module ActiveAdmin::Resource::Menu

def add_to_menu(menu_collection)
  if include_in_menu?
    @menu_item = menu_collection.add navigation_menu_name, menu_item_options
  end
end

def default_menu_options
  # These local variables are accessible to the procs.
  menu_resource_class = respond_to?(:resource_class) ? resource_class : self
  resource = self
  {
    id: resource_name.plural,
    label: proc { resource.plural_resource_label },
    url: proc { resource.route_collection_path(params, url_options) },
    if: proc { authorized?(Auth::READ, menu_resource_class) }
  }
end

def include_in_menu?
  @include_in_menu != false
end

def menu_item_options
  @menu_item_options ||= default_menu_options
end

def menu_item_options=(options)
  if options == false
    @include_in_menu = false
    @menu_item_options = {}
  else
    @include_in_menu = true
    @navigation_menu_name = options[:menu_name]
    @menu_item_options = default_menu_options.merge options
  end
end

def navigation_menu
  namespace.fetch_menu(navigation_menu_name)
end

def navigation_menu_name
  case @navigation_menu_name ||= DEFAULT_MENU
  when Proc
    controller.instance_exec(&@navigation_menu_name).to_sym
  else
    @navigation_menu_name
  end
end

def navigation_menu_name=(menu_name)
  self.menu_item_options = { menu_name: menu_name }
end