readFileSync(__dirname + '/../../../tmp/manifest.json', 'utf8'))

  url: (path) ->
    @manifest()[path]

css.coffee

reworkFunction = require('rework-plugin-function')

asset = require('./asset.coffee')

reworkAssetUrl = ->
  asset.env = env.name or 'development'
  reworkFunction('asset-url': (path) ->
    "url('#{asset.url(path)}')"
  )

gulp.task 'build:css', ->
  gulp.src("application.scss")
    .pipe(sass(includePaths: [baseDir, 'bower_components/']))
    .pipe(rework(reworkAssetUrl()))
    .pipe(gulp.dest(config.assets.dir))