(function ($) {
  $.fn.appear = function (fn, options) {
    var settings = $.extend(
      { data: undefined, one: true, accX: 0, accY: 0 },
      options
    );
    return this.each(function () {
      var t = $(this);
      t.appeared = false;
      if (!fn) {
        t.trigger("appear", settings.data);
        return;
      }
      var w = $(window);
      var check = function () {
        if (!t.is(":visible")) {
          t.appeared = false;
          return;
        }
        var a = w.scrollLeft();
        var b = w.scrollTop();
        var o = t.offset();
        var x = o.left;
        var y = o.top;
        var ax = settings.accX;
        var ay = settings.accY;
        var th = t.height();
        var wh = w.height();
        var tw = t.width();
        var ww = w.width();
        if (
          y + th + ay >= b &&
          y <= b + wh + ay &&
          x + tw + ax >= a &&
          x <= a + ww + ax
        ) {
          if (!t.appeared) t.trigger("appear", settings.data);
        } else {
          t.appeared = false;
        }
      };
      var modifiedFn = function () {
        t.appeared = true;
        if (settings.one) {
          w.unbind("scroll", check);
          var i = $.inArray(check, $.fn.appear.checks);
          if (i >= 0) $.fn.appear.checks.splice(i, 1);
        }
        fn.apply(this, arguments);
      };
      if (settings.one) t.one("appear", settings.data, modifiedFn);
      else t.bind("appear", settings.data, modifiedFn);
      w.scroll(check);
      $.fn.appear.checks.push(check);
      check();
    });
  };
  $.extend($.fn.appear, {
    checks: [],
    timeout: null,
    checkAll: function () {
      var length = $.fn.appear.checks.length;
      if (length > 0) while (length--) $.fn.appear.checks[length]();
    },
    run: function () {
      if ($.fn.appear.timeout) clearTimeout($.fn.appear.timeout);
      $.fn.appear.timeout = setTimeout($.fn.appear.checkAll, 20);
    },
  });
  $.each(
    [
      "append",
      "prepend",
      "after",
      "before",
      "attr",
      "removeAttr",
      "addClass",
      "removeClass",
      "toggleClass",
      "remove",
      "css",
      "show",
      "hide",
    ],
    function (i, n) {
      var old = $.fn[n];
      if (old) {
        $.fn[n] = function () {
          var r = old.apply(this, arguments);
          $.fn.appear.run();
          return r;
        };
      }
    }
  );
})(jQuery);