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[vchess.git] / client / src / base_rules.js
1 // (Orthodox) Chess rules are defined in ChessRules class.
2 // Variants generally inherit from it, and modify some parts.
3
4 import { ArrayFun } from "@/utils/array";
5 import { randInt, shuffle } from "@/utils/alea";
6
7 // class "PiPo": Piece + Position
8 export const PiPo = class PiPo {
9 // o: {piece[p], color[c], posX[x], posY[y]}
10 constructor(o) {
11 this.p = o.p;
12 this.c = o.c;
13 this.x = o.x;
14 this.y = o.y;
15 }
16 };
17
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)
22 constructor(o) {
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 };
27 }
28 };
29
30 // NOTE: x coords = top to bottom; y = left to right (from white player perspective)
31 export const ChessRules = class ChessRules {
32 //////////////
33 // MISC UTILS
34
35 // Some variants don't have flags:
36 static get HasFlags() {
37 return true;
38 }
39
40 // Some variants don't have en-passant
41 static get HasEnpassant() {
42 return true;
43 }
44
45 // Some variants cannot have analyse mode
46 static get CanAnalyze() {
47 return true;
48 }
49 // Patch: issues with javascript OOP, objects can't access static fields.
50 get canAnalyze() {
51 return V.CanAnalyze;
52 }
53
54 // Some variants show incomplete information,
55 // and thus show only a partial moves list or no list at all.
56 static get ShowMoves() {
57 return "all";
58 }
59 get showMoves() {
60 return V.ShowMoves;
61 }
62
63 // Some variants always show the same orientation
64 static get CanFlip() {
65 return true;
66 }
67 get canFlip() {
68 return V.CanFlip;
69 }
70
71 // Turn "wb" into "B" (for FEN)
72 static board2fen(b) {
73 return b[0] == "w" ? b[1].toUpperCase() : b[1];
74 }
75
76 // Turn "p" into "bp" (for board)
77 static fen2board(f) {
78 return f.charCodeAt() <= 90 ? "w" + f.toLowerCase() : "b" + f;
79 }
80
81 // Check if FEN describe a board situation correctly
82 static IsGoodFen(fen) {
83 const fenParsed = V.ParseFen(fen);
84 // 1) Check position
85 if (!V.IsGoodPosition(fenParsed.position)) return false;
86 // 2) Check turn
87 if (!fenParsed.turn || !V.IsGoodTurn(fenParsed.turn)) return false;
88 // 3) Check moves count
89 if (!fenParsed.movesCount || !(parseInt(fenParsed.movesCount) >= 0))
90 return false;
91 // 4) Check flags
92 if (V.HasFlags && (!fenParsed.flags || !V.IsGoodFlags(fenParsed.flags)))
93 return false;
94 // 5) Check enpassant
95 if (
96 V.HasEnpassant &&
97 (!fenParsed.enpassant || !V.IsGoodEnpassant(fenParsed.enpassant))
98 ) {
99 return false;
100 }
101 return true;
102 }
103
104 // Is position part of the FEN a priori correct?
105 static IsGoodPosition(position) {
106 if (position.length == 0) return false;
107 const rows = position.split("/");
108 if (rows.length != V.size.x) return false;
109 let kings = {};
110 for (let row of rows) {
111 let sumElts = 0;
112 for (let i = 0; i < row.length; i++) {
113 if (['K','k'].includes(row[i]))
114 kings[row[i]] = true;
115 if (V.PIECES.includes(row[i].toLowerCase())) sumElts++;
116 else {
117 const num = parseInt(row[i]);
118 if (isNaN(num)) return false;
119 sumElts += num;
120 }
121 }
122 if (sumElts != V.size.y) return false;
123 }
124 // Both kings should be on board:
125 if (Object.keys(kings).length != 2)
126 return false;
127 return true;
128 }
129
130 // For FEN checking
131 static IsGoodTurn(turn) {
132 return ["w", "b"].includes(turn);
133 }
134
135 // For FEN checking
136 static IsGoodFlags(flags) {
137 return !!flags.match(/^[01]{4,4}$/);
138 }
139
140 static IsGoodEnpassant(enpassant) {
141 if (enpassant != "-") {
142 const ep = V.SquareToCoords(enpassant);
143 if (isNaN(ep.x) || !V.OnBoard(ep)) return false;
144 }
145 return true;
146 }
147
148 // 3 --> d (column number to letter)
149 static CoordToColumn(colnum) {
150 return String.fromCharCode(97 + colnum);
151 }
152
153 // d --> 3 (column letter to number)
154 static ColumnToCoord(column) {
155 return column.charCodeAt(0) - 97;
156 }
157
158 // a4 --> {x:3,y:0}
159 static SquareToCoords(sq) {
160 return {
161 // NOTE: column is always one char => max 26 columns
162 // row is counted from black side => subtraction
163 x: V.size.x - parseInt(sq.substr(1)),
164 y: sq[0].charCodeAt() - 97
165 };
166 }
167
168 // {x:0,y:4} --> e8
169 static CoordsToSquare(coords) {
170 return V.CoordToColumn(coords.y) + (V.size.x - coords.x);
171 }
172
173 // Path to pieces
174 getPpath(b) {
175 return b; //usual pieces in pieces/ folder
176 }
177
178 // Aggregates flags into one object
179 aggregateFlags() {
180 return this.castleFlags;
181 }
182
183 // Reverse operation
184 disaggregateFlags(flags) {
185 this.castleFlags = flags;
186 }
187
188 // En-passant square, if any
189 getEpSquare(moveOrSquare) {
190 if (!moveOrSquare) return undefined;
191 if (typeof moveOrSquare === "string") {
192 const square = moveOrSquare;
193 if (square == "-") return undefined;
194 return V.SquareToCoords(square);
195 }
196 // Argument is a move:
197 const move = moveOrSquare;
198 const s = move.start,
199 e = move.end;
200 if (
201 Math.abs(s.x - e.x) == 2 &&
202 s.y == e.y &&
203 move.appear[0].p == V.PAWN
204 ) {
205 return {
206 x: (s.x + e.x) / 2,
207 y: s.y
208 };
209 }
210 return undefined; //default
211 }
212
213 // Can thing on square1 take thing on square2
214 canTake([x1, y1], [x2, y2]) {
215 return this.getColor(x1, y1) !== this.getColor(x2, y2);
216 }
217
218 // Is (x,y) on the chessboard?
219 static OnBoard(x, y) {
220 return x >= 0 && x < V.size.x && y >= 0 && y < V.size.y;
221 }
222
223 // Used in interface: 'side' arg == player color
224 canIplay(side, [x, y]) {
225 return this.turn == side && this.getColor(x, y) == side;
226 }
227
228 // On which squares is color under check ? (for interface)
229 getCheckSquares(color) {
230 return this.isAttacked(this.kingPos[color], [V.GetOppCol(color)])
231 ? [JSON.parse(JSON.stringify(this.kingPos[color]))] //need to duplicate!
232 : [];
233 }
234
235 /////////////
236 // FEN UTILS
237
238 // Setup the initial random (asymmetric) position
239 static GenRandInitFen(randomness) {
240 if (randomness == 0)
241 // Deterministic:
242 return "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w 0 1111 -";
243
244 let pieces = { w: new Array(8), b: new Array(8) };
245 // Shuffle pieces on first (and last rank if randomness == 2)
246 for (let c of ["w", "b"]) {
247 if (c == 'b' && randomness == 1) {
248 pieces['b'] = pieces['w'];
249 break;
250 }
251
252 let positions = ArrayFun.range(8);
253
254 // Get random squares for bishops
255 let randIndex = 2 * randInt(4);
256 const bishop1Pos = positions[randIndex];
257 // The second bishop must be on a square of different color
258 let randIndex_tmp = 2 * randInt(4) + 1;
259 const bishop2Pos = positions[randIndex_tmp];
260 // Remove chosen squares
261 positions.splice(Math.max(randIndex, randIndex_tmp), 1);
262 positions.splice(Math.min(randIndex, randIndex_tmp), 1);
263
264 // Get random squares for knights
265 randIndex = randInt(6);
266 const knight1Pos = positions[randIndex];
267 positions.splice(randIndex, 1);
268 randIndex = randInt(5);
269 const knight2Pos = positions[randIndex];
270 positions.splice(randIndex, 1);
271
272 // Get random square for queen
273 randIndex = randInt(4);
274 const queenPos = positions[randIndex];
275 positions.splice(randIndex, 1);
276
277 // Rooks and king positions are now fixed,
278 // because of the ordering rook-king-rook
279 const rook1Pos = positions[0];
280 const kingPos = positions[1];
281 const rook2Pos = positions[2];
282
283 // Finally put the shuffled pieces in the board array
284 pieces[c][rook1Pos] = "r";
285 pieces[c][knight1Pos] = "n";
286 pieces[c][bishop1Pos] = "b";
287 pieces[c][queenPos] = "q";
288 pieces[c][kingPos] = "k";
289 pieces[c][bishop2Pos] = "b";
290 pieces[c][knight2Pos] = "n";
291 pieces[c][rook2Pos] = "r";
292 }
293 // Add turn + flags + enpassant
294 return (
295 pieces["b"].join("") +
296 "/pppppppp/8/8/8/8/PPPPPPPP/" +
297 pieces["w"].join("").toUpperCase() +
298 " w 0 1111 -"
299 );
300 }
301
302 // "Parse" FEN: just return untransformed string data
303 static ParseFen(fen) {
304 const fenParts = fen.split(" ");
305 let res = {
306 position: fenParts[0],
307 turn: fenParts[1],
308 movesCount: fenParts[2]
309 };
310 let nextIdx = 3;
311 if (V.HasFlags) Object.assign(res, { flags: fenParts[nextIdx++] });
312 if (V.HasEnpassant) Object.assign(res, { enpassant: fenParts[nextIdx] });
313 return res;
314 }
315
316 // Return current fen (game state)
317 getFen() {
318 return (
319 this.getBaseFen() + " " +
320 this.getTurnFen() + " " +
321 this.movesCount +
322 (V.HasFlags ? " " + this.getFlagsFen() : "") +
323 (V.HasEnpassant ? " " + this.getEnpassantFen() : "")
324 );
325 }
326
327 getFenForRepeat() {
328 // Omit movesCount, only variable allowed to differ
329 return (
330 this.getBaseFen() + "_" +
331 this.getTurnFen() +
332 (V.HasFlags ? "_" + this.getFlagsFen() : "") +
333 (V.HasEnpassant ? "_" + this.getEnpassantFen() : "")
334 );
335 }
336
337 // Position part of the FEN string
338 getBaseFen() {
339 let position = "";
340 for (let i = 0; i < V.size.x; i++) {
341 let emptyCount = 0;
342 for (let j = 0; j < V.size.y; j++) {
343 if (this.board[i][j] == V.EMPTY) emptyCount++;
344 else {
345 if (emptyCount > 0) {
346 // Add empty squares in-between
347 position += emptyCount;
348 emptyCount = 0;
349 }
350 position += V.board2fen(this.board[i][j]);
351 }
352 }
353 if (emptyCount > 0) {
354 // "Flush remainder"
355 position += emptyCount;
356 }
357 if (i < V.size.x - 1) position += "/"; //separate rows
358 }
359 return position;
360 }
361
362 getTurnFen() {
363 return this.turn;
364 }
365
366 // Flags part of the FEN string
367 getFlagsFen() {
368 let flags = "";
369 // Add castling flags
370 for (let i of ["w", "b"]) {
371 for (let j = 0; j < 2; j++) flags += this.castleFlags[i][j] ? "1" : "0";
372 }
373 return flags;
374 }
375
376 // Enpassant part of the FEN string
377 getEnpassantFen() {
378 const L = this.epSquares.length;
379 if (!this.epSquares[L - 1]) return "-"; //no en-passant
380 return V.CoordsToSquare(this.epSquares[L - 1]);
381 }
382
383 // Turn position fen into double array ["wb","wp","bk",...]
384 static GetBoard(position) {
385 const rows = position.split("/");
386 let board = ArrayFun.init(V.size.x, V.size.y, "");
387 for (let i = 0; i < rows.length; i++) {
388 let j = 0;
389 for (let indexInRow = 0; indexInRow < rows[i].length; indexInRow++) {
390 const character = rows[i][indexInRow];
391 const num = parseInt(character);
392 // If num is a number, just shift j:
393 if (!isNaN(num)) j += num;
394 // Else: something at position i,j
395 else board[i][j++] = V.fen2board(character);
396 }
397 }
398 return board;
399 }
400
401 // Extract (relevant) flags from fen
402 setFlags(fenflags) {
403 // white a-castle, h-castle, black a-castle, h-castle
404 this.castleFlags = { w: [true, true], b: [true, true] };
405 for (let i = 0; i < 4; i++)
406 this.castleFlags[i < 2 ? "w" : "b"][i % 2] = fenflags.charAt(i) == "1";
407 }
408
409 //////////////////
410 // INITIALIZATION
411
412 // Fen string fully describes the game state
413 constructor(fen) {
414 if (!fen)
415 // In printDiagram() fen isn't supply because only getPpath() is used
416 // TODO: find a better solution!
417 return;
418 const fenParsed = V.ParseFen(fen);
419 this.board = V.GetBoard(fenParsed.position);
420 this.turn = fenParsed.turn[0]; //[0] to work with MarseilleRules
421 this.movesCount = parseInt(fenParsed.movesCount);
422 this.setOtherVariables(fen);
423 }
424
425 // Scan board for kings and rooks positions
426 scanKingsRooks(fen) {
427 this.INIT_COL_KING = { w: -1, b: -1 };
428 this.INIT_COL_ROOK = { w: [-1, -1], b: [-1, -1] };
429 this.kingPos = { w: [-1, -1], b: [-1, -1] }; //squares of white and black king
430 const fenRows = V.ParseFen(fen).position.split("/");
431 const startRow = { 'w': V.size.x - 1, 'b': 0 };
432 for (let i = 0; i < fenRows.length; i++) {
433 let k = 0; //column index on board
434 for (let j = 0; j < fenRows[i].length; j++) {
435 switch (fenRows[i].charAt(j)) {
436 case "k":
437 this.kingPos["b"] = [i, k];
438 this.INIT_COL_KING["b"] = k;
439 break;
440 case "K":
441 this.kingPos["w"] = [i, k];
442 this.INIT_COL_KING["w"] = k;
443 break;
444 case "r":
445 if (i == startRow['b']) {
446 if (this.INIT_COL_ROOK["b"][0] < 0) this.INIT_COL_ROOK["b"][0] = k;
447 else this.INIT_COL_ROOK["b"][1] = k;
448 }
449 break;
450 case "R":
451 if (i == startRow['w']) {
452 if (this.INIT_COL_ROOK["w"][0] < 0) this.INIT_COL_ROOK["w"][0] = k;
453 else this.INIT_COL_ROOK["w"][1] = k;
454 }
455 break;
456 default: {
457 const num = parseInt(fenRows[i].charAt(j));
458 if (!isNaN(num)) k += num - 1;
459 }
460 }
461 k++;
462 }
463 }
464 }
465
466 // Some additional variables from FEN (variant dependant)
467 setOtherVariables(fen) {
468 // Set flags and enpassant:
469 const parsedFen = V.ParseFen(fen);
470 if (V.HasFlags) this.setFlags(parsedFen.flags);
471 if (V.HasEnpassant) {
472 const epSq =
473 parsedFen.enpassant != "-"
474 ? this.getEpSquare(parsedFen.enpassant)
475 : undefined;
476 this.epSquares = [epSq];
477 }
478 // Search for king and rooks positions:
479 this.scanKingsRooks(fen);
480 }
481
482 /////////////////////
483 // GETTERS & SETTERS
484
485 static get size() {
486 return { x: 8, y: 8 };
487 }
488
489 // Color of thing on square (i,j). 'undefined' if square is empty
490 getColor(i, j) {
491 return this.board[i][j].charAt(0);
492 }
493
494 // Piece type on square (i,j). 'undefined' if square is empty
495 getPiece(i, j) {
496 return this.board[i][j].charAt(1);
497 }
498
499 // Get opponent color
500 static GetOppCol(color) {
501 return color == "w" ? "b" : "w";
502 }
503
504 // Pieces codes (for a clearer code)
505 static get PAWN() {
506 return "p";
507 }
508 static get ROOK() {
509 return "r";
510 }
511 static get KNIGHT() {
512 return "n";
513 }
514 static get BISHOP() {
515 return "b";
516 }
517 static get QUEEN() {
518 return "q";
519 }
520 static get KING() {
521 return "k";
522 }
523
524 // For FEN checking:
525 static get PIECES() {
526 return [V.PAWN, V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN, V.KING];
527 }
528
529 // Empty square
530 static get EMPTY() {
531 return "";
532 }
533
534 // Some pieces movements
535 static get steps() {
536 return {
537 r: [
538 [-1, 0],
539 [1, 0],
540 [0, -1],
541 [0, 1]
542 ],
543 n: [
544 [-1, -2],
545 [-1, 2],
546 [1, -2],
547 [1, 2],
548 [-2, -1],
549 [-2, 1],
550 [2, -1],
551 [2, 1]
552 ],
553 b: [
554 [-1, -1],
555 [-1, 1],
556 [1, -1],
557 [1, 1]
558 ]
559 };
560 }
561
562 ////////////////////
563 // MOVES GENERATION
564
565 // All possible moves from selected square
566 getPotentialMovesFrom([x, y]) {
567 switch (this.getPiece(x, y)) {
568 case V.PAWN:
569 return this.getPotentialPawnMoves([x, y]);
570 case V.ROOK:
571 return this.getPotentialRookMoves([x, y]);
572 case V.KNIGHT:
573 return this.getPotentialKnightMoves([x, y]);
574 case V.BISHOP:
575 return this.getPotentialBishopMoves([x, y]);
576 case V.QUEEN:
577 return this.getPotentialQueenMoves([x, y]);
578 case V.KING:
579 return this.getPotentialKingMoves([x, y]);
580 }
581 return []; //never reached
582 }
583
584 // Build a regular move from its initial and destination squares.
585 // tr: transformation
586 getBasicMove([sx, sy], [ex, ey], tr) {
587 let mv = new Move({
588 appear: [
589 new PiPo({
590 x: ex,
591 y: ey,
592 c: tr ? tr.c : this.getColor(sx, sy),
593 p: tr ? tr.p : this.getPiece(sx, sy)
594 })
595 ],
596 vanish: [
597 new PiPo({
598 x: sx,
599 y: sy,
600 c: this.getColor(sx, sy),
601 p: this.getPiece(sx, sy)
602 })
603 ]
604 });
605
606 // The opponent piece disappears if we take it
607 if (this.board[ex][ey] != V.EMPTY) {
608 mv.vanish.push(
609 new PiPo({
610 x: ex,
611 y: ey,
612 c: this.getColor(ex, ey),
613 p: this.getPiece(ex, ey)
614 })
615 );
616 }
617
618 return mv;
619 }
620
621 // Generic method to find possible moves of non-pawn pieces:
622 // "sliding or jumping"
623 getSlideNJumpMoves([x, y], steps, oneStep) {
624 let moves = [];
625 outerLoop: for (let step of steps) {
626 let i = x + step[0];
627 let j = y + step[1];
628 while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
629 moves.push(this.getBasicMove([x, y], [i, j]));
630 if (oneStep) continue outerLoop;
631 i += step[0];
632 j += step[1];
633 }
634 if (V.OnBoard(i, j) && this.canTake([x, y], [i, j]))
635 moves.push(this.getBasicMove([x, y], [i, j]));
636 }
637 return moves;
638 }
639
640 // What are the pawn moves from square x,y ?
641 getPotentialPawnMoves([x, y]) {
642 const color = this.turn;
643 let moves = [];
644 const [sizeX, sizeY] = [V.size.x, V.size.y];
645 const shiftX = color == "w" ? -1 : 1;
646 const firstRank = color == "w" ? sizeX - 1 : 0;
647 const startRank = color == "w" ? sizeX - 2 : 1;
648 const lastRank = color == "w" ? 0 : sizeX - 1;
649
650 // NOTE: next condition is generally true (no pawn on last rank)
651 if (x + shiftX >= 0 && x + shiftX < sizeX) {
652 const finalPieces =
653 x + shiftX == lastRank
654 ? [V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN]
655 : [V.PAWN];
656 if (this.board[x + shiftX][y] == V.EMPTY) {
657 // One square forward
658 for (let piece of finalPieces) {
659 moves.push(
660 this.getBasicMove([x, y], [x + shiftX, y], {
661 c: color,
662 p: piece
663 })
664 );
665 }
666 // Next condition because pawns on 1st rank can generally jump
667 if (
668 [startRank, firstRank].includes(x) &&
669 this.board[x + 2 * shiftX][y] == V.EMPTY
670 ) {
671 // Two squares jump
672 moves.push(this.getBasicMove([x, y], [x + 2 * shiftX, y]));
673 }
674 }
675 // Captures
676 for (let shiftY of [-1, 1]) {
677 if (
678 y + shiftY >= 0 &&
679 y + shiftY < sizeY &&
680 this.board[x + shiftX][y + shiftY] != V.EMPTY &&
681 this.canTake([x, y], [x + shiftX, y + shiftY])
682 ) {
683 for (let piece of finalPieces) {
684 moves.push(
685 this.getBasicMove([x, y], [x + shiftX, y + shiftY], {
686 c: color,
687 p: piece
688 })
689 );
690 }
691 }
692 }
693 }
694
695 if (V.HasEnpassant) {
696 // En passant
697 const Lep = this.epSquares.length;
698 const epSquare = this.epSquares[Lep - 1]; //always at least one element
699 if (
700 !!epSquare &&
701 epSquare.x == x + shiftX &&
702 Math.abs(epSquare.y - y) == 1
703 ) {
704 let enpassantMove = this.getBasicMove([x, y], [epSquare.x, epSquare.y]);
705 enpassantMove.vanish.push({
706 x: x,
707 y: epSquare.y,
708 p: "p",
709 c: this.getColor(x, epSquare.y)
710 });
711 moves.push(enpassantMove);
712 }
713 }
714
715 return moves;
716 }
717
718 // What are the rook moves from square x,y ?
719 getPotentialRookMoves(sq) {
720 return this.getSlideNJumpMoves(sq, V.steps[V.ROOK]);
721 }
722
723 // What are the knight moves from square x,y ?
724 getPotentialKnightMoves(sq) {
725 return this.getSlideNJumpMoves(sq, V.steps[V.KNIGHT], "oneStep");
726 }
727
728 // What are the bishop moves from square x,y ?
729 getPotentialBishopMoves(sq) {
730 return this.getSlideNJumpMoves(sq, V.steps[V.BISHOP]);
731 }
732
733 // What are the queen moves from square x,y ?
734 getPotentialQueenMoves(sq) {
735 return this.getSlideNJumpMoves(
736 sq,
737 V.steps[V.ROOK].concat(V.steps[V.BISHOP])
738 );
739 }
740
741 // What are the king moves from square x,y ?
742 getPotentialKingMoves(sq) {
743 // Initialize with normal moves
744 let moves = this.getSlideNJumpMoves(
745 sq,
746 V.steps[V.ROOK].concat(V.steps[V.BISHOP]),
747 "oneStep"
748 );
749 return moves.concat(this.getCastleMoves(sq));
750 }
751
752 getCastleMoves([x, y]) {
753 const c = this.getColor(x, y);
754 if (x != (c == "w" ? V.size.x - 1 : 0) || y != this.INIT_COL_KING[c])
755 return []; //x isn't first rank, or king has moved (shortcut)
756
757 // Castling ?
758 const oppCol = V.GetOppCol(c);
759 let moves = [];
760 let i = 0;
761 // King, then rook:
762 const finalSquares = [
763 [2, 3],
764 [V.size.y - 2, V.size.y - 3]
765 ];
766 castlingCheck: for (
767 let castleSide = 0;
768 castleSide < 2;
769 castleSide++ //large, then small
770 ) {
771 if (!this.castleFlags[c][castleSide]) continue;
772 // If this code is reached, rooks and king are on initial position
773
774 // Nothing on the path of the king ? (and no checks)
775 const finDist = finalSquares[castleSide][0] - y;
776 let step = finDist / Math.max(1, Math.abs(finDist));
777 i = y;
778 do {
779 if (
780 this.isAttacked([x, i], [oppCol]) ||
781 (this.board[x][i] != V.EMPTY &&
782 // NOTE: next check is enough, because of chessboard constraints
783 (this.getColor(x, i) != c ||
784 ![V.KING, V.ROOK].includes(this.getPiece(x, i))))
785 ) {
786 continue castlingCheck;
787 }
788 i += step;
789 } while (i != finalSquares[castleSide][0]);
790
791 // Nothing on the path to the rook?
792 step = castleSide == 0 ? -1 : 1;
793 for (i = y + step; i != this.INIT_COL_ROOK[c][castleSide]; i += step) {
794 if (this.board[x][i] != V.EMPTY) continue castlingCheck;
795 }
796 const rookPos = this.INIT_COL_ROOK[c][castleSide];
797
798 // Nothing on final squares, except maybe king and castling rook?
799 for (i = 0; i < 2; i++) {
800 if (
801 this.board[x][finalSquares[castleSide][i]] != V.EMPTY &&
802 this.getPiece(x, finalSquares[castleSide][i]) != V.KING &&
803 finalSquares[castleSide][i] != rookPos
804 ) {
805 continue castlingCheck;
806 }
807 }
808
809 // If this code is reached, castle is valid
810 moves.push(
811 new Move({
812 appear: [
813 new PiPo({ x: x, y: finalSquares[castleSide][0], p: V.KING, c: c }),
814 new PiPo({ x: x, y: finalSquares[castleSide][1], p: V.ROOK, c: c })
815 ],
816 vanish: [
817 new PiPo({ x: x, y: y, p: V.KING, c: c }),
818 new PiPo({ x: x, y: rookPos, p: V.ROOK, c: c })
819 ],
820 end:
821 Math.abs(y - rookPos) <= 2
822 ? { x: x, y: rookPos }
823 : { x: x, y: y + 2 * (castleSide == 0 ? -1 : 1) }
824 })
825 );
826 }
827
828 return moves;
829 }
830
831 ////////////////////
832 // MOVES VALIDATION
833
834 // For the interface: possible moves for the current turn from square sq
835 getPossibleMovesFrom(sq) {
836 return this.filterValid(this.getPotentialMovesFrom(sq));
837 }
838
839 // TODO: promotions (into R,B,N,Q) should be filtered only once
840 filterValid(moves) {
841 if (moves.length == 0) return [];
842 const color = this.turn;
843 return moves.filter(m => {
844 this.play(m);
845 const res = !this.underCheck(color);
846 this.undo(m);
847 return res;
848 });
849 }
850
851 // Search for all valid moves considering current turn
852 // (for engine and game end)
853 getAllValidMoves() {
854 const color = this.turn;
855 let potentialMoves = [];
856 for (let i = 0; i < V.size.x; i++) {
857 for (let j = 0; j < V.size.y; j++) {
858 if (this.getColor(i, j) == color) {
859 Array.prototype.push.apply(
860 potentialMoves,
861 this.getPotentialMovesFrom([i, j])
862 );
863 }
864 }
865 }
866 return this.filterValid(potentialMoves);
867 }
868
869 // Stop at the first move found
870 atLeastOneMove() {
871 const color = this.turn;
872 for (let i = 0; i < V.size.x; i++) {
873 for (let j = 0; j < V.size.y; j++) {
874 if (this.getColor(i, j) == color) {
875 const moves = this.getPotentialMovesFrom([i, j]);
876 if (moves.length > 0) {
877 for (let k = 0; k < moves.length; k++) {
878 if (this.filterValid([moves[k]]).length > 0) return true;
879 }
880 }
881 }
882 }
883 }
884 return false;
885 }
886
887 // Check if pieces of color in 'colors' are attacking (king) on square x,y
888 isAttacked(sq, colors) {
889 return (
890 this.isAttackedByPawn(sq, colors) ||
891 this.isAttackedByRook(sq, colors) ||
892 this.isAttackedByKnight(sq, colors) ||
893 this.isAttackedByBishop(sq, colors) ||
894 this.isAttackedByQueen(sq, colors) ||
895 this.isAttackedByKing(sq, colors)
896 );
897 }
898
899 // Generic method for non-pawn pieces ("sliding or jumping"):
900 // is x,y attacked by a piece of color in array 'colors' ?
901 isAttackedBySlideNJump([x, y], colors, piece, steps, oneStep) {
902 for (let step of steps) {
903 let rx = x + step[0],
904 ry = y + step[1];
905 while (V.OnBoard(rx, ry) && this.board[rx][ry] == V.EMPTY && !oneStep) {
906 rx += step[0];
907 ry += step[1];
908 }
909 if (
910 V.OnBoard(rx, ry) &&
911 this.getPiece(rx, ry) === piece &&
912 colors.includes(this.getColor(rx, ry))
913 ) {
914 return true;
915 }
916 }
917 return false;
918 }
919
920 // Is square x,y attacked by 'colors' pawns ?
921 isAttackedByPawn([x, y], colors) {
922 for (let c of colors) {
923 const pawnShift = c == "w" ? 1 : -1;
924 if (x + pawnShift >= 0 && x + pawnShift < V.size.x) {
925 for (let i of [-1, 1]) {
926 if (
927 y + i >= 0 &&
928 y + i < V.size.y &&
929 this.getPiece(x + pawnShift, y + i) == V.PAWN &&
930 this.getColor(x + pawnShift, y + i) == c
931 ) {
932 return true;
933 }
934 }
935 }
936 }
937 return false;
938 }
939
940 // Is square x,y attacked by 'colors' rooks ?
941 isAttackedByRook(sq, colors) {
942 return this.isAttackedBySlideNJump(sq, colors, V.ROOK, V.steps[V.ROOK]);
943 }
944
945 // Is square x,y attacked by 'colors' knights ?
946 isAttackedByKnight(sq, colors) {
947 return this.isAttackedBySlideNJump(
948 sq,
949 colors,
950 V.KNIGHT,
951 V.steps[V.KNIGHT],
952 "oneStep"
953 );
954 }
955
956 // Is square x,y attacked by 'colors' bishops ?
957 isAttackedByBishop(sq, colors) {
958 return this.isAttackedBySlideNJump(sq, colors, V.BISHOP, V.steps[V.BISHOP]);
959 }
960
961 // Is square x,y attacked by 'colors' queens ?
962 isAttackedByQueen(sq, colors) {
963 return this.isAttackedBySlideNJump(
964 sq,
965 colors,
966 V.QUEEN,
967 V.steps[V.ROOK].concat(V.steps[V.BISHOP])
968 );
969 }
970
971 // Is square x,y attacked by 'colors' king(s) ?
972 isAttackedByKing(sq, colors) {
973 return this.isAttackedBySlideNJump(
974 sq,
975 colors,
976 V.KING,
977 V.steps[V.ROOK].concat(V.steps[V.BISHOP]),
978 "oneStep"
979 );
980 }
981
982 // Is color under check after his move ?
983 underCheck(color) {
984 return this.isAttacked(this.kingPos[color], [V.GetOppCol(color)]);
985 }
986
987 /////////////////
988 // MOVES PLAYING
989
990 // Apply a move on board
991 static PlayOnBoard(board, move) {
992 for (let psq of move.vanish) board[psq.x][psq.y] = V.EMPTY;
993 for (let psq of move.appear) board[psq.x][psq.y] = psq.c + psq.p;
994 }
995 // Un-apply the played move
996 static UndoOnBoard(board, move) {
997 for (let psq of move.appear) board[psq.x][psq.y] = V.EMPTY;
998 for (let psq of move.vanish) board[psq.x][psq.y] = psq.c + psq.p;
999 }
1000
1001 // After move is played, update variables + flags
1002 updateVariables(move) {
1003 let piece = undefined;
1004 // TODO: update variables before move is played, and just use this.turn?
1005 // (doesn't work in general, think MarseilleChess)
1006 let c = undefined;
1007 if (move.vanish.length >= 1) {
1008 // Usual case, something is moved
1009 piece = move.vanish[0].p;
1010 c = move.vanish[0].c;
1011 } else {
1012 // Crazyhouse-like variants
1013 piece = move.appear[0].p;
1014 c = move.appear[0].c;
1015 }
1016 if (!['w','b'].includes(c)) {
1017 // Checkered, for example
1018 c = V.GetOppCol(this.turn);
1019 }
1020 const firstRank = c == "w" ? V.size.x - 1 : 0;
1021
1022 // Update king position + flags
1023 if (piece == V.KING && move.appear.length > 0) {
1024 this.kingPos[c][0] = move.appear[0].x;
1025 this.kingPos[c][1] = move.appear[0].y;
1026 if (V.HasFlags) this.castleFlags[c] = [false, false];
1027 return;
1028 }
1029 if (V.HasFlags) {
1030 // Update castling flags if rooks are moved
1031 const oppCol = V.GetOppCol(c);
1032 const oppFirstRank = V.size.x - 1 - firstRank;
1033 if (
1034 move.start.x == firstRank && //our rook moves?
1035 this.INIT_COL_ROOK[c].includes(move.start.y)
1036 ) {
1037 const flagIdx = move.start.y == this.INIT_COL_ROOK[c][0] ? 0 : 1;
1038 this.castleFlags[c][flagIdx] = false;
1039 } else if (
1040 move.end.x == oppFirstRank && //we took opponent rook?
1041 this.INIT_COL_ROOK[oppCol].includes(move.end.y)
1042 ) {
1043 const flagIdx = move.end.y == this.INIT_COL_ROOK[oppCol][0] ? 0 : 1;
1044 this.castleFlags[oppCol][flagIdx] = false;
1045 }
1046 }
1047 }
1048
1049 // After move is undo-ed *and flags resetted*, un-update other variables
1050 // TODO: more symmetry, by storing flags increment in move (?!)
1051 unupdateVariables(move) {
1052 // (Potentially) Reset king position
1053 const c = this.getColor(move.start.x, move.start.y);
1054 if (this.getPiece(move.start.x, move.start.y) == V.KING)
1055 this.kingPos[c] = [move.start.x, move.start.y];
1056 }
1057
1058 play(move) {
1059 // DEBUG:
1060 // if (!this.states) this.states = [];
1061 // const stateFen = this.getBaseFen() + this.getTurnFen() + this.getFlagsFen();
1062 // this.states.push(stateFen);
1063
1064 if (V.HasFlags) move.flags = JSON.stringify(this.aggregateFlags()); //save flags (for undo)
1065 if (V.HasEnpassant) this.epSquares.push(this.getEpSquare(move));
1066 V.PlayOnBoard(this.board, move);
1067 this.turn = V.GetOppCol(this.turn);
1068 this.movesCount++;
1069 this.updateVariables(move);
1070 }
1071
1072 undo(move) {
1073 if (V.HasEnpassant) this.epSquares.pop();
1074 if (V.HasFlags) this.disaggregateFlags(JSON.parse(move.flags));
1075 V.UndoOnBoard(this.board, move);
1076 this.turn = V.GetOppCol(this.turn);
1077 this.movesCount--;
1078 this.unupdateVariables(move);
1079
1080 // DEBUG:
1081 // const stateFen = this.getBaseFen() + this.getTurnFen() + this.getFlagsFen();
1082 // if (stateFen != this.states[this.states.length-1]) debugger;
1083 // this.states.pop();
1084 }
1085
1086 ///////////////
1087 // END OF GAME
1088
1089 // What is the score ? (Interesting if game is over)
1090 getCurrentScore() {
1091 if (this.atLeastOneMove())
1092 return "*";
1093
1094 // Game over
1095 const color = this.turn;
1096 // No valid move: stalemate or checkmate?
1097 if (!this.isAttacked(this.kingPos[color], [V.GetOppCol(color)]))
1098 return "1/2";
1099 // OK, checkmate
1100 return color == "w" ? "0-1" : "1-0";
1101 }
1102
1103 ///////////////
1104 // ENGINE PLAY
1105
1106 // Pieces values
1107 static get VALUES() {
1108 return {
1109 p: 1,
1110 r: 5,
1111 n: 3,
1112 b: 3,
1113 q: 9,
1114 k: 1000
1115 };
1116 }
1117
1118 // "Checkmate" (unreachable eval)
1119 static get INFINITY() {
1120 return 9999;
1121 }
1122
1123 // At this value or above, the game is over
1124 static get THRESHOLD_MATE() {
1125 return V.INFINITY;
1126 }
1127
1128 // Search depth: 2 for high branching factor, 4 for small (Loser chess, eg.)
1129 static get SEARCH_DEPTH() {
1130 return 3;
1131 }
1132
1133 getComputerMove() {
1134 const maxeval = V.INFINITY;
1135 const color = this.turn;
1136 let moves1 = this.getAllValidMoves();
1137
1138 if (moves1.length == 0)
1139 // TODO: this situation should not happen
1140 return null;
1141
1142 // Rank moves using a min-max at depth 2 (if search_depth >= 2!)
1143 for (let i = 0; i < moves1.length; i++) {
1144 if (V.SEARCH_DEPTH == 1) {
1145 moves1[i].eval = this.evalPosition();
1146 continue;
1147 }
1148 // Initial self evaluation is very low: "I'm checkmated"
1149 moves1[i].eval = (color == "w" ? -1 : 1) * maxeval;
1150 this.play(moves1[i]);
1151 const score1 = this.getCurrentScore();
1152 let eval2 = undefined;
1153 if (score1 == "*") {
1154 // Initial enemy evaluation is very low too, for him
1155 eval2 = (color == "w" ? 1 : -1) * maxeval;
1156 // Second half-move:
1157 let moves2 = this.getAllValidMoves();
1158 for (let j = 0; j < moves2.length; j++) {
1159 this.play(moves2[j]);
1160 const score2 = this.getCurrentScore();
1161 let evalPos = 0; //1/2 value
1162 switch (score2) {
1163 case "*":
1164 evalPos = this.evalPosition();
1165 break;
1166 case "1-0":
1167 evalPos = maxeval;
1168 break;
1169 case "0-1":
1170 evalPos = -maxeval;
1171 break;
1172 }
1173 if (
1174 (color == "w" && evalPos < eval2) ||
1175 (color == "b" && evalPos > eval2)
1176 ) {
1177 eval2 = evalPos;
1178 }
1179 this.undo(moves2[j]);
1180 }
1181 } else eval2 = score1 == "1/2" ? 0 : (score1 == "1-0" ? 1 : -1) * maxeval;
1182 if (
1183 (color == "w" && eval2 > moves1[i].eval) ||
1184 (color == "b" && eval2 < moves1[i].eval)
1185 ) {
1186 moves1[i].eval = eval2;
1187 }
1188 this.undo(moves1[i]);
1189 }
1190 moves1.sort((a, b) => {
1191 return (color == "w" ? 1 : -1) * (b.eval - a.eval);
1192 });
1193 // console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
1194
1195 // Skip depth 3+ if we found a checkmate (or if we are checkmated in 1...)
1196 if (V.SEARCH_DEPTH >= 3 && Math.abs(moves1[0].eval) < V.THRESHOLD_MATE) {
1197 for (let i = 0; i < moves1.length; i++) {
1198 this.play(moves1[i]);
1199 // 0.1 * oldEval : heuristic to avoid some bad moves (not all...)
1200 moves1[i].eval =
1201 0.1 * moves1[i].eval +
1202 this.alphabeta(V.SEARCH_DEPTH - 1, -maxeval, maxeval);
1203 this.undo(moves1[i]);
1204 }
1205 moves1.sort((a, b) => {
1206 return (color == "w" ? 1 : -1) * (b.eval - a.eval);
1207 });
1208 }
1209
1210 let candidates = [0];
1211 for (let j = 1; j < moves1.length && moves1[j].eval == moves1[0].eval; j++)
1212 candidates.push(j);
1213 return moves1[candidates[randInt(candidates.length)]];
1214 }
1215
1216 alphabeta(depth, alpha, beta) {
1217 const maxeval = V.INFINITY;
1218 const color = this.turn;
1219 const score = this.getCurrentScore();
1220 if (score != "*")
1221 return score == "1/2" ? 0 : (score == "1-0" ? 1 : -1) * maxeval;
1222 if (depth == 0) return this.evalPosition();
1223 const moves = this.getAllValidMoves();
1224 let v = color == "w" ? -maxeval : maxeval;
1225 if (color == "w") {
1226 for (let i = 0; i < moves.length; i++) {
1227 this.play(moves[i]);
1228 v = Math.max(v, this.alphabeta(depth - 1, alpha, beta));
1229 this.undo(moves[i]);
1230 alpha = Math.max(alpha, v);
1231 if (alpha >= beta) break; //beta cutoff
1232 }
1233 }
1234 else {
1235 // color=="b"
1236 for (let i = 0; i < moves.length; i++) {
1237 this.play(moves[i]);
1238 v = Math.min(v, this.alphabeta(depth - 1, alpha, beta));
1239 this.undo(moves[i]);
1240 beta = Math.min(beta, v);
1241 if (alpha >= beta) break; //alpha cutoff
1242 }
1243 }
1244 return v;
1245 }
1246
1247 evalPosition() {
1248 let evaluation = 0;
1249 // Just count material for now
1250 for (let i = 0; i < V.size.x; i++) {
1251 for (let j = 0; j < V.size.y; j++) {
1252 if (this.board[i][j] != V.EMPTY) {
1253 const sign = this.getColor(i, j) == "w" ? 1 : -1;
1254 evaluation += sign * V.VALUES[this.getPiece(i, j)];
1255 }
1256 }
1257 }
1258 return evaluation;
1259 }
1260
1261 /////////////////////////
1262 // MOVES + GAME NOTATION
1263 /////////////////////////
1264
1265 // Context: just before move is played, turn hasn't changed
1266 // TODO: un-ambiguous notation (switch on piece type, check directions...)
1267 getNotation(move) {
1268 if (move.appear.length == 2 && move.appear[0].p == V.KING)
1269 // Castle
1270 return move.end.y < move.start.y ? "0-0-0" : "0-0";
1271
1272 // Translate final square
1273 const finalSquare = V.CoordsToSquare(move.end);
1274
1275 const piece = this.getPiece(move.start.x, move.start.y);
1276 if (piece == V.PAWN) {
1277 // Pawn move
1278 let notation = "";
1279 if (move.vanish.length > move.appear.length) {
1280 // Capture
1281 const startColumn = V.CoordToColumn(move.start.y);
1282 notation = startColumn + "x" + finalSquare;
1283 }
1284 else notation = finalSquare;
1285 if (move.appear.length > 0 && move.appear[0].p != V.PAWN)
1286 // Promotion
1287 notation += "=" + move.appear[0].p.toUpperCase();
1288 return notation;
1289 }
1290 // Piece movement
1291 return (
1292 piece.toUpperCase() +
1293 (move.vanish.length > move.appear.length ? "x" : "") +
1294 finalSquare
1295 );
1296 }
1297 };