How to turn this into routes.rb entries

ApplicationController.rb

def subdomain_junk
    if request.subdomain == 'signup'
      unless ((request.path == new_user_registration_path) || (request.path == '/accounts/check_exists') || (request.path == '/users'))
        redirect_to new_user_registration_path
      end
    elsif request.path == new_user_registration_path
        unless ((request.subdomain == 'signup') || (request.path == '/accounts/check_exists'))
          if request.port == 80
            redir_url =  request.protocol + 'signup' + '.' + request.domain + new_user_registration_path
          else
            redir_url =  request.protocol + 'signup' + '.' + request.domain + ":" + request.port.to_s() + new_user_registration_path
          end
          redirect_to redir_url
        end
    else
      if request.port == 80
        redir_url =  request.protocol + 'www' + '.' + request.domain + home_index_path
      else
        redir_url =  request.protocol + 'www' + '.' + request.domain + ":" + request.port.to_s() + home_index_path
      end
      unless Account.exists?(:subdomain => request.subdomain)
        unless request.url == redir_url
          redirect_to redir_url
        end
      end
    end
  end