function winner(board)

{

    for (var i=0; i<3; ++i) {

        if (board.children[i].state != ""

                && board.children[i].state == board.children[i+3].state

                && board.children[i].state == board.children[i+6].state)

            return true

        if (board.children[i*3].state != ""

                && board.children[i*3].state == board.children[i*3+1].state

                && board.children[i*3].state == board.children[i*3+2].state)

            return true

    }

    if (board.children[0].state != ""

            && board.children[0].state == board.children[4].state != ""

            && board.children[0].state == board.children[8].state != "")

        return true

    if (board.children[2].state != ""

            && board.children[2].state == board.children[4].state != ""

            && board.children[2].state == board.children[6].state != "")

        return true

    return false

}

function restartGame()

{

    game.running = true

    for (var i=0; i<9; ++i)

        board.children[i].state = ""

}

function makeMove(pos, player)

{

    board.children[pos].state = player

    if (winner(board)) {

        gameFinished(player + " wins")

        return true

    } else {

        return false

    }

}

function canPlayAtPos(pos)

{

    return board.children[pos].state == ""

}

function computerTurn()

{

    var r = Math.random();

    if (r < game.difficulty)

        smartAI();

    else

        randomAI();

}

function smartAI()

{

    function boardCopy(a) {

        var ret = new Object;

        ret.children = new Array(9);

        for (var i = 0; i<9; i++) {

            ret.children[i] = new Object;

            ret.children[i].state = a.children[i].state;

        }

        return ret;

    }

    for (var i=0; i<9; i++) {

        var simpleBoard = boardCopy(board);

        if (canPlayAtPos(i)) {

            simpleBoard.children[i].state = "O";

            if (winner(simpleBoard)) {

                makeMove(i, "O")

                return

            }

        }

    }

    for (var i=0; i<9; i++) {

        var simpleBoard = boardCopy(board);

        if (canPlayAtPos(i)) {

            simpleBoard.children[i].state = "X";

            if (winner(simpleBoard)) {

                makeMove(i, "O")

                return

            }

        }

    }

    function thwart(a,b,c) {    //If they are at a, try b or c

        if (board.children[a].state == "X") {

            if (canPlayAtPos(b)) {

                makeMove(b, "O")

                return true

            } else if (canPlayAtPos(c)) {

                makeMove(c, "O")

                return true

            }

        }

        return false;

    }

    if (thwart(4,0,2)) return;

    if (thwart(0,4,3)) return;

    if (thwart(2,4,1)) return;

    if (thwart(6,4,7)) return;

    if (thwart(8,4,5)) return;

    if (thwart(1,4,2)) return;

    if (thwart(3,4,0)) return;

    if (thwart(5,4,8)) return;

    if (thwart(7,4,6)) return;

    for (var i =0; i<9; i++) {

        if (canPlayAtPos(i)) {

            makeMove(i, "O")

            return

        }

    }

    restartGame();

}

function randomAI()

{

    var unfilledPosns = new Array();

    for (var i=0; i<9; ++i) {

        if (canPlayAtPos(i))

            unfilledPosns.push(i);

    }

    if (unfilledPosns.length == 0) {

        restartGame();

    } else {

        var choice = unfilledPosns[Math.floor(Math.random() * unfilledPosns.length)];

        makeMove(choice, "O");

    }

}

function gameFinished(message)

{

    messageDisplay.text = message

    messageDisplay.visible = true

    game.running = false

}