auth.js

import React, { createContext, useReducer } from "react";

const AuthContext = createContext({
  user: null,
  login: userData => {},
  logout: () => {}
});

function authReducer(state, action) {
  switch (action.type) {
    case "LOGIN":
      return {
        ...state,
        user: action.payload
      };
    case "LOGOUT":
      return {
        ...state,
        user: null
      };

    default:
      return state;
  }
}

function AuthProvider(props) {
  const [state, dispatch] = useReducer(authReducer, { user: null });

  function login(userData) {
    dispatch({
      type: "LOGIN",
      payload: userData
    });
  }

  function logout() {
    dispatch({
      type: "LOGOUT"
    });
  }

  return (
    <AuthContext.Provider
      value={{ user: state.user, login, logout }}
      {...props}
    />
  );
}

export { AuthContext, AuthProvider };