saucy/app/helpers/members_helper.rb

module MembersHelper
  def link_to_current_with_sort text, default_sort
    current_sort = stringify(sort_params)

    current_params = request.params.except(:action, :controller)

    if default_sort == current_sort
      current_params.merge!(sort: invert_sort_order(current_sort))
    else
      current_params.merge!(sort: default_sort)
    end

    link_to text, members_path(current_params)
  end

  private

  def stringify(sort)
    "#{sort.keys.first.to_s}.#{sort.values.first.to_s}"
  end

  def invert_sort_order(sort)
    sort.sub(/\.(asc|desc)$/) { |x| x == '.asc' ? '.desc' : '.asc' }
  end
end