TicTacToe by Brekkjern

-- Constants
local player1 = 1
local player2 = 4

-- Variables

-- The playing board
local gameBoard = {
  [0] = {[0] = 0, [1] = 0, [2] = 0 },
  [1] = {[0] = 0, [1] = 0, [2] = 0 },
  [2] = {[0] = 0, [1] = 0, [2] = 0 }
}

-- Table for variable game information
local gameData = {
    cursorPos = {
      X = 1,
      Y = 1
    },
    enter = false,
    playerTurn = player1,
    winner = 0,
    turnCounter = 0
}

-- Enumeration for valid directional input
local validKeys = { [200] = true, [203] = true, [205] = true, [208] = true }

-- Table to store what the different keys do.
-- dirname corresponds to the respective arrow key
local keyboard = {
  [200] = { var = -1, axis = "Y", dirname = "Up" },
  [203] = { var = -1, axis = "X", dirname = "Left"},
  [205] = { var = 1, axis = "X", dirname = "Right"},
  [208] = { var = 1, axis = "Y", dirname = "Down"}
}

-- Function to make the cursor wrap around the playing field
local function updateGameCursor(key)
  local keyTable = keyboard[key]
  gameData.cursorPos[keyTable.axis] = math.fmod(3 + gameData.cursorPos[keyTable.axis] + keyTable.var, 3)
end

-- Rendering functions
local render = {}
function render.cell(X, Y)

  -- Check if the current cell is the selected one
  -- and make it green if true
  if X == gameData.cursorPos.X and Y == gameData.cursorPos.Y then
    term.setTextColor(colours.green)
  end

  if gameBoard[Y][X] == 0 then
    io.write("[ ]")
  elseif gameBoard[Y][X] == 1 then
    io.write("[X]")
  elseif gameBoard[Y][X] == 4 then
    io.write("[O]")
  end
  term.setTextColor(colours.white)
end

function render.line(Y)
  for X = 0, #gameBoard[Y] do
    render.cell(X, Y)
  end
end

function render.board()
  term.clear()
  term.setCursorPos(1,1)
  for Y = 0, #gameBoard do
    render.line(Y)

    if Y == 0 then
      io.write("\t Player: ")
      if gameData.playerTurn == 1 then
        io.write("X")
      else
        io.write("O")
      end
    elseif Y == 1 then
      io.write("\t Turn number: "..gameData.turnCounter)
    end
    io.write("\n")
  end
end

setmetatable(render, { __call = function(t, ...) return render.board() end })

-- Program loop
while gameData.winner == 0 do

  -- Helper function
  local function selectedCell()
    return gameBoard[gameData.cursorPos.Y][gameData.cursorPos.X]
  end

  -- Render the screen.
  render()

  -- Check for input after rendering.
  local event, param1, param2, param3 = os.pullEventRaw()

  -- Parse input
  if event == "key" then
    if validKeys[param1] then
      updateGameCursor(param1)
    end
    if param1 == 28 then
      gameData.enter = true
    end
  end

  -- If enter has been pressed and the cell is empty
  -- change the content of the cell to the player value
  if gameData.enter and selectedCell() == 0 then
    gameBoard[gameData.cursorPos.Y][gameData.cursorPos.X] = gameData.playerTurn
  else
    gameData.enter = false
  end

  -- Check if somebody won
  local winConditions = {
  -- Horizontals
  [1] = gameBoard[0][0] + gameBoard[0][1] + gameBoard[0][2],
  [2] = gameBoard[1][0] + gameBoard[1][1] + gameBoard[1][2],
  [3] = gameBoard[2][0] + gameBoard[2][1] + gameBoard[2][2],

  -- Diagonals
  [4] = gameBoard[0][0] + gameBoard[1][1] + gameBoard[2][2],
  [5] = gameBoard[2][0] + gameBoard[1][1] + gameBoard[0][2],

  -- Verticals
  [6] = gameBoard[0][0] + gameBoard[1][0] + gameBoard[2][0],
  [7] = gameBoard[0][1] + gameBoard[1][1] + gameBoard[2][1],
  [8] = gameBoard[0][2] + gameBoard[1][2] + gameBoard[2][2]
  }

  for k, v in ipairs(winConditions) do
    if v == (gameData.playerTurn * 3) then
      gameData.winner = gameData.playerTurn
    end
  end

  -- Change the player turn if a cell has been selected
  if gameData.enter and gameData.winner == 0 then
    if gameData.playerTurn == player1 then
      gameData.playerTurn = player2
    else
      gameData.playerTurn = player1
    end
    gameData.turnCounter = gameData.turnCounter + 1
  end
  gameData.enter = false

  -- If the board is full and there is no winner, end the game
  if gameData.turnCounter == 9 and gameData.winner == 0 then
    break
  end
end

-- Render one last time to show the final outcome
render()

-- Print who the winner is
if gameData.turnCounter == 9 then
  print("Tie")
else
  print("Winner is player "..gameData.winner.." after "..gameData.turnCounter.." turns!")
end