"use client";

import {
  createContext,
  useCallback,
  useContext,
  useEffect,
  useMemo,
  useState,
  type ReactNode,
} from "react";
import { isChinaUser } from "is-china-user";
import { dictionaries, type Dictionary, type Locale } from "~/lib/i18n";

const STORAGE_KEY = "nomadro-locale";

type LocaleContextValue = {
  locale: Locale;
  isChina: boolean;
  ready: boolean;
  t: Dictionary;
  setLocale: (locale: Locale) => void;
};

const LocaleContext = createContext<LocaleContextValue | null>(null);

function isLocale(value: string | null): value is Locale {
  return value === "zh" || value === "en";
}

export function LocaleProvider({ children }: { children: ReactNode }) {
  const [locale, setLocaleState] = useState<Locale>("zh");
  const [ready, setReady] = useState(false);

  useEffect(() => {
    let cancelled = false;

    try {
      // Prefer auto detection; only keep a locale if user unlocked and switched.
      const unlocked = window.sessionStorage.getItem("nomadro-lang-unlock") === "1";
      const saved = window.localStorage.getItem(STORAGE_KEY);

      if (unlocked && isLocale(saved)) {
        if (!cancelled) {
          setLocaleState(saved);
          setReady(true);
        }
        return;
      }

      const china = Boolean(isChinaUser());
      if (!cancelled) {
        setLocaleState(china ? "zh" : "en");
        setReady(true);
      }
    } catch {
      if (!cancelled) {
        setLocaleState("zh");
        setReady(true);
      }
    }

    return () => {
      cancelled = true;
    };
  }, []);

  useEffect(() => {
    if (!ready) return;
    document.documentElement.lang = dictionaries[locale].htmlLang;
  }, [locale, ready]);

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

  const value = useMemo<LocaleContextValue>(
    () => ({
      locale,
      isChina: locale === "zh",
      ready,
      t: dictionaries[locale],
      setLocale,
    }),
    [locale, ready, setLocale],
  );

  return (
    <LocaleContext.Provider value={value}>{children}</LocaleContext.Provider>
  );
}

export function useLocale() {
  const ctx = useContext(LocaleContext);
  if (!ctx) {
    throw new Error("useLocale must be used within LocaleProvider");
  }
  return ctx;
}