trollface.scala

import cats.{Applicative, Monad}
import cats.syntax.all._
import org.http4s._

sealed trait Route[F[_]] {
  def run(r: Request[F]): F[Response[F]]

  def <+>(other: Route[F]): Route[F]
}

case class PartialRoute[F[_]](pf: PartialFunction[Request[F], F[Response[F]]])(implicit F: Monad[F])
    extends Route[F] {

  def <+>(other: Route[F]): Route[F] = other match {
    case PartialRoute(pfother) => PartialRoute(pf.orElse(pfother))

    case EffectingRoute(eff) =>
      EffectingRoute[F] { r =>
        if (pf.isDefinedAt(r))
          pf(r).map(Some(_))
        else
          eff(r)
      }
  }

  def run(r: Request[F]): F[Response[F]] =
    pf.applyOrElse[Request[F], F[Response[F]]](r, _ => F.pure(Response.notFound[F]))
}

case class EffectingRoute[F[_]](eff: Request[F] => F[Option[Response[F]]])(implicit F: Monad[F])
    extends Route[F] {
  def run(r: Request[F]): F[Response[F]] = eff(r).flatMap(_.fold(Response.notFound[F].pure[F])(_.pure[F]))

  def <+>(other: Route[F]) = other match {
    case PartialRoute(pf) =>
      EffectingRoute[F] { r =>
        eff(r).flatMap {
          case Some(res) => F.pure(Some(res))
          case None =>
            if (pf.isDefinedAt(r))
              pf(r).map(s => Some(s))
            else F.pure(None)
        }
      }
  }
}