Advanced railway logic

[Optymistyk]

I have a design in mind consisting of three kinds of stations:
Train depot, where trains are stationed when not currently needed.
Loading station, where trains are loaded with items.
Unloading station, where trains are unloaded.

The idea is as follows:
Loading stations will only be enabled if they contain a certain ammount of resources.
Unloading stations will only be enabled if their inventory drops below a certain threshold(if they lack a certain ammount of resources)

A train loads up at one loading station but may unload at multiple unloading stations. For example there's a train that delivers iron plates. It loads up at the iron plate loading station and then delivers to circuit and iron gear unloading stations, where those items are then manufactured.

The issue is that if an unloading station is enabled but the loading station is disabled then the train will still go to the unloading station and unload nothing. On the other hand if the unloading stations are disabled but the loading station is enabled it will keep going to the loading station even though there's nowhere to unload the resources. Instead it should wait at the train depot until loading station is enabled and at least one unloading station is enabled.

I don't know how to do that without some excessive ammounts of circuitry, especially considering that there's gonna be a lot of trains and stations in the network, an iron plate delivery train, a copper plate train, a circuit train, a gear train, plastic train, coal train etc etc. and all the necessary loading/unloading/depot stations

[Serenity]

There are mods for that sort of stuff. Train Supply Manager or Logistics Train Network