// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract LuckyDraw {
    uint256 public jackpot;
    bool    public solved;
    address public solver;
    bytes32 private flag;

    constructor(bytes32 _flag) payable { 
        jackpot = msg.value; 
        flag = _flag;
    }

    function play(uint256 _guess) external payable {
        require(msg.value == 0.01 ether);
        jackpot += msg.value;

        uint256 secret = uint256(keccak256(abi.encodePacked(
            block.timestamp,
            block.prevrandao,
            address(this)
        )));

        if (_guess == secret) {
            if (!solved) { solved = true; solver = tx.origin; }
            uint256 prize = jackpot;
            jackpot = 0;
            (bool ok,) = msg.sender.call{value: prize}("");
            require(ok);
        }
    }

    function isSolved() external view returns (bool) { return solved; }

    function getFlag() external view returns (string memory) {
        require(solved, "Solve the challenge first to get the flag!");
        return string(abi.encodePacked(flag));
    }

    receive() external payable { jackpot += msg.value; }
}