x.js

const admin = require('firebase-admin')
const {DateTime} = require('luxon')
const _ = require('lodash')

const fbSource = admin.initializeApp(
  {
    credential: admin.credential.cert(require(`./serviceAccountKey.production.json`)),
    databaseURL: 'https://biblebox-prod.firebaseio.com',
  },
  'source',
)

const fbTarget = admin.initializeApp(
  {
    name: 'target',
    credential: admin.credential.cert(require(`./serviceAccountKey.push.json`)),
    databaseURL: 'https://biblebox-push.firebaseio.com',
  },
  'target',
)

const fsSource = fbSource.firestore()

const main = async () => {
  const lastOne = await (async () => {
    const q = await fsTarget.collection('notification_subscribers').orderBy('createdAt', 'desc').limit(1).get()
    if (q.size < 1) return
    const i = await fsSource.collection('notification_subscribers').doc(q.docs[0].id)
    return await i.get()
  })()

  const query = fsSource.collection('notification_subscribers').orderBy('createdAt', 'asc').limit(100)

  let s = await (lastOne ? query.startAfter(lastOne).get() : query.get())

  while (!s.empty) {
    await messaging.subscribeToTopic(s.docs.map(d => d.id), 'daily')
    const batch = fsTarget.batch()
    for (doc of s.docs) {
      await exportSubscriber(batch, doc.data())
    }
    await batch.commit()
    s = await query.startAfter(_.last(s.docs)).get()
  }
}

const fsTarget = fbTarget.firestore()
const messaging = fbTarget.messaging()

const increment = admin.firestore.FieldValue.increment(1)

const exportSubscriber = async (batch, {uid, token, platform, createdAt, updatedAt}) => {
  const ref = fsTarget.collection('notification_subscribers').doc(token)
  // const doc = await ref.get()

  // if (doc.exists) return

  const now = DateTime.fromJSDate(createdAt.toDate())
  await batch.create(ref, {token, platform, uid, subscribed: true, createdAt, updatedAt})
  batch.set(
    fsTarget.collection('notification_subscribers__counter').doc(now.toFormat('yyyy-MM-dd')),
    {date: admin.firestore.Timestamp.fromDate(now.startOf('day').toJSDate()), created: increment},
    {merge: true},
  )
  batch.set(fsTarget.collection('notification_subscribers__counter').doc('total'), {created: increment}, {merge: true})
}

main()