// This is an example of how to express Infinity in Json using the Play! Scala Json library.
// Infinity cannot be expressed as a Scalar value in Json, so I am using an object to hold it instead.
//
// Example of a finite value:
//  {
//    "value": 12.009,
//    "isInfinite": false
//  }
//
// Example of an infinite value:
//  {
//    "value": null,
//    "isInfinite": true
//  }
//
//  It should be used as any other reads, for example:
//  jsonPayload.as[PossiblyInfinite]

case class PossiblyInfinite(value: Double) {
  val isInfinite: Boolean = value.isInfinite
}

object PossiblyInfinite {

  def Infinite: PossiblyInfinite = PossiblyInfinite(Double.PositiveInfinity)

  private val VALUE_KEY = "value"
  private val IS_INFINITE_KEY = "isInfinite"

  implicit val writes: Writes[PossiblyInfinite] = new Writes[PossiblyInfinite] {
    override def writes(o: PossiblyInfinite): JsValue = {
      if (o.isInfinite) {
        Json.obj(VALUE_KEY -> JsNull, IS_INFINITE_KEY -> true)
      } else {
        Json.obj(VALUE_KEY -> o.value, IS_INFINITE_KEY -> false)
      }
    }
  }

  implicit object PossiblyInfiniteReads extends Reads[PossiblyInfinite] {
    override def reads(json: JsValue): JsResult[PossiblyInfinite] = {

      val maybeDouble = json.asOpt[Double]
      lazy val maybeValue = (json \ VALUE_KEY).asOpt[Double]
      lazy val maybeIsInfinite = (json \ IS_INFINITE_KEY).asOpt[Boolean]

      // If this was a scalar double, use its value
      if (maybeDouble.isDefined) {
        JsSuccess(PossiblyInfinite(maybeDouble.get))
      }

      // If it wasn't a scalar double, check the other properties
      else {
        (maybeValue, maybeIsInfinite) match {

          // Case 1: value is defined (it can't be Infinite here because JSON doesn't allow it)
          case (Some(value), _) => JsSuccess(PossiblyInfinite(value))

          // Case 2: isInfinite is true
          case (_, Some(true)) => JsSuccess(PossiblyInfinite.Infinite)

          // Case 3: there isn't enough information
          case _ => JsError(s"Either ${JsPath() \ VALUE_KEY} must be provided, or ${JsPath() \ IS_INFINITE_KEY} must be provided as true")
        }
      }
    }
  }
}