I have been tasked with writing a new shipping module for a client.

Functionally, it shouldn't be to difficult. I need to take the shopping cart info (weights), call an existing web service to retrieve the shipping cost, and display it to the user. After the order it accepted I will need to call another service to actually post the shipment information.

It should be know that I come from the Visual Studio/C#/ASP.NET world.
The PHP stuff all looks familiar, not to worried about that. However, I am having a couple problems.
First I cannot find ANY API information on how to write a plugin. The Wiki page stuff is pretty much useless. It also would be nice to get a list of available session variables, particularly the 'cart' object so I know what have to work with. Guessing property names just doesn't work

I have taken a copy of an existing shipping module (zones.php), and have managed to install and run it. However, how would one go about debugging such a creature? I am using Visual Studio Code as an editor. It seems that any code changes that I make are not reflected in the runtime in ZenCart. Currently I am stuck.

Looking for any help or advice on how I can move forward,

Thanks,
Bryan