composite-pattern-navigation menu

app_helpers_application_helper.rb

module ApplicationHelper
  ## ..snip

  def build_taxon_subtree(root)
    tree = Navigation::Tree("#{root.permalink}", root.name)

    Spree::Taxon.where(:parent_id => root.id).all.each do |taxon|
       count = Spree::Taxon.where(:parent_id => taxon.id).count
       if count > 0
         tree.add(build_taxon_subtree(taxon))
       else
         tree.add_leaf(taxon.name, seo_url(taxon))
       end
    end

    tree
  end

  def navigation_tree
    root_catalogue, root_categories = \
      [Config::TAXONS[:catalogue], Config::TAXONS[:categories]].map do |ident|
        Spree::Taxon.find_by_permalink!(ident)
    end

    Navigation::Root("main-menu").tap {|t|
      t.add_leaf t('navbar.home'), root_path

      Spree::Taxon.where(:parent_id => root_categories.id).all.each do |taxon|
        t.add_leaf taxon.name, seo_url(taxon)
      end

      t.add      build_taxon_subtree(root_catalogue)

      t.add_leaf t('navbar.digital_store'), '/cms/digital_store'
      t.add_leaf t('navbar.bookshop'), "/cms/bookshop"
      t.add_leaf t('navbar.club'), "/cms/club"

      t.add_leaf t('navbar.exibitions'), "/cms/exibitions", "separated"
      t.add_leaf t('navbar.partners'), "/cms/partners", "separated"
      t.add_leaf t('navbar.contact_us'), "/cms/contact_us", "separated"
    }
  end
end

lib_navigation.rb

module Navigation
  class << self
    def Root(id)
      Tree.new(id)
    end

    def Tree(id, label)
      SubTree.new(id, label)
    end
  end

  module ComponentsFactoryMethods
    def add(tree)
      self << tree
      self
    end

    def add_leaf(*args)
      self << Leaf.new(*args)
      self
    end
  end

  class Component < DelegateClass(Array)
    def initialize
      super([])
    end

    def render
      raise NotImplementedError.new("subclass me!")
    end
  end

  class Composite < Component
    def render_children(context)
      self.inject("") {|memo, n| memo << n.render(context)}
    end
  end

  class Leaf < Component
    attr_reader :title, :url, :type

    def initialize(title, url, type='normal')
      super()
      @title, @url, @type = title, url, type
    end

    def render(context)
      context.render(:partial => "shared/nav_leaf", :locals => { leaf: self })
    end
  end

  class Tree < Composite
    include ComponentsFactoryMethods
    attr_accessor :id

    def initialize(id=nil)
      super()
      @id = id
    end

    def render(context)
      context.render(:partial => partial, :locals => { :tree => self })
    end

    def partial
      "shared/nav_tree"
    end
  end

  class SubTree < Tree
    include ComponentsFactoryMethods
    attr_reader :title

    def initialize(id, title)
      super(id)
      @title = title
    end

    def partial
      "shared/nav_sub_tree"
    end
  end
end