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kyo-core-opt

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package kyo

import java.io.Closeable

import kyo.core._
import kyo.ios._
import java.util.ArrayList

object resources {

  private case object GetFinalizer

  type Resource[T] >: T // = T | GetFinalizer

  final class Resources private[resources] ()
      extends Effect[Resource, Resources] {

    private[resources] val finalizer: Finalizer > Resources =
      suspend(GetFinalizer.asInstanceOf[Resource[Finalizer]])

    def ensure(v: => Unit > IOs): Unit > (IOs with Resources) =
      finalizer.map(_.put(IOs(v)))

    def acquire[T <: Closeable](resource: => T): T > (IOs with Resources) = {
      lazy val v = resource
      ensure(v.close()).andThen(v)
    }

    def run[T, S](v: T > (Resources with S))(
        implicit f: Flat[T > (Resources with S)]
    ): T > (IOs with S) = {
      val finalizer = new Finalizer
      implicit def handler: Handler[Resource, Resources, Any] =
        new Handler[Resource, Resources, Any] {
          def pure[U](v: U) = v
          def apply[U, V, S2](
              m: Resource[U],
              f: U => V > (Resources with S2)
          ): V > (S2 with Resources) =
            m match {
              case GetFinalizer =>
                f(finalizer.asInstanceOf[U])
              case _ =>
                f(m.asInstanceOf[U])
            }
        }
      IOs.ensure(finalizer.run) {
        handle[T, Resources with S, Any](v).asInstanceOf[T > S]
      }
    }
  }
  val Resources = new Resources

  private class Finalizer extends ArrayList[Unit > IOs] {
    def put(close: Unit > IOs): Unit > IOs =
      IOs {
        add(close)
        ()
      }
    val run: Unit > IOs =
      IOs {
        while (size() > 0) IOs.run(remove(0))
      }
  }
}