# 1. Draw tic-tac-toe board.
# 2. Add board and playing loop.
# 3. Add click-to-play.

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

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

plot(x, y, 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)
  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)
  player = ifelse(test=(player == "X"), yes="O", no="X")
}