import deErrors from '@dorfteich/shared/i18n/de/errors.json';
import deLegal from '@dorfteich/shared/i18n/de/legal.json';
import deMails from '@dorfteich/shared/i18n/de/mails.json';
import enErrors from '@dorfteich/shared/i18n/en/errors.json';
import enLegal from '@dorfteich/shared/i18n/en/legal.json';
import enMails from '@dorfteich/shared/i18n/en/mails.json';
import { createInstance, type i18n as I18n } from 'i18next';

/**
 * Minimal i18next instance for user-facing api texts (error messages,
 * later e-mails). Kept separate from any request context — callers pass
 * the language explicitly.
 */
export const apiI18n: I18n = createInstance();

void apiI18n.init({
  resources: {
    en: { errors: enErrors, mails: enMails, legal: enLegal },
    de: { errors: deErrors, mails: deMails, legal: deLegal },
  },
  fallbackLng: 'en',
  supportedLngs: ['de', 'en'],
  interpolation: { escapeValue: false },
});

/** Best supported language for an Accept-Language header value. */
export function negotiateLanguage(acceptLanguage: string | undefined): 'de' | 'en' {
  if (!acceptLanguage) return 'en';
  // First matching language tag wins; quality factors are ignored on
  // purpose — with two languages the added complexity buys nothing.
  for (const part of acceptLanguage.split(',')) {
    const tag = part.trim().toLowerCase();
    if (tag.startsWith('de')) return 'de';
    if (tag.startsWith('en')) return 'en';
  }
  return 'en';
}

/** Localized message for an error code, or undefined when uncatalogued. */
export function translateErrorCode(code: string, language: 'de' | 'en'): string | undefined {
  const key = `errors:${code}`;
  return apiI18n.exists(key) ? apiI18n.t(key, { lng: language }) : undefined;
}