/*! Lazy Load XT v1.1.0 2016-01-12
 * http://ressio.github.io/lazy-load-xt
 * (C) 2016 RESS.io
 * Licensed under MIT */

(function ($, window, document, undefined) {
    var options = $.lazyLoadXT,
        srcsetSupport = (function () {
            return 'srcset' in (new Image());
        })(),
        reUrl = /^\s*(\S*)/,
        reWidth = /\S\s+(\d+)w/,
        reHeight = /\S\s+(\d+)h/,
        reDpr = /\S\s+([\d\.]+)x/,
        infty = [0, Infinity],
        one = [0, 1],
        srcsetOptions = {
            srcsetAttr: 'data-srcset',
            srcsetExtended: true,
            srcsetBaseAttr: 'data-srcset-base',
            srcsetExtAttr: 'data-srcset-ext'
        },
        viewport = {
            w: 0,
            h: 0,
            x: 0
        },
        property,
        limit;

    for (property in srcsetOptions) {
        if (options[property] === undefined) {
            options[property] = srcsetOptions[property];
        }
    }
    options.selector += ',img[' + options.srcsetAttr + ']';

    function mathFilter(array, action) {
        return Math[action].apply(null, $.map(array, function (item) {
            return item[property];
        }));
    }

    function compareMax(item) {
        return item[property] >= viewport[property] || item[property] === limit;
    }

    function compareMin(item) {
        return item[property] === limit;
    }

    function parseSrcset($el) {
        var srcset = $el.attr(options.srcsetAttr);

        if (!srcset) {
            return false;
        }

        var list = $.map(srcset.replace(/(\s[\d.]+[whx]),/g, '$1 @,@ ').split(' @,@ '), function (item) {
            return {
                url: reUrl.exec(item)[1],
                w: parseFloat((reWidth.exec(item) || infty)[1]),
                h: parseFloat((reHeight.exec(item) || infty)[1]),
                x: parseFloat((reDpr.exec(item) || one)[1])
            };
        });

        if (!list.length) {
            return false;
        }

        var documentElement = document.documentElement,
            whx,
            src;

        viewport = {
            w: window.innerWidth || documentElement.clientWidth,
            h: window.innerHeight || documentElement.clientHeight,
            x: window.devicePixelRatio || 1
        };

        // Notice for DOMtastic users: currently $.grep method is not implemented in DOMtastic

        for (whx in viewport) {
            property = whx;
            limit = mathFilter(list, 'max');
            list = $.grep(list, compareMax);
        }

        for (whx in viewport) {
            property = whx;
            limit = mathFilter(list, 'min');
            list = $.grep(list, compareMin);
        }

        src = list[0].url;

        if (options.srcsetExtended) {
            src = ($el.attr(options.srcsetBaseAttr) || '') + src + ($el.attr(options.srcsetExtAttr) || '');
        }

        return src;
    }

    $(document).on('lazyshow', 'img', function (e, $el) {
        var srcset = $el.attr(options.srcsetAttr);

        if (srcset) {
            if (!options.srcsetExtended && srcsetSupport) {
                $el.attr('srcset', srcset);
                $el.attr('data-srcset', '');
            } else {
                $el.lazyLoadXT.srcAttr = parseSrcset;
            }
        }
    });

})(window.jQuery || window.Zepto || window.$, window, document);
