val format = fields.length match {
  case 0 => c.abort(c.enclosingPosition, "Cannot create json formatter for case class with no fields")
  case 1 =>
    // Only one field, use the serializer for the field
    q"""
      implicit val jsonAnnotationFormat = {
        import play.api.libs.json._
        Format(
          __.read[${fields.head.tpt}].map(s => ${className.toTermName}(s)),
          new Writes[$className] { def writes(o: $className) = Json.toJson(o.${fields.head.name}) }
        )
      }
    """
  case _ =>
    // More than one field, use Play's Json.format[T] macro
    q"implicit val jsonAnnotationFormat = play.api.libs.json.Json.format[$className]"
}