(function () {
    const root = document.documentElement;

    function applyTheme(theme) {
        root.setAttribute("data-theme", theme);
        localStorage.setItem("theme", theme);
    }

    function getSystemTheme() {
        return window.matchMedia("(prefers-color-scheme: dark)").matches
            ? "dark"
            : "light";
    }

    function initTheme() {
        const savedTheme = localStorage.getItem("theme");
        applyTheme(savedTheme || getSystemTheme());
    }

    // expose globally
    window.setTheme = applyTheme;

    document.addEventListener("DOMContentLoaded", initTheme);
})();