AIsOfCatan.GameController.BuildCity C# (CSharp) Method

        public GameState BuildCity(Player player, Intersection intersection)
        {
            var r = player.Resources;
            if (!(r.Count(c => c == Resource.Ore) >= 3 && r.Count(c => c == Resource.Grain) >= 2))
                throw new InsufficientResourcesException("Not enough resources to buy a city");
            if (player.CitiesLeft == 0)
                throw new IllegalActionException("No more city pieces left of your color");

            Piece piece = board.GetPiece(intersection);
            if (piece == null || piece.Player != player.Id || piece.Token != Token.Settlement)
                throw new IllegalBuildPositionException("The chosen position does not contain one of your settlements");

            PayResource(player, Resource.Ore, 3);
            PayResource(player, Resource.Grain, 2);

            Log(new BuildPieceLogEvent(player.Id, Token.City, intersection));

            player.CitiesLeft--;
            player.SettlementsLeft++;

            board = board.PlacePiece(intersection, new Piece(Token.City, player.Id));
            return CurrentGamestate();
        }

 public GameState BuildCity(Intersection intersection)
 {
     if (!valid)
     {
         throw new IllegalActionException("Tried to perform an action on an invalid GameAction");
     }
     if (!isAfterDieRoll)
     {
         throw new IllegalActionException("Tried to build before the die roll");
     }
     return(controller.BuildCity(player, intersection));
 }