    function fillOrder(
        Order memory order,
        bytes calldata signature,
        uint256[] memory floorAssetTokenIds
    ) public payable returns (uint256 positionId) {
        /* ~~~ CHECKS ~~~ */

        bytes32 orderHash = hashOrder(order);

        // check signature is valid using EIP-712
        require(SignatureChecker.isValidSignatureNow(order.maker, orderHash, signature), "Invalid signature");

        // check order is not cancelled
        require(!cancelledOrders[orderHash], "Order has been cancelled");

        // check msg.sender is allowed to fill the order
        require(order.whitelist.length == 0 || isWhitelisted(order.whitelist, msg.sender), "Not whitelisted");

        // check duration is valid
        require(order.duration < 10_000 days, "Duration too long");

        // check order has not expired
        require(block.timestamp < order.expiration, "Order has expired");

        // check base asset exists
        require(order.baseAsset.code.length > 0, "baseAsset is not contract");
require(msg.sender != order.maker, "Invalid order taker");
