Appendix D · Contracts and on-chain calls

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

interface IBuybackBurner {
    enum Route { Curve, V4Pool }

    event BuybackBurn(address indexed token, uint256 amountIn, uint256 amountBurned, uint256 indexed slice);
    event OperatorChanged(address indexed previous, address indexed next);
    event Paused(bool paused);

    error NotOperator();
    error IsPaused();
    error OverCallCap();
    error OverDayCap();
    error SlippageTooHigh(uint256 received, uint256 minOut);

    /// @notice Buys `token` with `amountIn` wei of ETH through the specified route, then burns everything received.
    /// @param slice Slice number, included in the event for the ledger.
    function buyAndBurn(address token, Route route, uint256 amountIn, uint256 minOut, uint256 slice)
        external payable returns (uint256 amountBurned);

    function operator() external view returns (address);
    function maxPerCall() external view returns (uint256);
    function maxPerDay() external view returns (uint256);
    function spentToday() external view returns (uint256);
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import {IERC20} from "openzeppelin/token/ERC20/IERC20.sol";
import {SafeERC20} from "openzeppelin/token/ERC20/utils/SafeERC20.sol";
import {ReentrancyGuard} from "openzeppelin/utils/ReentrancyGuard.sol";
import {IBuybackBurner} from "./IBuybackBurner.sol";

contract BuybackBurner is IBuybackBurner, ReentrancyGuard {
    using SafeERC20 for IERC20;

    address public constant DEAD = 0x000000000000000000000000000000000000dEaD;

    address public immutable owner;
    uint256 public immutable maxPerCall;
    uint256 public immutable maxPerDay;
    address public operator;
    bool public paused;

    uint256 public currentDay;
    uint256 public spentToday;

    constructor(address _owner, address _operator, uint256 _maxPerCall, uint256 _maxPerDay) {
        owner = _owner;
        operator = _operator;
        maxPerCall = _maxPerCall;
        maxPerDay = _maxPerDay;
    }

    function buyAndBurn(address token, Route route, uint256 amountIn, uint256 minOut, uint256 slice)
        external payable nonReentrant returns (uint256 amountBurned)
    {
        if (msg.sender != operator) revert NotOperator();
        if (paused) revert IsPaused();
        if (msg.value != amountIn || amountIn > maxPerCall) revert OverCallCap();

        uint256 day = block.timestamp / 1 days;
        if (day != currentDay) { currentDay = day; spentToday = 0; }
        if (spentToday + amountIn > maxPerDay) revert OverDayCap();
        spentToday += amountIn;

        uint256 before = IERC20(token).balanceOf(address(this));
        if (route == Route.Curve) {
            _buyOnCurve(token, amountIn, minOut);
        } else {
            _buyOnV4Pool(token, amountIn, minOut);
        }
        amountBurned = IERC20(token).balanceOf(address(this)) - before;
        if (amountBurned < minOut) revert SlippageTooHigh(amountBurned, minOut);

        IERC20(token).safeTransfer(DEAD, amountBurned);
        emit BuybackBurn(token, amountIn, amountBurned, slice);
    }

    function setOperator(address next) external {
        require(msg.sender == owner, "owner");
        emit OperatorChanged(operator, next);
        operator = next;
    }

    function setPaused(bool p) external {
        require(msg.sender == owner, "owner");
        paused = p;
        emit Paused(p);
    }

    // Complete using the Pons ABI verified on testnet:
    // purchase on the token launch curve (before graduation).
    function _buyOnCurve(address token, uint256 amountIn, uint256 minOut) internal { /* TODO */ }

    // Complete: swap ETH -> token through the Meme hook Uniswap v4 pool (after graduation),
    // via Universal Router or PoolManager, including the hook tax in minOut.
    function _buyOnV4Pool(address token, uint256 amountIn, uint256 minOut) internal { /* TODO */ }

    receive() external payable {}
}