As someone who wrote more variants of button handling code than I have fingers (mostly for physical buttons): Buttons can be way more complex than people usually would suspect:

- Buttons need to be debounced so you don't trigger 10 presses because the contacts bounce 10 times up and down before they settle to the on state

- maybe you want different states and callbacks for single press, while pressed, double press, long press, very long press, release — all of which require to measure time and some thinking (e.g. how can you reach a long press when there is a short press before ?)

- how to properly implement key combinations? Does order matter? How would you handle a "both keys at the same time"-scenario if in reality they are many milliseconds apart?

And there are always tradeoffs, which is why I had to write more than once variant of the thing (that, and I got better at writing it).

how to reach "idle, down" ?