//
// simple text-mode version of Conway's game of life
//
// initial board configuration is read in from a file, one line
// per row, with X's for occupied cells and .'s for unoccupied cells.
//
case class Board(b : Array[Array[Boolean]])
val EmptyChar = '.'
val FullChar = 'X'

val usageMessage = "command-line argument:  file with initial configuration"
if (args.length < 1) {
  println(usageMessage)
}
else {
  try {
    val board = readBoard(args(0))
    if (board.b.length > 0)
      play(board)
  }
  catch {
    case e:java.io.FileNotFoundException => {
      println("could not open file " + args(0))
    }
  }
}

def readBoard(filename : String) : Board = {
  val source = scala.io.Source.fromFile(filename)
  val lines = source.getLines.toArray
  source.close
  val boardRows = Array.tabulate(lines.length)(i => buildRow(lines(i)))
  if (boardRows.length == 0) {
    println("no lines in input file")
    Board(boardRows)
  }
  else {
    if (!boardRows.forall(_.length == boardRows(0).length)) {
      println("not all lines the same length")
      Board(Array.fill(0,0)(false))
    }
    else {
      Board(boardRows)
    }
  }
}
def buildRow(line : String) : Array[Boolean] = {
  line.toArray.map(_ != EmptyChar) 
}

def printBoard(board : Board) = {
  for (row <- 0 until board.b.length) {
    println(board.b(row).map(if (_) FullChar else EmptyChar).mkString)
  }
}

def oneStep(board : Board) : Board = {
  Board(Array.tabulate(board.b.length, board.b(0).length)(
    (i,j) => newCellValue(board, i, j)))
}
def newCellValue(oldBoard : Board, row : Int, col : Int) : Boolean = {
  var neighbors = 0
  val lastRow = oldBoard.b.length-1
  val lastCol = oldBoard.b(0).length-1
  // neighbors above
  if (row > 0) {
    if ((col > 0) && oldBoard.b(row-1)(col-1)) neighbors += 1
    if (oldBoard.b(row-1)(col)) neighbors += 1
    if ((col < lastCol) && oldBoard.b(row-1)(col+1)) neighbors += 1
  }
  // neighbors in same row
  if ((col > 0) && oldBoard.b(row)(col-1)) neighbors += 1
  if ((col < lastCol) && oldBoard.b(row)(col+1)) neighbors += 1
  // neighbors below
  if (row < lastRow) {
    if ((col > 0) && oldBoard.b(row+1)(col-1)) neighbors += 1
    if (oldBoard.b(row+1)(col)) neighbors += 1
    if ((col < lastCol) && oldBoard.b(row+1)(col+1)) neighbors += 1
  }
  if (oldBoard.b(row)(col))
    (neighbors == 2) || (neighbors == 3)
  else
    neighbors == 3
}

def play(board : Board) : Unit = {
  println() ; printBoard(board); println()
  println("press enter for next step, any other text (and enter) to quit")
  val response = readLine
  if (response == "") {
    play(oneStep(board))
  }
}