let select = document.getElementById("themeswitcher");
let theme = document.getElementById("theme");

if (checkCookie("theme")) {
    setTheme(getCookie("theme"));
    select.value = getCookie("theme");
}

select.addEventListener("change", e => {
    let selTheme = select.options[select.selectedIndex].value;
    setTheme(selTheme);
    setCookie("theme", selTheme, 60);
});

function setTheme(themeName) {
    theme.href = "themes/" + themeName + ".css";
}

function getCookie(cname) {
    var name = cname + "=";
    var decodedCookie = decodeURIComponent(document.cookie);
    var ca = decodedCookie.split(";");
    for (var i = 0; i < ca.length; i++) {
        var c = ca[i];
        while (c.charAt(0) == " ") {
            c = c.substring(1);
        }
        if (c.indexOf(name) == 0) {
            return c.substring(name.length, c.length);
        }
    }
    return "";
}

function setCookie(cname, cvalue, exdays) {
    var d = new Date();
    d.setTime(d.getTime() + exdays * 24 * 60 * 60 * 1000);
    var expires = "expires=" + d.toUTCString();
    document.cookie = cname + "=" + cvalue + ";" + expires + ";path=/";
}

function checkCookie(cookieName) {
    return getCookie(cookieName) != "";
}