    function createVault(
        uint256 tokenIdOrAmount,
        address token,
        uint8 premiumIndex,
        uint8 durationDays,
        uint8 dutchAuctionStartingStrikeIndex,
        uint256 dutchAuctionReserveStrike,
        TokenType tokenType
    ) external returns (uint256 vaultId) {
        require(premiumIndex < premiumOptions.length, "Invalid premium index");
        require(dutchAuctionStartingStrikeIndex < strikeOptions.length, "Invalid strike index");
        require(dutchAuctionReserveStrike < strikeOptions[dutchAuctionStartingStrikeIndex], "Reserve strike too small");
        require(durationDays > 0, "durationDays too small");
        require(tokenType == TokenType.ERC721 || tokenType == TokenType.ERC20, "Invalid token type");

        Vault memory vault = Vault({
            tokenIdOrAmount: tokenIdOrAmount,
            token: token,
            premiumIndex: premiumIndex,
            durationDays: durationDays,
            dutchAuctionStartingStrikeIndex: dutchAuctionStartingStrikeIndex,
            currentExpiration: uint32(block.timestamp),
            isExercised: false,
            isWithdrawing: false,
            tokenType: tokenType,
            currentStrike: 0,
            dutchAuctionReserveStrike: dutchAuctionReserveStrike
        });

        // vault index should always be odd
        vaultIndex += 2;
        vaultId = vaultIndex;
        _vaults[vaultId] = vault;

        // give msg.sender vault token
        _mint(msg.sender, vaultId);

        emit NewVault(vaultId, msg.sender, token);

        // transfer the NFTs or ERC20s to the contract
        vault.tokenType == TokenType.ERC721
            ? ERC721(vault.token).transferFrom(msg.sender, address(this), vault.tokenIdOrAmount)
            : ERC20(vault.token).safeTransferFrom(msg.sender, address(this), vault.tokenIdOrAmount);
    }
    function exercise(uint256 optionId) external payable {
        
        // transfer the NFTs or ERC20s to the exerciser
        vault.tokenType == TokenType.ERC721
            ? ERC721(vault.token).transferFrom(address(this), msg.sender, vault.tokenIdOrAmount)
            : ERC20(vault.token).safeTransfer(msg.sender, vault.tokenIdOrAmount);
    }
    function withdraw(uint256 vaultId) external nonReentrant {
        
        // transfer the NFTs or ERC20s back to the owner
        vault.tokenType == TokenType.ERC721
            ? ERC721(vault.token).transferFrom(address(this), msg.sender, vault.tokenIdOrAmount)
            : ERC20(vault.token).safeTransfer(msg.sender, vault.tokenIdOrAmount);
    }
