/*
Plugin: jQuery Parallax
Version 1.1.3
Author: Ian Lunn
Twitter: @IanLunn
Author URL: http://www.ianlunn.co.uk/
Plugin URL: http://www.ianlunn.co.uk/plugins/jquery-parallax/

Dual licensed under the MIT and GPL licenses:
http://www.opensource.org/licenses/mit-license.php
http://www.gnu.org/licenses/gpl.html
*/

(function($) {
    var $window = $(window);
    var windowHeight = $window.height();

    $window.resize(
        function() {
            windowHeight = $window.height();
        }
    );

    $.fn.parallax = function(xpos, speedFactor, outerHeight) {
        var $this = $(this);
        var getHeight;
        var firstTop;
        var paddingTop = 0;

        //get the starting position of each element to have parallax applied to it
        $this.each(
            function() {
                firstTop = $this.offset().top;
            }
        );

        if (outerHeight) {
            getHeight = function(jqo) {
                return jqo.outerHeight(true);
            };
        } else {
            getHeight = function(jqo) {
                return jqo.height();
            };
        }

        // setup defaults if arguments aren't specified
        if (arguments.length < 1 || xpos === null) {
            xpos = "50%";
        }
        if (arguments.length < 2 || speedFactor === null) {
            speedFactor = 0.1;
        }
        if (arguments.length < 3 || outerHeight === null) {
            outerHeight = true;
        }

        // function to be called whenever the window is scrolled or resized
        function update() {
            var pos = $window.scrollTop();

            $this.each(
                function() {
                    var $element = $(this);
                    var top = $element.offset().top;
                    var height = getHeight($element);

                    // Check if totally above or totally below viewport
                    if (top + height < pos || top > pos + windowHeight) {
                        return;
                    }

                    $this.css('backgroundPosition', xpos + " " + Math.round((firstTop - pos) * speedFactor) + "px");
                }
            );
        }

        $window.bind('scroll', update)
               .resize(update);
        update();
    };
})(jQuery);
