(function () {
    "use strict";

    var root = document.documentElement;
    var onRuPage = location.pathname.indexOf("/ru/") === 0 || location.pathname === "/ru";
    var stored = null;
    var theme = null;

    try {
        stored = localStorage.getItem("cursorlang.lang");
        theme = localStorage.getItem("cursorlang.theme");
    } catch (error) {
        // Storage refused: what the URL says stands
    }

    // A stored choice always wins, on either page.
    if (stored === "ru" && !onRuPage) {
        location.replace("/ru/" + location.search + location.hash);
        return;
    }
    if (stored === "en" && onRuPage) {
        location.replace("/" + location.search + location.hash);
        return;
    }

    // No stored choice yet: send a browser set to Russian to the Russian page,
    // once. Never redirect away from a page a link already pointed at — a
    // shared /ru/ link, or a crawler fetching either URL directly, stands.
    if (!stored && !onRuPage && (navigator.language || "").toLowerCase().indexOf("ru") === 0) {
        location.replace("/ru/" + location.search + location.hash);
        return;
    }

    var lang = onRuPage ? "ru" : "en";
    root.setAttribute("data-lang", lang);
    root.setAttribute("lang", lang);

    if (theme === "dark" || theme === "light") {
        root.setAttribute("data-theme", theme);
    }
}());