.scala

import cats.data.StateT
import cats.implicits._

case class Appliance(power: Double, isOn: Boolean = false, grid: Option[Int] = None)
case class Grid(maxPower: Double)
case class World(grids: Vector[Grid] = Vector(), appliances: Vector[Appliance] = Vector())

object Main extends App {

  type Error = String
  type ErrorOr[A] = Either[Error, A]
  type EitherState[A] = StateT[ErrorOr, World, A]

  def newAppliance(power: Double): EitherState[Int] = StateT { world =>
    Right(world.copy(appliances = world.appliances :+ Appliance(power)), world.appliances.size)
  }

  def newGrid(maxPower: Int): EitherState[Int] = StateT { world =>
    Right((world.copy(grids = world.grids :+ Grid(maxPower)), world.grids.size))
  }

  def residualPower(world: World, gridId: Int): Double = {
    val grid = world.grids(gridId)
    val sumOfPower = world.appliances.filter { appliance => appliance.isOn && appliance.grid.contains(gridId) }.map { _.power }.sum
    grid.maxPower - sumOfPower
  }

  def plugInto(applianceId: Int, gridId: Int): EitherState[Unit] = StateT { world =>
    val appliance = world.appliances(applianceId).copy(isOn = false, grid = Some(gridId))
    Right(world.copy(appliances = world.appliances.updated(applianceId, appliance)), ())
  }

  def on(applianceId: Int): EitherState[Unit] = StateT { world =>
    val appliance = world.appliances(applianceId).copy(isOn = true)
    appliance.grid match {
      case Some(grid) if residualPower(world, grid) < appliance.power =>
        Left("Not Enough Power")
      case _ =>
        Right(world.copy(appliances = world.appliances.updated(applianceId, appliance)), ())
    }
  }

  def off(applianceId: Int): EitherState[Unit] = StateT { world =>
    val appliance = world.appliances(applianceId).copy(isOn = false)
    Right(world.copy(appliances = world.appliances.updated(applianceId, appliance)), ())
  }

  def printResidualPower(gridId: Int): EitherState[Unit] = StateT { world =>
    println(residualPower(world, gridId))
    Right(world, ())
  }

  val world = World()
  val program = for {
    tv <- newAppliance(150)
    radio <- newAppliance(30)
    airConditioner <- newAppliance(4000)
    grid <- newGrid(3000)
    _ <- plugInto(tv, grid)
    _ <- plugInto(radio, grid)
    _ <- plugInto(airConditioner, grid)
    _ <- printResidualPower(grid)
    _ <- on(tv)
//    _ <- on(airConditioner)
    _ <- printResidualPower(grid)
    _ <- on(radio)
    _ <- printResidualPower(grid)
  } yield ()

  println(program.run(world))
}