gistfile1.scala

case class Page[A](items: Seq[A], page: Int, offset: Long, total: Long) {
  lazy val prev = Option(page - 1).filter(_ >= 0)
  lazy val next = Option(page + 1).filter(_ => (offset + items.size) < total)
}

object Page {
  implicit val writes: Writes[Page[A]] = (
    (__ \ 'items).write[Seq[A]] ~
      (__ \ 'page).write[Int] ~
      (__ \ 'offset).write[Long] ~
      (__ \ 'total).write[Long]
    ) (unlift(Page.unapply))

}

Try

case class Page[A](items: Seq[A], page: Int, offset: Long, total: Long)
object Page {
  implicit def writes[A : Writes]: Writes[Page[A]] = (
    (__ \ 'items).write[Seq[A]] ~
    (__ \ 'page).write[Int] ~
    (__ \ 'offset).write[Long] ~
    (__ \ 'total).write[Long]
  ) (unlift(Page.unapply[A]))

}