dropNulls from BSONDocument

dropNulls.scala

import cats.free.Trampoline
import cats.instances.stream._
import cats.instances.try_._
import cats.syntax.nested._
import cats.syntax.traverse._
import reactivemongo.bson._

import scala.util.{Failure, Success, Try}

implicit class BSONValueOps(private val bv: BSONValue) extends AnyVal {
    def arrayOrDocument[X](
      or: => X,
      bsonArray: Stream[Try[BSONValue]] => X,
      bsonDocument: Stream[Try[BSONElement]] => X
    ): X = bv match {
      case BSONArray(stream) => bsonArray(stream)
      case BSONDocument(stream) => bsonDocument(stream)
      case _ => or
    }

    def dropNulls: Trampoline[BSONValue] =
      bv.arrayOrDocument(
        Trampoline.done(bv),
        arr => arr.nested.traverse(v => Trampoline.defer(v.dropNulls)).map(ns => BSONArray(ns.value)),
        vals => vals
          .collect { case Success(value) => value }
          .filter(_.value.code != BSONNull.code)
          .traverse(el => Trampoline.defer(el.value.dropNulls.map(v => Try(BSONElement(el.name, v)))))
          .map(BSONDocument.apply)
      )
  }