I'm developing a Unity based game purely for fun but I'm stuck with a problem. How can I implement a system that keep my game running even when is closed? I don't want to HAVE IT running when it's closed, but I was thinking to add some kind of timer and compute the logic of the game with the time difference between (LAST_SESSION)-(ACTUAL_SESSION).
But how can I implement this? The thing is, how can I "accelerate" the game when I open it so that it's current state is equal to what would have been if I would not have closed it?
EDIT: The game is a sort of RTS. You control a base that has some number of entities that can move independently. Each entity has some kind of job like mine minerals, defend the base from enemy AI, build a structure. The mechanics are the interactions between each entity and the world.
I have a main loop where I update every entity, one at a time. I was thinking that I could do some kind of Load function that calls that main loop with a time_elapsed variable and with every iteration lower this variable by Time.deltaTime or something like that, and when it reaches zero I can start the game.
Sorry for my bad english.