WIP - GuessGame Solidity Smart Contract

GuessGame.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.7;

// Start game with a passphrase & reward
// Contract creator needs to have funds?
// Each address can only guess once (use modifier for this)
// Once correct guess give reward
// Add a game over modifier
contract GuessGame {
    uint public reward;
    bytes32 private passphrase;
    mapping(address => bool) private didAddressGuessAlready;


    constructor(
        string memory _passphrase
    ) payable {
        reward = msg.value;
        passphrase = keccak256(abi.encodePacked(_passphrase));
    }

    modifier isGameOver() {
        if (reward == 0) revert("Reward was already won. Game over.");
        _;
    }

    modifier onlyOneGuessPerAddress() {
        if (didAddressGuessAlready[msg.sender] == false) {
            didAddressGuessAlready[msg.sender] = true;
        } else {
            revert("Only one guess per address is allowed.");
        }
        _;
    }

    function guess(string memory _guess) external payable isGameOver onlyOneGuessPerAddress returns (bool) {
        if (keccak256(abi.encodePacked(_guess)) != passphrase) {
            return false;
        }
        payable(msg.sender).transfer(reward);
        reward = 0;
        return true;
    }
}

Some learnings from this:

• You can map an address via msg.sender "address from = msg.sender
• Best way to store a list of addresses in via mapping (you want to avoid iteration as much as possible) reference
• modifiers can only access arguments by callsite (calling it with args - see below)

Calling modifiers with arguments:

   modifier checkHello(string memory _what) {
        if (compareStrings(_what, "what") == false) {
            revert("Wrong guess");
        }
        _;
    }
    
    function sayHello(string memory what) external checkHello(what) pure returns (string memory) {
        return "hello world 2";
    }

    function compareStrings(string memory a, string memory b) public pure returns (bool) {
        return (keccak256(abi.encodePacked((a))) == keccak256(abi.encodePacked((b))));
    }