If the requirements are complex, then you list the requirements, what you're doing with each one, how they connect, and the code reflects that. Breaking it into

If the requirements are complex, then you list the requirements, what you're doing with each one, how they connect, and the code reflects that. Breaking it into functions and modules for that often does enough. At the least, the design documentation will facilitate understanding even if the code itself is harder to understand. Spaghetti code is almost always just bad design and coding.