53-Solidity8.0-荷兰拍卖

NFT 荷兰式拍卖。

拍卖

1. NFT 卖方部署此合约，为 NFT 设定起始价格。
2. 拍卖持续7天。
3. NFT 的价格会随着时间的推移而下降。
4. 参与者可以通过存入高于智能合约计算的当前价格的 ETH 来购买。
5. 当买家购买 NFT 时拍卖结束。

源码：

pragma solidity ^0.8.10;

interface IERC721 {
    function transferFrom(
        address _from,
        address _to,
        uint _nftId
    ) external;
}

contract DutchAuction {
    uint private constant DURATION = 7 days;

    IERC721 public immutable nft;
    uint public immutable nftId;

    address payable public immutable seller;
    uint public immutable startingPrice;
    uint public immutable startAt;
    uint public immutable expiresAt;
    uint public immutable discountRate;

    constructor(
        uint _startingPrice,
        uint _discountRate,
        address _nft,
        uint _nftId
    ) {
        seller = payable(msg.sender);
        startingPrice = _startingPrice;
        startAt = block.timestamp;
        expiresAt = block.timestamp + DURATION;
        discountRate = _discountRate;

        require(_startingPrice >= _discountRate * DURATION, "starting price < min");

        nft = IERC721(_nft);
        nftId = _nftId;
    }

    function getPrice() public view returns (uint) {
        uint timeElapsed = block.timestamp - startAt;
        uint discount = discountRate * timeElapsed;
        return startingPrice - discount;
    }

    function buy() external payable {
        require(block.timestamp < expiresAt, "auction expired");

        uint price = getPrice();
        require(msg.value >= price, "ETH < price");

        nft.transferFrom(seller, msg.sender, nftId);
        uint refund = msg.value - price;
        if (refund > 0) {
            payable(msg.sender).transfer(refund);
        }
        selfdestruct(seller);
    }
}