Contextual JSON parsing

import com.elama.bidmanager.settings.Step
import io.circe.{HCursor, Json}
import scala.annotation.tailrec

object AstToSettingsUtils extends App {
  /** Extracts maxBidMaxPriceLimit from AST */
  def extractLimit(json: Json): Option[Int] = {
    @tailrec
    def f(json: Json, parent: String = "", result: Option[Int] = None): (Json, Option[Int]) = {
      val cursor = json.hcursor
      cursor.downField("kind").as[String] match {
        case Right("If")       => f(cursor.downField("body").focus.get)
        case Right("SetBid")   => f(cursor.downField("bid").focus.get)
        case Right(x@"Min")    => f(cursor.downField("right").focus.get, x)
        case Right("Constant") => Json.Null -> Some(toPercent(cursor))
        case Right("Multiply") if parent == "Min" => f(cursor.downField("right").focus.get)
        case _ => cursor.focus.get -> result
      }
    }

    f(json)._2
  }

  /** Extracts Step value and Step Type (amount/percent) from AST */
  def extractStep(json: Json): Option[Step] = {
    @tailrec
    def f(json: Json, parent: String = "", result: Option[Step] = None): (Json, Option[Step]) = {
      val cursor = json.hcursor
      cursor.downField("kind").as[String] match {
        case Right("If")         => f(cursor.downField("body").focus.get)
        case Right("SetBid")     => f(cursor.downField("bid").focus.get)
        case Right("Min")        => f(cursor.downField("left").focus.get)
        case Right(x@"Add")      => f(cursor.downField("right").focus.get, x)
        case Right(x@"Multiply") => f(cursor.downField("right").focus.get, x)
        case Right("Constant") if parent == "Multiply" => (Json.Null, Some(Step.Percent(toPercent(cursor))))
        case Right("Constant") if parent == "Add"      => (Json.Null, Some(Step.Amount(toAmount(cursor))))
        case _ => (cursor.focus.get, result)
      }
    }

    f(json)._2
  }

  private def toPercent(c: HCursor): Int = (c.downField("value").as[Double].right.get * 100).toInt - 100
  private def toAmount(c: HCursor): Double = c.downField("value").as[Double].right.get / 1000000
}