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package xyz.driver.json
import magnolia._
import spray.json._
import scala.language.experimental.macros
/** Mixin that enables automatic derivation of JSON formats for any product
* (case classes) or coproduct (sealed traits) types. */
trait DerivedFormats { self: BasicFormats =>
type Typeclass[T] = JsonFormat[T]
def combine[T](ctx: CaseClass[JsonFormat, T]): JsonFormat[T] =
new JsonFormat[T] {
override def write(value: T): JsValue =
if (ctx.isObject) {
JsString(ctx.typeName.short)
} else {
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 JsString(str) if ctx.isObject && str == ctx.typeName.short =>
ctx.rawConstruct(Seq.empty)
case js =>
deserializationError(
s"Cannot read JSON '$js' as a ${ctx.typeName.full}")
}
}
def dispatch[T](ctx: SealedTrait[JsonFormat, T]): JsonFormat[T] = {
val typeFieldName = ctx.annotations
.collectFirst {
case g: gadt => g.typeFieldName
}
.getOrElse("type")
new JsonFormat[T] {
override def write(value: T): JsValue = ctx.dispatch(value) { sub =>
sub.typeclass.write(sub.cast(value)) match {
case obj: JsObject =>
JsObject(
(Map(typeFieldName -> JsString(sub.typeName.short)) ++
obj.fields).toSeq: _*)
case js => js
}
}
override def read(js: JsValue): T = {
val typeName: String = js match {
case obj: JsObject if obj.fields.contains(typeFieldName) =>
obj.fields(typeFieldName).convertTo[String]
case JsString(str) =>
str
case _ =>
deserializationError(
s"Cannot deserialize JSON to ${ctx.typeName.full} " +
"because serialized type cannot be determined.")
}
ctx.subtypes.find(_.typeName.short == typeName) match {
case Some(tpe) => tpe.typeclass.read(js)
case None =>
deserializationError(
s"Cannot deserialize JSON to ${ctx.typeName.full} " +
s"because type '${typeName}' is unsupported.")
}
}
}
}
implicit def gen[T]: JsonFormat[T] = macro Magnolia.gen[T]
}
object DerivedFormats extends DerivedFormats with BasicFormats
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