Sangria scalar type derived from Circe encoder and decoder

package.scala

package org.shishkin.sangria

import cats.syntax.either._
import io.circe._
import sangria.execution.Resolver
import sangria.marshalling.circe._
import sangria.schema._
import sangria.validation.Violation

import scala.language.implicitConversions
import scala.reflect._
import scala.util._

package object schema {

  implicit def decodeResultAsEither[A](r: Decoder.Result[A]): Either[Violation, A] =
    r.leftMap(failure => CoercionViolation(failure.getMessage()))

  def deriveScalarType[A: ClassTag](implicit decoder: Decoder[A], encoder: Encoder[A]): ScalarType[A] = {
    val name = classTag[A].runtimeClass.getSimpleName
    ScalarType(
      name = name,
      coerceOutput = (v, _) =>
        CirceInputUnmarshaller.getScalarValue(encoder(v)),
      coerceUserInput = v =>
        decoder.decodeJson(CirceResultMarshaller.scalarNode(v, name, Set())),
      coerceInput = v =>
        decoder.decodeJson(Resolver.marshalScalarValue(v, CirceResultMarshaller, name, Set())))
  }
}