Deep remove specific empty json array in circe scala - json

Question

I want to remove deep empty json array from my json before/during processing by circe.
Incoming JSON
{
"config": {
"newFiles": [{
"type": "audio",
"value": "welcome1.mp3"
}],
"oldFiles": [],
"channel": "BC"
}
}
or
{
"config": {
"newFiles": [],
"oldFiles": [{
"type": "audio",
"value": "welcome1.mp3"
}],
"channel": "BC"
}
}
Resulted Json should look like
{
"config": {
"newFiles": [{
"type": "audio",
"value": "welcome1.mp3"
}],
"channel": "BC"
}
}
or
{
"config": {
"oldFiles": [{
"type": "audio",
"value": "welcome1.mp3"
}],
"channel": "BC"
}
}
What i understand that this can be done before decoding config as well as during decoding config.
The idea here is i want to handle only one of files (either new or old) at my case class level.
Method 1: Tried at config decoding level which works well.
case class File(`type`: String, value: String)
case class Config(files: List[File],
channel: String = "BC")
object Config{
implicit final val FileDecoder: Decoder[File] = deriveDecoder[File]
implicit val ConfigDecoder: Decoder[Config] = (h:HCursor) =>
for {
oldFiles <- h.get[List[File]]("oldFiles")
files <- if (oldFiles.isEmpty) h.get[List[File]]("newFiles") else h.get[List[File]]("oldFiles")
channel <- h.downField("channel").as[String]
}yield{
Config(files, channel)
}
}
case class Inventory(config: Config)
object Inventory {
implicit val InventoryDecoder: Decoder[Inventory] = deriveDecoder[Inventory]
}
Method 2: Tried before feeding into decoding which didn't worked out
Let me know what could be the elegant approach to handle it.
PS: I have multiple similar config decoders and if i handle this at config decoding level then there will be a lot of boiler plate code.

Answer 1

I have simplified the problem a little bit again, but combining this with the previous answer should be simple.
I also took advantage of cats.data.NonEmptyList
final case class Config(files: NonEmptyList[String], channel: String = "BC")
object Config {
implicit final val ConfigDecoder: Decoder[Config] =
(
(Decoder[NonEmptyList[String]].at(field = "newFiles") or Decoder[NonEmptyList[String]].at(field = "oldFiles")),
Decoder[String].at(field = "channel")
).mapN(Config.apply).at(field = "config")
}
This can be used like this:
val data =
"""[
{
"config": {
"newFiles": ["Foo", "Bar", "Baz"],
"oldFiles": [],
"channel": "BC"
}
},
{
"config": {
"newFiles": [],
"oldFiles": ["Quax"],
"channel": "BC"
}
}
]"""
parser.decode[List[Config]](data)
// res: Either[io.circe.Error, List[Config]] =
// Right(List(
// Config(NonEmptyList("Foo", "Bar", "Baz"), "BC"),
// Config(NonEmptyList("Quax"), "BC")
// ))
Note: I am assuming that at least one of the two lists must be non-empty and give priority to the new one.
You can see the code running here.