mission.scala

package com.rumblesan.marsrover

import cats._
import cats.instances.list._
import cats.instances.either._

import Commands.Command
import Headings.Heading

case class Mission(startX: Int, startY: Int, startHeading: Heading, commands: List[Command])

object Mission {

  sealed trait FailedMissionResult
  case class LostBot(bot: Bot) extends FailedMissionResult

  type MissionResult[Result] = Either[FailedMissionResult, Result]

  def run(mission: Mission, planet: Planet): MissionResult[Bot] = {
    val startBot = Bot(mission.startX, mission.startY, mission.startHeading)
    Foldable[List].foldM[MissionResult, Command, Bot](mission.commands, startBot)((bot, command) => {
      val newBot = Bot.command(bot, command)
      if (Planet.validPosition(planet, newBot.xPos, newBot.yPos)) {
        Right(newBot)
      } else if (Planet.checkMarker(planet, bot.xPos, bot.yPos)) {
        // Skip command
        Right(bot)
      } else {
        // Return last valid bot
        Left(LostBot(bot))
      }
    })
  }

}