Stripe upgrade/downgrade with webhooks script and functions. -- 2

What I want to do is: -Charge a customer the full plan price every time they upgrade, have the billing period start date switch to the day they upgrade -When a user downgrades their plan, allow them to do so without having them pay. No account_balance should get added from this. -I have webhooks on my website so I'd like to know under which webhook action the parts of the code go under. -I want an upgrade/downgrade function which does all of this and a webhook class which handles the other workings. What I don't want in the solution: -Having to create a new subscription -Having to create a new customer -Anything that would screw up my metrics, I want this done as efficiently as possible. -Setting the account_balance = 0 as I may sometimes give users credit to use. I want this SDK to be used in the code you are giving me: [login to view URL]