A game (and my feeling is a TCG in special) has a lot to do with communication. Usually a game has more or less strict rules, where the player (and if a programm is involved the program) can cling to and there is no need to put questions like "can I do this", "can I do that", "but now I would like to...".
With a trading card game you have to be more "open". Anything can happen when a new card enters the scene. So - all the game is about communication. Following communication partners can be found in the game JPortal
Match (the referee, the table, the rule "giver"...)
Card (any card)
Player (both players, internally allways called player/opponent, which changes continuously depending on the point of view)
In order to realize such communication, classically an event driven mechanism is envolved and ideally stateless instances of all partners, which can answer the communication, and all context of that communication is inclosed within that communication instance.
I failed!
Right now the communication in JPortal is not really stateless. I tried some time, but sooner or later some state illness came back. Actually another overhaul would be needed to get that out of the system, but I probably won't do it (unless really really REALLY R E A L L Y ! (and I mean it) needed).
I will try to exlpain now what I did.