Organizing with Private Functions

When game logic gets complex, private helper functions keep code clean and reusable.

The _endGame Helper:

We need to end the game from two places: when someone wins/draws, and when someone claims forfeit.

Instead of duplicating code, create a helper: function _endGame(address _winner, bool isDraw) private

Naming Convention:

Private internal functions often start with an underscore: _endGame

This makes it clear they're not part of the public interface.

What _endGame Does:

1. Set gameOver = true;
2. Set winner = _winner;
3. Store the pot: uint256 pot = stake;
4. If draw, split pot: both players get their stake back
5. If win, winner gets double: credits[_winner] += pot;
6. Reset game state so a new game can start
7. Emit GameEnded event

Create the _endGame helper function with proper win/draw logic.

Create _endGame helper function

Requirements:

Declares _endGame function

_endGame is private

Has _winner parameter

Has isDraw parameter

Sets gameOver to true

Sets winner to _winner parameter

Stores pot in variable

Uses if/else for isDraw logic

Credits both players on draw

Credits winner on win

Resets stake to 0

Resets gameActive to false

Emits GameEnded event

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract TicTacToe {
    uint64 constant ACCEPT_TIMEOUT = 1 days;
    uint64 constant MOVE_TIMEOUT = 1 days;

    event GameStarted(address indexed playerX, address indexed playerO, uint stake);
    event GameEnded(address indexed winner, bool isDraw);

    address public playerX;
    address public playerO;

    enum Cell { Empty, X, O }

    Cell[9] public board;

    bool public xTurn;
    bool public gameOver;
    address public winner;
    uint public stake;
    bool public gameActive;
    bool public gameAccepted;
    uint64 public acceptDeadline;
    uint64 public lastMoveAt;
    mapping(address => uint256) public credits;

    function startGame(address _opponent) public payable {
        require(!gameActive, "Game already active");
        require(_opponent != address(0), "Invalid opponent");
        require(_opponent != msg.sender, "Cannot play yourself");

        playerX = msg.sender;
        playerO = _opponent;
        xTurn = true;
        gameOver = false;
        winner = address(0);
        stake = msg.value;
        gameActive = true;
        gameAccepted = false;
        acceptDeadline = uint64(block.timestamp) + ACCEPT_TIMEOUT;

        for (uint i = 0; i < 9; i++) {
            board[i] = Cell.Empty;
        }

        emit GameStarted(playerX, playerO, stake);
    }

    function acceptGame() public payable {
        require(msg.value == stake, "Must match stake");
        require(msg.sender == playerO, "Only opponent can accept");
        require(block.timestamp <= acceptDeadline, "Accept period expired");
        require(!gameOver, "Game already over");

        gameAccepted = true;
        lastMoveAt = uint64(block.timestamp);
        stake = msg.value * 2;
    }

    function cancelUnaccepted() public {
        require(msg.sender == playerX, "Only starter can cancel");
        require(block.timestamp > acceptDeadline, "Accept period not expired");
        require(!gameAccepted, "Game already accepted");

        credits[playerX] += stake;
        stake = 0;
        gameActive = false;
    }

    function withdraw() public {
        require(credits[msg.sender] > 0, "No credits");
        uint256 amount = credits[msg.sender];
        credits[msg.sender] = 0;
        (bool success, ) = msg.sender.call{value: amount}("");
        require(success, "Transfer failed");
    }

    function claimForfeit() public {
        require(gameAccepted, "Game not started");
        require(!gameOver, "Game already over");
        require(block.timestamp > lastMoveAt + MOVE_TIMEOUT, "Timeout not reached");

        if (xTurn) {
            require(msg.sender == playerO, "Not your turn to claim");
        } else {
            require(msg.sender == playerX, "Not your turn to claim");
        }

        credits[msg.sender] += stake * 2;
        gameOver = true;
        winner = msg.sender;
    }

    function makeMove(uint _position) public {
        require(!gameOver, "Game over");
        require(_position < 9, "Invalid position");
        require(board[_position] == Cell.Empty, "Cell already taken");
        require(xTurn ? msg.sender == playerX : msg.sender == playerO, "Not your turn");

        Cell piece = xTurn ? Cell.X : Cell.O;
        board[_position] = piece;
        lastMoveAt = uint64(block.timestamp);

        if (checkWin()) {
            winner = msg.sender;
            gameOver = true;
            emit GameEnded(winner, false);
        } else if (checkDraw()) {
            winner = address(0);
            gameOver = true;
            emit GameEnded(winner, true);
        } else {
            xTurn = !xTurn;
        }
    }

    function checkWin() private view returns (bool) {
        // Check rows
        for (uint i = 0; i < 3; i++) {
            if (board[i*3] != Cell.Empty &&
                board[i*3] == board[i*3+1] &&
                board[i*3] == board[i*3+2]) {
                return true;
            }
        }

        // Check columns
        for (uint i = 0; i < 3; i++) {
            if (board[i] != Cell.Empty &&
                board[i] == board[i+3] &&
                board[i] == board[i+6]) {
                return true;
            }
        }

        // Check diagonals
        if (board[0] != Cell.Empty &&
            board[0] == board[4] &&
            board[0] == board[8]) {
            return true;
        }

        if (board[2] != Cell.Empty &&
            board[2] == board[4] &&
            board[2] == board[6]) {
            return true;
        }

        return false;
    }

    function checkDraw() private view returns (bool) {
        for (uint i = 0; i < 9; i++) {
            if (board[i] == Cell.Empty) {
                return false;
            }
        }
        return true;
    }
}