// read a board state and select a suitable move to return
public string SelectMove(string fen)
{
var Board = new Board(fen); // load the board
// store the enemy's last move
if (LastBoard != null)
{
var LastMove = BoardDiff(LastBoard, Board);
if (LastMove == null)
{
throw new Exception("could not determine last move using a board diff");
}
if (PastMoves.Count == 8)
{
PastMoves.Dequeue();
}
PastMoves.Enqueue(LastMove);
}
// assign engine's past moves to the board and search for the best move
Board.PastMoves = PastMoves;
MoveGen.MoveBoardPair Mbp = Searcher.Search(Board, Depth, QuiescentDepth, Alpha, Beta, MoveTimeLimit);
LastBoard = Mbp.Board;
return(Mbp.Move.ToString());
}
// perform a minimax search from the current board to try and select the best move
public MoveGen.MoveBoardPair Search(Board root, int depth, int qDepth, int alpha, int beta, TimeSpan time)
{
// guards
if (depth < 1 || qDepth < 1)
{
throw new ArgumentException("valid depth limits are greater than zero");
}
if (alpha > beta)
{
throw new ArgumentException("alpha cannot be greater than beta");
}
// start countdown
Countdown.Interval = time.TotalMilliseconds;
Countdown.Start();
Node RootNode = new Node(root);
Node.TopLevelActivePlayerWhite = root.ActiveColorWhite; // store for utility eval
MoveGen.MoveBoardPair Result = null;
int Value = int.MinValue;
int NextDepth;
for (int d = 1; d <= depth; d++) // step through depths
{
NextDepth = d - 1;
foreach (Node child in RootNode.Children) // step through children
{
if (Result == null)
{
Result = new MoveGen.MoveBoardPair(child.Board, child.LastMove); // default to first move
}
if (Timeout)
{
return(Result); // return best move if timed out
}
Value = MinV(child, NextDepth, qDepth, alpha, beta); // get minimized value from new board
if (Value > alpha)
{
alpha = Value; Result = new MoveGen.MoveBoardPair(child.Board, child.LastMove);
} // update alpha and best move if better val found
}
}
return(Result);
}
