auth.tsx

import React, {
  createContext,
  useState,
  useCallback,
  useContext,
  useEffect,
} from 'react';

import AsyncStorage, {
  useAsyncStorage,
} from '@react-native-community/async-storage';

import api from '../utils/apiClient';

interface AuthState {
  token?: string;
  user?: object;
}

interface SignInCredentials {
  email: string;
  password: string;
}

interface AuthContext {
  user?: object;
  loading: boolean;
  signIn(credentials: SignInCredentials): Promise<void>;
  signOut(): void;
}

const AuthContext = createContext<AuthContext | null>(null);

const AuthProvider: React.FC = ({ children }) => {
  const storagedToken = useAsyncStorage('@GoBarber:token');
  const storagedUser = useAsyncStorage('@GoBarber:user');

  const [data, setData] = useState<AuthState>({});
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    async function loadUserAndToken(): Promise<void> {
      const token = await storagedToken.getItem();
      const user = await storagedUser.getItem();

      if (token && user) {
        setData({ token, user: JSON.parse(user) });
      }

      setLoading(false);
    }

    loadUserAndToken();
  }, [storagedToken, storagedUser]);

  const signIn = useCallback(
    async credentials => {
      const response = await api.post('sessions', credentials);

      const { token, user } = response.data;

      await storagedToken.setItem(token);
      await storagedUser.setItem(JSON.stringify(user));

      setData({ token, user });
    },
    [storagedToken, storagedUser],
  );

  const signOut = useCallback(async () => {
    await AsyncStorage.clear();

    setData({});
  }, []);

  const user = data?.user;

  const value = React.useMemo(() => ({ loading, user, signIn, signOut }), [
    loading,
    signIn,
    signOut,
    user,
  ]);

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

function useAuth(): AuthContext {
  const context = useContext(AuthContext);

  if (!context) {
    throw new Error(`useAuth must be used within a AuthProvider`);
  }

  return context;
}

export { AuthProvider, useAuth };