var scrolltotop = {
    //startline: Integer. Number of pixels from top of doc scrollbar is scrolled before showing control
    //scrollto: Keyword (Integer, or "Scroll_to_Element_ID"). How far to scroll document up when control is clicked on (0=top).
    setting: {startline: 100, scrollto: 0, scrollduration: 1000, fadeduration: [500, 100]},
    controlHTML: '', //<img src="assets/img/up.png" style="width:51px; height:42px" /> //HTML for control, which is auto wrapped in DIV w/ ID="topcontrol"
    controlattrs: {offsetx: 5, offsety: 5}, //offset of control relative to right/ bottom of window corner
    anchorkeyword: '#top', //Enter href value of HTML anchors on the page that should also act as "Scroll Up" links

    state: {isvisible: false, shouldvisible: false},

    scrollup: function () {
        if (!this.cssfixedsupport) //if control is positioned using JavaScript
            this.$control.css({opacity: 0}); //hide control immediately after clicking it
        var dest = isNaN(this.setting.scrollto) ? this.setting.scrollto : parseInt(this.setting.scrollto);
        if (typeof dest === "string" && jQuery('#' + dest).length === 1) //check element set by string exists
            dest = jQuery('#' + dest).offset().top;
        else
            dest = 0;
        this.$body.animate({scrollTop: dest}, this.setting.scrollduration);
    },

    keepfixed: function () {
        var $window = jQuery(window);
        var controlx = $window.scrollLeft() + $window.width() - this.$control.width() - this.controlattrs.offsetx;
        var controly = $window.scrollTop() + $window.height() - this.$control.height() - this.controlattrs.offsety;
        this.$control.css({left: controlx + 'px', top: controly + 'px'})
    },

    togglecontrol: function () {
        var scrolltop = jQuery(window).scrollTop();
        if (!this.cssfixedsupport)
            this.keepfixed();
        this.state.shouldvisible = (scrolltop >= this.setting.startline);
        if (this.state.shouldvisible && !this.state.isvisible) {
            this.$control.stop().animate({opacity: 1}, this.setting.fadeduration[0]);
            this.state.isvisible = true
        }
        else if (this.state.shouldvisible === false && this.state.isvisible) {
            this.$control.stop().animate({opacity: 0}, this.setting.fadeduration[1]);
            this.state.isvisible = false
        }
    },

    init: function () {
        jQuery(document).ready(function ($) {
            var mainobj = scrolltotop;
            var iebrws = document.all;
            mainobj.cssfixedsupport = !iebrws || iebrws && document.compatMode === "CSS1Compat" && window.XMLHttpRequest; //not IE or IE7+ browsers in standards mode
            mainobj.$body = (window.opera) ? (document.compatMode === "CSS1Compat" ? $('html') : $('body')) : $('html,body');
            mainobj.$control = $('<div id="topcontrol" class="d-print-none">' + mainobj.controlHTML + '</div>')
                .css({
                    position: mainobj.cssfixedsupport ? 'fixed' : 'absolute',
                    bottom: mainobj.controlattrs.offsety,
                    right: mainobj.controlattrs.offsetx,
                    opacity: 0,
                    cursor: 'pointer'
                })
                .attr({title: 'Scroll Back to Top'})
                .click(function () {
                    mainobj.scrollup();
                    return false
                })
                .appendTo('body');
            if (document.all && !window.XMLHttpRequest && mainobj.$control.text() !== '') //loose check for IE6 and below, plus whether control contains any text
                mainobj.$control.css({width: mainobj.$control.width()}); //IE6- seems to require an explicit width on a DIV containing text
            mainobj.togglecontrol();
            $('a[href="' + mainobj.anchorkeyword + '"]').click(function () {
                mainobj.scrollup();
                return false
            });
            $(window).bind('scroll resize', function (e) {
                mainobj.togglecontrol()
            })
        })
    }
};

scrolltotop.init();