// ==UserScript==
// @name           Hatena::Bookmark - Favorite Users Ratio
// @namespace      http://d.hatena.ne.jp/KGA/
// @include        http://b.hatena.ne.jp/entry/*
// ==/UserScript==

(function() {
    var th = $X('//th[contains(., "お気に入り")]')[0];
    if (!th) return;
    var favs = $X('count(./following-sibling::td/ul[@class="userlist"]/li)', th, null, XPathResult.NUMBER_TYPE).wrappedJSObject.numberValue;

    var users = $X('id("entry-info")/li[@class="users"]//a/text()', null, null, XPathResult.STRING_TYPE).wrappedJSObject.stringValue;
    if (!users) return;
    var count = parseInt(users.match(/\d+/)[0]);

    var ratio = parseInt(favs / count * 100);

    th.appendChild(document.createElement('br'));
    th.appendChild(document.createTextNode([ratio, '% (', favs, '/', count, ')'].join('')));

    // very simple version of $X
    // $X(exp);
    // $X(exp, context);
    // $X(exp, context, resolver);
    // @source http://gist.github.com/29681.txt
    function $X (exp, context, resolver, result_type) {
        context || (context = document);
        var Doc = context.ownerDocument || context;
        var result = Doc.evaluate(exp, context, resolver, result_type || XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
            if (result_type) return result;
        for (var i = 0, len = result.snapshotLength, res = []; i < len; i++) {
            res.push(result.snapshotItem(i));
        }
        return res;
    }
})();