(function ($, window, document) {
    'use strict';

    // main function
    $.fn.scrollup = function (options) {

        // ensure that only one scrollup exists
        if (!$.data(document.body, 'scrollup')) {
            $.data(document.body, 'scrollup', true);
            $.fn.scrollup.init(options);
        }
    };

    // init
    $.fn.scrollup.init = function (options) {

        // define vars
        var o = $.fn.scrollup.settings = $.extend({}, $.fn.scrollup.defaults, options),
            triggervisible = false,
            animin, animout, animspeed, scrolldis, scrollevent, scrolltarget, $self;

        // create element
        if (o.scrolltrigger) {
            $self = $(o.scrolltrigger);
        } else {
            $self = $('<a/>', {
                id: o.scrollname,
                href: '#top'
            });
        }

        // set scrolltitle if there is one
        if (o.scrolltitle) {
            $self.attr('title', o.scrolltitle);
        }

        $self.appendto('body');

        // if not using an image display text
        if (!(o.scrollimg || o.scrolltrigger)) {
            $self.html(o.scrolltext);
        }

        // minimum css to make the magic happen
        $self.css({
            display: 'none',
            position: 'fixed',
            zindex: o.zindex
        });

        // active point overlay
        if (o.activeoverlay) {
            $('<div/>', {
                id: o.scrollname + '-active'
            }).css({
                position: 'absolute',
                'top': o.scrolldistance + 'px',
                width: '100%',
                bordertop: '1px dotted' + o.activeoverlay,
                zindex: o.zindex
            }).appendto('body');
        }

        // switch animation type
        switch (o.animation) {
            case 'fade':
                animin = 'fadein';
                animout = 'fadeout';
                animspeed = o.animationspeed;
                break;

            case 'slide':
                animin = 'slidedown';
                animout = 'slideup';
                animspeed = o.animationspeed;
                break;

            default:
                animin = 'show';
                animout = 'hide';
                animspeed = 0;
        }

        // if from top or bottom
        if (o.scrollfrom === 'top') {
            scrolldis = o.scrolldistance;
        } else {
            scrolldis = $(document).height() - $(window).height() - o.scrolldistance;
        }

        // scroll function
        scrollevent = $(window).scroll(function () {
            if ($(window).scrolltop() > scrolldis) {
                if (!triggervisible) {
                    $self[animin](animspeed);
                    triggervisible = true;
                }
            } else {
                if (triggervisible) {
                    $self[animout](animspeed);
                    triggervisible = false;
                }
            }
        });

        if (o.scrolltarget) {
            if (typeof o.scrolltarget === 'number') {
                scrolltarget = o.scrolltarget;
            } else if (typeof o.scrolltarget === 'string') {
                scrolltarget = math.floor($(o.scrolltarget).offset().top);
            }
        } else {
            scrolltarget = 0;
        }

        // to the top
        $self.click(function (e) {
            e.preventdefault();

            $('html, body').animate({
                scrolltop: scrolltarget
            }, o.scrollspeed, o.easingtype);
        });
    };

    // defaults
    $.fn.scrollup.defaults = {
        scrollname: 'scrollup',      // element id
        scrolldistance: 300,         // distance from top/bottom before showing element (px)
        scrollfrom: 'top',           // 'top' or 'bottom'
        scrollspeed: 300,            // speed back to top (ms)
        easingtype: 'linear',        // scroll to top easing (see http://easings.net/)
        animation: 'fade',           // fade, slide, none
        animationspeed: 200,         // animation in speed (ms)
        scrolltrigger: false,        // set a custom triggering element. can be an html string or jquery object
        scrolltarget: false,         // set a custom target element for scrolling to. can be element or number
        scrolltext: 'scroll to top', // text for element, can contain html
        scrolltitle: false,          // set a custom <a> title if required. defaults to scrolltext
        scrollimg: false,            // set true to use image
        activeoverlay: false,        // set css color to display scrollup active point, e.g '#00ffff'
        zindex: 2147483647           // z-index for the overlay
    };

    // destroy scrollup plugin and clean all modifications to the dom
    $.fn.scrollup.destroy = function (scrollevent) {
        $.removedata(document.body, 'scrollup');
        $('#' + $.fn.scrollup.settings.scrollname).remove();
        $('#' + $.fn.scrollup.settings.scrollname + '-active').remove();

        // if 1.7 or above use the new .off()
        if ($.fn.jquery.split('.')[1] >= 7) {
            $(window).off('scroll', scrollevent);

        // else use the old .unbind()
        } else {
            $(window).unbind('scroll', scrollevent);
        }
    };

    $.scrollup = $.fn.scrollup;

})(jquery, window, document);