github.com/jthegedus/firebase-gcp-examples/tree/master/functions-nextjs

example-app-file-structure

┌ components/       <-- React Components
| └ ...
├ helpers/
| └ utils.js        <-- Firestore data to JSON helper
├ nextjs/           <-- Next.js distribution directory
| └ ...                 configured in next.config.js
├ out/              <-- public/ + hoisted nextjs/ static content   
| └ ...
├ pages/            <-- Next.js Pages
| └ ...
├ public/           <-- Static assets
| └ ...
├ scripts/
| └ export.js       <-- Special-sauce static hoisting script
├ .gitignore
├ firebase.json
├ firestore.rules
├ next.config.js    <-- Next.js configuration
├ package-lock.json
├ package.json
└ server.js         <-- HTTPS Cloud Function for our Next.js Server