adam.scala

sealed trait State

case class WithOffer(offer: Offer) extends State
object WithOffer {
  implicit val hasOffer: HasOffer[WithOffer] = _.offer
}

case class WithoutOffer() extends State

case class WithPartner(partnerName: String) extends State

case class WithOfferAndPartner(offer: Offer, partnerName: String) extends State
object WithOfferAndPartner {
  implicit val hasOffer: HasOffer[WithOfferAndPartner] = _.offer
}


trait HasOffer[S] {
  def offer(s: S): Offer
}
object HasOffer {
  def getOffer[S: HasOffer](s: S): Offer = implicitly[HasOffer[S]].offer(s)
}

case class Offer(id: Int)

case class Merchant[S <: State](name: String, state: S)
object Merchant {
  def withoutOffer(name: String): Merchant[WithoutOffer] =
    Merchant[WithoutOffer](name, WithoutOffer())

  def withOffer(name: String, offer: Offer): Merchant[WithOffer] =
    addOffer(withoutOffer(name), offer)

  def addOffer(merchant: Merchant[WithoutOffer], offer: Offer): Merchant[WithOffer] =
    Merchant[WithOffer](merchant.name, WithOffer(offer))

  import scala.language.implicitConversions
  implicit def hasOffer[S <: State: HasOffer]: HasOffer[Merchant[S]] =
    (m: Merchant[S]) => HasOffer.getOffer(m.state)
}


object Main extends App {

  def printOffer(merchant: Merchant[WithOffer]): Unit = {
    println("offer: %s", HasOffer.getOffer(merchant))
  }

  printOffer(Merchant.withOffer("renan", Offer(1)))
  println(HasOffer.getOffer(Merchant.withOffer("renan", Offer(1))))
}