Add helpers for creating server-side redirects

web/lib/firebase/server-auth.ts

@@ -3,6 +3,7 @@ import fetch from 'node-fetch'
 import { IncomingMessage, ServerResponse } from 'http'
 import { FIREBASE_CONFIG, PROJECT_ID } from 'common/envs/constants'
 import { getAuthCookies, setAuthCookies } from './auth'
+import { GetServerSideProps, GetServerSidePropsContext } from 'next'
 
 const ensureApp = async () => {
   // Note: firebase-admin can only be imported from a server context,
@@ -61,3 +62,25 @@ export const getServerAuthenticatedUid = async (ctx: RequestContext) => {
   }
   return undefined
 }
+
+export const redirectIfLoggedIn = (dest: string, fn?: GetServerSideProps) => {
+  return async (ctx: GetServerSidePropsContext) => {
+    const uid = await getServerAuthenticatedUid(ctx)
+    if (uid == null) {
+      return fn != null ? await fn(ctx) : { props: {} }
+    } else {
+      return { redirect: { destination: dest, permanent: false } }
+    }
+  }
+}
+
+export const redirectIfLoggedOut = (dest: string, fn?: GetServerSideProps) => {
+  return async (ctx: GetServerSidePropsContext) => {
+    const uid = await getServerAuthenticatedUid(ctx)
+    if (uid == null) {
+      return { redirect: { destination: dest, permanent: false } }
+    } else {
+      return fn != null ? await fn(ctx) : { props: {} }
+    }
+  }
+}

web/pages/index.tsx

@@ -5,20 +5,9 @@ import { Page } from 'web/components/page'
 import { LandingPagePanel } from 'web/components/landing-page-panel'
 import { Col } from 'web/components/layout/col'
 import { ManifoldLogo } from 'web/components/nav/manifold-logo'
+import { redirectIfLoggedIn } from 'web/lib/firebase/server-auth'
 
-import { GetServerSideProps } from 'next'
+export const getServerSideProps = redirectIfLoggedIn('/home', async (_) => {
-import { getServerAuthenticatedUid } from 'web/lib/firebase/server-auth'
-
-export const getServerSideProps: GetServerSideProps = async (ctx) => {
-  const uid = await getServerAuthenticatedUid(ctx)
-  if (uid != null) {
-    return {
-      redirect: {
-        destination: '/home',
-        permanent: false,
-      },
-    }
-  }
   // These hardcoded markets will be shown in the frontpage for signed-out users:
   const hotContracts = await getContractsBySlugs([
     'will-max-go-to-prom-with-a-girl',
@@ -33,7 +22,7 @@ export const getServerSideProps: GetServerSideProps = async (ctx) => {
     'will-at-least-10-world-cities-have',
   ])
   return { props: { hotContracts } }
-}
+})
 
 export default function Home(props: { hotContracts: Contract[] }) {
   const { hotContracts } = props