(() => {
  const root = document.documentElement;
  const title = {
    cn: 'DBC 世界杯竞猜官网｜新材料应用创新平台 · BIOTEN 博碳生物',
    en: 'DBC | Advanced-Material Application Platform · BIOTEN'
  };
  const description = {
    cn: '世界杯竞猜官网连接材料研发、应用工程、验证交付与产业协同；BIOTEN 围绕 PHA 水性材料开展纸基包装、农业科技、日化个护与水性涂层应用开发。',
    en: 'DBC connects materials R&D, application engineering, validation delivery and industrial collaboration. BIOTEN develops PHA waterborne-material applications across paper packaging, agricultural technology, personal care and waterborne coatings.'
  };

  let applying = false;

  function isEnglish() {
    return root.dataset.lang === 'en' || root.lang.toLowerCase().startsWith('en');
  }

  function applyLanguage() {
    if (applying) return;
    applying = true;

    const language = isEnglish() ? 'en' : 'cn';
    document.querySelectorAll('[data-nav-cn][data-nav-en]').forEach((element) => {
      const value = element.dataset[language === 'en' ? 'navEn' : 'navCn'];
      if (typeof value === 'string' && element.textContent !== value) {
        element.textContent = value;
      }
    });

    document.querySelectorAll('[data-aria-cn][data-aria-en]').forEach((element) => {
      const value = element.dataset[language === 'en' ? 'ariaEn' : 'ariaCn'];
      if (value && element.getAttribute('aria-label') !== value) element.setAttribute('aria-label', value);
    });

    document.querySelectorAll('[data-alt-cn][data-alt-en]').forEach((element) => {
      const value = element.dataset[language === 'en' ? 'altEn' : 'altCn'];
      if (value && element.getAttribute('alt') !== value) element.setAttribute('alt', value);
    });

    if (document.title !== title[language]) document.title = title[language];
    const metaDescription = document.querySelector('meta[name="description"]');
    if (metaDescription && metaDescription.content !== description[language]) {
      metaDescription.content = description[language];
    }

    applying = false;
  }

  function scheduleApply() {
    window.requestAnimationFrame(applyLanguage);
    window.setTimeout(applyLanguage, 60);
    window.setTimeout(applyLanguage, 260);
  }

  const languageObserver = new MutationObserver(scheduleApply);
  languageObserver.observe(root, {
    attributes: true,
    attributeFilter: ['lang', 'data-lang']
  });

  if (document.head) {
    const headObserver = new MutationObserver(scheduleApply);
    headObserver.observe(document.head, { childList: true, characterData: true, subtree: true });
  }

  document.addEventListener('click', (event) => {
    if (event.target.closest('.language-toggle, [data-language-toggle], [aria-label*="English"], [aria-label*="中文"]')) {
      scheduleApply();
    }
  });

  if (document.readyState === 'loading') {
    document.addEventListener('DOMContentLoaded', scheduleApply, { once: true });
  } else {
    scheduleApply();
  }
})();