App.js

import React, {useState, useEffect} from 'react';
import { StyleSheet, Text, View } from 'react-native';
import * as SecureStore from "expo-secure-store";
import Auth from "./src/Auth";
import Main from "./src/Main";
import { ID_TOKEN_KEY } from "./config.js";

export default function App() {
  const [token, setToken] = useState(null);
  const [user, setUser] = useState(null);

  useEffect(() => {
    handleLogin();
  }, []);

  const handleLogin = (isNewUser = false) => {
    SecureStore.getItemAsync(ID_TOKEN_KEY).then(session => {
      if (session) {
        const sessionObj = JSON.parse(session);
        const { exp, token, id, name } = sessionObj;
        if (exp > Math.floor(new Date().getTime() / 1000)) {
          setToken(token);
          setUser({ id, name, isNewUser });
        } else {
          handleLogout();
        }
      }
    });
  };

  const handleLogout = () => {
    SecureStore.deleteItemAsync(ID_TOKEN_KEY);
    setToken(null);
  }

  return (
    <View style={styles.container}>
      {token && user && <Main token={token} user={user}/>}
      <Auth
        token={token}
        onLogin={handleLogin}
        onLogout={handleLogout}
      />
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  },
});