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import magnolia._
import spray.json._
import scala.language.experimental.macros
trait JsonFormatDerivation extends DefaultJsonProtocol {
type Typeclass[T] = JsonFormat[T]
def combine[T](ctx: CaseClass[JsonFormat, T]): JsonFormat[T] = new JsonFormat[T] {
override def write(value: T): JsValue = {
val fields: Seq[(String, JsValue)] = ctx.parameters.map { param =>
param.label -> param.typeclass.write(param.dereference(value))
}
JsObject(fields: _*)
}
override def read(value: JsValue): T = value match {
case obj: JsObject =>
ctx.construct { param =>
param.typeclass.read(obj.fields(param.label))
}
case js =>
deserializationError(s"Cannot read JSON '$js' as a ${ctx.typeName}")
}
}
def dispatch[T](ctx: SealedTrait[JsonFormat, T]): JsonFormat[T] = new JsonFormat[T] {
override def write(value: T): JsValue = {
ctx.dispatch(value) { sub =>
val obj = sub.typeclass.write(sub.cast(value)).asJsObject
JsObject((obj.fields ++ Map("type" -> JsString(sub.label))).toSeq: _*)
}
}
override def read(value: JsValue): T = value match {
case obj: JsObject if obj.fields.contains("type") =>
val fieldName = obj.fields("type").convertTo[String]
ctx.subtypes.find(_.label == fieldName) match {
case Some(tpe) => tpe.typeclass.read(obj)
case None =>
deserializationError(
s"Cannot deserialize JSON to ${ctx.typeName} because type field '${fieldName}' has an unsupported value.")
}
case js =>
deserializationError(s"Cannot read JSON '$js' as a ${ctx.typeName}")
}
}
implicit def gen[T]: JsonFormat[T] = macro Magnolia.gen[T]
}
object JsonFormatDerivation extends JsonFormatDerivation
trait DerivedFormats extends JsonFormatDerivation
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