javascript-gem-asset-rake-task.rb

require 'bundler'
require 'fileutils'
require 'sprockets/standalone'
require 'rake/hooks'

Bundler.require

GEM_ASSETS = %w(
  my-gem-asset
  my-other-gem-asset
  my-gem-asset-etc
)

gem_asset_path = Rails.root.join 'app', 'assets', 'gems'
javascript_asset_path = gem_asset_path.join 'javascripts'

desc "Convert any gem wrapped assets to standalone files"
Sprockets::Standalone::RakeTask.new(:javascript_gems) do |task, sprockets|
  sprockets.context_class.instance_eval do
    include ::Sprockets::Helpers::IsolatedHelper
    include ::Sprockets::Helpers::RailsHelper
  end

  task.assets   = GEM_ASSETS.map { |asset| javascript_asset_path.join("#{asset}.js.tmp").to_s }
  task.sources  = Rails.application.config.assets.paths.push(javascript_asset_path.to_s)
  task.output   = gem_asset_path
end

before 'javascript_gems:compile' do
  FileUtils.remove_dir gem_asset_path, force: true
  FileUtils.mkdir_p javascript_asset_path

  GEM_ASSETS.each do |asset|
    directories = asset.split('/')

    if directories.length > 1
      path = javascript_asset_path.join(*directories)

      FileUtils.mkdir_p javascript_asset_path.join(*directories[0...-1])
    else
      path = javascript_asset_path.join(asset)
    end

    File.open("#{path}.js.tmp", 'w') do |file|
      file.write("//= require #{asset}")
    end
  end
end

after 'javascript_gems:compile' do
  FileUtils.rm_f gem_asset_path.join('manifest.json')

  Dir.glob(javascript_asset_path.join('**/*.js.tmp')) do |file|
    File.rename file, file.gsub(/\.tmp/, '')
  end
end