/**
 * MeshBay i18n — lightweight string localization.
 *
 * Catalogues live one per language in `locales/` and are fetched on demand, so
 * a visitor downloads the language they read plus English as a fallback, never
 * the other eight.
 *
 * Usage:
 *   import { t, initLocale, setLocale, getLocale, LOCALES } from './i18n.js';
 *   await initLocale();          // once, before the first render
 *   t('nav.logout')              // "Logout"
 *   t('status.files', { n: 42 }) // "42 files"
 *
 * A catalogue value is a string, or an object keyed by Intl.PluralRules
 * category when it is rendered with a count:
 *   'status.files': { one: '{n} file', other: '{n} files' }
 * Polish needs `one`/`few`/`many`/`other` where English needs two, which is why
 * the plural category is chosen here rather than baked into the string.
 */

const LANG_KEY = 'mb_lang';
const FALLBACK = 'en';

export const LOCALES = [
  { code: 'en', name: 'English', flag: '\u{1F1EC}\u{1F1E7}' },
  { code: 'fr', name: 'Français', flag: '\u{1F1EB}\u{1F1F7}' },
  { code: 'es', name: 'Español', flag: '\u{1F1EA}\u{1F1F8}' },
  { code: 'pt-BR', name: 'Português (Brasil)', flag: '\u{1F1E7}\u{1F1F7}' },
  { code: 'zh-CN', name: '简体中文', flag: '\u{1F1E8}\u{1F1F3}' },
  { code: 'ja', name: '日本語', flag: '\u{1F1EF}\u{1F1F5}' },
  { code: 'de', name: 'Deutsch', flag: '\u{1F1E9}\u{1F1EA}' },
  { code: 'it', name: 'Italiano', flag: '\u{1F1EE}\u{1F1F9}' },
  { code: 'nl', name: 'Nederlands', flag: '\u{1F1F3}\u{1F1F1}' },
  { code: 'pl', name: 'Polski', flag: '\u{1F1F5}\u{1F1F1}' },
];

const _codes = LOCALES.map(l => l.code);
const _strings = {};
const _plurals = {};
let _locale = FALLBACK;

// ── Resolution ──────────────────────────────────────────────────────────────

/**
 * Match a requested tag against the registry, region-tolerantly.
 *
 * `navigator.language` is `pt-BR` or `zh-CN` on the machines those catalogues
 * are for, and `fr-CA` or `de-AT` on machines the base catalogue serves fine.
 * Trimming to the base first — which this used to do — sent a Brazilian browser
 * looking for a `pt` catalogue that does not exist.
 */
function _match(tag) {
  if (!tag) return null;
  const want = String(tag).replace('_', '-');
  const exact = _codes.find(c => c.toLowerCase() === want.toLowerCase());
  if (exact) return exact;
  const base = want.split('-')[0].toLowerCase();
  return _codes.find(c => c.split('-')[0].toLowerCase() === base) || null;
}

/**
 * Storage access throws outright in some privacy modes rather than returning
 * null. A language preference is not worth failing the boot over, so both
 * directions swallow it and the browser's own languages decide instead.
 */
function _stored(value) {
  try {
    if (value === undefined) return localStorage.getItem(LANG_KEY);
    localStorage.setItem(LANG_KEY, value);
  } catch {
    return null;
  }
  return value;
}

function _preferred() {
  const stored = _match(_stored());
  if (stored) return stored;
  for (const tag of navigator.languages || [navigator.language]) {
    const hit = _match(tag);
    if (hit) return hit;
  }
  return FALLBACK;
}

// ── Loading ─────────────────────────────────────────────────────────────────

async function _load(code) {
  if (_strings[code]) return true;
  try {
    const mod = await import(`./locales/${code}.js`);
    _strings[code] = mod.default;
    return true;
  } catch (err) {
    console.warn(`[MeshBay] locale ${code} failed to load:`, err);
    return false;
  }
}

/**
 * Load the active catalogue and the English fallback, then fix the locale.
 * Resolves even when a catalogue is missing — an untranslated interface beats
 * a blank page, so a failed load degrades to English rather than throwing.
 */
export async function initLocale() {
  const want = _preferred();
  const loads = [_load(want)];
  if (want !== FALLBACK) loads.push(_load(FALLBACK));
  const [ok] = await Promise.all(loads);
  _locale = ok ? want : FALLBACK;
  if (!_strings[FALLBACK]) await _load(FALLBACK);
  document.documentElement.lang = _locale;
  return _locale;
}

// ── Lookup ──────────────────────────────────────────────────────────────────

export function getLocale() { return _locale; }

export function setLocale(code) {
  const hit = _match(code);
  if (!hit) return false;
  _stored(hit);
  return true;
}

export function addLocale(code, strings) {
  _strings[code] = strings;
}

function _pluralRules(locale) {
  if (!_plurals[locale]) _plurals[locale] = new Intl.PluralRules(locale);
  return _plurals[locale];
}

/** A catalogue entry is a plain string, or plural categories to choose from. */
function _select(entry, locale, params) {
  if (typeof entry === 'string') return entry;
  if (!entry || typeof entry !== 'object') return null;
  const n = Number(params && params.n);
  const cat = _pluralRules(locale).select(Number.isFinite(n) ? n : 0);
  return entry[cat] ?? entry.other ?? null;
}

export function t(key, params) {
  let s = _select(_strings[_locale] && _strings[_locale][key], _locale, params);
  if (s == null) {
    s = _select(_strings[FALLBACK] && _strings[FALLBACK][key], FALLBACK, params);
  }
  if (s == null) return key;
  if (params) {
    for (const [k, v] of Object.entries(params)) {
      // split/join rather than replace: a value is often a filename, and
      // String.replace reads `$&` and friends in the replacement.
      s = s.split(`{${k}}`).join(v);
    }
  }
  return s;
}