If anyone wants to build this by themselves, I recommend using an optimization solver library like OptaPlanner. It basically implements standard optimization algorithms you can read in academic papers (which are interesting to read!) so you don’t have to.

You can probably write a basic planner in under an hour with all the constraints you can think of. You can just continue to fiddle with the constraints and weights until you are happy without having to worry about duplicates or errors.

I’ve used it to solve cost optimization problems for companies I’ve worked with and it works really well.