# 1. Draw tic-tac-toe board.
# 2. Add board and playing loop.
# 3. Add click-to-play.
# 4. Add check for a win.

rm(list=ls()) # clear all defined objects

won = function(board, player, debug=FALSE) {
  if (debug) {
    cat(sep="", "player=", player, ", board=", "\n")
    print(board)
  }
  return(
         all(board[1:3, 1] == player) |   # check columns 1-3
         all(board[1:3, 2] == player) |
         all(board[1:3, 3] == player) |
         all(board[1, 1:3] == player) | # check rows 1-3
         all(board[2, 1:3] == player) |
         all(board[3, 1:3] == player) |
         all(diag(board) == player) |   # check diagonals
         all(diag(board[3:1, ]) == player)
         )
}
test.board = matrix(data=c("X","O","", "O","X","O", "X","O","X"), nrow=3, ncol=3)
stopifnot( won(test.board, "X"))
stopifnot(!won(test.board, "O"))
test.board[2, 2] = "O"
stopifnot(!won(test.board, "X"))
stopifnot( won(test.board, "O"))

x = rep(x=1:3, each=3)
y = rep(x=1:3, times=3)

plot(x, y, type="n", xlim=c(0, 4), ylim=c(4, 0))
segments(x0=c(0.5, 0.5, 1.5, 2.5), y0=c(1.5, 2.5, 0.5, 0.5),
         x1=c(3.5, 3.5, 1.5, 2.5), y1=c(1.5, 2.5, 3.5, 3.5))

board = matrix(data=rep(x="", times=9), nrow=3, ncol=3)
player = "X"
for (i in 1:9) {
  index = identify(x, y, n=1, plot=FALSE)
  col = x[index]
  row = y[index]
  board[row, col] = player
  text(x=col, y=row, labels=player)
  cat(sep="", "i=", i, ", player=", player, ", index=", index,
      ", row=", row, ", col=", col, ", board:", "\n")
  print(board)
  if (won(board, player, debug=TRUE)) {
    text(x=2, y=1/3, labels=paste(player, " won!"), col="red")
    break
  }
  player = ifelse(test=(player == "X"), yes="O", no="X")
}