Example for a contract for playing high-stakes Roulette on the blockchain

High-Stakes Roulette Example

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

contract BankOwned {
    address public bankAddress;

    constructor() {
        bankAddress = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == bankAddress);
        _;
    }
}

contract Roulette is BankOwned {
    uint256 public immutable TIMEOUT_FOR_BANK_REVEAL = 1 days;
    uint256 public immutable ROULETTE_NUMBER_COUNT = 37;

    // prettier-ignore
    bool[37] isNumberRed = [false, true, false, true, false, true, false, true, false, true, false, false, true, false, true, false, true, false, true, true, false, true, false, true, false, true, false, true, false, false, true, false, true, false, true, false, true];

    struct GameRound {
        bytes32 bankHash;
        uint256 bankSecretValue;
        uint256 userValue;
        bool hasUserBetOnRed;
        uint256 timeWhenSecretUserValueSubmitted;
        uint256 lockedFunds;
    }

    mapping(address => bool) public hasRequestedGame;
    mapping(address => GameRound) public gameRounds;
    mapping(address => uint256) public registeredFunds;

    event NewGameRequest(address indexed user);

    function increaseFunds() external payable {
        require(msg.value > 0, "Must send ETH");
        registeredFunds[msg.sender] += msg.value;
    }

    function withdrawMoney() external {
        require(registeredFunds[msg.sender] > 0);

        uint256 funds = registeredFunds[msg.sender];
        registeredFunds[msg.sender] = 0;

        (bool wasSuccessful, ) = msg.sender.call{value: funds}("");
        require(wasSuccessful, "ETH transfer failed");
    }

    function initializeGame() external {
        require(!hasRequestedGame[msg.sender], "Already requested game");

        hasRequestedGame[msg.sender] = true;
        emit NewGameRequest(msg.sender);
    }

    function setInitialBankHash(bytes32 bankHash, address userAddress) external onlyOwner {
        require(gameRounds[userAddress].bankHash == 0x0, "Bank hash already set");
        gameRounds[userAddress].bankHash = bankHash;
    }

    function placeBet(
        bool hasUserBetOnRed,
        uint256 userValue,
        uint256 _betAmount
    ) external {
        require(gameRounds[msg.sender].bankHash != 0x0, "Bank hash not yet set");
        require(userValue == 0, "Already placed bet");
        require(registeredFunds[bankAddress] >= _betAmount, "Not enough bank funds");
        require(registeredFunds[msg.sender] >= _betAmount, "Not enough user funds");

        gameRounds[msg.sender].userValue = userValue;
        gameRounds[msg.sender].hasUserBetOnRed = hasUserBetOnRed;
        gameRounds[msg.sender].lockedFunds = _betAmount * 2;
        gameRounds[userAddress].timeWhenSecretUserValueSubmitted = block.timestamp;

        registeredFunds[msg.sender] -= _betAmount;
        registeredFunds[bankAddress] -= _betAmount;
    }

    function sendBankSecretValue(uint256 bankSecretValue, address userAddress) external {
        require(gameRounds[userAddress].userValue != 0, "User has no value set");
        require(gameRounds[userAddress].bankSecretValue == 0, "Already revealed");
        require(keccak256(abi.encodePacked(bankSecretValue)) == gameRounds[userAddress].bankHash, "Bank reveal not matching commitment");

        gameRounds[userAddress].bankSecretValue = bankSecretValue;

        _evaluateBet(userAddress);
        _resetContractFor(userAddress);

        gameRounds[userAddress].bankHash = bytes32(bankSecretValue);
    }

    function checkBankSecretValueTimeout() external {
        require(gameRounds[msg.sender].bankHash != 0, "Bank hash not set");
        require(gameRounds[msg.sender].bankSecretValue == 0, "Bank secret is set");
        require(gameRounds[msg.sender].userValue != 0, "User value not set");
        require(block.timestamp > (gameRounds[msg.sender].timeWhenSecretUserValueSubmitted + TIMEOUT_FOR_BANK_REVEAL), "Timeout not yet reached");

        registeredFunds[msg.sender] += gameRounds[msg.sender].lockedFunds;
        _resetContractFor(msg.sender);
    }

    function _resetContractFor(address userAddress) private {
        gameRounds[userAddress] = GameRound(0x0, 0, 0, false, 0, 0);
    }

    function _evaluateBet(address userAddress) private {
        uint256 random = gameRounds[userAddress].bankSecretValue ^ gameRounds[userAddress].userValue;
        uint256 number = random % ROULETTE_NUMBER_COUNT;
        uint256 winningAmount = gameRounds[userAddress].lockedFunds;

        bool isNeitherRedNorBlack = number == 0;
        bool isRed = isNumberRed[number];
        bool hasUserBetOnRed = gameRounds[userAddress].hasUserBetOnRed;

        address winner;

        if (isNeitherRedNorBlack) winner = bankAddress;
        else if (isRed == hasUserBetOnRed) winner = userAddress;
        else winner = bankAddress;

        registeredFunds[winner] += winningAmount;
    }
}