// 链下订单撮合：签名校验 + 版税拆分的数学（纯 TS + BigInt，无外部库）
type Address = string;

interface Listing {
  seller: Address;      // 卖家
  nft: Address;         // NFT 合约地址
  tokenId: bigint;      // 具体 NFT 编号
  price: bigint;        // 成交价（wei）
  royaltyBps: bigint;   // 版税（1/10000）
  deadline: bigint;     // 截止时间戳
  nonce: bigint;        // 防重放序号
}

class Marketplace {
  usedNonces: Set<string>; // 已消费的 (seller:nft:tokenId:nonce)
  creatorRoyalty: Map<string, bigint>; // nft合约 => 版税bps（项目方预设）

  constructor() {
    this.usedNonces = new Set();
    this.creatorRoyalty = new Map();
  }

  // 成交结算：返回 [买方支付, 卖家所得, 创作者版税]
  fillOrder(
    order: Listing,
    fundsDeposited: bigint,
    _signatureValid: boolean
  ): [bigint, bigint, bigint] {
    if (!_signatureValid) throw new Error("签名无效");
    if (fundsDeposited < order.price) throw new Error("支付不足");
    const nonceKey = `${order.seller}:${order.nft}:${order.tokenId}:${order.nonce}`;
    if (this.usedNonces.has(nonceKey)) throw new Error("订单已执行/取消");
    this.usedNonces.add(nonceKey);

    const royalty = (order.price * order.royaltyBps) / 10000n; // 版税
    const sellerNet = order.price - royalty;                    // 卖家净得
    return [order.price, sellerNet, royalty]; // [买方支付, 卖家, 创作者]
  }
}

// 验证：售价 1 ETH，版税 5% => 版税 0.05 ETH，卖家净得 0.95 ETH
const WEI = 10n ** 18n;
const mk = new Marketplace();
const order: Listing = {
  seller: "0xSeller",
  nft: "0xNft",
  tokenId: 1n,
  price: 1n * WEI,
  royaltyBps: 500n, // 5%
  deadline: 2000n,
  nonce: 0n,
};
const [pay, seller, creator] = mk.fillOrder(order, 1n * WEI, true);
console.log(
  "版税 =", Number(creator) / Number(WEI), "ETH,",
  "卖家净得 =", Number(seller) / Number(WEI), "ETH"
);
// 输出：版税 = 0.05 ETH  卖家净得 = 0.95 ETH

interface IERC2981 {
    /// @notice 返回给定 tokenId/售价下的版税接收者与金额
    function royaltyInfo(uint256 tokenId, uint256 salePrice)
        external view returns (address receiver, uint256 royaltyAmount);
}