application_helper.rb

def nav_link(name, path, options={})
  options[:class] = append_class(options[:class], "#{"active" if active_path?(path)}")
  options[:role] ||= "menuitem"
  link_to name, path, options
end

def active_path?(path)
  request.path == path
end

# This respects 'cancan' rules which the above cannot.
def admin_link(name, class_obj = nil, options={})
  class_obj, name = name, name.name.underscore.humanize.pluralize if class_obj.nil?
  return unless can? :manage, class_obj # for non-admin users, you might want to check if they can? :read, class_obj
  path = url_for(class_obj)
  options[:class] = append_class(options[:class], "#{"active" if active_path?(path)}")
  options[:role] ||= "menuitem"
  content_tag :li, role:"presentation" do
    link_to name, path, options
  end
end

# Here is how to use admin_link
# admin_link(User)
# admin_link("User", Member)

def extract_class(class_string = "")
  (class_string || "").split(" ").flatten
end
def stringify_class(klass=[])
  Array(klass).compact.uniq.join(" ")
end

def append_class(original_class, *fields)
  klass = extract_class(original_class)
  klass.concat(fields)
  stringify_class(klass)
end