def active?(*routes)
  routes.any? do |route|
    n, ca = route.match(/\//) ? route.split('/') : [nil, route]
    c, a = ca.match(/\#/) ? ca.split('#').map { |s| s.blank? ? nil : s } : [ca, nil] if ca
    (n ? controller.class.to_s.split('::')[0...-1].join('::') == n.camelize : true) &&
    (c ? "#{controller_name}_controller".camelize == "#{c.camelize}Controller" : true) &&
    (a ? action_name == a : true)
  end
end

# given these routes in config/routes.rb:
resources :pages, :only => :show
namespace :admin do
  resources :pages, :except => :show
end

# when on pages controller, show action
active?('pages') # => true
active?('pages#show') # => true
active?('#show') # => true

# when in the admin namespace, on the pages controller, edit action
active?('admin/') # => true
active?('admin/pages') # => true
active?('admin/pages#edit') # => true
active?('admin/pages#new', 'admin/pages#edit') # => true
active?('pages') # => true
active?('pages#edit') # => true
active?('#edit') # => true
active?('admin/#edit') # => true