import { AuthSession, type AuthState } from '@pipu/core';
import Constants from 'expo-constants';
import { createContext, useCallback, useContext, useEffect, useMemo, useState, useSyncExternalStore, type ReactNode } from 'react';

import { currentServer, refreshStoreFor, rememberServer, setCurrentServer } from './storage';

interface SessionCtx {
  /** Адрес сервера; null — сервер не выбран (экран подключения). */
  server: string | null;
  session: AuthSession | null;
  ready: boolean;
  connect: (url: string, version: string) => Promise<void>;
  disconnect: () => Promise<void>;
}

const Ctx = createContext<SessionCtx | null>(null);

function deviceName(): string {
  return Constants.deviceName ?? 'Android';
}

function makeSession(url: string) {
  return new AuthSession({ baseUrl: url, clientType: 'android', deviceName: deviceName(), refreshStore: refreshStoreFor(url) });
}

/** Текущий сервер и сессия на нём; при запуске восстанавливает вход по сохранённому refresh-токену. */
export function SessionProvider({ children }: { children: ReactNode }) {
  const [server, setServer] = useState<string | null>(null);
  const [session, setSession] = useState<AuthSession | null>(null);
  const [ready, setReady] = useState(false);

  useEffect(() => {
    void (async () => {
      const url = await currentServer();
      if (url) {
        const s = makeSession(url);
        await s.restore();
        setServer(url);
        setSession(s);
      }
      setReady(true);
    })();
  }, []);

  const connect = useCallback(async (url: string, version: string) => {
    await rememberServer({ url, version });
    await setCurrentServer(url);
    const s = makeSession(url);
    await s.restore(); // на этом сервере уже могли войти раньше
    setServer(url);
    setSession(s);
  }, []);

  const disconnect = useCallback(async () => {
    await setCurrentServer(null);
    setServer(null);
    setSession(null);
  }, []);

  const value = useMemo(() => ({ server, session, ready, connect, disconnect }), [server, session, ready, connect, disconnect]);
  return <Ctx.Provider value={value}>{children}</Ctx.Provider>;
}

export function useSessionCtx(): SessionCtx {
  const c = useContext(Ctx);
  if (!c) throw new Error('useSessionCtx outside SessionProvider');
  return c;
}

/** Сессия вошедшего пользователя (экраны внутри приложения). */
export function useSession(): AuthSession {
  const { session } = useSessionCtx();
  if (!session) throw new Error('no session');
  return session;
}

const UNKNOWN: AuthState = { status: 'unknown' };

export function useAuthState(): AuthState {
  const { session } = useSessionCtx();
  return useSyncExternalStore(
    (fn) => session?.subscribe(fn) ?? (() => undefined),
    () => session?.state ?? UNKNOWN,
  );
}

export function useUser() {
  const state = useAuthState();
  if (state.status !== 'signed_in') throw new Error('not signed in');
  return state.user;
}