/// <summary>
/// Determines if the neighboring square is empty.
/// Returns true if the neighboring square exists and is empty. Otherwise returns false.
/// </summary>
/// <param name="boardLocation"></param>
/// <param name="direction"></param>
/// <returns></returns>
public bool NeighboringLocationIsEmpty(BoardLocation boardLocation, Direction direction)
{
var neighbor = boardLocation.Neighbor(direction);
if (neighbor.HasValue && this[neighbor.Value] == ChessPiece.None)
{
return(true);
}
return(false);
}
/// <summary>
/// Determines if the neighboring square is occupied by the given player.
/// Returns true if the neighboring square exists and is occupied by the given player. Otherwise returns false.
/// </summary>
/// <param name="boardLocation"></param>
/// <param name="direction"></param>
/// <returns></returns>
public bool NeighboringLocationIsOccupiedBy(BoardLocation boardLocation, Direction direction, Player player)
{
var neighbor = boardLocation.Neighbor(direction);
if ((neighbor.HasValue) &&
(this[neighbor.Value].BelongsTo(player)))
{
return(true);
}
return(false);
}
/// <summary>
/// Determines if the neighboring square is empty or occupied by the supplied player.
/// Returns true if the neighboring square exists and is either empty or has a piece belonging to the given player. Otherwise returns false.
/// </summary>
/// <param name="boardLocation"></param>
/// <param name="direction"></param>
/// <returns></returns>
public bool NeighboringLocationIsEmptyOrOccupiedBy(BoardLocation boardLocation, Direction direction, Player player)
{
var neighbor = boardLocation.Neighbor(direction);
var piece = this[neighbor.Value];
if ((neighbor.HasValue) &&
(piece.BelongsTo(player) || piece == ChessPiece.None))
{
return(true);
}
return(false);
}
public static List <BoardLocation> Neighbors(this BoardLocation currentLocation)
{
List <BoardLocation> boardLocations = new List <BoardLocation>();
foreach (Direction dir in Enum.GetValues(typeof(Direction)))
{
var result = currentLocation.Neighbor(dir);
if (result.HasValue)
{
boardLocations.Add(result.Value);
}
}
return(boardLocations);
}
private bool PieceIsPinned(Board board, BoardLocation piecesLocation, BoardLocation kingsLocation, Direction direction)
{
BoardLocation?currentLocation = piecesLocation.Neighbor(direction);
while (currentLocation != null)
{
//get the piece
var piece = board[currentLocation.Value];
if (currentLocation == kingsLocation)
{
return(true);
}
else if (board[currentLocation.Value] != ChessPiece.None)
{
break;
}
currentLocation = currentLocation.Neighbor(direction);
}
return(false);
}
public static BoardLocation?Neighbor(this BoardLocation?currentLocation, Direction direction) => currentLocation?.Neighbor(direction);
private void AddDirectionalThreats(
Board board,
Player player,
BoardLocation playerKingLocation,
BoardLocation opposingPieceBoardLocation,
Direction direction,
ThreatMatrix threatMatrix)
{
//get the next square in the given direction
BoardLocation?currentLocation = opposingPieceBoardLocation.Neighbor(direction);
//for directional threats the king might be pinned...
var kingCouldBePinned = playerKingLocation.IsInGivenDirectionFrom(opposingPieceBoardLocation, direction);
var threatDirection = direction.ToThreatDirection();
while (currentLocation != null)
{
//get the piece
var piece = board[currentLocation.Value];
//as long as we are empty we can keep moving!
if (piece == ChessPiece.None)
{
//empty square, no pin possible
AddThreat(threatMatrix, playerKingLocation, opposingPieceBoardLocation, currentLocation.Value, threatDirection);
}
else
{
ThreatDirection?pinDirection = null;
//our piece which MIGHT have a pin if our king is on the same directional vector..check for it
if ((piece.BelongsTo(player)) &&
(kingCouldBePinned) &&
PieceIsPinned(board, currentLocation.Value, playerKingLocation, direction))
{
pinDirection = direction.ToThreatDirection();
}
AddThreat(
threatMatrix,
playerKingLocation,
opposingPieceBoardLocation,
currentLocation.Value,
threatDirection,
pinDirection);
//NOTE: This is a hack, but its a domain hack. From a threat perspective, we can pretend
//that the enemy king is 'invisible'. This will allow long range threats to penetrate the king
//and proceed to any columns, rows, or diagonals he is on. This in turn will help us
//when determining the kings moves by making 'backing up' an invalid strategy for him.
//without this check, a king himself would demarcate the end of a long range threat (since a piece is like a stop)
//but THAT would create the problem of making it seem like the square behind him was 'safe'. For Example:
// | | | | | | | | | |
// | |WR|BK| | To=> | |WR| |BK| would be allowed
// | | | | | | | | | |
//Where it is kind of a hack is by treating the king as invisible it means the white rook is threatening
//'beyond' a piece. Theoretically, this would then also allow it to move into those spaces, in essence just
//'hoping over' the king. This would be a HUGE problem if not for the golden rule of chess that it is impossible
//to make a move that actually captures a king. The game literally ends as soon as a board state emerges where
//a king is able to captured on the next turn. Not sure why this is, I am sure it harkens back to some
//haughty rule about how 'ignoble' it would be to ever allow the capture of a royal.
if (piece.IsKing(player) == false)
{
//short circuit search since we are done
break;
}
}
currentLocation = currentLocation.Neighbor(direction);
}
}
private void FindPawnMoves(
List <Move> moves,
ThreatMatrix threats,
Player player,
BoardLocation playerPieceLocation,
ThreatDirection?playerPieceThreatDirection)
{
var opposingPlayer = player.OpposingPlayer();
var marchDirection = player == Player.White ? Direction.North : Direction.South;
var gradeAttackDirection = player == Player.White ? Direction.NorthEast : Direction.SouthWest;
var slopeAttackDirection = player == Player.White ? Direction.NorthWest : Direction.SouthEast;
//check to see if we can move up/down
//note that any diagonal or horizontal threats will block these moves
if ((playerPieceThreatDirection.HasThreats(ThreatDirection.Horizontal | ThreatDirection.Diagonal) == false) &&
(_board.NeighboringLocationIsEmpty(playerPieceLocation, marchDirection)))
{
var firstMarchLocation = playerPieceLocation.Neighbor(marchDirection).Value;
var row = firstMarchLocation.Row();
if (row == 0 || row == 7)//we can assume this is a pawn promotion
{
moves.Add(new Move(playerPieceLocation, firstMarchLocation, SpecialMoveType.PawnPromotionKnight));
moves.Add(new Move(playerPieceLocation, firstMarchLocation, SpecialMoveType.PawnPromotionBishop));
moves.Add(new Move(playerPieceLocation, firstMarchLocation, SpecialMoveType.PawnPromotionRook));
moves.Add(new Move(playerPieceLocation, firstMarchLocation, SpecialMoveType.PawnPromotionQueen));
}
else
{
moves.Add(new Move(playerPieceLocation, firstMarchLocation));
}
//we can also move up two spaces if the next northern square is empty
if ((playerPieceLocation.IsPawnStartingLocation(player)) &&
(_board.NeighboringLocationIsEmpty(firstMarchLocation, marchDirection)))
{
moves.Add(new Move(playerPieceLocation, firstMarchLocation.Neighbor(marchDirection).Value));
}
}
//check to see if we can move along the grade
//note that any line or slope threats will block this move
if (playerPieceThreatDirection.HasThreats(ThreatDirection.Line | ThreatDirection.Slope) == false)
{
//if we have an opposing piece in the next square, make hte move
if (_board.NeighboringLocationIsOccupiedBy(playerPieceLocation, gradeAttackDirection, opposingPlayer))
{
var neighbor = playerPieceLocation.Neighbor(gradeAttackDirection).Value;
var row = neighbor.Row();
//capture pawn promotion
if (row == 0 || row == 7)
{
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor], SpecialMoveType.PawnPromotionKnight));
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor], SpecialMoveType.PawnPromotionBishop));
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor], SpecialMoveType.PawnPromotionRook));
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor], SpecialMoveType.PawnPromotionQueen));
}
else//normal capture
{
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor]));
}
}
else if (LastMoveAllowsEnPassantFor(playerPieceLocation, gradeAttackDirection))
{//we can do an en passant.
var neighbor = playerPieceLocation.Neighbor(gradeAttackDirection).Value;
moves.Add(new Move(playerPieceLocation, neighbor, CurrentPlayer == Player.White ? ChessPiece.BlackPawn : ChessPiece.WhitePawn, SpecialMoveType.AuPassant));
}
}
//check to see if we can move along the slope
//note that any line or grade threats will block this move
if (playerPieceThreatDirection.HasThreats(ThreatDirection.Line | ThreatDirection.Grade) == false)
{
//if we have an opposing piece in the next square, make hte move
if (_board.NeighboringLocationIsOccupiedBy(playerPieceLocation, slopeAttackDirection, opposingPlayer))
{
var neighbor = playerPieceLocation.Neighbor(slopeAttackDirection).Value;
var row = neighbor.Row();
//capture pawn promotion
if (row == 0 || row == 7)
{
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor], SpecialMoveType.PawnPromotionKnight));
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor], SpecialMoveType.PawnPromotionBishop));
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor], SpecialMoveType.PawnPromotionRook));
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor], SpecialMoveType.PawnPromotionQueen));
}
else//normal capture
{
moves.Add(new Move(playerPieceLocation, neighbor, _board[neighbor]));
}
}
else if (LastMoveAllowsEnPassantFor(playerPieceLocation, slopeAttackDirection))
{//we can do an en passant.
var neighbor = playerPieceLocation.Neighbor(slopeAttackDirection).Value;
moves.Add(new Move(playerPieceLocation, neighbor, CurrentPlayer == Player.White ? ChessPiece.BlackPawn : ChessPiece.WhitePawn, SpecialMoveType.AuPassant));
}
}
}
