gistfile1.scala

package derivation

import shapeless._
import shapeless.ops.coproduct.Length
import shapeless.ops.nat.ToInt

import scala.util.Random

sealed trait Animal
case class Cat(name: String, fish: Int) extends Animal
case class Dog(name: String, bones: Int) extends Animal
case class Cow(name: String) extends Animal

object Arbitrary {
  def apply[T](implicit a: Arbitrary[T]) = a

  implicit val arbitraryHNil: Arbitrary[HNil] = new Arbitrary[HNil] {
    def value = HNil
  }
  implicit def arbitraryHCon[H, T <: HList](
   implicit h: Arbitrary[H], t: Arbitrary[T]): Arbitrary[H :: T] = new Arbitrary[H :: T] {
    def value = h.value :: t.value
  }
  implicit val arbitraryCNil: Arbitrary[CNil] = new Arbitrary[CNil] {
    def value = ???
  }
  implicit def arbitraryCCon[H, T <: Coproduct, N <: Nat](
   implicit h: Arbitrary[H],
   t: Arbitrary[T],
   l: Length.Aux[T, N],
   n: ToInt[N]): Arbitrary[H :+: T] = new Arbitrary[H :+: T] {
    def value = {
      val choice = Random.nextInt(1 + n())
      if(choice == 0) Inl(h.value) else Inr(t.value)
    }

  }
  /*implicit def arbitaryCLast[H](implicit h: Arbitrary[H]): Arbitrary[H :+: CNil] = new Arbitrary[H :+: CNil] {
    def value = Inl(h.value)
  }*/


  implicit val arbitraryInt: Arbitrary[Int] = new Arbitrary[Int] {
    def value = Random.nextInt(10)
  }
  implicit val arbitraryString: Arbitrary[String] = new Arbitrary[String] {
    def value = s"<<${Random.nextInt(10)}>>"
  }

  implicit def arbitraryGen[T, R](implicit
    gen: Generic.Aux[T, R],
    arbitraryRepr: Arbitrary[R]): Arbitrary[T] = new Arbitrary[T] {
      def value: T = gen.from(arbitraryRepr.value)
  }
}

trait Arbitrary[T] {
  def value: T
}

object Demo extends App {
  for(i <- 1 to 10) println(Arbitrary[Animal].value)
}