freedom.scala

package freedom

import scala.collection.JavaConverters._

import java.awt.Color
import java.awt.image.BufferedImage

import cats.data.Coproduct
import cats.free.{ Free, Inject }
import cats.{ ~>, Id }

object Freedom extends App {

  import interaction._
  import logging._
  import rendering._

  type InteractOrLog[A] = Coproduct[InteractionOp, LoggingOp, A]
  type App[A] = Coproduct[InteractOrLog, RenderingOp, A]

  val img = new BufferedImage(250, 250, BufferedImage.TYPE_INT_RGB)
  val g = img.createGraphics()

  val interp = DefaultInterpreter or ConsoleInterpreter or new GInterpreter(g)

  def drawText(text: String)(implicit I: Interaction[App], L: Logging[App], R: Rendering[App]) = {

    import I._, R._, L._

    for {
      _ <- tell("here's a message")
      _ <- setColor(Color.orange)
      _ <- debug("set the color")
      _ <- fillRect(25, 25, 50, 50)
      _ <- debug("filled the rect")
      _ <- setColor(Color.blue)
      _ <- drawString(text, 10, 10)
      _ <- debug(s"rendered: $text")
    } yield ()

  }

  // Compilation Error
  // [error] /home/brandy/workspace/freedom/src/main/scala/freedom/Minimal.scala:63: could not find implicit value for parameter I: freedom.interaction.Interaction[freedom.Freedom.App]
  // [error]   drawText("Hello Free!") foldMap interp
  // [error]           ^
  // [error] one error found
  drawText("Hello Free!") foldMap interp

  // Dump the results for inspection
  javax.imageio.ImageIO.write(img, "png", new java.io.File("/home/brandy/Desktop/free-image.png"))

}

object interaction {

  sealed trait InteractionOp[A]
  case class Tell(message: String) extends InteractionOp[Unit]

  class Interaction[F[_]](implicit I: Inject[InteractionOp, F]) {
    def tell(message: String) = Free.inject[InteractionOp, F](Tell(message))
  }

  object Interaction {
    implicit def instance[F[_]](implicit I: Inject[InteractionOp, F]): Interaction[F] = new Interaction[F]
  }

  object DefaultInterpreter extends (InteractionOp ~> Id) {
    def apply[A](fa: InteractionOp[A]): Id[A] = {
      fa match {
        case Tell(message) => println(message)
      }
    }
  }

}

object logging {

  sealed trait LoggingOp[A]
  case class Debug(message: String) extends LoggingOp[Unit]

  class Logging[F[_]](implicit I: Inject[LoggingOp, F]) {
    def debug(message: String) = Free.inject[LoggingOp, F](Debug(message))
  }

  object Logging {
    implicit def instance[F[_]](implicit I: Inject[LoggingOp, F]): Logging[F] = new Logging[F]
  }

  object ConsoleInterpreter extends (LoggingOp ~> Id) {
    def apply[A](fa: LoggingOp[A]): Id[A] = {
      fa match {
        case Debug(message) => println(message)
      }
    }
  }

}

object rendering {

  import java.awt._

  sealed trait RenderingOp[A]
  case class FillRect(x: Int, y: Int, width: Int, height: Int) extends RenderingOp[Unit]
  case class DrawString(str: String, x: Int, y: Int) extends RenderingOp[Unit]
  case class SetColor(c: Color) extends RenderingOp[Unit]

  class Rendering[F[_]](implicit I: Inject[RenderingOp, F]) {
    def drawString(str: String, x: Int, y: Int) = Free.inject[RenderingOp, F](DrawString(str, x, y))
    def fillRect(x: Int, y: Int, width: Int, height: Int) = Free.inject[RenderingOp, F](FillRect(x, y, width, height))
    def setColor(c: Color) = Free.inject[RenderingOp, F](SetColor(c))
  }

  object Rendering {
    implicit def instance[F[_]](implicit I: Inject[RenderingOp, F]): Rendering[F] = new Rendering[F]
  }

  class GInterpreter(g: Graphics2D) extends (RenderingOp ~> Id) {
    def apply[A](fa: RenderingOp[A]): Id[A] = {
      fa match {
        case DrawString(str, x, y) => g.drawString(str, x, y)
        case FillRect(x, y, width, height) => g.fillRect(x, y, width, height)
        case SetColor(c) => g.setColor(c)
      }
    }
  }

}