Some opaque logic

user.rb

      # Avoid linking an active user to franchises for which the user
      # is inactive.
      #
      # * If the source user is inactive in all franchises, the user
      #   should be linked to all of the franchises in which it was
      #   present.
      #
      # * If the source user is active in all franchises, the
      #   destination user should be linked to all of the franchises
      #   in which it was present.
      #
      # * If the source user was active in some franchises and   
      #   inactive in others, the destination user should only be
      #   linked to the franchises in which the source user was
      #   active.
      #
      # This is complicated by the fact that we do not migrate all of
      # a source user's franchises at once, but instead we migrate
      # them one after the other.  The only think we know about is the
      # current destination user, and the new source user.
      def migrate_existing_user
        load_existing_user
        case [existing_user_active?, new_user_active?]
        when [false, false]
          link_user_to_franchise
        when [false, true]
          delete_existing_franchise_links
          link_user_to_franchise
        when [true, false]
        when [true, true]
          link_user_to_franchise
        end
      end