scala-ddd-cats.scala

package app

import cats.free._
import cats._

class DDD[ID, E] {

  def resolveBy(id: ID): Free[RepositoryDSL, Option[E]] = Free.liftF(ResolveBy(id))

  def store(id: ID, entity: E): Free[RepositoryDSL, Unit] = Free.liftF(Store(id, entity))

  sealed abstract class RepositoryDSL[A]

  final case class ResolveBy(id: ID) extends RepositoryDSL[Option[E]]

  final case class Store(id: ID, entity: E) extends RepositoryDSL[Unit]

}

object Sample extends App {
  type UserId = Int
  final case class User(id: UserId, name: String)

  val ddd = new DDD[UserId, User]


  val user1 = User(1, "aaa")
  val user2 = User(2, "bbb")

  val program = for {
    _ <- ddd.store(user1.id, user1)
    _ <- ddd.store(user2.id, user2)
    user <- ddd.resolveBy(user1.id)
  } yield user

  // TODO: SqlActionをDBIO.sequenceで返したい
  val interpreter = new (ddd.RepositoryDSL ~> Id) {
    val database = collection.mutable.Map.empty[UserId, User]
    override def apply[A](fa: ddd.RepositoryDSL[A]) = fa match {
      case ddd.ResolveBy(id) =>
        database.get(id).asInstanceOf[A] 
      case ddd.Store(id, entity) =>
        database.put(id, entity)
        ()
    }
  }

  // TODO: SqlActionをDBIOを返したい → 取得したdb.run(action)したい
  val result: Option[User] = program.foldMap(interpreter)
  println(result)

}