/**
 * 管理后台的外观偏好：语言（中/英）与主题（浅色/深色）。
 * 保存在 localStorage，刷新后保持，管理员与普通用户共用。
 */
import { createContext, useCallback, useContext, useEffect, useMemo, useState } from 'react';
import type { ReactNode } from 'react';

import { translate } from './adminI18n';
import type { AdminLang } from './adminI18n';

export type AdminThemeMode = 'light' | 'dark';

interface AdminPrefs {
  lang: AdminLang;
  themeMode: AdminThemeMode;
  setLang: (lang: AdminLang) => void;
  setThemeMode: (mode: AdminThemeMode) => void;
  /** 按当前语言翻译文案（未收录时原样返回） */
  t: (text: string) => string;
}

const STORAGE_KEY = 'cosmo_admin_prefs';
const AdminPrefsContext = createContext<AdminPrefs | null>(null);

function readStoredPrefs(): { lang: AdminLang; themeMode: AdminThemeMode } {
  const fallback = { lang: 'zh' as AdminLang, themeMode: 'light' as AdminThemeMode };
  try {
    const raw = localStorage.getItem(STORAGE_KEY);
    if (!raw) return fallback;
    const parsed = JSON.parse(raw) as Partial<{ lang: AdminLang; themeMode: AdminThemeMode }>;
    return {
      lang: parsed.lang === 'en' ? 'en' : 'zh',
      themeMode: parsed.themeMode === 'dark' ? 'dark' : 'light',
    };
  } catch {
    return fallback;
  }
}

export function AdminPrefsProvider({ children }: { children: ReactNode }) {
  const [prefs, setPrefs] = useState(readStoredPrefs);

  useEffect(() => {
    localStorage.setItem(STORAGE_KEY, JSON.stringify(prefs));
  }, [prefs]);

  const setLang = useCallback((lang: AdminLang) => setPrefs((current) => ({ ...current, lang })), []);
  const setThemeMode = useCallback(
    (themeMode: AdminThemeMode) => setPrefs((current) => ({ ...current, themeMode })),
    [],
  );

  const value = useMemo<AdminPrefs>(
    () => ({
      lang: prefs.lang,
      themeMode: prefs.themeMode,
      setLang,
      setThemeMode,
      t: (text: string) => translate(text, prefs.lang),
    }),
    [prefs.lang, prefs.themeMode, setLang, setThemeMode],
  );

  return <AdminPrefsContext.Provider value={value}>{children}</AdminPrefsContext.Provider>;
}

export function useAdminPrefs(): AdminPrefs {
  const context = useContext(AdminPrefsContext);
  if (!context) throw new Error('useAdminPrefs must be used inside AdminPrefsProvider');
  return context;
}