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Json/Protobuf convertors for ScalaPB

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package scalapb_argonaut

import com.google.protobuf.any.{Any => PBAny}
import argonaut._
import scalapb_json._

object AnyFormat {
  val anyWriter: (Printer, PBAny) => Json = { 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).obj match {
      case Some(fields) =>
        Json.obj((("@type" -> Json.jString(any.typeUrl)) :: fields.toList) *)
      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, Json) => PBAny = { case (parser, json) =>
    json.obj match {
      case Some(obj) =>
        obj.toMap.get("@type").flatMap(_.string) match {
          case Some(typeUrl) =>
            val cmp = parser.typeRegistry
              .findType(typeUrl)
              .getOrElse(throw new JsonFormatException(s"""Unknown type: "$typeUrl""""))
            val message = parser.fromJson(json, true)(cmp)
            PBAny(typeUrl = typeUrl, value = message.toByteString)

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

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