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Json/Protobuf convertors for ScalaPB

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package scalapb_playjson

import com.google.protobuf.any.{Any => PBAny}
import play.api.libs.json._
import scalapb_json._

object AnyFormat {
  val anyWriter: (Printer, PBAny) => JsValue = { case (printer, any) =>
    // Find the companion so it can be used to JSON-serialize the message. Perhaps this can be circumvented by
    // including the original GeneratedMessage with the Any (at least in memory).
    val cmp = printer.typeRegistry
      .findType(any.typeUrl)
      .getOrElse(
        throw new IllegalStateException(
          s"Unknown type ${any.typeUrl}; you may have to register it via FormatRegistry.registerCompanion"
        )
      )

    // Unpack the message...
    val message = any.unpack(cmp)

    // ... and add the @type marker to the resulting JSON
    printer.toJson(message) match {
      case JsObject(fields) => JsObject(("@type" -> JsString(any.typeUrl)) +: fields.toSeq)
      case value =>
        // Safety net, this shouldn't happen
        throw new IllegalStateException(
          s"Message of type ${any.typeUrl} emitted non-object JSON: $value"
        )
    }
  }

  val anyParser: (Parser, JsValue) => PBAny = {
    case (parser, obj @ JsObject(_)) =>
      (obj \ "@type").validate[String] match {
        case JsSuccess(typeUrl, _) =>
          val cmp = parser.typeRegistry
            .findType(typeUrl)
            .getOrElse(throw new JsonFormatException(s"""Unknown type: "$typeUrl""""))
          val message = parser.fromJson(obj, true)(cmp)
          PBAny(typeUrl = typeUrl, value = message.toByteString)

        case unknown =>
          throw new JsonFormatException(s"Expected string @type field, got $unknown")
      }

    case (_, unknown) =>
      throw new JsonFormatException(s"Expected an object, got $unknown")
  }
}