internal ChessMove[] GetBoardThreats(out bool ownKingUnderThreat, PiecePlayer playerToEvaluate)
{
ChessBoardLocation kingLocation = new ChessBoardLocation(-1, -1);
List <ChessMove> opponentMoves = new List <ChessMove>();
var player = playerToEvaluate == PiecePlayer.White ? PiecePlayer.Black : PiecePlayer.White;
for (int i = 0; i < BOARD_SIZE; i++)
{
for (int j = 0; j < BOARD_SIZE; j++)
{
if (_pieces[i, j].Player == playerToEvaluate)
{
var moves = GetAvailableMoves(playerToEvaluate, i, j, false);
opponentMoves.AddRange(moves);
}
else if (_pieces[i, j].Player == player && _pieces[i, j].Rank == PieceRank.King)
{
kingLocation = new ChessBoardLocation(i, j);
}
}
}
ownKingUnderThreat = opponentMoves.Where(o =>
o.To.HorizontalLocation == kingLocation.HorizontalLocation &&
o.To.VerticalLocation == kingLocation.VerticalLocation).Any();
if (ownKingUnderThreat == true)
{
// Currently board has been verified as "check".
// Now let's verify that is it also "checkmate".
}
return(opponentMoves.ToArray());
}
public ChessMove(PieceRank rank, PiecePlayer player, int horizontalLocationFrom, int verticalLocationFrom, int horizontalLocationTo, int verticalLocationTo, ChessSpecialMove specialMove)
{
Rank = rank;
Player = player;
From = new ChessBoardLocation(horizontalLocationFrom, verticalLocationFrom);
To = new ChessBoardLocation(horizontalLocationTo, verticalLocationTo);
SpecialMove = specialMove;
}
private bool IsOccupiedByOpponent(PiecePlayer player, int column, int row)
{
if (column < 0 || column > BOARD_SIZE - 1 || row < 0 || row > BOARD_SIZE - 1)
{
// Out of bounds
return(false);
}
return(_pieces[column, row].Player != player && _pieces[column, row].Player != PiecePlayer.None);
}
internal void SetBoard(string board)
{
CleanUp();
string[] rows = board.Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
for (int i = 0; i < rows.Length; i++)
{
for (int j = 0; j < rows[i].Length; j++)
{
char piece = rows[i][j];
PiecePlayer pieceColor = char.ToLower(piece) == piece ? PiecePlayer.Black : PiecePlayer.White;
PieceRank pieceRank;
switch (char.ToLower(piece))
{
case '-':
pieceColor = PiecePlayer.None;
pieceRank = PieceRank.None;
break;
case 'k':
pieceRank = PieceRank.King;
break;
case 'q':
pieceRank = PieceRank.Queen;
break;
case 'b':
pieceRank = PieceRank.Bishop;
break;
case 'r':
pieceRank = PieceRank.Rook;
break;
case 'p':
pieceRank = PieceRank.Pawn;
break;
case 'n':
pieceRank = PieceRank.Knight;
break;
default:
throw new ArgumentOutOfRangeException("board");
}
_pieces[j, i] = new ChessBoardPiece(pieceColor, pieceRank);
}
}
}
private void GetKnightMove(PiecePlayer player, List <ChessMove> moves, int column, int row)
{
moves.Add(new ChessMove(PieceRank.Knight, player, column, row, column - 1, row + 2));
moves.Add(new ChessMove(PieceRank.Knight, player, column, row, column - 1, row - 2));
moves.Add(new ChessMove(PieceRank.Knight, player, column, row, column + 1, row + 2));
moves.Add(new ChessMove(PieceRank.Knight, player, column, row, column + 1, row - 2));
moves.Add(new ChessMove(PieceRank.Knight, player, column, row, column - 2, row + 1));
moves.Add(new ChessMove(PieceRank.Knight, player, column, row, column - 2, row - 1));
moves.Add(new ChessMove(PieceRank.Knight, player, column, row, column + 2, row + 1));
moves.Add(new ChessMove(PieceRank.Knight, player, column, row, column + 2, row - 1));
}
private void GetPawnMovesEnPassant(PiecePlayer player, List <ChessMove> moves, int column, int row, int columnDelta, int rowDelta)
{
// En passant move:
if (_previousMove != null && IsOccupiedByOpponent(player, column + columnDelta, row) == true)
{
ChessBoardPiece piece = GetPiece(column + columnDelta, row);
if (piece.Rank == PieceRank.Pawn && piece.Player != player)
{
if (_previousMove.To.HorizontalLocation == column + columnDelta && _previousMove.To.VerticalLocation == row && Math.Abs(_previousMove.To.VerticalLocation - _previousMove.From.VerticalLocation) == 2)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column + columnDelta, row + rowDelta, ChessSpecialMove.EnPassant));
}
}
}
}
private void GetKingMove(PiecePlayer player, List <ChessMove> moves, int column, int row, bool validateCheck)
{
moves.Add(new ChessMove(PieceRank.King, player, column, row, column - 1, row - 1));
moves.Add(new ChessMove(PieceRank.King, player, column, row, column, row - 1));
moves.Add(new ChessMove(PieceRank.King, player, column, row, column - 1, row));
moves.Add(new ChessMove(PieceRank.King, player, column, row, column + 1, row + 1));
moves.Add(new ChessMove(PieceRank.King, player, column, row, column, row + 1));
moves.Add(new ChessMove(PieceRank.King, player, column, row, column + 1, row));
moves.Add(new ChessMove(PieceRank.King, player, column, row, column + 1, row - 1));
moves.Add(new ChessMove(PieceRank.King, player, column, row, column - 1, row + 1));
// Check castling moves (rules from Wikipedia: http://en.wikipedia.org/wiki/Chess)
// - Neither of the pieces involved in castling may have been previously
// moved during the game.
// - There must be no pieces between the king and the rook.
// - The king may not be in check, nor may the king pass through squares
// that are under attack by enemy pieces, nor move to a square where it is in check.
int kingStartColumn = 4;
int kingStartRow = player == PiecePlayer.White ? 7 : 0;
if (column == kingStartColumn && row == kingStartRow)
{
// King is at start location. Has it moved earlier?
var kingsEarlierMove = _moves.Where(
m => m.First().Player == player && m.First().Rank == PieceRank.King).FirstOrDefault();
if (kingsEarlierMove != null)
{
// King has already moved so castling is not anymore available
return;
}
// Left hand side rook
GetKingCastlingMove(player, moves, column, row, 0, validateCheck);
// Right hand side rook
GetKingCastlingMove(player, moves, column, row, 7, validateCheck);
}
}
private void GetHorizontalAndVerticalMoves(PieceRank rank, PiecePlayer player, List <ChessMove> moves, int column, int row)
{
// To left
for (int i = column - 1; i >= 0; i--)
{
if (IsOccupiedByOpponent(player, i, row) == true)
{
moves.Add(new ChessMove(rank, player, column, row, i, row));
}
else if (IsEmpty(i, row) == true)
{
moves.Add(new ChessMove(rank, player, column, row, i, row));
continue;
}
break;
}
// To right
for (int i = column + 1; i < BOARD_SIZE; i++)
{
if (IsOccupiedByOpponent(player, i, row) == true)
{
moves.Add(new ChessMove(rank, player, column, row, i, row));
}
else if (IsEmpty(i, row) == true)
{
moves.Add(new ChessMove(rank, player, column, row, i, row));
continue;
}
break;
}
// To up
for (int i = row - 1; i >= 0; i--)
{
if (IsOccupiedByOpponent(player, column, i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column, i));
}
else if (IsEmpty(column, i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column, i));
continue;
}
break;
}
// To down
for (int i = row + 1; i < BOARD_SIZE; i++)
{
if (IsOccupiedByOpponent(player, column, i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column, i));
}
else if (IsEmpty(column, i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column, i));
continue;
}
break;
}
}
private void GetDiagonalMoves(PieceRank rank, PiecePlayer player, List <ChessMove> moves, int column, int row)
{
// To north-east
for (int i = 1; i <= BOARD_SIZE; i++)
{
if (IsOccupiedByOpponent(player, column + i, row - i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column + i, row - i));
}
else if (IsEmpty(column + i, row - i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column + i, row - i));
continue;
}
break;
}
// To south-east
for (int i = 1; i <= BOARD_SIZE; i++)
{
if (IsOccupiedByOpponent(player, column + i, row + i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column + i, row + i));
}
else if (IsEmpty(column + i, row + i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column + i, row + i));
continue;
}
break;
}
// To north-west
for (int i = 1; i <= BOARD_SIZE; i++)
{
if (IsOccupiedByOpponent(player, column - i, row - i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column - i, row - i));
}
else if (IsEmpty(column - i, row - i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column - i, row - i));
continue;
}
break;
}
// To south-west
for (int i = 1; i <= BOARD_SIZE; i++)
{
if (IsOccupiedByOpponent(player, column - i, row + i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column - i, row + i));
}
else if (IsEmpty(column - i, row + i) == true)
{
moves.Add(new ChessMove(rank, player, column, row, column - i, row + i));
continue;
}
break;
}
}
private void GetQueenMove(PiecePlayer player, List <ChessMove> moves, int column, int row)
{
GetHorizontalAndVerticalMoves(PieceRank.Queen, player, moves, column, row);
GetDiagonalMoves(PieceRank.Queen, player, moves, column, row);
}
private void GetBishopMove(PiecePlayer player, List <ChessMove> moves, int column, int row)
{
GetDiagonalMoves(PieceRank.Bishop, player, moves, column, row);
}
private void GetRookMove(PiecePlayer player, List <ChessMove> moves, int column, int row)
{
GetHorizontalAndVerticalMoves(PieceRank.Rook, player, moves, column, row);
}
private void GetPawnMoves(PiecePlayer player, List <ChessMove> moves, int column, int row)
{
ChessSpecialMove specialMove = ChessSpecialMove.None;
if (player == PiecePlayer.White)
{
if (row == 1)
{
specialMove = ChessSpecialMove.Promotion;
}
if (IsOccupiedByOpponent(player, column, row - 1) == false)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column, row - 1, specialMove));
}
if (row == 6 && IsEmpty(column, row - 1) == true && IsEmpty(column, row - 2) == true)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column, row - 2));
}
// Move only available for pawn if there is opponent piece:
if (IsOccupiedByOpponent(player, column + 1, row - 1) == true)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column + 1, row - 1, specialMove));
}
if (IsOccupiedByOpponent(player, column - 1, row - 1) == true)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column - 1, row - 1, specialMove));
}
GetPawnMovesEnPassant(player, moves, column, row, -1, -1);
GetPawnMovesEnPassant(player, moves, column, row, 1, -1);
}
else
{
if (row == 6)
{
specialMove = ChessSpecialMove.Promotion;
}
if (IsOccupiedByOpponent(player, column, row + 1) == false)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column, row + 1, specialMove));
}
if (row == 1 && IsEmpty(column, row + 1) == true && IsEmpty(column, row + 2) == true)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column, row + 2));
}
// Move only available for pawn if there is opponent piece:
if (IsOccupiedByOpponent(player, column + 1, row + 1) == true)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column + 1, row + 1, specialMove));
}
if (IsOccupiedByOpponent(player, column - 1, row + 1) == true)
{
moves.Add(new ChessMove(PieceRank.Pawn, player, column, row, column - 1, row + 1, specialMove));
}
GetPawnMovesEnPassant(player, moves, column, row, -1, 1);
GetPawnMovesEnPassant(player, moves, column, row, 1, 1);
}
}
private void GetKingCastlingMove(PiecePlayer player, List <ChessMove> moves, int column, int row, int rookColumn, bool validateCheck)
{
var rookPosition = _pieces[rookColumn, row];
if (rookPosition.Player != player || rookPosition.Rank != PieceRank.Rook)
{
// Not current players rook
return;
}
var rookRow = player == PiecePlayer.White ? 1 : 8;
// Rook is at start location. Has it moved earlier?
var rooksEarlierMove = _moves.Where(
m => m.First().Player == player && m.First().Rank == PieceRank.Rook &&
m.First().From.VerticalLocation == rookRow &&
m.First().From.HorizontalLocation == rookColumn).FirstOrDefault();
if (rooksEarlierMove != null)
{
// Rook has already moved so castling is not anymore available
return;
}
bool ownKingUnderThreat = false;
ChessMove[] opponentMoves = new ChessMove[0];
if (validateCheck == true)
{
opponentMoves = GetBoardThreats(
out ownKingUnderThreat,
CurrentPlayer == PiecePlayer.White ? PiecePlayer.Black : PiecePlayer.White);
}
if (ownKingUnderThreat == false)
{
// Set defaults to left hand side rook castling
int delta = -2;
int startColumn = 2;
int endColumn = column;
if (rookColumn > endColumn)
{
delta = 2;
startColumn = column + 1;
endColumn = rookColumn;
}
for (int currentColumn = startColumn; currentColumn < endColumn; currentColumn++)
{
if (_pieces[currentColumn, row].Player != PiecePlayer.None)
{
return;
}
ChessMove opponentMove = opponentMoves.Where(
o => o.To.HorizontalLocation == currentColumn && o.To.VerticalLocation == row).FirstOrDefault();
if (opponentMove != null)
{
return;
}
}
// This castling move is valid
moves.Add(new ChessMove(PieceRank.King, player, column, row, column + delta, row, ChessSpecialMove.Castling));
}
}
private ChessMove[] GetAvailableMoves(PiecePlayer player, int column, int row, bool validateCheck)
{
List <ChessMove> moves = new List <ChessMove>();
if (player == PiecePlayer.None)
{
// Game over already
return(moves.ToArray());
}
if (_pieces[column, row].Player == player)
{
switch (_pieces[column, row].Rank)
{
case PieceRank.Pawn:
GetPawnMoves(player, moves, column, row);
break;
case PieceRank.Knight:
GetKnightMove(player, moves, column, row);
break;
case PieceRank.Bishop:
GetBishopMove(player, moves, column, row);
break;
case PieceRank.Rook:
GetRookMove(player, moves, column, row);
break;
case PieceRank.Queen:
GetQueenMove(player, moves, column, row);
break;
case PieceRank.King:
GetKingMove(player, moves, column, row, validateCheck);
break;
default:
break;
}
// Validate all moves
for (int i = moves.Count - 1; i >= 0; i--)
{
bool invalidMove = false;
ChessMove move = moves[i];
if (move.To.HorizontalLocation < 0 || move.To.HorizontalLocation > BOARD_SIZE - 1)
{
// Out of bounds
invalidMove = true;
}
else if (move.To.VerticalLocation < 0 || move.To.VerticalLocation > BOARD_SIZE - 1)
{
// Out of bounds
invalidMove = true;
}
else if (_pieces[move.To.HorizontalLocation, move.To.VerticalLocation].Player == player)
{
// Already occupied by team mate
invalidMove = true;
}
if (invalidMove == false && validateCheck == true)
{
// Let's see if this move would cause check
MakeMove(move, false);
GetBoardThreats(out var ownKingUnderThreat);
if (ownKingUnderThreat == true)
{
invalidMove = true;
}
Undo();
}
if (invalidMove == true)
{
moves.RemoveAt(i);
}
}
}
return(moves.ToArray());
}
public ChessBoardPiece(PiecePlayer player, PieceRank rank)
{
Player = player;
Rank = rank;
}
