squants exercise with Circe

Main.scala

package exercise.squants.with_circe

import eu.timepit.refined.types.string.NonEmptyString
import io.circe.parser.parse
import squants.market.{Money, Price}
import cats.syntax.either._
import io.circe.refined._
import io.circe._
import io.circe.generic.auto._
import squants.space.Volume
import cats.syntax.apply._
import cats.instances.try_._
import scala.util.{Failure, Try}

case class Order(
  name:      NonEmptyString,
  quantity:  Volume,
  unitPrice: Price[Volume]
)
object Main {
  def makeDecoder[A](f: String => Try[A]): Decoder[A] = Decoder.decodeString.emap {
    f(_).toEither.leftMap(_.getMessage)
  }
  private  val priceUnit = "([^/]*)/(.*)".r
  implicit val volumeDecoder: Decoder[Volume] = makeDecoder(Volume(_))
  implicit val priceDecoder:  Decoder[Price[Volume]]  = makeDecoder {
    case priceUnit(p, u) => (Money(p), Volume(u)) mapN (_ / _)
    case _               => Failure(new Exception("cannot parse unit price"))
  }
  val rawJson: String = """{
      "name":      "crude oil",
      "quantity":  "456 L",
      "unitPrice": "64.39 USD/42 gal"
    }
    """
  def main(args: Array[String]): Unit = {
    val result: Either[Error, Order] = parse(rawJson) flatMap (_.as[Order])
    println(result)
  }
}