Capistrano task to precomile assets locally, if necessary

deploy.rb

namespace :deploy do
  namespace :assets do
    task :precompile, :roles => :web, :except => { :no_release => true } do
      assets_path = File.join(release_path, "public/assets")
      assets_empty = capture("ls -x #{assets_path}").length == 0

      has_current_release = capture("if [ -d #{current_path} ]; then echo -n \"yes\"; fi") == "yes"

      compile_assets = false

      if has_current_release
        from = source.next_revision(current_revision)
        if capture("cd #{latest_release} && #{source.local.log(from)} vendor/assets/ lib/assets/ app/assets/ | wc -l").to_i > 0
          compile_assets = true
        end
      end

      if compile_assets or assets_empty
        run_locally("rake assets:clean && rake assets:precompile")
        run_locally "cd public && tar -jcf assets.tar.bz2 assets"
        top.upload "public/assets.tar.bz2", "#{shared_path}", :via => :scp
        run "cd #{shared_path} && tar -jxf assets.tar.bz2 && rm assets.tar.bz2"
        run_locally "rm public/assets.tar.bz2"
        run_locally("rake assets:clean")
      else
        logger.info "Skipping asset pre-compilation because there were no asset changes"
      end
    end
  end
end