(function ($) {

    function sameOrChild(n1, n2) {
        // http://www.quirksmode.org/blog/archives/2006/01/contains_for_mo.html
        return n1 === n2 || (typeof (n1.contains) !== 'undefined' ? n1.contains(n2) : !!(n1.compareDocumentPosition(n2) & 16));
    }

    function focusHandler(event) {
        event = $.event.fix(event || window.event), $this = $(this), isFocused = $this.data('focus.isFocused');
        if (!isFocused) {
            $this.data('focus.isFocused', true);
            event.type = 'focusin';
            return $.event.handle.apply(this, [event]);
        }
    }

    function blurHandler(event) {
        var args = [].slice.call(arguments, 1), $this = $(this);
        event = $.event.fix(event || window.event);

        window.setTimeout(function () {
            if (!sameOrChild($this.get(0), document.activeElement)) {
                $this.data('focus.isFocused', false);
                event.type = 'focusout';
                return $.event.handle.apply($this.get(0), [event]);
            }
        }, 0);
    }

    function setupEvents(elem) {
        var $elem = $(elem), ref = $elem.data('focus.handlerReferences') || 0;
        if (ref == 0) {
            if (elem.addEventListener) {
                elem.addEventListener('focus', focusHandler, true);
                elem.addEventListener('blur', blurHandler, true);
            }
            else {
                elem.onfocusin = focusHandler;
                elem.onfocusout = blurHandler;
            }
        }
        $elem.data('focus.handlerReferences', ref + 1)
        $elem.data('focus.isFocused', sameOrChild(elem, document.activeElement));
    }

    function teardownEvents(elem) {
        var $elem = $(elem), ref = $elem.data('focus.handlerReferences') || 0;
        if (ref == 1) {
            if (elem.removeEventListener) {
                elem.removeEventListener('focus', focusHandler, true);
                elem.removeEventListener('blur', blurHandler, true);
            }
            else {
                elem.onfocusin = null;
                elem.onfocusout = null;
            }
            $elem.removeData('focus.handlerReferences')
            $elem.removeData('focus.isFocused');
        }
        else {
            $elem.data('focus.handlerReferences', ref - 1);
        }
    }

    $.each(['focusin', 'focusout'], function (i, x) {
        $.event.special[x] = {
            setup: function () { setupEvents(this); },
            teardown: function () { teardownEvents(this); }
        };
    });

    $.fn.extend({
        focusin: function (fn) {
            return fn ? this.bind('focusin', fn) : this.trigger('focusin');
        },
        focusout: function (fn) {
            return fn ? this.bind('focusout', fn) : this.trigger('focusout');
        }
    });

})(jQuery);