b83a409b8c37a98d6e366b959a1e64a3a56733cd
1 // (Orthodox) Chess rules are defined in ChessRules class.
2 // Variants generally inherit from it, and modify some parts.
4 import { ArrayFun
} from "@/utils/array";
5 import { randInt
, shuffle
} from "@/utils/alea";
7 // class "PiPo": Piece + Position
8 export const PiPo
= class PiPo
{
9 // o: {piece[p], color[c], posX[x], posY[y]}
18 export const Move
= class Move
{
19 // o: {appear, vanish, [start,] [end,]}
20 // appear,vanish = arrays of PiPo
21 // start,end = coordinates to apply to trigger move visually (think castle)
23 this.appear
= o
.appear
;
24 this.vanish
= o
.vanish
;
25 this.start
= o
.start
? o
.start : { x: o
.vanish
[0].x
, y: o
.vanish
[0].y
};
26 this.end
= o
.end
? o
.end : { x: o
.appear
[0].x
, y: o
.appear
[0].y
};
30 // NOTE: x coords = top to bottom; y = left to right (from white player perspective)
31 export const ChessRules
= class ChessRules
{
35 // Some variants don't have flags:
36 static get HasFlags() {
41 static get HasCastle() {
45 // Pawns specifications
46 static get PawnSpecs() {
48 directions: { 'w': -1, 'b': 1 },
50 promotions: [V
.ROOK
, V
.KNIGHT
, V
.BISHOP
, V
.QUEEN
],
52 captureBackward: false,
57 // En-passant captures need a stack of squares:
58 static get HasEnpassant() {
62 // Some variants cannot have analyse mode
63 static get CanAnalyze() {
66 // Patch: issues with javascript OOP, objects can't access static fields.
71 // Some variants show incomplete information,
72 // and thus show only a partial moves list or no list at all.
73 static get ShowMoves() {
80 // Some variants always show the same orientation
81 static get CanFlip() {
88 static get IMAGE_EXTENSION() {
89 // All pieces should be in the SVG format
93 // Turn "wb" into "B" (for FEN)
95 return b
[0] == "w" ? b
[1].toUpperCase() : b
[1];
98 // Turn "p" into "bp" (for board)
100 return f
.charCodeAt() <= 90 ? "w" + f
.toLowerCase() : "b" + f
;
103 // Check if FEN describes a board situation correctly
104 static IsGoodFen(fen
) {
105 const fenParsed
= V
.ParseFen(fen
);
107 if (!V
.IsGoodPosition(fenParsed
.position
)) return false;
109 if (!fenParsed
.turn
|| !V
.IsGoodTurn(fenParsed
.turn
)) return false;
110 // 3) Check moves count
111 if (!fenParsed
.movesCount
|| !(parseInt(fenParsed
.movesCount
) >= 0))
114 if (V
.HasFlags
&& (!fenParsed
.flags
|| !V
.IsGoodFlags(fenParsed
.flags
)))
116 // 5) Check enpassant
119 (!fenParsed
.enpassant
|| !V
.IsGoodEnpassant(fenParsed
.enpassant
))
126 // Is position part of the FEN a priori correct?
127 static IsGoodPosition(position
) {
128 if (position
.length
== 0) return false;
129 const rows
= position
.split("/");
130 if (rows
.length
!= V
.size
.x
) return false;
132 for (let row
of rows
) {
134 for (let i
= 0; i
< row
.length
; i
++) {
135 if (['K','k'].includes(row
[i
])) kings
[row
[i
]] = true;
136 if (V
.PIECES
.includes(row
[i
].toLowerCase())) sumElts
++;
138 const num
= parseInt(row
[i
]);
139 if (isNaN(num
)) return false;
143 if (sumElts
!= V
.size
.y
) return false;
145 // Both kings should be on board:
146 if (Object
.keys(kings
).length
!= 2) return false;
151 static IsGoodTurn(turn
) {
152 return ["w", "b"].includes(turn
);
156 static IsGoodFlags(flags
) {
157 // NOTE: a little too permissive to work with more variants
158 return !!flags
.match(/^[a-z]{4,4}$/);
161 static IsGoodEnpassant(enpassant
) {
162 if (enpassant
!= "-") {
163 const ep
= V
.SquareToCoords(enpassant
);
164 if (isNaN(ep
.x
) || !V
.OnBoard(ep
)) return false;
169 // 3 --> d (column number to letter)
170 static CoordToColumn(colnum
) {
171 return String
.fromCharCode(97 + colnum
);
174 // d --> 3 (column letter to number)
175 static ColumnToCoord(column
) {
176 return column
.charCodeAt(0) - 97;
180 static SquareToCoords(sq
) {
182 // NOTE: column is always one char => max 26 columns
183 // row is counted from black side => subtraction
184 x: V
.size
.x
- parseInt(sq
.substr(1)),
185 y: sq
[0].charCodeAt() - 97
190 static CoordsToSquare(coords
) {
191 return V
.CoordToColumn(coords
.y
) + (V
.size
.x
- coords
.x
);
196 return b
; //usual pieces in pieces/ folder
199 // Path to promotion pieces (usually the same)
201 return this.getPpath(b
);
204 // Aggregates flags into one object
206 return this.castleFlags
;
210 disaggregateFlags(flags
) {
211 this.castleFlags
= flags
;
214 // En-passant square, if any
215 getEpSquare(moveOrSquare
) {
216 if (!moveOrSquare
) return undefined;
217 if (typeof moveOrSquare
=== "string") {
218 const square
= moveOrSquare
;
219 if (square
== "-") return undefined;
220 return V
.SquareToCoords(square
);
222 // Argument is a move:
223 const move = moveOrSquare
;
224 const s
= move.start
,
227 Math
.abs(s
.x
- e
.x
) == 2 &&
229 move.appear
[0].p
== V
.PAWN
236 return undefined; //default
239 // Can thing on square1 take thing on square2
240 canTake([x1
, y1
], [x2
, y2
]) {
241 return this.getColor(x1
, y1
) !== this.getColor(x2
, y2
);
244 // Is (x,y) on the chessboard?
245 static OnBoard(x
, y
) {
246 return x
>= 0 && x
< V
.size
.x
&& y
>= 0 && y
< V
.size
.y
;
249 // Used in interface: 'side' arg == player color
250 canIplay(side
, [x
, y
]) {
251 return this.turn
== side
&& this.getColor(x
, y
) == side
;
254 // On which squares is color under check ? (for interface)
255 getCheckSquares(color
) {
257 this.underCheck(color
)
258 ? [JSON
.parse(JSON
.stringify(this.kingPos
[color
]))] //need to duplicate!
266 // Setup the initial random (asymmetric) position
267 static GenRandInitFen(randomness
) {
270 return "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w 0 ahah -";
272 let pieces
= { w: new Array(8), b: new Array(8) };
274 // Shuffle pieces on first (and last rank if randomness == 2)
275 for (let c
of ["w", "b"]) {
276 if (c
== 'b' && randomness
== 1) {
277 pieces
['b'] = pieces
['w'];
282 let positions
= ArrayFun
.range(8);
284 // Get random squares for bishops
285 let randIndex
= 2 * randInt(4);
286 const bishop1Pos
= positions
[randIndex
];
287 // The second bishop must be on a square of different color
288 let randIndex_tmp
= 2 * randInt(4) + 1;
289 const bishop2Pos
= positions
[randIndex_tmp
];
290 // Remove chosen squares
291 positions
.splice(Math
.max(randIndex
, randIndex_tmp
), 1);
292 positions
.splice(Math
.min(randIndex
, randIndex_tmp
), 1);
294 // Get random squares for knights
295 randIndex
= randInt(6);
296 const knight1Pos
= positions
[randIndex
];
297 positions
.splice(randIndex
, 1);
298 randIndex
= randInt(5);
299 const knight2Pos
= positions
[randIndex
];
300 positions
.splice(randIndex
, 1);
302 // Get random square for queen
303 randIndex
= randInt(4);
304 const queenPos
= positions
[randIndex
];
305 positions
.splice(randIndex
, 1);
307 // Rooks and king positions are now fixed,
308 // because of the ordering rook-king-rook
309 const rook1Pos
= positions
[0];
310 const kingPos
= positions
[1];
311 const rook2Pos
= positions
[2];
313 // Finally put the shuffled pieces in the board array
314 pieces
[c
][rook1Pos
] = "r";
315 pieces
[c
][knight1Pos
] = "n";
316 pieces
[c
][bishop1Pos
] = "b";
317 pieces
[c
][queenPos
] = "q";
318 pieces
[c
][kingPos
] = "k";
319 pieces
[c
][bishop2Pos
] = "b";
320 pieces
[c
][knight2Pos
] = "n";
321 pieces
[c
][rook2Pos
] = "r";
322 flags
+= V
.CoordToColumn(rook1Pos
) + V
.CoordToColumn(rook2Pos
);
324 // Add turn + flags + enpassant
326 pieces
["b"].join("") +
327 "/pppppppp/8/8/8/8/PPPPPPPP/" +
328 pieces
["w"].join("").toUpperCase() +
329 " w 0 " + flags
+ " -"
333 // "Parse" FEN: just return untransformed string data
334 static ParseFen(fen
) {
335 const fenParts
= fen
.split(" ");
337 position: fenParts
[0],
339 movesCount: fenParts
[2]
342 if (V
.HasFlags
) Object
.assign(res
, { flags: fenParts
[nextIdx
++] });
343 if (V
.HasEnpassant
) Object
.assign(res
, { enpassant: fenParts
[nextIdx
] });
347 // Return current fen (game state)
350 this.getBaseFen() + " " +
351 this.getTurnFen() + " " +
353 (V
.HasFlags
? " " + this.getFlagsFen() : "") +
354 (V
.HasEnpassant
? " " + this.getEnpassantFen() : "")
359 // Omit movesCount, only variable allowed to differ
361 this.getBaseFen() + "_" +
363 (V
.HasFlags
? "_" + this.getFlagsFen() : "") +
364 (V
.HasEnpassant
? "_" + this.getEnpassantFen() : "")
368 // Position part of the FEN string
371 for (let i
= 0; i
< V
.size
.x
; i
++) {
373 for (let j
= 0; j
< V
.size
.y
; j
++) {
374 if (this.board
[i
][j
] == V
.EMPTY
) emptyCount
++;
376 if (emptyCount
> 0) {
377 // Add empty squares in-between
378 position
+= emptyCount
;
381 position
+= V
.board2fen(this.board
[i
][j
]);
384 if (emptyCount
> 0) {
386 position
+= emptyCount
;
388 if (i
< V
.size
.x
- 1) position
+= "/"; //separate rows
397 // Flags part of the FEN string
401 for (let c
of ["w", "b"])
402 flags
+= this.castleFlags
[c
].map(V
.CoordToColumn
).join("");
406 // Enpassant part of the FEN string
408 const L
= this.epSquares
.length
;
409 if (!this.epSquares
[L
- 1]) return "-"; //no en-passant
410 return V
.CoordsToSquare(this.epSquares
[L
- 1]);
413 // Turn position fen into double array ["wb","wp","bk",...]
414 static GetBoard(position
) {
415 const rows
= position
.split("/");
416 let board
= ArrayFun
.init(V
.size
.x
, V
.size
.y
, "");
417 for (let i
= 0; i
< rows
.length
; i
++) {
419 for (let indexInRow
= 0; indexInRow
< rows
[i
].length
; indexInRow
++) {
420 const character
= rows
[i
][indexInRow
];
421 const num
= parseInt(character
);
422 // If num is a number, just shift j:
423 if (!isNaN(num
)) j
+= num
;
424 // Else: something at position i,j
425 else board
[i
][j
++] = V
.fen2board(character
);
431 // Extract (relevant) flags from fen
433 // white a-castle, h-castle, black a-castle, h-castle
434 this.castleFlags
= { w: [-1, -1], b: [-1, -1] };
435 for (let i
= 0; i
< 4; i
++) {
436 this.castleFlags
[i
< 2 ? "w" : "b"][i
% 2] =
437 V
.ColumnToCoord(fenflags
.charAt(i
));
444 // Fen string fully describes the game state
447 // In printDiagram() fen isn't supply because only getPpath() is used
448 // TODO: find a better solution!
450 const fenParsed
= V
.ParseFen(fen
);
451 this.board
= V
.GetBoard(fenParsed
.position
);
452 this.turn
= fenParsed
.turn
[0]; //[0] to work with MarseilleRules
453 this.movesCount
= parseInt(fenParsed
.movesCount
);
454 this.setOtherVariables(fen
);
457 // Scan board for kings positions
459 this.INIT_COL_KING
= { w: -1, b: -1 };
460 this.kingPos
= { w: [-1, -1], b: [-1, -1] }; //squares of white and black king
461 const fenRows
= V
.ParseFen(fen
).position
.split("/");
462 const startRow
= { 'w': V
.size
.x
- 1, 'b': 0 };
463 for (let i
= 0; i
< fenRows
.length
; i
++) {
464 let k
= 0; //column index on board
465 for (let j
= 0; j
< fenRows
[i
].length
; j
++) {
466 switch (fenRows
[i
].charAt(j
)) {
468 this.kingPos
["b"] = [i
, k
];
469 this.INIT_COL_KING
["b"] = k
;
472 this.kingPos
["w"] = [i
, k
];
473 this.INIT_COL_KING
["w"] = k
;
476 const num
= parseInt(fenRows
[i
].charAt(j
));
477 if (!isNaN(num
)) k
+= num
- 1;
485 // Some additional variables from FEN (variant dependant)
486 setOtherVariables(fen
) {
487 // Set flags and enpassant:
488 const parsedFen
= V
.ParseFen(fen
);
489 if (V
.HasFlags
) this.setFlags(parsedFen
.flags
);
490 if (V
.HasEnpassant
) {
492 parsedFen
.enpassant
!= "-"
493 ? this.getEpSquare(parsedFen
.enpassant
)
495 this.epSquares
= [epSq
];
497 // Search for kings positions:
501 /////////////////////
505 return { x: 8, y: 8 };
508 // Color of thing on square (i,j). 'undefined' if square is empty
510 return this.board
[i
][j
].charAt(0);
513 // Piece type on square (i,j). 'undefined' if square is empty
515 return this.board
[i
][j
].charAt(1);
518 // Get opponent color
519 static GetOppCol(color
) {
520 return color
== "w" ? "b" : "w";
523 // Pieces codes (for a clearer code)
530 static get KNIGHT() {
533 static get BISHOP() {
544 static get PIECES() {
545 return [V
.PAWN
, V
.ROOK
, V
.KNIGHT
, V
.BISHOP
, V
.QUEEN
, V
.KING
];
553 // Some pieces movements
584 // All possible moves from selected square
585 getPotentialMovesFrom([x
, y
]) {
586 switch (this.getPiece(x
, y
)) {
588 return this.getPotentialPawnMoves([x
, y
]);
590 return this.getPotentialRookMoves([x
, y
]);
592 return this.getPotentialKnightMoves([x
, y
]);
594 return this.getPotentialBishopMoves([x
, y
]);
596 return this.getPotentialQueenMoves([x
, y
]);
598 return this.getPotentialKingMoves([x
, y
]);
600 return []; //never reached
603 // Build a regular move from its initial and destination squares.
604 // tr: transformation
605 getBasicMove([sx
, sy
], [ex
, ey
], tr
) {
606 const initColor
= this.getColor(sx
, sy
);
607 const initPiece
= this.getPiece(sx
, sy
);
613 c: tr
? tr
.c : initColor
,
614 p: tr
? tr
.p : initPiece
627 // The opponent piece disappears if we take it
628 if (this.board
[ex
][ey
] != V
.EMPTY
) {
633 c: this.getColor(ex
, ey
),
634 p: this.getPiece(ex
, ey
)
642 // Generic method to find possible moves of non-pawn pieces:
643 // "sliding or jumping"
644 getSlideNJumpMoves([x
, y
], steps
, oneStep
) {
646 outerLoop: for (let step
of steps
) {
649 while (V
.OnBoard(i
, j
) && this.board
[i
][j
] == V
.EMPTY
) {
650 moves
.push(this.getBasicMove([x
, y
], [i
, j
]));
651 if (oneStep
) continue outerLoop
;
655 if (V
.OnBoard(i
, j
) && this.canTake([x
, y
], [i
, j
]))
656 moves
.push(this.getBasicMove([x
, y
], [i
, j
]));
661 // Special case of en-passant captures: treated separately
662 getEnpassantCaptures([x
, y
], shiftX
) {
663 const Lep
= this.epSquares
.length
;
664 const epSquare
= this.epSquares
[Lep
- 1]; //always at least one element
665 let enpassantMove
= null;
668 epSquare
.x
== x
+ shiftX
&&
669 Math
.abs(epSquare
.y
- y
) == 1
671 enpassantMove
= this.getBasicMove([x
, y
], [epSquare
.x
, epSquare
.y
]);
672 enpassantMove
.vanish
.push({
676 c: this.getColor(x
, epSquare
.y
)
679 return !!enpassantMove
? [enpassantMove
] : [];
682 // Consider all potential promotions:
683 addPawnMoves([x1
, y1
], [x2
, y2
], moves
, promotions
) {
684 let finalPieces
= [V
.PAWN
];
685 const color
= this.turn
;
686 const lastRank
= (color
== "w" ? 0 : V
.size
.x
- 1);
687 if (x2
== lastRank
) {
688 // promotions arg: special override for Hiddenqueen variant
689 if (!!promotions
) finalPieces
= promotions
;
690 else if (!!V
.PawnSpecs
.promotions
)
691 finalPieces
= V
.PawnSpecs
.promotions
;
694 for (let piece
of finalPieces
) {
695 tr
= (piece
!= V
.PAWN
? { c: color
, p: piece
} : null);
696 moves
.push(this.getBasicMove([x1
, y1
], [x2
, y2
], tr
));
700 // What are the pawn moves from square x,y ?
701 getPotentialPawnMoves([x
, y
], promotions
) {
702 const color
= this.turn
;
703 const [sizeX
, sizeY
] = [V
.size
.x
, V
.size
.y
];
704 const pawnShiftX
= V
.PawnSpecs
.directions
[color
];
705 const firstRank
= (color
== "w" ? sizeX
- 1 : 0);
706 const startRank
= (color
== "w" ? sizeX
- 2 : 1);
708 // Pawn movements in shiftX direction:
709 const getPawnMoves
= (shiftX
) => {
711 // NOTE: next condition is generally true (no pawn on last rank)
712 if (x
+ shiftX
>= 0 && x
+ shiftX
< sizeX
) {
713 if (this.board
[x
+ shiftX
][y
] == V
.EMPTY
) {
714 // One square forward
715 this.addPawnMoves([x
, y
], [x
+ shiftX
, y
], moves
, promotions
);
716 // Next condition because pawns on 1st rank can generally jump
718 V
.PawnSpecs
.twoSquares
&&
719 [startRank
, firstRank
].includes(x
) &&
720 this.board
[x
+ 2 * shiftX
][y
] == V
.EMPTY
723 moves
.push(this.getBasicMove([x
, y
], [x
+ 2 * shiftX
, y
]));
727 if (V
.PawnSpecs
.canCapture
) {
728 for (let shiftY
of [-1, 1]) {
734 this.board
[x
+ shiftX
][y
+ shiftY
] != V
.EMPTY
&&
735 this.canTake([x
, y
], [x
+ shiftX
, y
+ shiftY
])
738 [x
, y
], [x
+ shiftX
, y
+ shiftY
],
743 V
.PawnSpecs
.captureBackward
&&
744 x
- shiftX
>= 0 && x
- shiftX
< V
.size
.x
&&
745 this.board
[x
- shiftX
][y
+ shiftY
] != V
.EMPTY
&&
746 this.canTake([x
, y
], [x
- shiftX
, y
+ shiftY
])
749 [x
, y
], [x
+ shiftX
, y
+ shiftY
],
760 let pMoves
= getPawnMoves(pawnShiftX
);
761 if (V
.PawnSpecs
.bidirectional
)
762 pMoves
= pMoves
.concat(getPawnMoves(-pawnShiftX
));
764 if (V
.HasEnpassant
) {
765 // NOTE: backward en-passant captures are not considered
766 // because no rules define them (for now).
767 Array
.prototype.push
.apply(
769 this.getEnpassantCaptures([x
, y
], pawnShiftX
)
776 // What are the rook moves from square x,y ?
777 getPotentialRookMoves(sq
) {
778 return this.getSlideNJumpMoves(sq
, V
.steps
[V
.ROOK
]);
781 // What are the knight moves from square x,y ?
782 getPotentialKnightMoves(sq
) {
783 return this.getSlideNJumpMoves(sq
, V
.steps
[V
.KNIGHT
], "oneStep");
786 // What are the bishop moves from square x,y ?
787 getPotentialBishopMoves(sq
) {
788 return this.getSlideNJumpMoves(sq
, V
.steps
[V
.BISHOP
]);
791 // What are the queen moves from square x,y ?
792 getPotentialQueenMoves(sq
) {
793 return this.getSlideNJumpMoves(
795 V
.steps
[V
.ROOK
].concat(V
.steps
[V
.BISHOP
])
799 // What are the king moves from square x,y ?
800 getPotentialKingMoves(sq
) {
801 // Initialize with normal moves
802 let moves
= this.getSlideNJumpMoves(
804 V
.steps
[V
.ROOK
].concat(V
.steps
[V
.BISHOP
]),
807 if (V
.HasCastle
) moves
= moves
.concat(this.getCastleMoves(sq
));
811 // "castleInCheck" arg to let some variants castle under check
812 getCastleMoves([x
, y
], castleInCheck
) {
813 const c
= this.getColor(x
, y
);
814 if (x
!= (c
== "w" ? V
.size
.x
- 1 : 0) || y
!= this.INIT_COL_KING
[c
])
815 return []; //x isn't first rank, or king has moved (shortcut)
818 const oppCol
= V
.GetOppCol(c
);
822 const finalSquares
= [
824 [V
.size
.y
- 2, V
.size
.y
- 3]
829 castleSide
++ //large, then small
831 if (this.castleFlags
[c
][castleSide
] >= V
.size
.y
) continue;
832 // If this code is reached, rook and king are on initial position
834 // NOTE: in some variants this is not a rook, but let's keep variable name
835 const rookPos
= this.castleFlags
[c
][castleSide
];
836 const castlingPiece
= this.getPiece(x
, rookPos
);
837 if (this.getColor(x
, rookPos
) != c
)
838 // Rook is here but changed color (see Benedict)
841 // Nothing on the path of the king ? (and no checks)
842 const finDist
= finalSquares
[castleSide
][0] - y
;
843 let step
= finDist
/ Math
.max(1, Math
.abs(finDist
));
847 (!castleInCheck
&& this.isAttacked([x
, i
], oppCol
)) ||
848 (this.board
[x
][i
] != V
.EMPTY
&&
849 // NOTE: next check is enough, because of chessboard constraints
850 (this.getColor(x
, i
) != c
||
851 ![V
.KING
, castlingPiece
].includes(this.getPiece(x
, i
))))
853 continue castlingCheck
;
856 } while (i
!= finalSquares
[castleSide
][0]);
858 // Nothing on the path to the rook?
859 step
= castleSide
== 0 ? -1 : 1;
860 for (i
= y
+ step
; i
!= rookPos
; i
+= step
) {
861 if (this.board
[x
][i
] != V
.EMPTY
) continue castlingCheck
;
864 // Nothing on final squares, except maybe king and castling rook?
865 for (i
= 0; i
< 2; i
++) {
867 this.board
[x
][finalSquares
[castleSide
][i
]] != V
.EMPTY
&&
868 this.getPiece(x
, finalSquares
[castleSide
][i
]) != V
.KING
&&
869 finalSquares
[castleSide
][i
] != rookPos
871 continue castlingCheck
;
875 // If this code is reached, castle is valid
879 new PiPo({ x: x
, y: finalSquares
[castleSide
][0], p: V
.KING
, c: c
}),
880 new PiPo({ x: x
, y: finalSquares
[castleSide
][1], p: castlingPiece
, c: c
})
883 new PiPo({ x: x
, y: y
, p: V
.KING
, c: c
}),
884 new PiPo({ x: x
, y: rookPos
, p: castlingPiece
, c: c
})
887 Math
.abs(y
- rookPos
) <= 2
888 ? { x: x
, y: rookPos
}
889 : { x: x
, y: y
+ 2 * (castleSide
== 0 ? -1 : 1) }
900 // For the interface: possible moves for the current turn from square sq
901 getPossibleMovesFrom(sq
) {
902 return this.filterValid(this.getPotentialMovesFrom(sq
));
905 // TODO: promotions (into R,B,N,Q) should be filtered only once
907 if (moves
.length
== 0) return [];
908 const color
= this.turn
;
909 return moves
.filter(m
=> {
911 const res
= !this.underCheck(color
);
917 // Search for all valid moves considering current turn
918 // (for engine and game end)
920 const color
= this.turn
;
921 let potentialMoves
= [];
922 for (let i
= 0; i
< V
.size
.x
; i
++) {
923 for (let j
= 0; j
< V
.size
.y
; j
++) {
924 if (this.getColor(i
, j
) == color
) {
925 Array
.prototype.push
.apply(
927 this.getPotentialMovesFrom([i
, j
])
932 return this.filterValid(potentialMoves
);
935 // Stop at the first move found
937 const color
= this.turn
;
938 for (let i
= 0; i
< V
.size
.x
; i
++) {
939 for (let j
= 0; j
< V
.size
.y
; j
++) {
940 if (this.getColor(i
, j
) == color
) {
941 const moves
= this.getPotentialMovesFrom([i
, j
]);
942 if (moves
.length
> 0) {
943 for (let k
= 0; k
< moves
.length
; k
++) {
944 if (this.filterValid([moves
[k
]]).length
> 0) return true;
953 // Check if pieces of given color are attacking (king) on square x,y
954 isAttacked(sq
, color
) {
956 this.isAttackedByPawn(sq
, color
) ||
957 this.isAttackedByRook(sq
, color
) ||
958 this.isAttackedByKnight(sq
, color
) ||
959 this.isAttackedByBishop(sq
, color
) ||
960 this.isAttackedByQueen(sq
, color
) ||
961 this.isAttackedByKing(sq
, color
)
965 // Generic method for non-pawn pieces ("sliding or jumping"):
966 // is x,y attacked by a piece of given color ?
967 isAttackedBySlideNJump([x
, y
], color
, piece
, steps
, oneStep
) {
968 for (let step
of steps
) {
969 let rx
= x
+ step
[0],
971 while (V
.OnBoard(rx
, ry
) && this.board
[rx
][ry
] == V
.EMPTY
&& !oneStep
) {
977 this.getPiece(rx
, ry
) == piece
&&
978 this.getColor(rx
, ry
) == color
986 // Is square x,y attacked by 'color' pawns ?
987 isAttackedByPawn([x
, y
], color
) {
988 const pawnShift
= (color
== "w" ? 1 : -1);
989 if (x
+ pawnShift
>= 0 && x
+ pawnShift
< V
.size
.x
) {
990 for (let i
of [-1, 1]) {
994 this.getPiece(x
+ pawnShift
, y
+ i
) == V
.PAWN
&&
995 this.getColor(x
+ pawnShift
, y
+ i
) == color
1004 // Is square x,y attacked by 'color' rooks ?
1005 isAttackedByRook(sq
, color
) {
1006 return this.isAttackedBySlideNJump(sq
, color
, V
.ROOK
, V
.steps
[V
.ROOK
]);
1009 // Is square x,y attacked by 'color' knights ?
1010 isAttackedByKnight(sq
, color
) {
1011 return this.isAttackedBySlideNJump(
1020 // Is square x,y attacked by 'color' bishops ?
1021 isAttackedByBishop(sq
, color
) {
1022 return this.isAttackedBySlideNJump(sq
, color
, V
.BISHOP
, V
.steps
[V
.BISHOP
]);
1025 // Is square x,y attacked by 'color' queens ?
1026 isAttackedByQueen(sq
, color
) {
1027 return this.isAttackedBySlideNJump(
1031 V
.steps
[V
.ROOK
].concat(V
.steps
[V
.BISHOP
])
1035 // Is square x,y attacked by 'color' king(s) ?
1036 isAttackedByKing(sq
, color
) {
1037 return this.isAttackedBySlideNJump(
1041 V
.steps
[V
.ROOK
].concat(V
.steps
[V
.BISHOP
]),
1046 // Is color under check after his move ?
1048 return this.isAttacked(this.kingPos
[color
], V
.GetOppCol(color
));
1054 // Apply a move on board
1055 static PlayOnBoard(board
, move) {
1056 for (let psq
of move.vanish
) board
[psq
.x
][psq
.y
] = V
.EMPTY
;
1057 for (let psq
of move.appear
) board
[psq
.x
][psq
.y
] = psq
.c
+ psq
.p
;
1059 // Un-apply the played move
1060 static UndoOnBoard(board
, move) {
1061 for (let psq
of move.appear
) board
[psq
.x
][psq
.y
] = V
.EMPTY
;
1062 for (let psq
of move.vanish
) board
[psq
.x
][psq
.y
] = psq
.c
+ psq
.p
;
1069 // if (!this.states) this.states = [];
1070 // const stateFen = this.getFen() + JSON.stringify(this.kingPos);
1071 // this.states.push(stateFen);
1074 if (V
.HasFlags
) move.flags
= JSON
.stringify(this.aggregateFlags()); //save flags (for undo)
1075 if (V
.HasEnpassant
) this.epSquares
.push(this.getEpSquare(move));
1076 V
.PlayOnBoard(this.board
, move);
1077 this.turn
= V
.GetOppCol(this.turn
);
1079 this.postPlay(move);
1082 updateCastleFlags(move, piece
) {
1083 const c
= V
.GetOppCol(this.turn
);
1084 const firstRank
= (c
== "w" ? V
.size
.x
- 1 : 0);
1085 // Update castling flags if rooks are moved
1086 const oppCol
= V
.GetOppCol(c
);
1087 const oppFirstRank
= V
.size
.x
- 1 - firstRank
;
1088 if (piece
== V
.KING
&& move.appear
.length
> 0)
1089 this.castleFlags
[c
] = [V
.size
.y
, V
.size
.y
];
1091 move.start
.x
== firstRank
&& //our rook moves?
1092 this.castleFlags
[c
].includes(move.start
.y
)
1094 const flagIdx
= (move.start
.y
== this.castleFlags
[c
][0] ? 0 : 1);
1095 this.castleFlags
[c
][flagIdx
] = V
.size
.y
;
1097 move.end
.x
== oppFirstRank
&& //we took opponent rook?
1098 this.castleFlags
[oppCol
].includes(move.end
.y
)
1100 const flagIdx
= (move.end
.y
== this.castleFlags
[oppCol
][0] ? 0 : 1);
1101 this.castleFlags
[oppCol
][flagIdx
] = V
.size
.y
;
1105 // After move is played, update variables + flags
1107 const c
= V
.GetOppCol(this.turn
);
1108 let piece
= undefined;
1109 if (move.vanish
.length
>= 1)
1110 // Usual case, something is moved
1111 piece
= move.vanish
[0].p
;
1113 // Crazyhouse-like variants
1114 piece
= move.appear
[0].p
;
1116 // Update king position + flags
1117 if (piece
== V
.KING
&& move.appear
.length
> 0) {
1118 this.kingPos
[c
][0] = move.appear
[0].x
;
1119 this.kingPos
[c
][1] = move.appear
[0].y
;
1122 if (V
.HasCastle
) this.updateCastleFlags(move, piece
);
1129 if (V
.HasEnpassant
) this.epSquares
.pop();
1130 if (V
.HasFlags
) this.disaggregateFlags(JSON
.parse(move.flags
));
1131 V
.UndoOnBoard(this.board
, move);
1132 this.turn
= V
.GetOppCol(this.turn
);
1134 this.postUndo(move);
1137 // const stateFen = this.getFen() + JSON.stringify(this.kingPos);
1138 // if (stateFen != this.states[this.states.length-1]) debugger;
1139 // this.states.pop();
1142 // After move is undo-ed *and flags resetted*, un-update other variables
1143 // TODO: more symmetry, by storing flags increment in move (?!)
1145 // (Potentially) Reset king position
1146 const c
= this.getColor(move.start
.x
, move.start
.y
);
1147 if (this.getPiece(move.start
.x
, move.start
.y
) == V
.KING
)
1148 this.kingPos
[c
] = [move.start
.x
, move.start
.y
];
1154 // What is the score ? (Interesting if game is over)
1156 if (this.atLeastOneMove()) return "*";
1158 const color
= this.turn
;
1159 // No valid move: stalemate or checkmate?
1160 if (!this.underCheck(color
)) return "1/2";
1162 return (color
== "w" ? "0-1" : "1-0");
1169 static get VALUES() {
1180 // "Checkmate" (unreachable eval)
1181 static get INFINITY() {
1185 // At this value or above, the game is over
1186 static get THRESHOLD_MATE() {
1190 // Search depth: 2 for high branching factor, 4 for small (Loser chess, eg.)
1191 static get SEARCH_DEPTH() {
1196 const maxeval
= V
.INFINITY
;
1197 const color
= this.turn
;
1198 let moves1
= this.getAllValidMoves();
1200 if (moves1
.length
== 0)
1201 // TODO: this situation should not happen
1204 // Rank moves using a min-max at depth 2 (if search_depth >= 2!)
1205 for (let i
= 0; i
< moves1
.length
; i
++) {
1206 this.play(moves1
[i
]);
1207 const score1
= this.getCurrentScore();
1208 if (score1
!= "*") {
1212 : (score1
== "1-0" ? 1 : -1) * maxeval
;
1214 if (V
.SEARCH_DEPTH
== 1 || score1
!= "*") {
1215 if (!moves1
[i
].eval
) moves1
[i
].eval
= this.evalPosition();
1216 this.undo(moves1
[i
]);
1219 // Initial self evaluation is very low: "I'm checkmated"
1220 moves1
[i
].eval
= (color
== "w" ? -1 : 1) * maxeval
;
1221 // Initial enemy evaluation is very low too, for him
1222 let eval2
= (color
== "w" ? 1 : -1) * maxeval
;
1223 // Second half-move:
1224 let moves2
= this.getAllValidMoves();
1225 for (let j
= 0; j
< moves2
.length
; j
++) {
1226 this.play(moves2
[j
]);
1227 const score2
= this.getCurrentScore();
1228 let evalPos
= 0; //1/2 value
1231 evalPos
= this.evalPosition();
1241 (color
== "w" && evalPos
< eval2
) ||
1242 (color
== "b" && evalPos
> eval2
)
1246 this.undo(moves2
[j
]);
1249 (color
== "w" && eval2
> moves1
[i
].eval
) ||
1250 (color
== "b" && eval2
< moves1
[i
].eval
)
1252 moves1
[i
].eval
= eval2
;
1254 this.undo(moves1
[i
]);
1256 moves1
.sort((a
, b
) => {
1257 return (color
== "w" ? 1 : -1) * (b
.eval
- a
.eval
);
1259 // console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
1261 // Skip depth 3+ if we found a checkmate (or if we are checkmated in 1...)
1262 if (V
.SEARCH_DEPTH
>= 3 && Math
.abs(moves1
[0].eval
) < V
.THRESHOLD_MATE
) {
1263 for (let i
= 0; i
< moves1
.length
; i
++) {
1264 this.play(moves1
[i
]);
1265 // 0.1 * oldEval : heuristic to avoid some bad moves (not all...)
1267 0.1 * moves1
[i
].eval
+
1268 this.alphabeta(V
.SEARCH_DEPTH
- 1, -maxeval
, maxeval
);
1269 this.undo(moves1
[i
]);
1271 moves1
.sort((a
, b
) => {
1272 return (color
== "w" ? 1 : -1) * (b
.eval
- a
.eval
);
1276 let candidates
= [0];
1277 for (let j
= 1; j
< moves1
.length
&& moves1
[j
].eval
== moves1
[0].eval
; j
++)
1279 return moves1
[candidates
[randInt(candidates
.length
)]];
1282 alphabeta(depth
, alpha
, beta
) {
1283 const maxeval
= V
.INFINITY
;
1284 const color
= this.turn
;
1285 const score
= this.getCurrentScore();
1287 return score
== "1/2" ? 0 : (score
== "1-0" ? 1 : -1) * maxeval
;
1288 if (depth
== 0) return this.evalPosition();
1289 const moves
= this.getAllValidMoves();
1290 let v
= color
== "w" ? -maxeval : maxeval
;
1292 for (let i
= 0; i
< moves
.length
; i
++) {
1293 this.play(moves
[i
]);
1294 v
= Math
.max(v
, this.alphabeta(depth
- 1, alpha
, beta
));
1295 this.undo(moves
[i
]);
1296 alpha
= Math
.max(alpha
, v
);
1297 if (alpha
>= beta
) break; //beta cutoff
1302 for (let i
= 0; i
< moves
.length
; i
++) {
1303 this.play(moves
[i
]);
1304 v
= Math
.min(v
, this.alphabeta(depth
- 1, alpha
, beta
));
1305 this.undo(moves
[i
]);
1306 beta
= Math
.min(beta
, v
);
1307 if (alpha
>= beta
) break; //alpha cutoff
1315 // Just count material for now
1316 for (let i
= 0; i
< V
.size
.x
; i
++) {
1317 for (let j
= 0; j
< V
.size
.y
; j
++) {
1318 if (this.board
[i
][j
] != V
.EMPTY
) {
1319 const sign
= this.getColor(i
, j
) == "w" ? 1 : -1;
1320 evaluation
+= sign
* V
.VALUES
[this.getPiece(i
, j
)];
1327 /////////////////////////
1328 // MOVES + GAME NOTATION
1329 /////////////////////////
1331 // Context: just before move is played, turn hasn't changed
1332 // TODO: un-ambiguous notation (switch on piece type, check directions...)
1334 if (move.appear
.length
== 2 && move.appear
[0].p
== V
.KING
)
1336 return move.end
.y
< move.start
.y
? "0-0-0" : "0-0";
1338 // Translate final square
1339 const finalSquare
= V
.CoordsToSquare(move.end
);
1341 const piece
= this.getPiece(move.start
.x
, move.start
.y
);
1342 if (piece
== V
.PAWN
) {
1345 if (move.vanish
.length
> move.appear
.length
) {
1347 const startColumn
= V
.CoordToColumn(move.start
.y
);
1348 notation
= startColumn
+ "x" + finalSquare
;
1350 else notation
= finalSquare
;
1351 if (move.appear
.length
> 0 && move.appear
[0].p
!= V
.PAWN
)
1353 notation
+= "=" + move.appear
[0].p
.toUpperCase();
1358 piece
.toUpperCase() +
1359 (move.vanish
.length
> move.appear
.length
? "x" : "") +