Untitled

<html>
<head><title>Foo</title></head>
<body>
  <%= render :partial => (current_user ? "/shared/user_widget_bar" : "/shared/login_bar") %>
  <%= yield %>
</body>
</html>

before_filter :generate_user_widget
 def generate_user_widget
   if current_user
     @avatar = ...
     @unread_messages = ...
   end
 end

class SiteA::SiteAParentController < ApplicationController
   before_filter :generate_user_widget
   ...
end

class SiteA::ProductController < SiteA::SiteAParentController
  def index
    ...
  end
end

class UsersComponent < Components::Base
  def details(user_or_id)
    @user = user_or_id.is_a?(User) ? user_or_id : User.find(user_or_id)
    render
  end
end

class UsersController < ApplicationController
  def show
    return :text => component("users/detail", params[:id])
  end
end

<%= component "users/detail", @user %>