Finding methods and inserting code programmatically Follow

Forgive me if this has already been answered, I have search the example openapi code, and searched this forum and the web in general and have not found an answer.

I want to loop thru my code, finding method signatures that match a given string and insert code directly after them and directly before the ending brace.

an extension of this is the ability to find arbitrary code and wrap that text with other text.

Any help, example code or pointing into the right direction would be greatly appreciated.