/*

* Viewport - jQuery selectors for finding elements in viewport
*
* Copyright (c) 2008-2009 Mika Tuupola
*
* Licensed under the MIT license:
*   http://www.opensource.org/licenses/mit-license.php
*
* Project home:
*  http://www.appelsiini.net/projects/viewport
*
*/

(function($) {

$.belowthefold = function(element, settings) {
    var fold = $(window).height() + $(window).scrollTop();
    return fold <= $(element).offset().top - settings.threshold;
};

$.abovethetop = function(element, settings) {
    var top = $(window).scrollTop();
    return top >= $(element).offset().top + $(element).height() - settings.threshold;
};

$.rightofscreen = function(element, settings) {
    var fold = $(window).width() + $(window).scrollLeft();
    return fold <= $(element).offset().left - settings.threshold;
};

$.leftofscreen = function(element, settings) {
    var left = $(window).scrollLeft();
    return left >= $(element).offset().left + $(element).width() - settings.threshold;
};

$.inviewport = function(element, settings) {
    return !$.rightofscreen(element, settings) && !$.leftofscreen(element, settings) && !$.belowthefold(element, settings) && !$.abovethetop(element, settings);
};

$.extend($.expr[':'], {
    "below-the-fold": function(a, i, m) {
        return $.belowthefold(a, {threshold : 0});
    },
    "above-the-top": function(a, i, m) {
        return $.abovethetop(a, {threshold : 0});
    },
    "left-of-screen": function(a, i, m) {
        return $.leftofscreen(a, {threshold : 0});
    },
    "right-of-screen": function(a, i, m) {
        return $.rightofscreen(a, {threshold : 0});
    },
    "in-viewport": function(a, i, m) {
        return $.inviewport(a, {threshold : 0});
    }
});

})(jQuery);