5bf47f76430401f0f748bc3b1ff49f4f0d8374f8
[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
50 // Some variants show incomplete information,
51 // and thus show only a partial moves list or no list at all.
52 static get ShowMoves() {
53 return "all";
54 }
55
56 // Path to pieces
57 static getPpath(b) {
58 return b; //usual pieces in pieces/ folder
59 }
60
61 // Turn "wb" into "B" (for FEN)
62 static board2fen(b) {
63 return b[0] == "w" ? b[1].toUpperCase() : b[1];
64 }
65
66 // Turn "p" into "bp" (for board)
67 static fen2board(f) {
68 return f.charCodeAt() <= 90 ? "w" + f.toLowerCase() : "b" + f;
69 }
70
71 // Check if FEN describe a board situation correctly
72 static IsGoodFen(fen) {
73 const fenParsed = V.ParseFen(fen);
74 // 1) Check position
75 if (!V.IsGoodPosition(fenParsed.position)) return false;
76 // 2) Check turn
77 if (!fenParsed.turn || !V.IsGoodTurn(fenParsed.turn)) return false;
78 // 3) Check moves count
79 if (!fenParsed.movesCount || !(parseInt(fenParsed.movesCount) >= 0))
80 return false;
81 // 4) Check flags
82 if (V.HasFlags && (!fenParsed.flags || !V.IsGoodFlags(fenParsed.flags)))
83 return false;
84 // 5) Check enpassant
85 if (
86 V.HasEnpassant &&
87 (!fenParsed.enpassant || !V.IsGoodEnpassant(fenParsed.enpassant))
88 ) {
89 return false;
90 }
91 return true;
92 }
93
94 // Is position part of the FEN a priori correct?
95 static IsGoodPosition(position) {
96 if (position.length == 0) return false;
97 const rows = position.split("/");
98 if (rows.length != V.size.x) return false;
99 let kings = {};
100 for (let row of rows) {
101 let sumElts = 0;
102 for (let i = 0; i < row.length; i++) {
103 if (['K','k'].includes(row[i]))
104 kings[row[i]] = true;
105 if (V.PIECES.includes(row[i].toLowerCase())) sumElts++;
106 else {
107 const num = parseInt(row[i]);
108 if (isNaN(num)) return false;
109 sumElts += num;
110 }
111 }
112 if (sumElts != V.size.y) return false;
113 }
114 // Both kings should be on board:
115 if (Object.keys(kings).length != 2)
116 return false;
117 return true;
118 }
119
120 // For FEN checking
121 static IsGoodTurn(turn) {
122 return ["w", "b"].includes(turn);
123 }
124
125 // For FEN checking
126 static IsGoodFlags(flags) {
127 return !!flags.match(/^[01]{4,4}$/);
128 }
129
130 static IsGoodEnpassant(enpassant) {
131 if (enpassant != "-") {
132 const ep = V.SquareToCoords(enpassant);
133 if (isNaN(ep.x) || !V.OnBoard(ep)) return false;
134 }
135 return true;
136 }
137
138 // 3 --> d (column number to letter)
139 static CoordToColumn(colnum) {
140 return String.fromCharCode(97 + colnum);
141 }
142
143 // d --> 3 (column letter to number)
144 static ColumnToCoord(column) {
145 return column.charCodeAt(0) - 97;
146 }
147
148 // a4 --> {x:3,y:0}
149 static SquareToCoords(sq) {
150 return {
151 // NOTE: column is always one char => max 26 columns
152 // row is counted from black side => subtraction
153 x: V.size.x - parseInt(sq.substr(1)),
154 y: sq[0].charCodeAt() - 97
155 };
156 }
157
158 // {x:0,y:4} --> e8
159 static CoordsToSquare(coords) {
160 return V.CoordToColumn(coords.y) + (V.size.x - coords.x);
161 }
162
163 // Aggregates flags into one object
164 aggregateFlags() {
165 return this.castleFlags;
166 }
167
168 // Reverse operation
169 disaggregateFlags(flags) {
170 this.castleFlags = flags;
171 }
172
173 // En-passant square, if any
174 getEpSquare(moveOrSquare) {
175 if (!moveOrSquare) return undefined;
176 if (typeof moveOrSquare === "string") {
177 const square = moveOrSquare;
178 if (square == "-") return undefined;
179 return V.SquareToCoords(square);
180 }
181 // Argument is a move:
182 const move = moveOrSquare;
183 const [sx, sy, ex] = [move.start.x, move.start.y, move.end.x];
184 // NOTE: next conditions are first for Atomic, and last for Checkered
185 if (
186 move.appear.length > 0 &&
187 Math.abs(sx - ex) == 2 &&
188 move.appear[0].p == V.PAWN &&
189 ["w", "b"].includes(move.appear[0].c)
190 ) {
191 return {
192 x: (sx + ex) / 2,
193 y: sy
194 };
195 }
196 return undefined; //default
197 }
198
199 // Can thing on square1 take thing on square2
200 canTake([x1, y1], [x2, y2]) {
201 return this.getColor(x1, y1) !== this.getColor(x2, y2);
202 }
203
204 // Is (x,y) on the chessboard?
205 static OnBoard(x, y) {
206 return x >= 0 && x < V.size.x && y >= 0 && y < V.size.y;
207 }
208
209 // Used in interface: 'side' arg == player color
210 canIplay(side, [x, y]) {
211 return this.turn == side && this.getColor(x, y) == side;
212 }
213
214 // On which squares is color under check ? (for interface)
215 getCheckSquares(color) {
216 return this.isAttacked(this.kingPos[color], [V.GetOppCol(color)])
217 ? [JSON.parse(JSON.stringify(this.kingPos[color]))] //need to duplicate!
218 : [];
219 }
220
221 /////////////
222 // FEN UTILS
223
224 // Setup the initial random (assymetric) position
225 static GenRandInitFen() {
226 let pieces = { w: new Array(8), b: new Array(8) };
227 // Shuffle pieces on first and last rank
228 for (let c of ["w", "b"]) {
229 let positions = ArrayFun.range(8);
230
231 // Get random squares for bishops
232 let randIndex = 2 * randInt(4);
233 const bishop1Pos = positions[randIndex];
234 // The second bishop must be on a square of different color
235 let randIndex_tmp = 2 * randInt(4) + 1;
236 const bishop2Pos = positions[randIndex_tmp];
237 // Remove chosen squares
238 positions.splice(Math.max(randIndex, randIndex_tmp), 1);
239 positions.splice(Math.min(randIndex, randIndex_tmp), 1);
240
241 // Get random squares for knights
242 randIndex = randInt(6);
243 const knight1Pos = positions[randIndex];
244 positions.splice(randIndex, 1);
245 randIndex = randInt(5);
246 const knight2Pos = positions[randIndex];
247 positions.splice(randIndex, 1);
248
249 // Get random square for queen
250 randIndex = randInt(4);
251 const queenPos = positions[randIndex];
252 positions.splice(randIndex, 1);
253
254 // Rooks and king positions are now fixed,
255 // because of the ordering rook-king-rook
256 const rook1Pos = positions[0];
257 const kingPos = positions[1];
258 const rook2Pos = positions[2];
259
260 // Finally put the shuffled pieces in the board array
261 pieces[c][rook1Pos] = "r";
262 pieces[c][knight1Pos] = "n";
263 pieces[c][bishop1Pos] = "b";
264 pieces[c][queenPos] = "q";
265 pieces[c][kingPos] = "k";
266 pieces[c][bishop2Pos] = "b";
267 pieces[c][knight2Pos] = "n";
268 pieces[c][rook2Pos] = "r";
269 }
270 return (
271 pieces["b"].join("") +
272 "/pppppppp/8/8/8/8/PPPPPPPP/" +
273 pieces["w"].join("").toUpperCase() +
274 " w 0 1111 -"
275 ); //add turn + flags + enpassant
276 }
277
278 // "Parse" FEN: just return untransformed string data
279 static ParseFen(fen) {
280 const fenParts = fen.split(" ");
281 let res = {
282 position: fenParts[0],
283 turn: fenParts[1],
284 movesCount: fenParts[2]
285 };
286 let nextIdx = 3;
287 if (V.HasFlags) Object.assign(res, { flags: fenParts[nextIdx++] });
288 if (V.HasEnpassant) Object.assign(res, { enpassant: fenParts[nextIdx] });
289 return res;
290 }
291
292 // Return current fen (game state)
293 getFen() {
294 return (
295 this.getBaseFen() +
296 " " +
297 this.getTurnFen() +
298 " " +
299 this.movesCount +
300 (V.HasFlags ? " " + this.getFlagsFen() : "") +
301 (V.HasEnpassant ? " " + this.getEnpassantFen() : "")
302 );
303 }
304
305 // Position part of the FEN string
306 getBaseFen() {
307 let position = "";
308 for (let i = 0; i < V.size.x; i++) {
309 let emptyCount = 0;
310 for (let j = 0; j < V.size.y; j++) {
311 if (this.board[i][j] == V.EMPTY) emptyCount++;
312 else {
313 if (emptyCount > 0) {
314 // Add empty squares in-between
315 position += emptyCount;
316 emptyCount = 0;
317 }
318 position += V.board2fen(this.board[i][j]);
319 }
320 }
321 if (emptyCount > 0) {
322 // "Flush remainder"
323 position += emptyCount;
324 }
325 if (i < V.size.x - 1) position += "/"; //separate rows
326 }
327 return position;
328 }
329
330 getTurnFen() {
331 return this.turn;
332 }
333
334 // Flags part of the FEN string
335 getFlagsFen() {
336 let flags = "";
337 // Add castling flags
338 for (let i of ["w", "b"]) {
339 for (let j = 0; j < 2; j++) flags += this.castleFlags[i][j] ? "1" : "0";
340 }
341 return flags;
342 }
343
344 // Enpassant part of the FEN string
345 getEnpassantFen() {
346 const L = this.epSquares.length;
347 if (!this.epSquares[L - 1]) return "-"; //no en-passant
348 return V.CoordsToSquare(this.epSquares[L - 1]);
349 }
350
351 // Turn position fen into double array ["wb","wp","bk",...]
352 static GetBoard(position) {
353 const rows = position.split("/");
354 let board = ArrayFun.init(V.size.x, V.size.y, "");
355 for (let i = 0; i < rows.length; i++) {
356 let j = 0;
357 for (let indexInRow = 0; indexInRow < rows[i].length; indexInRow++) {
358 const character = rows[i][indexInRow];
359 const num = parseInt(character);
360 if (!isNaN(num)) j += num;
361 //just shift j
362 //something at position i,j
363 else board[i][j++] = V.fen2board(character);
364 }
365 }
366 return board;
367 }
368
369 // Extract (relevant) flags from fen
370 setFlags(fenflags) {
371 // white a-castle, h-castle, black a-castle, h-castle
372 this.castleFlags = { w: [true, true], b: [true, true] };
373 if (!fenflags) return;
374 for (let i = 0; i < 4; i++)
375 this.castleFlags[i < 2 ? "w" : "b"][i % 2] = fenflags.charAt(i) == "1";
376 }
377
378 //////////////////
379 // INITIALIZATION
380
381 constructor(fen) {
382 this.re_init(fen);
383 }
384
385 // Fen string fully describes the game state
386 re_init(fen) {
387 const fenParsed = V.ParseFen(fen);
388 this.board = V.GetBoard(fenParsed.position);
389 this.turn = fenParsed.turn[0]; //[0] to work with MarseilleRules
390 this.movesCount = parseInt(fenParsed.movesCount);
391 this.setOtherVariables(fen);
392 }
393
394 // Scan board for kings and rooks positions
395 scanKingsRooks(fen) {
396 this.INIT_COL_KING = { w: -1, b: -1 };
397 this.INIT_COL_ROOK = { w: [-1, -1], b: [-1, -1] };
398 this.kingPos = { w: [-1, -1], b: [-1, -1] }; //squares of white and black king
399 const fenRows = V.ParseFen(fen).position.split("/");
400 for (let i = 0; i < fenRows.length; i++) {
401 let k = 0; //column index on board
402 for (let j = 0; j < fenRows[i].length; j++) {
403 switch (fenRows[i].charAt(j)) {
404 case "k":
405 this.kingPos["b"] = [i, k];
406 this.INIT_COL_KING["b"] = k;
407 break;
408 case "K":
409 this.kingPos["w"] = [i, k];
410 this.INIT_COL_KING["w"] = k;
411 break;
412 case "r":
413 if (this.INIT_COL_ROOK["b"][0] < 0) this.INIT_COL_ROOK["b"][0] = k;
414 else this.INIT_COL_ROOK["b"][1] = k;
415 break;
416 case "R":
417 if (this.INIT_COL_ROOK["w"][0] < 0) this.INIT_COL_ROOK["w"][0] = k;
418 else this.INIT_COL_ROOK["w"][1] = k;
419 break;
420 default: {
421 const num = parseInt(fenRows[i].charAt(j));
422 if (!isNaN(num)) k += num - 1;
423 }
424 }
425 k++;
426 }
427 }
428 }
429
430 // Some additional variables from FEN (variant dependant)
431 setOtherVariables(fen) {
432 // Set flags and enpassant:
433 const parsedFen = V.ParseFen(fen);
434 if (V.HasFlags) this.setFlags(parsedFen.flags);
435 if (V.HasEnpassant) {
436 const epSq =
437 parsedFen.enpassant != "-"
438 ? this.getEpSquare(parsedFen.enpassant)
439 : undefined;
440 this.epSquares = [epSq];
441 }
442 // Search for king and rooks positions:
443 this.scanKingsRooks(fen);
444 }
445
446 /////////////////////
447 // GETTERS & SETTERS
448
449 static get size() {
450 return { x: 8, y: 8 };
451 }
452
453 // Color of thing on suqare (i,j). 'undefined' if square is empty
454 getColor(i, j) {
455 return this.board[i][j].charAt(0);
456 }
457
458 // Piece type on square (i,j). 'undefined' if square is empty
459 getPiece(i, j) {
460 return this.board[i][j].charAt(1);
461 }
462
463 // Get opponent color
464 static GetOppCol(color) {
465 return color == "w" ? "b" : "w";
466 }
467
468 // Pieces codes (for a clearer code)
469 static get PAWN() {
470 return "p";
471 }
472 static get ROOK() {
473 return "r";
474 }
475 static get KNIGHT() {
476 return "n";
477 }
478 static get BISHOP() {
479 return "b";
480 }
481 static get QUEEN() {
482 return "q";
483 }
484 static get KING() {
485 return "k";
486 }
487
488 // For FEN checking:
489 static get PIECES() {
490 return [V.PAWN, V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN, V.KING];
491 }
492
493 // Empty square
494 static get EMPTY() {
495 return "";
496 }
497
498 // Some pieces movements
499 static get steps() {
500 return {
501 r: [
502 [-1, 0],
503 [1, 0],
504 [0, -1],
505 [0, 1]
506 ],
507 n: [
508 [-1, -2],
509 [-1, 2],
510 [1, -2],
511 [1, 2],
512 [-2, -1],
513 [-2, 1],
514 [2, -1],
515 [2, 1]
516 ],
517 b: [
518 [-1, -1],
519 [-1, 1],
520 [1, -1],
521 [1, 1]
522 ]
523 };
524 }
525
526 ////////////////////
527 // MOVES GENERATION
528
529 // All possible moves from selected square (assumption: color is OK)
530 getPotentialMovesFrom([x, y]) {
531 switch (this.getPiece(x, y)) {
532 case V.PAWN:
533 return this.getPotentialPawnMoves([x, y]);
534 case V.ROOK:
535 return this.getPotentialRookMoves([x, y]);
536 case V.KNIGHT:
537 return this.getPotentialKnightMoves([x, y]);
538 case V.BISHOP:
539 return this.getPotentialBishopMoves([x, y]);
540 case V.QUEEN:
541 return this.getPotentialQueenMoves([x, y]);
542 case V.KING:
543 return this.getPotentialKingMoves([x, y]);
544 }
545 return []; //never reached
546 }
547
548 // Build a regular move from its initial and destination squares.
549 // tr: transformation
550 getBasicMove([sx, sy], [ex, ey], tr) {
551 let mv = new Move({
552 appear: [
553 new PiPo({
554 x: ex,
555 y: ey,
556 c: tr ? tr.c : this.getColor(sx, sy),
557 p: tr ? tr.p : this.getPiece(sx, sy)
558 })
559 ],
560 vanish: [
561 new PiPo({
562 x: sx,
563 y: sy,
564 c: this.getColor(sx, sy),
565 p: this.getPiece(sx, sy)
566 })
567 ]
568 });
569
570 // The opponent piece disappears if we take it
571 if (this.board[ex][ey] != V.EMPTY) {
572 mv.vanish.push(
573 new PiPo({
574 x: ex,
575 y: ey,
576 c: this.getColor(ex, ey),
577 p: this.getPiece(ex, ey)
578 })
579 );
580 }
581 return mv;
582 }
583
584 // Generic method to find possible moves of non-pawn pieces:
585 // "sliding or jumping"
586 getSlideNJumpMoves([x, y], steps, oneStep) {
587 let moves = [];
588 outerLoop: for (let step of steps) {
589 let i = x + step[0];
590 let j = y + step[1];
591 while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
592 moves.push(this.getBasicMove([x, y], [i, j]));
593 if (oneStep !== undefined) continue outerLoop;
594 i += step[0];
595 j += step[1];
596 }
597 if (V.OnBoard(i, j) && this.canTake([x, y], [i, j]))
598 moves.push(this.getBasicMove([x, y], [i, j]));
599 }
600 return moves;
601 }
602
603 // What are the pawn moves from square x,y ?
604 getPotentialPawnMoves([x, y]) {
605 const color = this.turn;
606 let moves = [];
607 const [sizeX, sizeY] = [V.size.x, V.size.y];
608 const shiftX = color == "w" ? -1 : 1;
609 const firstRank = color == "w" ? sizeX - 1 : 0;
610 const startRank = color == "w" ? sizeX - 2 : 1;
611 const lastRank = color == "w" ? 0 : sizeX - 1;
612 const pawnColor = this.getColor(x, y); //can be different for checkered
613
614 // NOTE: next condition is generally true (no pawn on last rank)
615 if (x + shiftX >= 0 && x + shiftX < sizeX) {
616 const finalPieces =
617 x + shiftX == lastRank
618 ? [V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN]
619 : [V.PAWN];
620 // One square forward
621 if (this.board[x + shiftX][y] == V.EMPTY) {
622 for (let piece of finalPieces) {
623 moves.push(
624 this.getBasicMove([x, y], [x + shiftX, y], {
625 c: pawnColor,
626 p: piece
627 })
628 );
629 }
630 // Next condition because pawns on 1st rank can generally jump
631 if (
632 [startRank, firstRank].includes(x) &&
633 this.board[x + 2 * shiftX][y] == V.EMPTY
634 ) {
635 // Two squares jump
636 moves.push(this.getBasicMove([x, y], [x + 2 * shiftX, y]));
637 }
638 }
639 // Captures
640 for (let shiftY of [-1, 1]) {
641 if (
642 y + shiftY >= 0 &&
643 y + shiftY < sizeY &&
644 this.board[x + shiftX][y + shiftY] != V.EMPTY &&
645 this.canTake([x, y], [x + shiftX, y + shiftY])
646 ) {
647 for (let piece of finalPieces) {
648 moves.push(
649 this.getBasicMove([x, y], [x + shiftX, y + shiftY], {
650 c: pawnColor,
651 p: piece
652 })
653 );
654 }
655 }
656 }
657 }
658
659 if (V.HasEnpassant) {
660 // En passant
661 const Lep = this.epSquares.length;
662 const epSquare = this.epSquares[Lep - 1]; //always at least one element
663 if (
664 !!epSquare &&
665 epSquare.x == x + shiftX &&
666 Math.abs(epSquare.y - y) == 1
667 ) {
668 let enpassantMove = this.getBasicMove([x, y], [epSquare.x, epSquare.y]);
669 enpassantMove.vanish.push({
670 x: x,
671 y: epSquare.y,
672 p: "p",
673 c: this.getColor(x, epSquare.y)
674 });
675 moves.push(enpassantMove);
676 }
677 }
678
679 return moves;
680 }
681
682 // What are the rook moves from square x,y ?
683 getPotentialRookMoves(sq) {
684 return this.getSlideNJumpMoves(sq, V.steps[V.ROOK]);
685 }
686
687 // What are the knight moves from square x,y ?
688 getPotentialKnightMoves(sq) {
689 return this.getSlideNJumpMoves(sq, V.steps[V.KNIGHT], "oneStep");
690 }
691
692 // What are the bishop moves from square x,y ?
693 getPotentialBishopMoves(sq) {
694 return this.getSlideNJumpMoves(sq, V.steps[V.BISHOP]);
695 }
696
697 // What are the queen moves from square x,y ?
698 getPotentialQueenMoves(sq) {
699 return this.getSlideNJumpMoves(
700 sq,
701 V.steps[V.ROOK].concat(V.steps[V.BISHOP])
702 );
703 }
704
705 // What are the king moves from square x,y ?
706 getPotentialKingMoves(sq) {
707 // Initialize with normal moves
708 let moves = this.getSlideNJumpMoves(
709 sq,
710 V.steps[V.ROOK].concat(V.steps[V.BISHOP]),
711 "oneStep"
712 );
713 return moves.concat(this.getCastleMoves(sq));
714 }
715
716 getCastleMoves([x, y]) {
717 const c = this.getColor(x, y);
718 if (x != (c == "w" ? V.size.x - 1 : 0) || y != this.INIT_COL_KING[c])
719 return []; //x isn't first rank, or king has moved (shortcut)
720
721 // Castling ?
722 const oppCol = V.GetOppCol(c);
723 let moves = [];
724 let i = 0;
725 // King, then rook:
726 const finalSquares = [
727 [2, 3],
728 [V.size.y - 2, V.size.y - 3]
729 ];
730 castlingCheck: for (
731 let castleSide = 0;
732 castleSide < 2;
733 castleSide++ //large, then small
734 ) {
735 if (!this.castleFlags[c][castleSide]) continue;
736 // If this code is reached, rooks and king are on initial position
737
738 // Nothing on the path of the king ? (and no checks)
739 const finDist = finalSquares[castleSide][0] - y;
740 let step = finDist / Math.max(1, Math.abs(finDist));
741 i = y;
742 do {
743 if (
744 this.isAttacked([x, i], [oppCol]) ||
745 (this.board[x][i] != V.EMPTY &&
746 // NOTE: next check is enough, because of chessboard constraints
747 (this.getColor(x, i) != c ||
748 ![V.KING, V.ROOK].includes(this.getPiece(x, i))))
749 ) {
750 continue castlingCheck;
751 }
752 i += step;
753 } while (i != finalSquares[castleSide][0]);
754
755 // Nothing on the path to the rook?
756 step = castleSide == 0 ? -1 : 1;
757 for (i = y + step; i != this.INIT_COL_ROOK[c][castleSide]; i += step) {
758 if (this.board[x][i] != V.EMPTY) continue castlingCheck;
759 }
760 const rookPos = this.INIT_COL_ROOK[c][castleSide];
761
762 // Nothing on final squares, except maybe king and castling rook?
763 for (i = 0; i < 2; i++) {
764 if (
765 this.board[x][finalSquares[castleSide][i]] != V.EMPTY &&
766 this.getPiece(x, finalSquares[castleSide][i]) != V.KING &&
767 finalSquares[castleSide][i] != rookPos
768 ) {
769 continue castlingCheck;
770 }
771 }
772
773 // If this code is reached, castle is valid
774 moves.push(
775 new Move({
776 appear: [
777 new PiPo({ x: x, y: finalSquares[castleSide][0], p: V.KING, c: c }),
778 new PiPo({ x: x, y: finalSquares[castleSide][1], p: V.ROOK, c: c })
779 ],
780 vanish: [
781 new PiPo({ x: x, y: y, p: V.KING, c: c }),
782 new PiPo({ x: x, y: rookPos, p: V.ROOK, c: c })
783 ],
784 end:
785 Math.abs(y - rookPos) <= 2
786 ? { x: x, y: rookPos }
787 : { x: x, y: y + 2 * (castleSide == 0 ? -1 : 1) }
788 })
789 );
790 }
791
792 return moves;
793 }
794
795 ////////////////////
796 // MOVES VALIDATION
797
798 // For the interface: possible moves for the current turn from square sq
799 getPossibleMovesFrom(sq) {
800 return this.filterValid(this.getPotentialMovesFrom(sq));
801 }
802
803 // TODO: promotions (into R,B,N,Q) should be filtered only once
804 filterValid(moves) {
805 if (moves.length == 0) return [];
806 const color = this.turn;
807 return moves.filter(m => {
808 this.play(m);
809 const res = !this.underCheck(color);
810 this.undo(m);
811 return res;
812 });
813 }
814
815 // Search for all valid moves considering current turn
816 // (for engine and game end)
817 getAllValidMoves() {
818 const color = this.turn;
819 const oppCol = V.GetOppCol(color);
820 let potentialMoves = [];
821 for (let i = 0; i < V.size.x; i++) {
822 for (let j = 0; j < V.size.y; j++) {
823 // Next condition "!= oppCol" to work with checkered variant
824 if (this.board[i][j] != V.EMPTY && this.getColor(i, j) != oppCol) {
825 Array.prototype.push.apply(
826 potentialMoves,
827 this.getPotentialMovesFrom([i, j])
828 );
829 }
830 }
831 }
832 return this.filterValid(potentialMoves);
833 }
834
835 // Stop at the first move found
836 atLeastOneMove() {
837 const color = this.turn;
838 const oppCol = V.GetOppCol(color);
839 for (let i = 0; i < V.size.x; i++) {
840 for (let j = 0; j < V.size.y; j++) {
841 if (this.board[i][j] != V.EMPTY && this.getColor(i, j) != oppCol) {
842 const moves = this.getPotentialMovesFrom([i, j]);
843 if (moves.length > 0) {
844 for (let k = 0; k < moves.length; k++) {
845 if (this.filterValid([moves[k]]).length > 0) return true;
846 }
847 }
848 }
849 }
850 }
851 return false;
852 }
853
854 // Check if pieces of color in 'colors' are attacking (king) on square x,y
855 isAttacked(sq, colors) {
856 return (
857 this.isAttackedByPawn(sq, colors) ||
858 this.isAttackedByRook(sq, colors) ||
859 this.isAttackedByKnight(sq, colors) ||
860 this.isAttackedByBishop(sq, colors) ||
861 this.isAttackedByQueen(sq, colors) ||
862 this.isAttackedByKing(sq, colors)
863 );
864 }
865
866 // Is square x,y attacked by 'colors' pawns ?
867 isAttackedByPawn([x, y], colors) {
868 for (let c of colors) {
869 let pawnShift = c == "w" ? 1 : -1;
870 if (x + pawnShift >= 0 && x + pawnShift < V.size.x) {
871 for (let i of [-1, 1]) {
872 if (
873 y + i >= 0 &&
874 y + i < V.size.y &&
875 this.getPiece(x + pawnShift, y + i) == V.PAWN &&
876 this.getColor(x + pawnShift, y + i) == c
877 ) {
878 return true;
879 }
880 }
881 }
882 }
883 return false;
884 }
885
886 // Is square x,y attacked by 'colors' rooks ?
887 isAttackedByRook(sq, colors) {
888 return this.isAttackedBySlideNJump(sq, colors, V.ROOK, V.steps[V.ROOK]);
889 }
890
891 // Is square x,y attacked by 'colors' knights ?
892 isAttackedByKnight(sq, colors) {
893 return this.isAttackedBySlideNJump(
894 sq,
895 colors,
896 V.KNIGHT,
897 V.steps[V.KNIGHT],
898 "oneStep"
899 );
900 }
901
902 // Is square x,y attacked by 'colors' bishops ?
903 isAttackedByBishop(sq, colors) {
904 return this.isAttackedBySlideNJump(sq, colors, V.BISHOP, V.steps[V.BISHOP]);
905 }
906
907 // Is square x,y attacked by 'colors' queens ?
908 isAttackedByQueen(sq, colors) {
909 return this.isAttackedBySlideNJump(
910 sq,
911 colors,
912 V.QUEEN,
913 V.steps[V.ROOK].concat(V.steps[V.BISHOP])
914 );
915 }
916
917 // Is square x,y attacked by 'colors' king(s) ?
918 isAttackedByKing(sq, colors) {
919 return this.isAttackedBySlideNJump(
920 sq,
921 colors,
922 V.KING,
923 V.steps[V.ROOK].concat(V.steps[V.BISHOP]),
924 "oneStep"
925 );
926 }
927
928 // Generic method for non-pawn pieces ("sliding or jumping"):
929 // is x,y attacked by a piece of color in array 'colors' ?
930 isAttackedBySlideNJump([x, y], colors, piece, steps, oneStep) {
931 for (let step of steps) {
932 let rx = x + step[0],
933 ry = y + step[1];
934 while (V.OnBoard(rx, ry) && this.board[rx][ry] == V.EMPTY && !oneStep) {
935 rx += step[0];
936 ry += step[1];
937 }
938 if (
939 V.OnBoard(rx, ry) &&
940 this.getPiece(rx, ry) === piece &&
941 colors.includes(this.getColor(rx, ry))
942 ) {
943 return true;
944 }
945 }
946 return false;
947 }
948
949 // Is color under check after his move ?
950 underCheck(color) {
951 return this.isAttacked(this.kingPos[color], [V.GetOppCol(color)]);
952 }
953
954 /////////////////
955 // MOVES PLAYING
956
957 // Apply a move on board
958 static PlayOnBoard(board, move) {
959 for (let psq of move.vanish) board[psq.x][psq.y] = V.EMPTY;
960 for (let psq of move.appear) board[psq.x][psq.y] = psq.c + psq.p;
961 }
962 // Un-apply the played move
963 static UndoOnBoard(board, move) {
964 for (let psq of move.appear) board[psq.x][psq.y] = V.EMPTY;
965 for (let psq of move.vanish) board[psq.x][psq.y] = psq.c + psq.p;
966 }
967
968 // After move is played, update variables + flags
969 updateVariables(move) {
970 let piece = undefined;
971 let c = undefined;
972 if (move.vanish.length >= 1) {
973 // Usual case, something is moved
974 piece = move.vanish[0].p;
975 c = move.vanish[0].c;
976 } else {
977 // Crazyhouse-like variants
978 piece = move.appear[0].p;
979 c = move.appear[0].c;
980 }
981 if (c == "c") {
982 //if (!["w","b"].includes(c))
983 // 'c = move.vanish[0].c' doesn't work for Checkered
984 c = V.GetOppCol(this.turn);
985 }
986 const firstRank = c == "w" ? V.size.x - 1 : 0;
987
988 // Update king position + flags
989 if (piece == V.KING && move.appear.length > 0) {
990 this.kingPos[c][0] = move.appear[0].x;
991 this.kingPos[c][1] = move.appear[0].y;
992 if (V.HasFlags) this.castleFlags[c] = [false, false];
993 return;
994 }
995 if (V.HasFlags) {
996 // Update castling flags if rooks are moved
997 const oppCol = V.GetOppCol(c);
998 const oppFirstRank = V.size.x - 1 - firstRank;
999 if (
1000 move.start.x == firstRank && //our rook moves?
1001 this.INIT_COL_ROOK[c].includes(move.start.y)
1002 ) {
1003 const flagIdx = move.start.y == this.INIT_COL_ROOK[c][0] ? 0 : 1;
1004 this.castleFlags[c][flagIdx] = false;
1005 } else if (
1006 move.end.x == oppFirstRank && //we took opponent rook?
1007 this.INIT_COL_ROOK[oppCol].includes(move.end.y)
1008 ) {
1009 const flagIdx = move.end.y == this.INIT_COL_ROOK[oppCol][0] ? 0 : 1;
1010 this.castleFlags[oppCol][flagIdx] = false;
1011 }
1012 }
1013 }
1014
1015 // After move is undo-ed *and flags resetted*, un-update other variables
1016 // TODO: more symmetry, by storing flags increment in move (?!)
1017 unupdateVariables(move) {
1018 // (Potentially) Reset king position
1019 const c = this.getColor(move.start.x, move.start.y);
1020 if (this.getPiece(move.start.x, move.start.y) == V.KING)
1021 this.kingPos[c] = [move.start.x, move.start.y];
1022 }
1023
1024 play(move) {
1025 // DEBUG:
1026 // if (!this.states) this.states = [];
1027 // const stateFen = this.getBaseFen() + this.getTurnFen() + this.getFlagsFen();
1028 // this.states.push(stateFen);
1029
1030 if (V.HasFlags) move.flags = JSON.stringify(this.aggregateFlags()); //save flags (for undo)
1031 if (V.HasEnpassant) this.epSquares.push(this.getEpSquare(move));
1032 V.PlayOnBoard(this.board, move);
1033 this.turn = V.GetOppCol(this.turn);
1034 this.movesCount++;
1035 this.updateVariables(move);
1036 }
1037
1038 undo(move) {
1039 if (V.HasEnpassant) this.epSquares.pop();
1040 if (V.HasFlags) this.disaggregateFlags(JSON.parse(move.flags));
1041 V.UndoOnBoard(this.board, move);
1042 this.turn = V.GetOppCol(this.turn);
1043 this.movesCount--;
1044 this.unupdateVariables(move);
1045
1046 // DEBUG:
1047 // const stateFen = this.getBaseFen() + this.getTurnFen() + this.getFlagsFen();
1048 // if (stateFen != this.states[this.states.length-1]) debugger;
1049 // this.states.pop();
1050 }
1051
1052 ///////////////
1053 // END OF GAME
1054
1055 // What is the score ? (Interesting if game is over)
1056 getCurrentScore() {
1057 if (this.atLeastOneMove())
1058 return "*";
1059
1060 // Game over
1061 const color = this.turn;
1062 // No valid move: stalemate or checkmate?
1063 if (!this.isAttacked(this.kingPos[color], [V.GetOppCol(color)]))
1064 return "1/2";
1065 // OK, checkmate
1066 return color == "w" ? "0-1" : "1-0";
1067 }
1068
1069 ///////////////
1070 // ENGINE PLAY
1071
1072 // Pieces values
1073 static get VALUES() {
1074 return {
1075 p: 1,
1076 r: 5,
1077 n: 3,
1078 b: 3,
1079 q: 9,
1080 k: 1000
1081 };
1082 }
1083
1084 // "Checkmate" (unreachable eval)
1085 static get INFINITY() {
1086 return 9999;
1087 }
1088
1089 // At this value or above, the game is over
1090 static get THRESHOLD_MATE() {
1091 return V.INFINITY;
1092 }
1093
1094 // Search depth: 2 for high branching factor, 4 for small (Loser chess, eg.)
1095 static get SEARCH_DEPTH() {
1096 return 3;
1097 }
1098
1099 // NOTE: works also for extinction chess because depth is 3...
1100 getComputerMove() {
1101 const maxeval = V.INFINITY;
1102 const color = this.turn;
1103 // Some variants may show a bigger moves list to the human (Switching),
1104 // thus the argument "computer" below (which is generally ignored)
1105 let moves1 = this.getAllValidMoves("computer");
1106 if (moves1.length == 0)
1107 //TODO: this situation should not happen
1108 return null;
1109
1110 // Can I mate in 1 ? (for Magnetic & Extinction)
1111 for (let i of shuffle(ArrayFun.range(moves1.length))) {
1112 this.play(moves1[i]);
1113 let finish = Math.abs(this.evalPosition()) >= V.THRESHOLD_MATE;
1114 if (!finish) {
1115 const score = this.getCurrentScore();
1116 if (["1-0", "0-1"].includes(score)) finish = true;
1117 }
1118 this.undo(moves1[i]);
1119 if (finish) return moves1[i];
1120 }
1121
1122 // Rank moves using a min-max at depth 2
1123 for (let i = 0; i < moves1.length; i++) {
1124 // Initial self evaluation is very low: "I'm checkmated"
1125 moves1[i].eval = (color == "w" ? -1 : 1) * maxeval;
1126 this.play(moves1[i]);
1127 const score1 = this.getCurrentScore();
1128 let eval2 = undefined;
1129 if (score1 == "*") {
1130 // Initial enemy evaluation is very low too, for him
1131 eval2 = (color == "w" ? 1 : -1) * maxeval;
1132 // Second half-move:
1133 let moves2 = this.getAllValidMoves("computer");
1134 for (let j = 0; j < moves2.length; j++) {
1135 this.play(moves2[j]);
1136 const score2 = this.getCurrentScore();
1137 let evalPos = 0; //1/2 value
1138 switch (score2) {
1139 case "*":
1140 evalPos = this.evalPosition();
1141 break;
1142 case "1-0":
1143 evalPos = maxeval;
1144 break;
1145 case "0-1":
1146 evalPos = -maxeval;
1147 break;
1148 }
1149 if (
1150 (color == "w" && evalPos < eval2) ||
1151 (color == "b" && evalPos > eval2)
1152 ) {
1153 eval2 = evalPos;
1154 }
1155 this.undo(moves2[j]);
1156 }
1157 } else eval2 = score1 == "1/2" ? 0 : (score1 == "1-0" ? 1 : -1) * maxeval;
1158 if (
1159 (color == "w" && eval2 > moves1[i].eval) ||
1160 (color == "b" && eval2 < moves1[i].eval)
1161 ) {
1162 moves1[i].eval = eval2;
1163 }
1164 this.undo(moves1[i]);
1165 }
1166 moves1.sort((a, b) => {
1167 return (color == "w" ? 1 : -1) * (b.eval - a.eval);
1168 });
1169
1170 let candidates = [0]; //indices of candidates moves
1171 for (let j = 1; j < moves1.length && moves1[j].eval == moves1[0].eval; j++)
1172 candidates.push(j);
1173 let currentBest = moves1[candidates[randInt(candidates.length)]];
1174
1175 // Skip depth 3+ if we found a checkmate (or if we are checkmated in 1...)
1176 if (V.SEARCH_DEPTH >= 3 && Math.abs(moves1[0].eval) < V.THRESHOLD_MATE) {
1177 // From here, depth >= 3: may take a while, so we control time
1178 const timeStart = Date.now();
1179 for (let i = 0; i < moves1.length; i++) {
1180 if (Date.now() - timeStart >= 5000)
1181 //more than 5 seconds
1182 return currentBest; //depth 2 at least
1183 this.play(moves1[i]);
1184 // 0.1 * oldEval : heuristic to avoid some bad moves (not all...)
1185 moves1[i].eval =
1186 0.1 * moves1[i].eval +
1187 this.alphabeta(V.SEARCH_DEPTH - 1, -maxeval, maxeval);
1188 this.undo(moves1[i]);
1189 }
1190 moves1.sort((a, b) => {
1191 return (color == "w" ? 1 : -1) * (b.eval - a.eval);
1192 });
1193 } else return currentBest;
1194 // console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
1195
1196 candidates = [0];
1197 for (let j = 1; j < moves1.length && moves1[j].eval == moves1[0].eval; j++)
1198 candidates.push(j);
1199 return moves1[candidates[randInt(candidates.length)]];
1200 }
1201
1202 alphabeta(depth, alpha, beta) {
1203 const maxeval = V.INFINITY;
1204 const color = this.turn;
1205 const score = this.getCurrentScore();
1206 if (score != "*")
1207 return score == "1/2" ? 0 : (score == "1-0" ? 1 : -1) * maxeval;
1208 if (depth == 0) return this.evalPosition();
1209 const moves = this.getAllValidMoves("computer");
1210 let v = color == "w" ? -maxeval : maxeval;
1211 if (color == "w") {
1212 for (let i = 0; i < moves.length; i++) {
1213 this.play(moves[i]);
1214 v = Math.max(v, this.alphabeta(depth - 1, alpha, beta));
1215 this.undo(moves[i]);
1216 alpha = Math.max(alpha, v);
1217 if (alpha >= beta) break; //beta cutoff
1218 }
1219 } //color=="b"
1220 else {
1221 for (let i = 0; i < moves.length; i++) {
1222 this.play(moves[i]);
1223 v = Math.min(v, this.alphabeta(depth - 1, alpha, beta));
1224 this.undo(moves[i]);
1225 beta = Math.min(beta, v);
1226 if (alpha >= beta) break; //alpha cutoff
1227 }
1228 }
1229 return v;
1230 }
1231
1232 evalPosition() {
1233 let evaluation = 0;
1234 // Just count material for now
1235 for (let i = 0; i < V.size.x; i++) {
1236 for (let j = 0; j < V.size.y; j++) {
1237 if (this.board[i][j] != V.EMPTY) {
1238 const sign = this.getColor(i, j) == "w" ? 1 : -1;
1239 evaluation += sign * V.VALUES[this.getPiece(i, j)];
1240 }
1241 }
1242 }
1243 return evaluation;
1244 }
1245
1246 /////////////////////////
1247 // MOVES + GAME NOTATION
1248 /////////////////////////
1249
1250 // Context: just before move is played, turn hasn't changed
1251 // TODO: un-ambiguous notation (switch on piece type, check directions...)
1252 getNotation(move) {
1253 if (move.appear.length == 2 && move.appear[0].p == V.KING)
1254 //castle
1255 return move.end.y < move.start.y ? "0-0-0" : "0-0";
1256
1257 // Translate final square
1258 const finalSquare = V.CoordsToSquare(move.end);
1259
1260 const piece = this.getPiece(move.start.x, move.start.y);
1261 if (piece == V.PAWN) {
1262 // Pawn move
1263 let notation = "";
1264 if (move.vanish.length > move.appear.length) {
1265 // Capture
1266 const startColumn = V.CoordToColumn(move.start.y);
1267 notation = startColumn + "x" + finalSquare;
1268 } //no capture
1269 else notation = finalSquare;
1270 if (move.appear.length > 0 && move.appear[0].p != V.PAWN)
1271 //promotion
1272 notation += "=" + move.appear[0].p.toUpperCase();
1273 return notation;
1274 }
1275 // Piece movement
1276 return (
1277 piece.toUpperCase() +
1278 (move.vanish.length > move.appear.length ? "x" : "") +
1279 finalSquare
1280 );
1281 }
1282 };