'use strict';

const I18N = (() => {
  const SUPPORTED_LANGS = ['fr', 'en'];
  const DEFAULT_LANG = 'fr';
  const STORAGE_KEY = 'republican-calendar-lang';

  let currentLang = DEFAULT_LANG;
  let common = {};
  let months = {};
  let about = {};
  const changeListeners = [];

  function detectInitialLang() {
    try {
      const stored = localStorage.getItem(STORAGE_KEY);
      if (stored && SUPPORTED_LANGS.includes(stored)) return stored;
    } catch (error) {
      // localStorage unavailable (private mode, etc.): fall through to default.
    }
    return DEFAULT_LANG;
  }

  function getByPath(object, path) {
    return path.split('.').reduce((node, key) => (node && node[key] !== undefined ? node[key] : undefined), object);
  }

  function t(path, fallback) {
    const value = getByPath(common, path);
    return value !== undefined ? value : (fallback !== undefined ? fallback : path);
  }

  function applyStaticTranslations() {
    document.documentElement.lang = currentLang;
    document.querySelectorAll('[data-i18n]').forEach((element) => {
      const key = element.getAttribute('data-i18n');
      const value = getByPath(common, key);
      if (value !== undefined) {
        element.textContent = value;
      }
    });
  }

  async function fetchJson(url) {
    const response = await fetch(url, { cache: 'no-store' });
    if (!response.ok) {
      throw new Error(`Failed to load ${url}: ${response.status}`);
    }
    return response.json();
  }

  async function load(lang) {
    const targetLang = SUPPORTED_LANGS.includes(lang) ? lang : DEFAULT_LANG;
    const [commonData, monthsData, aboutData] = await Promise.all([
      fetchJson(`locales/${targetLang}/common.json`),
      fetchJson(`locales/${targetLang}/months.json`),
      fetchJson(`locales/${targetLang}/about.json`),
    ]);
    currentLang = targetLang;
    common = commonData;
    months = monthsData;
    about = aboutData;
    applyStaticTranslations();
    changeListeners.forEach((listener) => listener(currentLang));
  }

  async function setLang(lang) {
    if (!SUPPORTED_LANGS.includes(lang) || lang === currentLang) return;
    try {
      localStorage.setItem(STORAGE_KEY, lang);
    } catch (error) {
      // Ignore storage failures; language just won't persist across reloads.
    }
    await load(lang);
  }

  function onChange(listener) {
    changeListeners.push(listener);
  }

  return {
    SUPPORTED_LANGS,
    get currentLang() { return currentLang; },
    get common() { return common; },
    get months() { return months; },
    get about() { return about; },
    detectInitialLang,
    load,
    setLang,
    onChange,
    t,
  };
})();