[Firebase] Move a collection in Cloud Firestore with a Cloud Function

index.js

exports.mv = functions.https.onRequest(request => {
  const mv = async (collRefSource, collRefDest) => {
    const querySnapshot = await collRefSource.get();
    querySnapshot.forEach(async docSnapshot => {
      (async () => {
        await collRefDest.doc(docSnapshot.id).set(docSnapshot.data());
        docSnapshot.ref.delete();
      })();
      const collRefs = await docSnapshot.ref.getCollections();
      for (const collRef of collRefs)
        mv(collRef, collRefDest.doc(docSnapshot.id).collection(collRef.id))
    });
  };
  const collRefSource = admin.firestore().collection(request.query.collPathSource);
  const collRefDest = admin.firestore().collection(request.query.collPathDest);
  mv(collRefSource, collRefDest);
});
// Example: https://us-central1-{project-id}.cloudfunctions.net/mv?collPathSource=collection1%2Fdocument1%2Fcollection2&collPathDest=collection3