/// <summary>
/// Limitation: castling moves decoded from a string can't be undone
/// </summary>
public void UndoMove(Move move)
{
#if DEBUG
_moveHistory.Pop();
#endif
_colorToMove = 1 - _colorToMove;
var state = _gameStateHistory.Pop();
if (state.CapturedPiece != Piece.None)
{
if (move.IsEnPassant)
{
var enPassantOffset = WhiteToMove ? 8 : -8;
EnemyPieces.Add(state.CapturedPiece, move.EndSquare + enPassantOffset);
}
else
{
EnemyPieces.Add(state.CapturedPiece, move.EndSquare);
}
// Restore original piece position, replacing with pawn in case of promotion move
PiecesToMove.Move(move.EndSquare, move.StartSquare, move.PromotionPiece != Piece.None ? Piece.Pawn : Piece.None);
}
else if (move.IsCastling)
{
// Return rook and King to it's original square
(int rookOriginalSquare, int rookEndSquare) = GetCastlingRookMove(move);
PiecesToMove.RemoveAt(rookEndSquare);
PiecesToMove.RemoveAt(GetCastlingKingSqare(move));
PiecesToMove.Add(Piece.King, move.StartSquare);
PiecesToMove.Add(Piece.Rook, rookOriginalSquare);
}
else
{
// Restore original piece position, replacing with pawn in case of promotion move
PiecesToMove.Move(move.EndSquare, move.StartSquare, move.PromotionPiece != Piece.None ? Piece.Pawn : Piece.None);
}
TotalMoves -= _colorToMove;
#if MOVE_CONSISTENCY_CHECK
var previousPosition = _fenHistory.Pop();
var restoredPosition = _fenWriter.Write(this, true);
if (previousPosition != restoredPosition)
{
System.Diagnostics.Debugger.Break();
}
#endif
}
public Position MakeMove(Move move)
{
#if DEBUG
_moveHistory.Push(move);
#endif
#if MOVE_CONSISTENCY_CHECK
_fenHistory.Push(_fenWriter.Write(this, true));
#endif
// Get the curent state to apply changes on top of it
var state = CurrentState;
state.HalfMoveClock++;
state.CapturedPiece = Piece.None;
int newEnPassantSquare = -1;
// Adjust castling flags before actually moving pieces
Castling enemyCastlingOptions = state[1 - _colorToMove];
Castling castlingOptions = state[_colorToMove];
if (enemyCastlingOptions != 0 && EnemyPieces[move.EndSquare] == Piece.Rook)
{
// One of the rooks was captured
enemyCastlingOptions &= move.EndSquare % Constants.BoardFiles == QueenSideRookFile ? ~Castling.QueenSide : ~Castling.KingSide;
}
if (castlingOptions != 0)
{
if (PiecesToMove[move.StartSquare] == Piece.Rook)
{
// One of the rooks was moved
castlingOptions &= move.StartSquare % Constants.BoardFiles == QueenSideRookFile ? ~Castling.QueenSide : ~Castling.KingSide;
}
else if (PiecesToMove[move.StartSquare] == Piece.King)
{
// King was moved
castlingOptions = 0;
}
}
if (EnemyPieces[move.EndSquare] != Piece.None)
{
// Capture, remove enemy piece from the board and reset the clock
state.CapturedPiece = EnemyPieces[move.EndSquare];
state.HalfMoveClock = 0;
EnemyPieces.RemoveAt(move.EndSquare);
PiecesToMove.Move(move.StartSquare, move.EndSquare, move.PromotionPiece);
}
else if (PiecesToMove[move.StartSquare] == Piece.Pawn)
{
// Reset the clock on pawn moves
state.HalfMoveClock = 0;
var enPassantOffset = WhiteToMove ? 8 : -8;
if (move.EndSquare == state.EnPassantSquare)
{
// EnPassant, remove enemy pawn from the board
state.CapturedPiece = Piece.Pawn;
EnemyPieces.RemoveAt(move.EndSquare + enPassantOffset);
}
else if (move.StartSquare - move.EndSquare == enPassantOffset * 2)
{
// EnPassant is possible next move
newEnPassantSquare = move.EndSquare + enPassantOffset;
}
PiecesToMove.Move(move.StartSquare, move.EndSquare, move.PromotionPiece);
}
else if (PiecesToMove[move.StartSquare] == Piece.King &&
(Math.Abs(move.StartSquare - move.EndSquare) == 2 || PiecesToMove[move.EndSquare] == Piece.Rook))
{
// Castling
// To support general chess 960 case remove king and rook from the board and put them to the final sqares
(int rookStartSquare, int rookEndSquare) = GetCastlingRookMove(move);
PiecesToMove.RemoveAt(rookStartSquare);
PiecesToMove.RemoveAt(move.StartSquare);
PiecesToMove.Add(Piece.King, GetCastlingKingSqare(move));
PiecesToMove.Add(Piece.Rook, rookEndSquare);
}
else
{
// General piece move
PiecesToMove.Move(move.StartSquare, move.EndSquare, move.PromotionPiece);
}
state[1 - _colorToMove] = enemyCastlingOptions;
state[_colorToMove] = castlingOptions;
state.EnPassantSquare = newEnPassantSquare;
_gameStateHistory.Push(state);
// Increment total moves after the black's move only
TotalMoves += _colorToMove;
_colorToMove = 1 - _colorToMove;
return(this);
}