securebit-chat/src/i18n/index.js

/**
 * Language selection and string lookup.
 *
 * Every locale is a real page at a real URL (/, /de/, ...), generated at build time,
 * because the app is client-rendered: a language that exists only as a runtime string
 * swap has no URL for a crawler to index. This module is the runtime half — it decides
 * which locale the current page is, and hands components their strings.
 *
 * The rule that matters: the URL wins over everything. Someone who opens /de/ gets
 * German even if they once chose English here, or a shared link would open in whatever
 * language the recipient happened to pick last, which makes links unshareable.
 */

import { DEFAULT_LOCALE, SUPPORTED_LOCALES, LOCALE_META, DICTIONARIES } from './generated.js';

export { DEFAULT_LOCALE, SUPPORTED_LOCALES, LOCALE_META };

const STORAGE_KEY = 'securebit-locale';

/** The locale a path belongs to, or null for the default locale at the root. */
export function localeFromPathname(pathname = '/') {
    const segment = String(pathname).split('/')[1];
    return SUPPORTED_LOCALES.includes(segment) && segment !== DEFAULT_LOCALE ? segment : null;
}

/**
 * Best match for a browser's language list. "de-AT" should get German if German is all
 * we have, so the base tag is tried after the full one, in the order the browser gave.
 */
export function localeFromLanguages(languages = []) {
    for (const tag of languages) {
        const lower = String(tag).toLowerCase();
        const exact = SUPPORTED_LOCALES.find((code) => code.toLowerCase() === lower);
        if (exact) return exact;
        const base = lower.split('-')[0];
        const partial = SUPPORTED_LOCALES.find((code) => code.toLowerCase().split('-')[0] === base);
        if (partial) return partial;
    }
    return null;
}

/**
 * Which locale to render, given everything we know. Pure, so the precedence can be
 * tested without a browser: URL, then a previous explicit choice, then the browser's
 * languages, then the default.
 */
export function detectLocale({ pathname = '/', stored = null, languages = [] } = {}) {
    const fromPath = localeFromPathname(pathname);
    if (fromPath) return fromPath;

    // The root path is the default locale's own page, not an absence of information —
    // redirecting away from it would break every link to the site's canonical URL.
    if (isLocaleRoot(pathname)) return DEFAULT_LOCALE;

    if (stored && SUPPORTED_LOCALES.includes(stored)) return stored;
    return localeFromLanguages(languages) || DEFAULT_LOCALE;
}

/** True for "/" and "/index.html" — the pages the default locale is served from. */
function isLocaleRoot(pathname) {
    return pathname === '/' || pathname === '/index.html';
}

/**
 * The URL of the current page in another locale. Switching keeps you where you are
 * rather than dumping you back on the home page.
 */
export function localeHref(code, pathname = '/') {
    const current = localeFromPathname(pathname);
    const rest = current ? String(pathname).slice(current.length + 1) : String(pathname);
    const tail = rest.replace(/^\/+/, '');
    return code === DEFAULT_LOCALE ? `/${tail}` : `/${code}/${tail}`;
}

/** Remember an explicit choice. Storage can throw in private mode; a preference is not worth an exception. */
export function rememberLocale(code) {
    try {
        localStorage.setItem(STORAGE_KEY, code);
    } catch (_) {
        // Private mode or blocked storage: the URL still carries the choice.
    }
}

export function storedLocale() {
    try {
        return localStorage.getItem(STORAGE_KEY);
    } catch (_) {
        return null;
    }
}

/**
 * The locale of the page as actually loaded. Resolved once: it cannot change without a
 * navigation, and t() is called dozens of times per render — re-reading localStorage
 * on each of those would be a synchronous storage hit per string.
 */
let resolvedLocale = null;
export function currentLocale() {
    if (resolvedLocale) return resolvedLocale;
    // A window may exist without the parts this needs: test harnesses and workers both
    // provide partial shims. Reading through them blindly threw and took the caller with
    // it, which for t() means a missing string becomes a crash.
    const w = typeof window === 'undefined' ? null : window;
    if (!w || !w.location) return DEFAULT_LOCALE;
    resolvedLocale = detectLocale({
        pathname: w.location.pathname || '/',
        stored: storedLocale(),
        languages: w.navigator?.languages || [],
    });
    return resolvedLocale;
}

/**
 * A locale the visitor would probably rather read, when it is not the one they are on.
 * Used to offer a link, never to redirect: an automatic redirect sends Googlebot —
 * which crawls from one place — to a single locale and leaves the rest unindexed.
 */
export function suggestedLocale({ pathname = '/', languages = [], stored = null } = {}) {
    const shown = localeFromPathname(pathname) || DEFAULT_LOCALE;
    // An explicit past choice outranks the browser's list: someone who picked a
    // language once meant it, and it is exactly when their page does not match that
    // choice that the offer is worth making.
    const preferred = (SUPPORTED_LOCALES.includes(stored) && stored) || localeFromLanguages(languages);
    return preferred && preferred !== shown ? preferred : null;
}

/**
 * A list-valued string, for the handful of places where the copy is a set of short
 * labels rather than a sentence — a language may need a different number of them, so
 * the count belongs to the translation, not to the component.
 */
export function tList(key, locale = currentLocale()) {
    const value = DICTIONARIES[locale]?.[key] ?? DICTIONARIES[DEFAULT_LOCALE]?.[key];
    return Array.isArray(value) ? value : [];
}

/**
 * The rows a language switcher renders. Built here rather than in the component so the
 * URLs can be tested without a DOM, and so the switcher stays what it must be: a list
 * of real links. A control that swaps strings in place would leave every language on
 * one URL, which is the thing this whole arrangement exists to avoid.
 */
export function languageLinks({ pathname = '/', active = DEFAULT_LOCALE } = {}) {
    return SUPPORTED_LOCALES.map((code) => ({
        code,
        href: localeHref(code, pathname),
        hrefLang: LOCALE_META[code]?.htmlLang || code,
        // Listed in its own language: someone looking for German is looking for
        // "Deutsch", not for the English word for it.
        label: LOCALE_META[code]?.nativeName || code,
        // Short code for the collapsed switcher.
        abbr: LOCALE_META[code]?.abbr || code.toUpperCase(),
        isCurrent: code === active,
    }));
}

/**
 * Look up a string. Falls back to the default locale and then to the key itself, so a
 * missing translation shows English rather than blank UI.
 */
export function t(key, vars, locale = currentLocale()) {
    const template =
        DICTIONARIES[locale]?.[key] ??
        DICTIONARIES[DEFAULT_LOCALE]?.[key] ??
        key;
    if (!vars) return template;
    return String(template).replace(/\{(\w+)\}/g, (match, name) =>
        Object.prototype.hasOwnProperty.call(vars, name) ? String(vars[name]) : match
    );
}