Add simple authentication logic

src/App.js

@@ -1,5 +1,13 @@
+import { lazy } from 'react';
+import { useUser } from './context/user';
+
+const AuthenticatedApp = lazy(() => import('./AuthenticatedApp'));
+const UnauthenticatedApp = lazy(() => import('./UnauthenticatedApp'));
+
 function App() {
-  return <h1>Hello World!</h1>;
+  const user = useUser();
+
+  return <div>{user ? <AuthenticatedApp /> : <UnauthenticatedApp />}</div>;
 }
 
 export default App;

src/AuthenticatedApp.js

@@ -0,0 +1,15 @@
+import { useAuthState } from './context/auth';
+
+function AuthenticatedApp() {
+  const { logout, isPending } = useAuthState();
+
+  return (
+    <div>
+      <h2>You're logged in!</h2>
+      <button onClick={logout}>Logout</button>
+      {isPending && <h1>Loading...</h1>}
+    </div>
+  );
+}
+
+export default AuthenticatedApp;

src/UnauthenticatedApp.js

@@ -0,0 +1,15 @@
+import { useAuthState } from './context/auth';
+
+function UnauthenticatedApp() {
+  const { login, isPending } = useAuthState();
+
+  return (
+    <div>
+      <h2>Please, log in!</h2>
+      <button onClick={login}>Log in</button>
+      {isPending && <h1>Loading...</h1>}
+    </div>
+  );
+}
+
+export default UnauthenticatedApp;

src/context/auth.js

@@ -0,0 +1,59 @@
+import { createContext, useContext, useState } from 'react';
+
+const sleep = time => new Promise(resolve => setTimeout(resolve, time));
+const getUser = () => sleep(1000).then(() => ({ username: 'Leonardo' }));
+
+const AuthContext = createContext();
+
+function AuthProvider(props) {
+  const [state, setState] = useState({
+    status: 'idle',
+    user: null,
+    error: null,
+  });
+
+  if (state.status === 'error' && state.error) {
+    return (
+      <div>
+        <h1>Something went wrong!</h1>
+        <pre>{state.error.message ?? 'Unhandled error!'}</pre>
+      </div>
+    );
+  }
+
+  const login = () => {
+    setState({ ...state, status: 'pending' });
+    return getUser().then(user =>
+      setState({ status: 'success', user: user, error: null })
+    );
+  };
+
+  const logout = () => {
+    setState({ ...state, status: 'pending' });
+    return getUser().then(() =>
+      setState({ status: 'success', user: null, error: null })
+    );
+  };
+
+  return <AuthContext.Provider value={{ state, login, logout }} {...props} />;
+}
+
+function useAuthState() {
+  const { state, login, logout } = useContext(AuthContext);
+  const isPending = state.status === 'pending';
+  const isError = state.status === 'error';
+  const isSuccess = state.status === 'success';
+  const isAuthenticated = state.user && isSuccess;
+
+  return {
+    user: state.user,
+    isPending,
+    isError,
+    isSuccess,
+    isAuthenticated,
+    login,
+    logout,
+  };
+}
+
+export { AuthProvider, useAuthState };

src/context/index.js

@@ -0,0 +1,12 @@
+import { AuthProvider } from './auth';
+import { UserProvider } from './user';
+
+function AppProviders({ children }) {
+  return (
+    <AuthProvider>
+      <UserProvider>{children}</UserProvider>
+    </AuthProvider>
+  );
+}
+
+export default AppProviders;

src/context/user.js

@@ -0,0 +1,14 @@
+import { createContext, useContext } from 'react';
+import { useAuthState } from './auth';
+
+const UserContext = createContext();
+
+function UserProvider(props) {
+  return <UserContext.Provider value={useAuthState().user} {...props} />;
+}
+
+function useUser() {
+  return useContext(UserContext);
+}
+
+export { UserProvider, useUser };

src/index.js

@@ -3,11 +3,14 @@ import ReactDOM from 'react-dom/client';
 import './index.css';
 import App from './App';
 import reportWebVitals from './reportWebVitals';
+import AppProviders from './context';
 
 const root = ReactDOM.createRoot(document.getElementById('root'));
 root.render(
   <React.StrictMode>
-    <App />
+    <AppProviders>
+      <App />
+    </AppProviders>
   </React.StrictMode>
 );