Assets compiling for non rails project with Sprockets

Rakefile

require 'sprockets'
require 'logger'
require 'fileutils'
require 'pathname'
require 'json'

ROOT       = Pathname(File.dirname(__FILE__))
LOGGER     = Logger.new(STDOUT)

BASE_PATH  = "path/to/assets"
BUILD_DIR  = ROOT.join("#{BASE_PATH}", "public")
SOURCE_DIR = ROOT.join("#{BASE_PATH}", "assets")
BUNDLES    = %w( app.js styles.css )
DEBUG      = true

task :default => :compile

desc "Compila Assets"
task :compile => :clean do
    puts "Compilando assets #{BASE_PATH}"
    sprockets = Sprockets::Environment.new(ROOT) do |env|
        env.logger = LOGGER if DEBUG
    end

    sprockets.append_path SOURCE_DIR.join("scripts").to_s
    sprockets.append_path SOURCE_DIR.join("styles").to_s

    BUNDLES.each do |bundle|
        puts "Generando: #{bundle}"
        assets = sprockets.find_asset(bundle)
        ext = bundle.split(".")[1]
        name = assets.pathname.basename(assets.pathname.extname)

        FileUtils.mkpath BUILD_DIR.join(ext)
        assets.write_to BUILD_DIR.join(ext, "#{name}.#{ext}")
    end
end

desc "Limpia los directorios de build"
task :clean do
    puts "Limpiando directorio"
    BUNDLES.each do |bundle|
        ext = bundle.split(".")[1]
        FileUtils.rm_rf BUILD_DIR.join(ext)
    end
end