ransack multi column sort

  #usage example: <%=multi_sort_link(@q, :state_name, ["state_country asc", :state_name]) %>
  #if order (ASC/DESC) is specified, the sorting will not be inverted in sort
  def multi_sort_link(search, field, attribute, *args)
    # Extract out a routing proxy for url_for scoping later
    if search.is_a?(Array)
      routing_proxy = search.shift
      search = search.first
    end


    raise TypeError, "First argument must be a Ransack::Search!" unless
      Ransack::Search === search

    search_params = params[search.context.search_key].presence ||
      {}.with_indifferent_access

    #attribute is a hash
    attr_name = field if field.is_a?(String)
    attr_name = field.to_s if field.is_a?(Symbol)

    options = args.first.is_a?(Hash) ? args.shift.dup : {}
    default_order = options.delete :default_order

    sort_params = []
    current_dir = "ASC"
    attribute.each do |value|
      if value.is_a?(Symbol)
        field_name, dir = value.to_s.split(" ")
      else
        field_name, dir = value.split(" ")
      end


      #invert direction when no direction specified
      if dir.nil?
        if existing_sort = search.sorts.detect { |s| s.name == field_name }
          prev_attr, prev_dir = existing_sort.name, existing_sort.dir
        end

        current_dir = prev_attr == attr_name ? prev_dir : nil
        if current_dir
          new_dir = current_dir == 'desc' ? 'asc' : 'desc'
        else
          new_dir = default_order || 'asc'
        end
      else
        new_dir = dir
      end

      sort_params << field_name+" #{new_dir}"
    end

    name = (
      if args.size > 0 && !args.first.is_a?(Hash)
        args.shift.to_s
      else
        Ransack::Translate.attribute(field, :context => search.context)
      end
      )

    html_options = args.first.is_a?(Hash) ? args.shift.dup : {}
    css = ['sort_link', current_dir].compact.join(' ')
    html_options[:class] = [css, html_options[:class]].compact.join(' ')
    query_hash = {}
    query_hash[search.context.search_key] = search_params
    .merge(:s => sort_params)



    options.merge!(query_hash)
    options_for_url = params.merge options

    url = if routing_proxy && respond_to?(routing_proxy)
      send(routing_proxy).url_for(options_for_url)
    else
      url_for(options_for_url)
    end

    link_to(
      [ERB::Util.h(name), order_indicator_for(current_dir)]
        .compact
        .join(' ')
        .html_safe,
      url,
      html_options
      )
  end