Ants.scala

package langtonsant

import scala.annotation.tailrec
import scala.collection.immutable.Map

object Ants extends App {

  val columnNb = 50
  val rowNb = 50

  val grid = (0 until (rowNb * columnNb)).toList.map(_ => 0)

  loop(State(grid, c2dtoc1d(25, 25), "n"))

  def flip(grid: List[Int], index: Int): List[Int] = {
    val state = grid(index)
    grid.updated(index, if (state == 0) 1 else 0)
  }

  def step(oldState: State): State = {
    render(oldState.grid)

    //    println(oldState)
    val newDirection = if (oldState.grid(oldState.position) == 1) turnRight(oldState.direction)
    else turnLeft(oldState.direction)

    val newPosition = move(oldState.position, newDirection)
    State(flip(oldState.grid, oldState.position), newPosition, newDirection)
  }

  @tailrec
  def loop(state: State): State = {
    loop(step(state))
  }

  def render(grid: List[Int]) {
    println(grid.sliding(rowNb, columnNb).map(_.map(x => if (x == 0) "." else "#").mkString(" ")).mkString("\n"))
    println
  }
  def c1dtoc2d(index: Int): Position = {
    Position((index % columnNb), (index / columnNb))
  }

  def c2dtoc1d(x: Int, y: Int) = {
    x + (y * columnNb)
  }

  def move(position: Int, direction: String): Int = {
    val pos = c1dtoc2d(position)
    direction match {
      case "w" => c2dtoc1d((pos.x - 1) % rowNb, pos.y)
      case "e" => c2dtoc1d((pos.x + 1) % rowNb, pos.y)
      case "n" => c2dtoc1d(pos.x, (pos.y - 1) % columnNb)
      case "s" => c2dtoc1d(pos.x, (pos.y + 1) % columnNb)
    }
  }

  def turnLeft = Map("w" -> "s", "s" -> "e", "e" -> "n", "n" -> "w")

  def turnRight = Map("w" -> "n", "s" -> "w", "e" -> "s", "n" -> "e")

  case class State(grid: List[Int], position: Int, direction: String)

  case class Position(x: Int, y: Int)

}