public int searchTree(final int levelsToTop, int alpha, final int beta) {
if (board.isDraw()) {
return scorer.drawValue();
}
if (levelsToTop == iterativeDepth) {
return scorer.staticScore(board);
}
final MoveContainer moves = moveContainers[levelsToTop];
final BoardHashEntry hashEntry = hashTable.get(board.getHashCode());
prioritizeHashEntry(hashEntry, moves);
board.makeNullMove();
board.generateValidMoves(moves);
if (moves.isEmpty()) {
return scorer.endOfGameValue(board.isInCheck(), levelsToTop);
}
for (int m = 0; m < moves.size(); m++) {
final Move move = moves.get(m);
board.makeMove(move);
final int childScore = -searchTree(levelsToTop + 1, -beta, -alpha);
board.undoMove();
if (childScore > alpha) {
// narrowing alpha beta window
alpha = childScore;
movePath.markMove(levelsToTop, iterativeDepth, m);
if (alpha >= beta) {
// pruned!
break;
}
}
}
unprioritizeHashEntry(hashEntry, moves);
hashTable.set(
board.getHashCode(),
alpha,
0,
movePath.getRaw(levelsToTop),
board.getMoveNumber(),
BoardHashEntry.ValueBounds.PV);
return alpha;
}
@Override
public MovePath search(
final Board board, final int depth, final int startAlpha, final int startBeta) {
this.iterativeDepth = depth;
this.board = board;
final int score = searchTree(0, startAlpha, startBeta);
movePath.setScore(score);
movePath.setDepth(iterativeDepth);
EngineUtil.verifyPV(movePath, board, hashTable);
return movePath;
}
@Override
public Field move(
Moveable moveable,
SetterOfPosition setterOfPosition,
MovePath movePath,
ResourceHolder resourceHolder)
throws FieldsNotConnectedException, MoveNotPossibleException, NotEnoughResourceException {
if (canMove(moveable, movePath, resourceHolder)) {
resourceHolder.pay(movePath.cost().asPayment());
setterOfPosition.setPosition(movePath.getTarget());
return movePath.getTarget();
} else if (!resourceHolder.canPay(movePath.cost().asPayment())) {
throw new NotEnoughResourceException(
resourceHolder.get(MovePoint.class), movePath.cost().getAmount());
} else {
throw new MoveNotPossibleException();
}
}
@Override
public MovePath iterativeSearch(
final Board board, final int maxLevel, final int startAlpha, final int startBeta) {
this.board = board;
for (int i = 1; i <= maxLevel; i++) {
search(board, i);
if (movePath.getEndBoardCondition() == BoardCondition.CHECKMATE) {
break;
}
}
return movePath;
}
@Override
public boolean canMove(Moveable moveable, MovePath movePath, ResourceHolder resourceHolder) {
if (moveable == null || movePath == null || resourceHolder == null) {
return false;
}
Moveable testMoveable = moveable.cloneMoveable();
ResourceHolder testResourceHolder = resourceHolder.cloneResourceHolder();
boolean canMove = true;
for (Field field : movePath.getPathFields()) {
try {
testMoveable.move(field, testResourceHolder);
} catch (Exception e) {
canMove = false;
break;
}
}
return canMove;
}