server/core/src/stores/l10nStore.ts

import { defineStore } from 'pinia';
import { ref, computed } from 'vue';
import { DEFAULT_LOCALE } from '@KTXC/l10n/config';
import { mergeCatalog, applyLocale, applyFallbackLocale } from '@KTXC/l10n/runtime';
import { useUserStore } from '@KTXC/stores/userStore';

const CORE_NAMESPACE = 'core';
const SETTING_KEY = 'core.locale';
const RTL_LANGUAGES = ['ar', 'fa', 'he', 'ur'];

export type TranslationCatalog = Record<string, unknown>;
export type TranslationLoader = (locale: string) => Promise<TranslationCatalog | null>;

export interface L10nInitPayload {
  locale?: string;
  fallback?: string;
  available?: string[];
}

export const useL10nStore = defineStore('l10nStore', () => {
  const locale = ref(DEFAULT_LOCALE);
  const fallbackLocale = ref(DEFAULT_LOCALE);
  const available = ref<string[]>([DEFAULT_LOCALE]);

  const isRtl = computed(() => RTL_LANGUAGES.includes(locale.value.split('-')[0]));

  // Translation loaders know where their namespace's messages come from. The
  // store only coordinates them as the active locale changes.
  const translationLoaders = new Map<string, TranslationLoader>([
    [CORE_NAMESPACE, async (target: string) => {
      const response = await fetch(`/l10n/${target}.json`, {
        headers: { Accept: 'application/json' },
      });
      return response.ok ? await response.json() : null;
    }],
  ]);

  // catalog fetch results per "namespace:locale": true = merged, false = not on server
  const catalogState = new Map<string, boolean>();

  async function loadCatalog(namespace: string, target: string): Promise<boolean> {
    const cacheKey = `${namespace}:${target}`;
    const known = catalogState.get(cacheKey);
    if (known !== undefined) return known;
    const loader = translationLoaders.get(namespace);
    if (!loader) return false;
    try {
      const messages = await loader(target);
      if (!messages) {
        catalogState.set(cacheKey, false);
        return false;
      }
      mergeCatalog(target, namespace, messages);
      catalogState.set(cacheKey, true);
      return true;
    } catch (error) {
      // network error: leave state unset so a later attempt can retry
      console.warn(`L10N - Failed to load ${namespace} catalog for ${target}:`, error);
      return false;
    }
  }

  async function loadCoreCatalog(target: string): Promise<boolean> {
    return loadCatalog(CORE_NAMESPACE, target);
  }

  /** Load every registered namespace (core + modules) for a locale. */
  async function loadCatalogs(target: string): Promise<void> {
    await Promise.all(
      [...translationLoaders.keys()].map((namespace) => loadCatalog(namespace, target)),
    );
  }

  /**
   * Register a namespace-specific translation loader. The caller owns catalog
   * discovery and transport; this store owns locale orchestration and merging.
   */
  async function registerLoader(namespace: string, loader: TranslationLoader): Promise<void> {
    translationLoaders.set(namespace, loader);
    for (const cacheKey of catalogState.keys()) {
      if (cacheKey.startsWith(`${namespace}:`)) catalogState.delete(cacheKey);
    }
    await loadCatalog(namespace, fallbackLocale.value);
    if (locale.value !== fallbackLocale.value) {
      await loadCatalog(namespace, locale.value);
    }
  }

  async function activate(target: string): Promise<void> {
    await loadCatalogs(fallbackLocale.value);
    if (target !== fallbackLocale.value) {
      await loadCatalogs(target);
    }
    locale.value = target;
    applyLocale(target);
    document.documentElement.setAttribute('lang', target);
    document.documentElement.setAttribute('dir', isRtl.value ? 'rtl' : 'ltr');
  }

  /**
   * Locale candidates from browser preferences: each tag plus its base
   * language, in preference order ('de-AT' -> 'de-AT', 'de').
   */
  function browserCandidates(): string[] {
    const candidates: string[] = [];
    for (const tag of navigator.languages ?? [navigator.language]) {
      if (!tag) continue;
      const base = tag.split('-')[0];
      if (!candidates.includes(tag)) candidates.push(tag);
      if (!candidates.includes(base)) candidates.push(base);
    }
    return candidates;
  }

  /**
   * Bootstrap from the /init l10n block (private shell), or from browser
   * preferences alone when there is no session (public shell).
   */
  async function init(payload?: L10nInitPayload | null): Promise<void> {
    if (payload?.fallback) {
      fallbackLocale.value = payload.fallback;
      applyFallbackLocale(payload.fallback);
    }
    if (payload?.available?.length) {
      available.value = payload.available;
    }
    if (payload?.locale) {
      await activate(payload.locale);
      return;
    }
    // No resolved locale: probe browser candidates against served catalogs
    for (const candidate of browserCandidates()) {
      if (candidate === fallbackLocale.value || (await loadCoreCatalog(candidate))) {
        await activate(candidate);
        return;
      }
    }
    await activate(fallbackLocale.value);
  }

  /** Switch locale; persists as the user's `core.locale` setting by default. */
  async function setLocale(target: string, persist = true): Promise<void> {
    await activate(target);
    if (persist) {
      useUserStore().setSetting(SETTING_KEY, target);
    }
  }

  return {
    locale,
    available,
    isRtl,
    init,
    setLocale,
    registerLoader,
  };
});