/** Remove pseudo-legal EP square if it is not legal, ie would leave king in check. */
public static void fixupEPSquare(Position pos)
{
int epSquare = pos.getEpSquare();
if (epSquare >= 0) {
MoveGen MG = new MoveGen();
MoveGen.MoveList moves = MG.pseudoLegalMoves(pos);
MoveGen.RemoveIllegal(pos, moves);
bool epValid = false;
for (int mi = 0; mi < moves.size; mi++) {
Move m = moves.m[mi];
if (m.to == epSquare) {
if (pos.getPiece(m.from) == (pos.whiteMove ? Piece.WPAWN : Piece.BPAWN)) {
epValid = true;
break;
}
}
}
if (!epValid) {
pos.setEpSquare(-1);
}
}
}
/*throws ChessParseError*/
/** Parse a FEN string and return a chess Position object. */
public static Position readFEN(string fen)
{
Position pos = new Position();
string[] words = fen.Split(' ');
if (words.Length < 2) {
throw new ChessParseError(/* "Too few pieces " */);
}
// Piece placement
int row = 7;
int col = 0;
for (int i = 0; i < words[0].Length; i++) {
char c = words[0][i];
switch (c) {
case '1': col += 1; break;
case '2': col += 2; break;
case '3': col += 3; break;
case '4': col += 4; break;
case '5': col += 5; break;
case '6': col += 6; break;
case '7': col += 7; break;
case '8': col += 8; break;
case '/': row--; col = 0; break;
case 'P': safeSetPiece(pos, col, row, Piece.WPAWN); col++; break;
case 'N': safeSetPiece(pos, col, row, Piece.WKNIGHT); col++; break;
case 'B': safeSetPiece(pos, col, row, Piece.WBISHOP); col++; break;
case 'R': safeSetPiece(pos, col, row, Piece.WROOK); col++; break;
case 'Q': safeSetPiece(pos, col, row, Piece.WQUEEN); col++; break;
case 'K': safeSetPiece(pos, col, row, Piece.WKING); col++; break;
case 'p': safeSetPiece(pos, col, row, Piece.BPAWN); col++; break;
case 'n': safeSetPiece(pos, col, row, Piece.BKNIGHT); col++; break;
case 'b': safeSetPiece(pos, col, row, Piece.BBISHOP); col++; break;
case 'r': safeSetPiece(pos, col, row, Piece.BROOK); col++; break;
case 'q': safeSetPiece(pos, col, row, Piece.BQUEEN); col++; break;
case 'k': safeSetPiece(pos, col, row, Piece.BKING); col++; break;
default: throw new ChessParseError(/* "Invalid piece" */);
}
}
if (words[1].Length == 0) {
throw new ChessParseError(/*"Invalid side"*/);
}
pos.setWhiteMove(words[1][0] == 'w');
// Castling rights
int castleMask = 0;
if (words.Length > 2) {
for (int i = 0; i < words[2].Length; i++) {
char c = words[2][i];
switch (c) {
case 'K':
castleMask |= (1 << Position.H1_CASTLE);
break;
case 'Q':
castleMask |= (1 << Position.A1_CASTLE);
break;
case 'k':
castleMask |= (1 << Position.H8_CASTLE);
break;
case 'q':
castleMask |= (1 << Position.A8_CASTLE);
break;
case '-':
break;
default:
throw new ChessParseError(/* "Invalid castling flags" */);
}
}
}
pos.setCastleMask(castleMask);
if (words.Length > 3) {
// En passant target square
string epstring = words[3];
if (epstring != "-") {
if (epstring.Length < 2) {
throw new ChessParseError(/* "Invalid en passant square" */);
}
pos.setEpSquare(getSquare(epstring));
}
}
try {
if (words.Length > 4) {
pos.halfMoveClock = int.Parse(words[4]);
}
if (words.Length > 5) {
pos.fullMoveCounter = int.Parse(words[5]);
}
} catch (NumberFormatException nfe) {
// Ignore errors here, since the fields are optional
}
// Each side must have exactly one king
int wKings = 0;
int bKings = 0;
for (int x = 0; x < 8; x++) {
for (int y = 0; y < 8; y++) {
int p = pos.getPiece(Position.getSquare(x, y));
if (p == Piece.WKING) {
wKings++;
} else if (p == Piece.BKING) {
bKings++;
}
}
}
if (wKings != 1) {
throw new ChessParseError(/* "White must have exactly one king" */);
}
if (bKings != 1) {
throw new ChessParseError(/* "Black must have exactly one king" */);
}
// Make sure king can not be captured
Position pos2 = new Position(pos);
pos2.setWhiteMove(!pos.whiteMove);
if (MoveGen.inCheck(pos2)) {
throw new ChessParseError(/* "King capture possible" */);
}
fixupEPSquare(pos);
return pos;
}