enable vercel analytics

pages/robots.txt.ts

@@ -0,0 +1,32 @@
+import { baseUrl } from "../lib/config";
+import type { GetServerSideProps } from "next";
+
+export const getServerSideProps: GetServerSideProps<Record<string, never>> = async (context) => {
+  const { res } = context;
+
+  // this production check should be unnecessary because "noindex" and "nofollow" are also set in a meta tag (see
+  // DefaultSeo's props in pages/_app.tsx), but it doesn't hurt...
+  const robots = `User-agent: *
+${
+  process.env.NEXT_PUBLIC_VERCEL_ENV !== "production"
+    ? `Disallow: /`
+    : `Allow: /
+
+Sitemap: ${baseUrl}/sitemap.xml`
+}
+`;
+
+  res.setHeader("content-type", "text/plain; charset=utf-8");
+  // cache on edge for one week
+  res.setHeader("cache-control", "public, max-age=0, s-maxage=604800, stale-while-revalidate");
+
+  res.write(robots);
+  res.end();
+
+  return {
+    props: {},
+  };
+};
+
+// eslint-disable-next-line import/no-anonymous-default-export
+export default () => null;