Change stream utilities.

import scala.concurrent.{ ExecutionContext, Future }

import reactivemongo.api.ChangeStreams.FullDocumentStrategy

import reactivemongo.api.bson.BSONDocument
import reactivemongo.api.bson.collection.BSONCollection

def peekNext(
  coll: BSONCollection,
  strategy: FullDocumentStrategy)(
  implicit ec: ExecutionContext): Future[Option[BSONDocument]] =
  coll.watch[BSONDocument](fullDocumentStrategy = Some(strategy)).
    cursor.headOption

def doIt(coll: BSONCollection)(
  implicit ec: ExecutionContext): Future[Unit] = for {
    _ <- peekNext(coll, FullDocumentStrategy.Default)
    _ <- peekNext(coll, FullDocumentStrategy.UpdateLookup)
  } yield ()