module MenuHelper
  # Represents a group of menus.  A menu bar can either be the main menu bar
  # or a menu bar nested within a menu.
  class MenuBar < HtmlElement
    # The css class to apply for all menu bars
    cattr_accessor :menu_bar_class
    @@menu_bar_class = 'menubar'
    
    # The css class to apply when a sub-menu bar is selected
    cattr_accessor :selected_class
    @@selected_class = 'menubar-selected'
    
    # The request context in which this menu bar is being rendered
    attr_reader :request_controller
    
    # The menus within this menu bar
    attr_reader :menus
    
    # The configuration options for this menu bar
    attr_reader :options
    
    def initialize(request_controller, options = {}, html_options = {}) #:nodoc:
      super(html_options)
      
      # Set up default options
      options.assert_valid_keys(:parent_menu, :auto_set_ids, :attach_active_submenus, :content_for)
      options.reverse_merge!(:auto_set_ids => true, :attach_active_submenus => true, :content_for => 'menu_bar')
      @options = options
      
      # Set context of the menu bar (the request and any parent)
      @request_controller = request_controller
      
      # No menus initially associated
      @menus = []
      
      # Set up default html options
      self[:class] = "#{self[:class]} #{menu_bar_class} #{menu_bar_class}-#{level}".strip
      
      yield self if block_given?
    end
    
    # Gets the nesting level of this menu bar.  The top-level menu bar will
    # always have a nesting level of 1.
    def level
      @level ||= begin
        level = 1
        
        # Keep walking up the tree, until first-level menus are encountered
        menu = parent_menu
        while menu
          level += 1
          menu = menu.parent_menu
        end
        
        level
      end
    end
    
    # The menu in which this menu bar is being displayed.  This will be nil if
    # this is the main menu bar.
    def parent_menu
      @options[:parent_menu]
    end
    
    # Shoulds elements have default ids automatically applied to them?
    def auto_set_ids?
      @options[:auto_set_ids]
    end
    
    # Should menu bars in sub-menus be attached to this menu bar?
    def attach_active_submenus?
      @options[:attach_active_submenus]
    end
    
    # The instance variable to use when rendering the current active sub-menu
    # bar
    def content_for_variable
      "@content_for_#{@options[:content_for]}_level_#{level}"
    end
    
    # Is this menu bar selected?  A menu bar is considered selected if it has
    # a parent menu and that parent menu is selected.
    def selected?
      parent_menu && menus.any? {|menu| menu.selected?}
    end
    
    # Creates a new menu in this bar with the given id.  The content
    # within the menu is, by default, set to a humanized version of the id.
    # 
    # == URLs with routes
    # 
    # If you have named routes set up in the application, the menu attempts
    # to automatically figure out what URL you're trying to link to.  It
    # does this by looking at the id of the menu and the id of its parent.
    # 
    # For example, a menu bar with the id 'home' and a menu with the id
    # 'contact_us' will attempt to look for the following named routes as
    # the URL to link to (in order of priority):
    # 1. home_contact_us_url
    # 2. contact_us_url
    # 
    # Example routes.rb:
    # 
    #   ActionController::Routing::Routes.draw do |map|
    #     map.with_options(:controller => 'home') do |home|
    #       home.home '', :action => 'index'
    #       home.home_search 'search', :action => 'search'
    #     end
    #     
    #     map.with_options(:controller => 'about_us') do |about_us|
    #       about_us.about_us 'about_us', :action => 'index'
    #     end
    #   end
    # 
    # Example menu bar:
    # 
    #   menu_bar :home do |home|
    #     home.menu :about_us   # => Links to about_us_url
    #     home.menu :search     # => Links to home_search_url
    #   end
    # 
    # == URLs with url_for
    # 
    # If neither of these named routes are being used, the url will be based
    # on the options passed into the menu.  The url_options takes the same
    # values as +url_for+.  By default, the name of the controller will be
    # guessed in the following order:
    # 1. The id of the menu ('contact_us' => ContactUsController)
    # 2. The controller of the parent menu/menu bar
    # 3. The request controller
    # 
    # To override the default controller being linked to, you can explicitly
    # define it like so:
    #   menu :contact, 'Contact Us', :controller => 'about_us'
    # 
    # Examples:
    # 
    #   menu :home do |home|
    #     home.menu :about, 'About Us', :action => 'about_us'                       # => Links to {:controller => 'home', :action => 'about_us'}
    #     home.menu :who_we_are                                                     # => Links to {:controller => 'home', :action => 'who_we_are'}
    #     home.menu :contact_us, :controller => 'contact', :action => 'index'  # => Links to {:controller => 'contact', :action => 'index'}
    #     home.menu :search                                                         # => Links to {:controller => 'search'}
    #   end
    # 
    # You can also link to an explicit URL like so:
    # 
    #   home.menu :search, 'http://www.google.com'
    # 
    # == Turning off links
    # 
    # If you don't want a menu to link to a URL, you can turn off linking like
    # so:
    # 
    #   home.menu :contact_us, {}, :link => false
    # 
    # == Defining content and html attributes
    # 
    # By default, the content within a menu will be set as a humanized
    # version of the menu's id.  Examples of menus which customize the
    # content and/or html attributes are below:
    # 
    #   home.menu :contact                                          # => <li id="contact"><a href="/contact">Contact</a></li>
    #   home.menu :contact, 'Contact Us'                            # => <li id="contact"><a href="/contact">Contact Us</a></li>
    #   home.menu :contact, {}, :class => 'pretty'                  # => <li id="contact" class="pretty"><a href="/contact">Contact</a></li>
    #   home.menu :contact, 'Get in touch!', {}, :class => 'pretty' # => <li id="contact" class="pretty"><a href="/contact">Contact Us</a></li>
    # 
    # == Sub-menus
    # 
    # Menus can also have their own sub-menus by passing in a block.  You can
    # create sub-menus in the same manner that the main menus are created.
    # For example,
    # 
    #   home.menu :about do |about|
    #     about.menu :who_we_are
    #     about.menu :contact_us
    #   end
    def menu(id, content = nil, url_options = {}, html_options = {}, &block)
      menu = Menu.new(self, id, content, url_options, html_options, &block)
      @menus << menu
      
      menu
    end
    
    # Builds the actual html of the menu bar
    def html
      html_options = @html_options.dup
      html_options[:class] = "#{html_options[:class]} #{selected_class}".strip if selected?
      
      content_tag(tag_name, content, html_options)
    end
    
    private
      # Unordered list
      def tag_name
        'ul'
      end
      
      # Generate the html for the menu bar
      def content
        @menus.inject('') {|html, menu| html << menu.html(@menus.last == menu)}
      end
  end
end