function showSubMenu($sub) {
  if ($sub.length > 0) {
    var $ul = $('ul', $sub);
    
    var w = $sub
              .css({ display: 'block' })
              .width();

    var h = $ul.height();

    $ul
      .height(4);

    $sub
      .css({ marginLeft: -w / 2 + 18 })
      .show();

    $ul
      .animate({ height: h }, { duration: 300, queue: false });
  }
}

function hideSubMenu($sub) {
  if ($sub.length > 0) {
    var $ul = $('ul', $sub);

    $ul
      .stop()
      .animate({ height: 4 }, { duration: 300, queue: false, complete: function () {
        $sub
          .hide();

        $ul
          .removeAttr('style');
      }});
  }
}

$(document).ready(function () {

  // Sezione corrente
  $cur_li = $('.menu li.hover');
  $cur_sub = $('.sub_menu', $cur_li);

  // Menu e sottoMenu
  $('.menu > ul > li')
    .hover(
      function () {
        $cur_li.removeClass('hover');
        $(this).addClass('hover');

        var $sub_menu = $('.sub_menu', this);
        showSubMenu($sub_menu);
      },
      function () {
        $(this).removeClass('hover');

        var $sub_menu = $('.sub_menu', this);
        hideSubMenu($sub_menu);

        $cur_li.addClass('hover');
      }
    );

});