gistfile1.txt

class Application
  before :back_navigation

  # maintain a back trace stack in session[:page_history], removing
  # any path loops.  back_resource() in global_helper will then 
  # use session[:page_history]. 
  def back_navigation
    session[:page_history] ||= []
    previous_page = request.env['HTTP_REFERER'].to_s
    current_page = (request.env['rack.url_scheme'] + 
                    '://' + 
                    request.env['HTTP_HOST'] + 
                    request.env['REQUEST_PATH']
                   ).to_s
    unless previous_page.nil?
      session[:page_history] << previous_page
      session[:page_history].compact!
      index = session[:page_history].index(current_page)
      unless index.nil?
        if index == 0
          session[:page_history].clear
        else
          session[:page_history] = session[:page_history][0..(index - 1)]
        end
      end
    end
  end
end

module Merb
  module GlobalHelpers
    # returns a resource, either then last one in the session[:page_history]
    # stack or if none available, the resource specified in the args
    def back_resource(*args)
      session[:page_history] ||= []
      session[:page_history].last || resource(*args)
    end
  end
end