wip(pages/signup): redirect logged in users to profile

Temporary fix for #181 that clears any edits on the signup page due to
SWR revalidating the global user object. Instead of allowing users to
edit their profiles directly on the org signup page, TB now just
redirects them to their profile pages.

pages/[org]/signup.tsx

@@ -1,8 +1,8 @@
 import { ParsedUrlQuery } from 'querystring';
 
 import { GetStaticPaths, GetStaticProps, GetStaticPropsContext } from 'next';
+import Router, { useRouter } from 'next/router';
 import { useEffect, useState } from 'react';
-import { useRouter } from 'next/router';
 import useTranslation from 'next-translate/useTranslation';
 
 import { AspectHeader, EmptyHeader } from 'components/navigation';
@@ -15,6 +15,7 @@ import { PageProps, getPageProps } from 'lib/page';
 import { OrgContext } from 'lib/context/org';
 import { db } from 'lib/api/firebase';
 import usePage from 'lib/hooks/page';
+import { useUser } from 'lib/context/user';
 import { withI18n } from 'lib/intl';
 
 import common from 'locales/en/common.json';
@@ -42,6 +43,18 @@ function SignupPage({ org, ...props }: SignupPageProps): JSX.Element {
     });
   }, [org, query]);
 
+  // Redirect to the user's profile page if they're logged in. Temporary fix for
+  // the revalidation problem that would clear any edits on this signup page.
+  // @see {@link https://github.com/tutorbookapp/tutorbook/issues/181}
+  const { loggedIn } = useUser();
+  useEffect(() => {
+    void Router.prefetch('/profile');
+  }, []);
+  useEffect(() => {
+    if (!loggedIn) return;
+    void Router.replace('/profile');
+  }, [loggedIn]);
+
   return (
     <OrgContext.Provider value={{ org: org ? Org.fromJSON(org) : undefined }}>
       <Page