Automatic ejs template compilation

compiled_templates.erb

var <%= "#{Rails.application.class.parent_name}" %> = <%= "#{Rails.application.class.parent_name}" %> || {};
<%= "#{Rails.application.class.parent_name}" %>.Templates = <%= templates %>;

Gemfile

group :development do
  gem 'ejs'
  gem 'rb-fsevent' # optional
  gem 'listen'
end

jstemplates.rake

require 'erb'
require 'ejs'
require 'listen'

namespace :jst do
  @assets_path = File.join(Rails.root, 'lib', 'assets')
  @javascripts_path = File.join(Rails.root, 'app', 'assets', 'javascripts')
  @templates_path = File.join(@javascripts_path, 'templates')
  @erb_template = File.join(@assets_path, 'compiled_templates.erb')
  @template_file = File.join(@javascripts_path, 'templates.js')

  desc "Compile the javascript templates"
  task :build => :environment do
    begin
      templates = templates_hash @templates_path
      compiled_templates = ERB.new(File.read(@erb_template))
      templates = template_string templates
      File.open(@template_file, "w+") { |f| f << compiled_templates.result(binding) }
      puts "#{@template_file.gsub(Rails.root.to_s, '')} was built successfully"
    rescue Exception => e
      puts "There was an error compiling the templates: #{e.message}\n"
      raise e
    end
  end

  desc "Watch the templates for changes and compile automatically"
  task :watch => :environment do
    puts "Watching for js template changes. Press Ctrl+C to quit"
    Listen.to(@templates_path, filter: /\.jst$/) do
      Rake::Task["jst:build"].execute
    end
  end

  def templates_hash(path, data = {}, namespace = nil)
    Dir.foreach(path) do |entry|
      next if entry =~ /^\./

      full_path = File.join(path, entry)

      if File.directory?(full_path)
        namespace = File.basename(entry, '.jst')
        templates_hash(full_path, data[namespace] = {})
      else
        template_name = File.basename(entry, '.jst')
        data[template_name] = EJS.compile(File.read(full_path))
      end
    end

    data
  end

  def template_string(templates, result="{")
    templates.map do |key, value|
      result << "'#{key}':"
      if value.is_a?(Hash)
        result << "{"
        template_string(value, result)
      else
        result << "#{value},"
      end
    end
    result << "}"
  end

end