Replacing all JSON String values recursively with Circe

Using the CIRCE library & Cats, it would be incredibly useful to be able to transform all the string values of an arbitrary Json object such as

{
  "topLevelStr" : "topLevelVal", 
  "topLevelInt" : 123, 
  "nested" : { "nestedStr" : "nestedVal" },
  "array" : [
    { "insideArrayStr" : "insideArrayVal1", "insideArrayInt" : 123},
    { "insideArrayStr" : "insideArrayVal2", "insideArrayInt" : 123}
   ]
}

Is it possble to transform all string values (topLevelVal, nestedVal, insideArrayVal1, insideArrayVal2) to upper case (or any arbitrary string transformation for that matter)?

You can write recursive function by yourself. It should be something like that:

import io.circe.{Json, JsonObject}
import io.circe.parser._


def transform(js: Json, f: String => String): Json = js
  .mapString(f)
  .mapArray(_.map(transform(_, f)))
  .mapObject(obj => {
    val updatedObj = obj.toMap.map {
      case (k, v) => f(k) -> transform(v, f)
    }
    JsonObject.apply(updatedObj.toSeq: _*)
  })

val jsonString =
  """
    |{
    |"topLevelStr" : "topLevelVal",
    |"topLevelInt" : 123, 
    | "nested" : { "nestedStr" : "nestedVal" },
    | "array" : [
    |   {
    |      "insideArrayStr" : "insideArrayVal1",
    |      "insideArrayInt" : 123
    |   }
    |  ]
    |}
  """.stripMargin

val json: Json = parse(jsonString).right.get
println(transform(json, s => s.toUpperCase))