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

var CLS_PREVIEW = 'post_preview';

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;

    addScriptsToPost($(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;

    var reflink = $(this);
    var pNum = reflink.text().match(/\d+/);

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

    var post = $('#' + pNum);
    if (post.length > 0 && isElementInViewport(post)) {
        // If post is on the same page and visible, just highlight it
        post.addClass('highlight');
    } else {
        var x = reflink.offset().left;
        var y = reflink.offset().top;

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

        cln.style.cssText = 'left:' + x + 'px; top:' + y + 'px';

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

        cln.innerHTML = LOADING_MSG;

        if (post.length > 0) {
            // If post is on the same page but not visible, generate preview from it
            var postClone = post.clone();
            postClone.removeAttr('style');
            var postdata = postClone.wrap("<div/>").parent().html();

            mkPreview(cln, postdata);
        } else {
            // If post is from other page, load it
            $.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) {
            if (el.nextSibling.className == CLS_PREVIEW) {
                $del(el.nextSibling);
            } else {
                break;
            }
        }
    }

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

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