(() => {
  const LANGS = [
    "zh-Hans", "zh-Hant", "en-US", "ja", "ko", "es-MX", "fr-FR",
    "de-DE", "pt-BR", "ru", "ar-SA", "it", "th", "vi", "id",
  ];

  const UI = {
    "zh-Hans": { home: "首页", privacy: "隐私政策", terms: "用户协议", toDark: "暗黑", toLight: "日间" },
    "zh-Hant": { home: "首頁", privacy: "隱私政策", terms: "使用者協議", toDark: "深色", toLight: "日間" },
    "en-US": { home: "Home", privacy: "Privacy Policy", terms: "Terms of Use", toDark: "Dark", toLight: "Light" },
    ja: { home: "ホーム", privacy: "プライバシー", terms: "利用規約", toDark: "ダーク", toLight: "ライト" },
    ko: { home: "홈", privacy: "개인정보", terms: "이용약관", toDark: "어둡게", toLight: "밝게" },
    "es-MX": { home: "Inicio", privacy: "Privacidad", terms: "Condiciones", toDark: "Oscuro", toLight: "Claro" },
    "fr-FR": { home: "Accueil", privacy: "Confidentialité", terms: "Conditions", toDark: "Sombre", toLight: "Clair" },
    "de-DE": { home: "Start", privacy: "Datenschutz", terms: "Nutzung", toDark: "Dunkel", toLight: "Hell" },
    "pt-BR": { home: "Início", privacy: "Privacidade", terms: "Termos", toDark: "Escuro", toLight: "Claro" },
    ru: { home: "Главная", privacy: "Конфиденциальность", terms: "Условия", toDark: "Тёмная", toLight: "Светлая" },
    "ar-SA": { home: "الرئيسية", privacy: "الخصوصية", terms: "الشروط", toDark: "داكن", toLight: "فاتح" },
    it: { home: "Home", privacy: "Privacy", terms: "Condizioni", toDark: "Scuro", toLight: "Chiaro" },
    th: { home: "หน้าแรก", privacy: "ความเป็นส่วนตัว", terms: "ข้อกำหนด", toDark: "มืด", toLight: "สว่าง" },
    vi: { home: "Trang chủ", privacy: "Quyền riêng tư", terms: "Điều khoản", toDark: "Tối", toLight: "Sáng" },
    id: { home: "Beranda", privacy: "Privasi", terms: "Ketentuan", toDark: "Gelap", toLight: "Terang" },
  };

  const HTML_LANG = {
    "zh-Hans": "zh-CN",
    "zh-Hant": "zh-TW",
    "en-US": "en",
    ja: "ja",
    ko: "ko",
    "es-MX": "es-MX",
    "fr-FR": "fr",
    "de-DE": "de",
    "pt-BR": "pt-BR",
    ru: "ru",
    "ar-SA": "ar",
    it: "it",
    th: "th",
    vi: "vi",
    id: "id",
  };

  function norm(tag) {
    if (!tag) return "";
    const raw = String(tag).trim().replace(/_/g, "-");
    if (LANGS.includes(raw)) return raw;
    const lower = raw.toLowerCase();
    if (lower === "zh" || lower === "zh-cn" || lower === "zh-sg" || lower === "zh-hans") return "zh-Hans";
    if (lower === "zh-tw" || lower === "zh-hk" || lower === "zh-mo" || lower === "zh-hant") return "zh-Hant";
    if (lower.startsWith("en")) return "en-US";
    if (lower.startsWith("ja")) return "ja";
    if (lower.startsWith("ko")) return "ko";
    if (lower.startsWith("es")) return "es-MX";
    if (lower.startsWith("fr")) return "fr-FR";
    if (lower.startsWith("de")) return "de-DE";
    if (lower.startsWith("pt")) return "pt-BR";
    if (lower.startsWith("ru")) return "ru";
    if (lower.startsWith("ar")) return "ar-SA";
    if (lower.startsWith("it")) return "it";
    if (lower.startsWith("th")) return "th";
    if (lower.startsWith("vi")) return "vi";
    if (lower === "id" || lower.startsWith("id-") || lower.startsWith("in")) return "id";
    return "";
  }

  function detectLang() {
    const query = new URLSearchParams(location.search).get("lang");
    if (query) return norm(query) || "zh-Hans";
    try {
      const saved = norm(localStorage.getItem("spark-legal-lang"));
      if (saved) return saved;
    } catch (_) { /* ignore */ }
    const list = navigator.languages && navigator.languages.length
      ? navigator.languages
      : [navigator.language || ""];
    for (const item of list) {
      const code = norm(item);
      if (code) return code;
    }
    return "zh-Hans";
  }

  function effectiveTheme() {
    const chosen = document.documentElement.getAttribute("data-theme");
    if (chosen === "dark" || chosen === "light") return chosen;
    return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
  }

  function applyTheme(mode) {
    if (mode === "light" || mode === "dark") {
      document.documentElement.setAttribute("data-theme", mode);
    } else {
      document.documentElement.removeAttribute("data-theme");
    }
    paintThemeButton();
  }

  function paintThemeButton() {
    const button = document.getElementById("theme");
    const lang = document.documentElement.getAttribute("data-lang") || "zh-Hans";
    const ui = UI[lang] || UI["zh-Hans"];
    if (!button) return;
    const dark = effectiveTheme() === "dark";
    button.textContent = dark ? ui.toLight : ui.toDark;
    button.setAttribute("aria-pressed", dark ? "true" : "false");
  }

  function applyLang(code) {
    const safe = LANGS.includes(code) ? code : "zh-Hans";
    document.querySelectorAll("article[data-lang]").forEach((node) => {
      node.hidden = node.getAttribute("data-lang") !== safe;
    });
    document.documentElement.lang = HTML_LANG[safe] || "zh-CN";
    document.documentElement.dir = safe === "ar-SA" ? "rtl" : "ltr";
    document.documentElement.setAttribute("data-lang", safe);
    const heading = document.querySelector(`article[data-lang="${safe}"] h1`);
    if (heading && heading.textContent) {
      document.title = `${heading.textContent.trim()} — Spark Messenger`;
    }
    const ui = UI[safe];
    document.querySelectorAll("[data-i18n]").forEach((node) => {
      const key = node.getAttribute("data-i18n");
      if (ui[key]) node.textContent = ui[key];
    });
    const select = document.getElementById("lang");
    if (select) select.value = safe;
    paintThemeButton();
  }

  applyLang(detectLang());

  try {
    const savedTheme = localStorage.getItem("spark-legal-theme");
    if (savedTheme === "light" || savedTheme === "dark") applyTheme(savedTheme);
    else paintThemeButton();
  } catch (_) {
    paintThemeButton();
  }

  const select = document.getElementById("lang");
  if (select) {
    select.addEventListener("change", () => {
      applyLang(select.value);
      try { localStorage.setItem("spark-legal-lang", select.value); } catch (_) { /* ignore */ }
      const url = new URL(location.href);
      url.searchParams.set("lang", select.value);
      history.replaceState(null, "", url);
    });
  }

  const themeButton = document.getElementById("theme");
  if (themeButton) {
    themeButton.addEventListener("click", () => {
      const next = effectiveTheme() === "dark" ? "light" : "dark";
      applyTheme(next);
      try { localStorage.setItem("spark-legal-theme", next); } catch (_) { /* ignore */ }
    });
  }

  const media = window.matchMedia("(prefers-color-scheme: dark)");
  const onScheme = () => {
    if (!document.documentElement.getAttribute("data-theme")) paintThemeButton();
  };
  if (typeof media.addEventListener === "function") media.addEventListener("change", onScheme);
  else if (typeof media.addListener === "function") media.addListener(onScheme);
})();