I have never tried to code a swerve drive as it makes my brain hurt, but one way you could do it with all four wheels ganged would be to make one stick drive the robot in a traditional "arcade" style" and then use a pot / z-axis to control module rotation, making the extremes of motion completely sideways to the left or right. This passes on a lot of the tricky controls issues to the driver, who'd better be smart
This is what I did with Vex a few years back.