Proof of concepts simple page views with Next.js middleware

_middleware.js

// posts/_middleware.js
import { NextResponse } from 'next/server'

const config = {
  dataset: process.env.NEXT_PUBLIC_SANITY_DATASET || 'production',
  projectId: process.env.NEXT_PUBLIC_SANITY_PROJECT_ID,
  apiVersion: '2021-10-21',
}
const baseUrl = cdn => `https://${config.projectId}.api${cdn ? 'cdn' : ''}.sanity.io/v${config.apiVersion}`
const queryUrl = baseUrl() + `/data/query/${config.dataset}/`
const mutateUrl = baseUrl() + `/data/mutate/${config.dataset}`
const query = `*[slug.current == $slug][0]{
  ...,
  "stats": *[_type == "stats" && post._ref == ^._id][0]
}`

export async function middleware(req, ev) {
  const { href } = req.nextUrl
  const getStats = new URL(queryUrl)
  getStats.searchParams.append('query', query)
  getStats.searchParams.append('$slug', `"${href.replace('/posts/', '')}"`)

  const { result } = await fetch(getStats.href).then(res => res.json())

  const { _id } = result
  const res = await fetch(mutateUrl, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Authorization': 'Bearer ' + process.env.SANITY_API_TOKEN
    },
    body: JSON.stringify({
      mutations: [
        _id ? {
          createIfNotExists: {
            _id: 'stats.' + _id,
            _type: 'stats',
            views: 1,
            post: {
              _type: 'reference',
              _ref: _id
            }
          }
        } : undefined,
        {
          patch: {
            id: 'stats.' + _id,
            setIfMissing: { 'views': 1 },
            inc: {
              views: 1
            },
          }
        }]
    })
  }).then(res => res.json())


  return NextResponse.next()
}