localStorage.js

// imagina que isso aqui é uma classe
const localStorageWrapper = {
  set: (key, value) => localStorage.setItem(key, JSON.stringify(value)),
  get: (key) => {
    const value = localStorage.getItem(key)

    return value ? JSON.parse(value) : value
  }
}

const NS_USERS = "users";
const NS_LOGGED_USER = "logged_user";

// verifica se um usuário existe no localStorage
export const login = ({ username, password }) => {
  const user = (localStorageWrapper.get(NS_USERS) || {})[username];
  if (!user || user.password !== password) {
    throw new Error("Invalid User/Password");
  }

  localStorageWrapper.set(NS_LOGGED_USER, user);

  return true;
};

// grava um usuário no localStorage
export const register = ({ username, password }) => {
  const users = localStorageWrapper.get(NS_USERS) || {};
  if (users[username]) {
    throw new Error("User already exists");
  }

  const user = {
    username,
    password
  };

  localStorageWrapper.set(NS_USERS, {
    ...users,
    [username]: user
  });

  return user;
};

export const isLogged = () => !!localStorageWrapper.get(NS_LOGGED_USER);

export const logout = () => localStorageWrapper.set(NS_LOGGED_USER, null);

export const getUser = () =>
  isLogged && localStorageWrapper.get(NS_LOGGED_USER);

export default {
  register,
  login,
  isLogged,
  getUser
};