Compile assets (haml -> html) via rake task

compile_haml_asset_pipeline.rb

require 'fileutils'
require "haml"
require "sprockets"

class HamlTemplate < Tilt::HamlTemplate
  def prepare
    @options = @options.merge :format => :html5
    super
  end
end

# Don't move this line!
Sprockets.register_engine '.haml', HamlTemplate

Rake::Task['assets:precompile'].enhance do
  Rake::Task['assets:precompile_static_html'].invoke
  #Rake::Task['static'].invoke
end

namespace :assets do
  desc 'Compile the static 404 and 500 html template with the asset paths.'
  task :precompile_static_html do
    invoke_or_reboot_rake_task 'assets:precompile_static_html:all'
  end

  namespace :precompile_static_html do
    def internal_precompile_static_html
      # Ensure that action view is loaded and the appropriate
      # sprockets hooks get executed

      _ = Sprockets::Engines
      _ = ActionView::Base

      config = Rails.application.config
      config.assets.compile = true
      config.assets.digest  = true

      env = Rails.application.assets
      target = Rails.public_path

      static_files = config.assets.digests.keys.grep(/static/).map { |path| path.gsub("static\/", "") }

      compiler = Sprockets::StaticCompiler.new(
        env,
        target,
        static_files,
        :manifest_path => config.assets.manifest,
        :digest => false,
        :manifest => false
      )

      compiler.compile
    end

    task :all do
      ruby_rake_task('assets:precompile_static_html:primary', false)
    end

    task :primary => ['assets:environment', 'tmp:cache:clear'] do
      internal_precompile_static_html
    end
  end
end

task :static => ['assets:environment', 'tmp:cache:clear', 'assets:precompile'] do
  rm_rf("public/static")
  mkdir_p("public/static")

  #DO THIS AS PRODUCTION!
  session = ActionDispatch::Integration::Session.new(Rails.application)
  session.get("/thepage")

  all_asset_digests = Rails.application.config.assets.digests

  File.open("public/static/404.html", "w") do |handle|
    handle.write session.body
  end
end