function $X(path, root) {
    return document.evaluate(path, root || document, null, 6, null);
}
function $x(path, root) {
    return document.evaluate(path, root || document, null, 8, null).singleNodeValue;
}

function $del(el) {
    if(el) el.parentNode.removeChild(el);
}

function $each(list, fn) {
    if(!list) return;
    var i = list.snapshotLength;
    if(i > 0) while(i--) fn(list.snapshotItem(i), i);
}

function mkPreview(cln, html) {
    cln.innerHTML = html;

    highlightCode($(cln));
    addRefLinkPreview(cln);
};

function isElementInViewport (el) {
    //special bonus for those using jQuery
    if (typeof jQuery === "function" && el instanceof jQuery) {
        el = el[0];
    }

    var rect = el.getBoundingClientRect();

    return (
        rect.top >= 0 &&
        rect.left >= 0 &&
        rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) && /*or $(window).height() */
        rect.right <= (window.innerWidth || document.documentElement.clientWidth) /*or $(window).width() */
    );
}

function addRefLinkPreview(node) {
    $each($X('.//a[starts-with(text(),">>")]', node || document), function(link) {
        link.addEventListener('mouseover', showPostPreview, false);
        link.addEventListener('mouseout', delPostPreview, false);
    });
}

function showPostPreview(e) {
    var doc = document;
    //ref id
    var pNum = $(this).text().match(/\d+/);

    if (pNum == null || pNum.length == 0) {
        return;
    }

    var post = $('#' + pNum);
    if (post.length > 0 && isElementInViewport(post)) {
        post.addClass('highlight');
    } else {
        var x = e.clientX + (doc.documentElement.scrollLeft || doc.body.scrollLeft) + 2;
        var y = e.clientY + (doc.documentElement.scrollTop || doc.body.scrollTop);

        var cln = doc.createElement('div');
        cln.id = 'pstprev_' + pNum;
        cln.className = 'post_preview';

        cln.style.cssText = 'top:' + y + 'px;' + (x < doc.body.clientWidth/2 ? 'left:' + x + 'px' : 'right:' + parseInt(doc.body.clientWidth - x + 1) + 'px');

        cln.addEventListener('mouseout', delPostPreview, false);

        cln.innerHTML = "<div class=\"post\">" + gettext('Loading...') + "</div>";

        if(post.length > 0) {
            var postdata = post.clone().wrap("<div/>").parent().html();

            mkPreview(cln, postdata);
        } else {
            $.ajax({
                url: '/api/post/' + pNum + '/?truncated'
            })
                .success(function(data) {
                    var postdata = $(data).wrap("<div/>").parent().html();

                    //make preview
                    mkPreview(cln, postdata);

                })
                .error(function() {
                    cln.innerHTML = "<div class=\"post\">"
                        + gettext('Post not found') + "</div>";
                });
        }

        $del(doc.getElementById(cln.id));

        //add preview
        $(cln).fadeIn(200);
        $('body').append(cln);
    }
}

function delPostPreview(e) {
    var el = $x('ancestor-or-self::*[starts-with(@id,"pstprev")]', e.relatedTarget);
    if(!el) {
        $each($X('.//div[starts-with(@id,"pstprev")]'), function(clone) {
            $del(clone)
        });
    } else {
        while(el.nextSibling) $del(el.nextSibling);
    }

    $('.highlight').removeClass('highlight');
}

function addPreview() {
    $('.post').find('a').each(function() {
        showPostPreview($(this));
    });
}