如何编写一个拍卖的智能合约

contract SimpleAuction {

    //拍卖的受益人
    address payable public beneficiary;
    //拍卖的结束时间
    uint public auctionEndTime;

    // 最高出价的人
    address public highestBidder;
    // 最高出价的价格
    uint public highestBid;

    // 这个map用来存放出价的人以及对应的出价，便于拍卖结束后退还
    mapping(address => uint) pendingReturns;

    //标识拍卖结束了，一旦结束就不能改了
    bool ended;

// 用来记录当前出价最高的事件
event HighestBidIncreased(address bidder, uint amount);
// 用来记录拍卖结束后
event AuctionEnded(address winner, uint amount);

/// 拍卖已经结束
error AuctionAlreadyEnded();

/// 已经有更高的出价者了
error BidNotHighEnough(uint highestBid);

/// 拍卖还未结束
error AuctionNotYetEnded();

/// auctionEnd 方法已经被调用了
error AuctionEndAlreadyCalled();

/// @title A simulator for trees
/// @author Larry A. Gardner
/// @notice You can use this contract for only the most basic simulation
/// @dev All function calls are currently implemented without side effects
/// @custom:experimental This is an experimental contract.
contract Tree {
    /// @notice Calculate tree age in years, rounded up, for live trees
    /// @dev The Alexandr N. Tetearing algorithm could increase precision
    /// @param rings The number of rings from dendrochronological sample
    /// @return Age in years, rounded up for partial years
    function age(uint256 rings) external virtual pure returns (uint256) {
        return rings + ;
    }

    /// @notice Returns the amount of leaves the tree has.
    /// @dev Returns only a fixed number.
    function leaves() external virtual pure returns(uint256) {
        return ;
    }
}

// 通过构造函数初始化受益人和拍卖的结束时间
constructor(
        uint biddingTime,
        address payable beneficiaryAddress
) {
    beneficiary = beneficiaryAddress;
    auctionEndTime = block.timestamp + biddingTime;
}

function bid() external payable {

        if (block.timestamp > auctionEndTime)
            revert AuctionAlreadyEnded();

        if (msg.value <= highestBid)
            revert BidNotHighEnough(highestBid);

        if (highestBid != ) {

            pendingReturns[highestBidder] += highestBid;
        }
        highestBidder = msg.sender;
        highestBid = msg.value;
        emit HighestBidIncreased(msg.sender, msg.value);
    }

  function withdraw() external returns (bool) {
        uint amount = pendingReturns[msg.sender];
        if (amount > ) {
            pendingReturns[msg.sender] = ;

            if (!payable(msg.sender).send(amount)) {
                // No need to call throw here, just reset the amount owing
                pendingReturns[msg.sender] = amount;
                return false;
            }
        }
        return true;
    }

    function auctionEnd() external {

        if (block.timestamp < auctionEndTime)
            revert AuctionNotYetEnded();
        if (ended)
            revert AuctionEndAlreadyCalled();

        ended = true;
        emit AuctionEnded(highestBidder, highestBid);
        beneficiary.transfer(highestBid);
    }

[vm]from: 0x5B3...eddC4to: SimpleAuction.bid() 0xD7A...F771Bvalue:  weidata: 0x199...8aeeflogs: hash: 0x9b7...a19d1
transact to SimpleAuction.bid errored: VM error: revert.

revert
    The transaction has been reverted to the initial state.
Error provided by the contract:
BidNotHighEnough : 已经有更高的出价者了
Parameters:
{
 "highestBid": {
  "value": "0"
 }
}