import { SUPPORTED_LANGUAGE_CODES } from './constants';
import type { LanguageCode } from '../types/runtime';

const SUPPORTED_LANGUAGE_SET = new Set<string>(SUPPORTED_LANGUAGE_CODES);

export function normalizeLocale(locale: string | null | undefined): string {
  return locale?.trim().toLowerCase().split('_').join('-') ?? '';
}

export function resolveSupportedLanguage(
  locale: string | null | undefined,
  fallback: LanguageCode = 'zh',
): LanguageCode {
  const normalizedLocale = normalizeLocale(locale);
  if (!normalizedLocale) return fallback;

  const [baseLanguage] = normalizedLocale.split('-');
  return SUPPORTED_LANGUAGE_SET.has(baseLanguage) ? (baseLanguage as LanguageCode) : fallback;
}

export function detectSystemLanguage(): LanguageCode {
  if (typeof navigator === 'undefined') return 'zh';
  return resolveSupportedLanguage(navigator.language);
}