var initphotoswipefromdom = function(galleryselector) {

    // parse slide data (url, title, size ...) from dom elements 
    // (children of galleryselector)
    var parsethumbnailelements = function(el) {
        var thumbelements = el.childnodes,
            numnodes = thumbelements.length,
            items = [],
            figureel,
            childelements,
            linkel,
            size,
            item;

        for(var i = 0; i < numnodes; i++) {


            figureel = thumbelements[i]; // <figure> element

            // include only element nodes 
            if(figureel.nodetype !== 1) {
                continue;
            }

            linkel = figureel.children[0]; // <a> element
            
            size = linkel.getattribute('data-size').split('x');

            // create slide object
            item = {
                src: linkel.getattribute('href'),
                w: parseint(size[0], 10),
                h: parseint(size[1], 10)
            };

            

            if(figureel.children.length > 1) {
                // <figcaption> content
                item.title = figureel.children[1].innerhtml; 
            }
 
            if(linkel.children.length > 0) {
                // <img> thumbnail element, retrieving thumbnail url
                item.msrc = linkel.children[0].getattribute('src');
            } 
           
            item.el = figureel; // save link to element for getthumbboundsfn
            items.push(item);
        }

        return items;
    };

    // find nearest parent element
    var closest = function closest(el, fn) {
        return el && ( fn(el) ? el : closest(el.parentnode, fn) );
    };

    // triggers when user clicks on thumbnail
    var onthumbnailsclick = function(e) {
        e = e || window.event;
        e.preventdefault ? e.preventdefault() : e.returnvalue = false;

        var etarget = e.target || e.srcelement;

        var clickedlistitem = closest(etarget, function(el) {
            return el.tagname === 'li';
        });

        if(!clickedlistitem) {
            return;
        }


        // find index of clicked item
        var clickedgallery = clickedlistitem.parentnode,
            childnodes = clickedlistitem.parentnode.childnodes,
            numchildnodes = childnodes.length,
            nodeindex = 0,
            index;

        for (var i = 0; i < numchildnodes; i++) {
            if(childnodes[i].nodetype !== 1) { 
                continue; 
            }

            if(childnodes[i] === clickedlistitem) {
                index = nodeindex;
                break;
            }
            nodeindex++;
        }



        if(index >= 0) {
            openphotoswipe( index, clickedgallery );
        }
        return false;
    };

    // parse picture index and gallery index from url (#&pid=1&gid=2)
    var photoswipeparsehash = function() {
        var hash = window.location.hash.substring(1),
        params = {};

        if(hash.length < 5) {
            return params;
        }

        var vars = hash.split('&');
        for (var i = 0; i < vars.length; i++) {
            if(!vars[i]) {
                continue;
            }
            var pair = vars[i].split('=');  
            if(pair.length < 2) {
                continue;
            }           
            params[pair[0]] = pair[1];
        }

        if(params.gid) {
            params.gid = parseint(params.gid, 10);
        }

        if(!params.hasownproperty('pid')) {
            return params;
        }
        params.pid = parseint(params.pid, 10);
        return params;
    };

    var openphotoswipe = function(index, galleryelement, disableanimation) {
        var pswpelement = document.queryselectorall('.pswp')[0],
            gallery,
            options,
            items;

        items = parsethumbnailelements(galleryelement);

        // define options (if needed)
        options = {
            index: index,
            history: false,
            taptoclose: true,
            // define gallery index (for url)
            galleryuid: galleryelement.getattribute('data-pswp-uid'),

            getthumbboundsfn: function(index) {
                // see options -> getthumbboundsfn section of docs for more info
                var thumbnail = items[index].el.getelementsbytagname('img')[0], // find thumbnail
                    pageyscroll = window.pageyoffset || document.documentelement.scrolltop,
                    rect = thumbnail.getboundingclientrect(); 

                return {x:rect.left, y:rect.top + pageyscroll, w:rect.width};
            },

            // history & focus options are disabled on codepen
            // remove these lines in real life: 
           historyenabled: false,
           focus: false 

        };

        if(disableanimation) {
            options.showanimationduration = 0;
        }

        // pass data to photoswipe and initialize it
        gallery = new photoswipe( pswpelement, photoswipeui_default, items, options);
        gallery.init();
    };

    // loop through all gallery elements and bind events
    var galleryelements = document.queryselectorall( galleryselector );

    for(var i = 0, l = galleryelements.length; i < l; i++) {
        galleryelements[i].setattribute('data-pswp-uid', i+1);
        galleryelements[i].onclick = onthumbnailsclick;
    }

    // parse url and open gallery if it contains #&pid=3&gid=1
    var hashdata = photoswipeparsehash();
    if(hashdata.pid > 0 && hashdata.gid > 0) {
        openphotoswipe( hashdata.pid - 1 ,  galleryelements[ hashdata.gid - 1 ], true );
    }
};

// execute above function
initphotoswipefromdom('.my-gallery');