import { createContext, useCallback, useContext, useEffect, useMemo, useState, type ReactNode } from "react";
import en from "./en";
import zh from "./zh";

export type Locale = "zh" | "en";

const STORAGE_KEY = "netx-locale";

const MESSAGES: Record<Locale, typeof zh> = { zh, en };

function resolveMessage(obj: unknown, path: string): string {
  const keys = path.split(".");
  let cur: unknown = obj;
  for (const k of keys) {
    if (cur == null || typeof cur !== "object") return path;
    cur = (cur as Record<string, unknown>)[k];
  }
  return typeof cur === "string" ? cur : path;
}

function interpolate(text: string, vars?: Record<string, string | number>): string {
  if (!vars) return text;
  let out = text;
  for (const [k, v] of Object.entries(vars)) {
    out = out.replace(new RegExp(`\\{\\{${k}\\}\\}`, "g"), String(v));
  }
  return out;
}

type I18nContextValue = {
  locale: Locale;
  setLocale: (locale: Locale) => void;
  t: (key: string, vars?: Record<string, string | number>) => string;
};

const I18nContext = createContext<I18nContextValue | null>(null);

export function I18nProvider({ children }: { children: ReactNode }) {
  const [locale, setLocaleState] = useState<Locale>(() => {
    try {
      const saved = localStorage.getItem(STORAGE_KEY);
      return saved === "en" ? "en" : "zh";
    } catch {
      return "zh";
    }
  });

  const setLocale = useCallback((next: Locale) => {
    setLocaleState(next);
    try {
      localStorage.setItem(STORAGE_KEY, next);
    } catch {
      /* ignore */
    }
  }, []);

  const t = useCallback(
    (key: string, vars?: Record<string, string | number>) => {
      const raw = resolveMessage(MESSAGES[locale], key);
      return interpolate(raw, vars);
    },
    [locale],
  );

  useEffect(() => {
    document.documentElement.lang = locale === "en" ? "en" : "zh-CN";
  }, [locale]);

  const value = useMemo(() => ({ locale, setLocale, t }), [locale, setLocale, t]);

  return <I18nContext.Provider value={value}>{children}</I18nContext.Provider>;
}

export function useI18n() {
  const ctx = useContext(I18nContext);
  if (!ctx) throw new Error("useI18n must be used within I18nProvider");
  return ctx;
}