module RevelryContent
  module Generators
    class JsGenerator < ::Rails::Generators::Base
      JS_FILE_EXTENSIONS = %w(
        .coffee
        .coffee.erb
        .js.coffee
        .js.coffee.rb
        .js
        .js.rb
      )

      def add_js_assets
        insert_into_file js_app_bundle, before: %r{(//|#)= require_tree \.} do
          "#{ js_require_marker }= require revelry_content\n"
        end
      end

      private

      def js_app_bundle
        File.join(js_base_dir, "application#{ js_file_extname }")
      end

      def test_js_format(fmt)
        File.exist?(File.join(js_base_dir, "application#{ fmt }"))
      end

      def js_base_dir
        File.join('app', 'assets', 'javascripts')
      end

      def js_file_extname
        JS_FILE_EXTENSIONS.find { |fmt| test_js_format(fmt) }
      end

      def js_require_marker
        '#' if js_file_extname.include?('coffee')
        '//'
      end
    end
  end
end