engine/app/cells/admin/menu_cell.rb

class Admin::MenuCell < Cell::Base

  include ::Rails.application.routes.url_helpers

  delegate :sections, :to => :parent_controller

  attr_accessor :list

  def initialize(*args)
    super
    self.list = []
  end

  def show(args = {})
    self.build_list
    render
  end

  def url_options
    super.reverse_merge(
      :host => request.host_with_port,
      :protocol => request.protocol,
      :_path_segments => request.symbolized_path_parameters
    ).merge(:script_name => request.script_name)
  end

  class MenuProxy

    def initialize(cell)
      @cell = cell
    end

    def method_missing(meth, *args)
      @cell.send(meth, *args)
    end

  end

  def self.update_for(name, &block)
    method_name = "build_list_with_#{name}".to_sym
    previous_method_name = "build_list_without_#{name}".to_sym

    self.send(:define_method, method_name) do
      self.send(previous_method_name)
      block.call(MenuProxy.new(self))
    end

    # Note: this might cause "stack level too deep" if called twice for the same name
    alias_method_chain :build_list, name.to_sym
  end

  protected

  def build_list
    raise 'the build_list method must be overridden'
  end

  def build_item(name, attributes)
    unless attributes.key?(:label)
      attributes[:label] = localize_label(name)
    end

    attributes.merge!(:name => name, :class => name.to_s.dasherize.downcase)
  end

  def add(name, attributes)
    self.list << build_item(name, attributes)
  end

  def add_after(pivot, name, attributes)
    index = self.list.index { |i| i[:name] == pivot }
    self.list.insert(index + 1, self.build_item(name, attributes))
  end

  def add_before(pivot, name, attributes)
    index = self.list.index { |i| i[:name] == pivot }
    self.list.insert(index, self.build_item(name, attributes))
  end

  def modify(name, attributes)
    self.find(name).merge!(attributes)
  end

  def remove(name)
    self.list.delete_if { |i| i[:name] == name }
  end

  def find(name)
    self.list.detect { |i| i[:name] == name }
  end

  def localize_label(label)
    I18n.t("admin.shared.menu.#{label}")
  end

end