def.scala

object Input {
  implicit def inputCodec: CodecJson[Input] = {

    def encoder(data: Input): Json = 
      data match {
        case train: Train => Train.trainCodec.encode(train)
        case predict: Predict => Predict.predictCodec.encode(predict)
      }
    
    def decoder(json: HCursor): DecodeResult[Input] = 
      Predict.predictCodec.decode(json).fold(
        (failReason, cursor) => Train.trainCodec.decode(json),
        successResult => DecodeResult.ok(successResult)
      )
      

    CodecJson[Input](encoder, decoder)
  }
}