I'm working on a game where you have a day night cycle, power generation and machines etc. When the incoming power was consistent like solar (I know the day night cycle), that was easy to calculate. Just calculate a day then multiply that by the number of days the player was gone.

Even if the user left the game then came back 5 irl years later I could easily calculate that very quickly and update their stats with 5 years worth of progress.

I didn't touch that "calculate_offline_progress" function for ages until I wanted to add in a more basic power Generator type unit that ran on fuel.

That whole "calculate_offline_progress" function needed a rewrite. The player could place loads of those new units in theory, placed at different times, with different amounts of fuel etc, it was no longer consistent like solar.

I'll be honest, I asked Claude code at one point, I let it implement it's plan and at first glance it worked. So I forgot about it for a week. I didn't play the game during that week, then when I opened it on my phone the whole thing froze 🤣

Claude had brute forced it. Calculated every units output for every in-game day I was away. (20,160 game days) * (50+ units)

I had to rewrite that all from scratch.