A Phonegap development workflow with Rack and Sprockets - http://abhishiv.tumblr.com/post/15994872384/phonegap-and-sprockets-sitting-in-a-tree

config.ru

require 'sprockets'
require 'rack/rewrite'

project_root = File.expand_path(File.dirname(__FILE__))

assets = Sprockets::Environment.new(project_root) do |env|
  env.logger = Logger.new(STDOUT)
end

assets.append_path(File.join(project_root, 'assets'))
assets.append_path(File.join(project_root, 'assets', 'javascripts'))
assets.append_path(File.join(project_root, 'assets', 'stylesheets'))
assets.append_path(File.join(project_root, 'assets', 'images'))

map "/build" do
  run assets
end

use Rack::Static, :urls => [""] 

run lambda { |env|
  [
    200, 
    {
      'Content-Type'  => 'text/html', 
      'Cache-Control' => 'public, max-age=86400' 
    },
    File.open('public/index.html', File::RDONLY)
  ]
}

Gemfile

source :rubygems

gem 'rake'
gem 'rack'
gem 'rack-rewrite'
gem 'thin'

gem 'sprockets', '2.2.0'
gem 'sass'
gem 'coffee-script'

Rakefile

require 'rubygems'
require 'bundler'
require 'pathname'
require 'logger'
require 'fileutils'

Bundler.require

module Sprockets
  class StaticCompiler
    attr_accessor :env, :target, :paths

    def initialize(env, target, paths, options = {})
      @env = env
      @target = target
      @paths = paths
      @digest = options.key?(:digest) ? options.delete(:digest) : true
      @manifest = options.key?(:manifest) ? options.delete(:manifest) : true
      @manifest_path = options.delete(:manifest_path) || target
      @zip_files = options.delete(:zip_files) || /\.(?:css|html|js|svg|txt|xml)$/
    end

    def compile
      manifest = {}
      env.each_logical_path do |logical_path|
        next unless compile_path?(logical_path)
        if asset = env.find_asset(logical_path)
          manifest[logical_path] = write_asset(asset)
        end
      end
      write_manifest(manifest) if @manifest
    end

    def write_manifest(manifest)
      FileUtils.mkdir_p(@manifest_path)
      File.open("#{@manifest_path}/manifest.yml", 'wb') do |f|
        YAML.dump(manifest, f)
      end
    end

    def write_asset(asset)
      path_for(asset).tap do |path|
        filename = File.join(target, path)
        FileUtils.mkdir_p File.dirname(filename)
        asset.write_to(filename)
      end
    end

    def compile_path?(logical_path)
      paths.each do |path|
        case path
        when Regexp
          return true if path.match(logical_path)
        when Proc
          return true if path.call(logical_path)
        else
          return true if File.fnmatch(path.to_s, logical_path)
        end
      end
      false
    end

    def path_for(asset)
      @digest ? asset.digest_path : asset.logical_path
    end
  end
end

ROOT        = Pathname(File.dirname(__FILE__))
LOGGER      = Logger.new(STDOUT)
BUNDLES     = %w( application.css application.js )
BUILD_DIR   = ROOT.join("build")
SOURCE_DIR  = ROOT.join("assets")

task :compile do
  enviorment = Sprockets::Environment.new(ROOT) do |env|
    env.logger = LOGGER
  end

  enviorment.append_path(SOURCE_DIR.join('javascripts').to_s)
  enviorment.append_path(SOURCE_DIR.join('stylesheets').to_s)
  enviorment.append_path(SOURCE_DIR.join('images').to_s)

  comp = Sprockets::StaticCompiler.new enviorment, BUILD_DIR, [/\.(png|jpg)$/, /^(application|ie)\.(css|js)$/], {:digest => false, :zip_files => false, :manifest => false }
  comp.compile


end