The forwardCallbackResult method is where the main XAYA game logic resides. Its signature is:

public static string forwardCallbackResult(string oldState, 
	string blockData, 
	string undoData, 
	out string newData)

oldState is the current game state. It must be cast as a GameState.

GameState state = JsonConvert.DeserializeObject<GameState>(oldState);

blockData contains all the moves and should be deserialised.

dynamic blockDataS = JsonConvert.DeserializeObject(blockData);

undoData is the undo data for the current game state. It needs to be updated so that the current set of moves can be rewound. For this, we create a new set of undo data for the current set of moves and store that in undoData at the end of the method.

newData is where the new game state is stored at the end of the method.