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

// 创建语言代码集合用于快速查找
const SUPPORTED_LANGUAGE_CODE_SET = new Set<string>(SUPPORTED_LANGUAGE_CODES);

/**
 * 标准化语言代码（处理 zh-CN、zh_TW 等变体）
 */
export function normalizeLocale(locale: string | null | undefined): string {
  return locale?.trim().toLowerCase().replaceAll('_', '-') ?? '';
}

/**
 * 解析支持的语言代码
 * @param locale 原始语言代码（如 'zh-CN', 'en-US'）
 * @param fallback 回退语言代码，默认为 'zh'
 * @returns 支持的语言代码
 */
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_CODE_SET.has(baseLanguage)
    ? (baseLanguage as LanguageCode)
    : fallback;
}

/**
 * 检测系统语言
 */
export function detectSystemLanguage(): LanguageCode {
  if (typeof navigator === 'undefined') return 'zh';
  return resolveSupportedLanguage(navigator.language);
}