Rename a field across documents

/* eslint-disable no-console */
import {getCliClient} from 'sanity/cli'
import {Transaction} from '@sanity/client'

type Doc = {
  _id: string
  _rev: string
  name: string
}

type DocPatch = {
  id: string
  patch: {
    set: {fullname: string}
    unset: string[]
    ifRevisionID: string
  }
}

// Gets the client configuration from `sanity.cli.ts` and returns a client.
// Will include write token when run with `sanity exec --with-user-token`
const client = getCliClient()

// Fetch the documents we want to migrate, and return only the fields we need.
const fetchDocuments = () =>
  client.fetch(`*[_type == 'author' && defined(name)][0...100] {_id, _rev, name}`)

// Build a patch for each document, represented as a tuple of `[documentId, patch]`
const buildPatches = (docs: Doc[]) =>
  docs.map(
    (doc: Doc): DocPatch => ({
      id: doc._id,
      patch: {
        set: {fullname: doc.name},
        unset: ['name'],
        // this will cause the migration to fail if any of the documents has been
        // modified since it was fetched.
        ifRevisionID: doc._rev,
      },
    })
  )

const createTransaction = (patches: DocPatch[]): Transaction =>
  patches.reduce(
    (tx: Transaction, patch: DocPatch) => tx.patch(patch.id, patch.patch),
    client.transaction()
  )

const commitTransaction = (tx: Transaction) => tx.commit()

const migrateNextBatch = async (): Promise<void> => {
  const documents = await fetchDocuments()
  const patches = buildPatches(documents)
  if (patches.length === 0) {
    console.log('No more documents to migrate!')
    process.exit(1)
  }
  console.log(
    `Migrating batch:\n %s`,
    patches.map((patch) => `${patch.id} => ${JSON.stringify(patch.patch)}`).join('\n')
  )
  const transaction = createTransaction(patches)
  await commitTransaction(transaction)
  return migrateNextBatch()
}

migrateNextBatch().catch((err: any) => {
  console.error(err)
  process.exit(1)
})