case object EnumOne extends Enumeration {
  val e1, e2 = Value
}

case object EnumTwo extends Enumeration {
  val e3, e4 = Value
}

object EnumerationCodecProvider extends CodecProvider {
  def isEnumVal[T](clazz: Class[T]): Boolean = {
   // I had to check the class name to know if it is a Enumeration Val or Value, since the   Enumeration#Val class is private 
    clazz.getName.equals("scala.Enumeration$Val") ||
      clazz.getName.equals("scala.Enumeration$Value")
  }

  override def get[T](clazz: Class[T], registry: CodecRegistry): Codec[T] = {
    if (isEnumVal(clazz)) {
      EnumerationCodec.asInstanceOf[Codec[T]]
    } else {
      null
    }
  }

  object EnumerationCodec extends Codec[Enumeration#Value] {
    private val enumMap: Map[String, String => Enumeration#Value] = Map(
      "enum_one" -> EnumOne,
      "enum_two" -> EnumTwo
    )

    override def decode(reader: BsonReader, decoderContext: DecoderContext): Enumeration#Value = {
      val identifier = reader.getCurrentName

      val enumValue = reader.readString()
      // I used the enumMap indexed with the collection key (identifier) to get the Enumeration class
      enumMap(identifier).withName(enumValue)
      }
    }

    override def encode(writer: BsonWriter, value: Enumeration#Value, encoderContext: EncoderContext): Unit = {
      writer.writeString(value.toString)
    }

    override def getEncoderClass: Class[Enumeration#Value] = classOf[Enumeration#Value]
  }
}