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[vchess.git] / public / javascripts / base_rules.js
1 // (Orthodox) Chess rules are defined in ChessRules class.
2 // Variants generally inherit from it, and modify some parts.
3
4 class PiPo //Piece+Position
5 {
6 // o: {piece[p], color[c], posX[x], posY[y]}
7 constructor(o)
8 {
9 this.p = o.p;
10 this.c = o.c;
11 this.x = o.x;
12 this.y = o.y;
13 }
14 }
15
16 // TODO: for animation, moves should contains "moving" and "fading" maybe...
17 class Move
18 {
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 {
24 this.appear = o.appear;
25 this.vanish = o.vanish;
26 this.start = !!o.start ? o.start : {x:o.vanish[0].x, y:o.vanish[0].y};
27 this.end = !!o.end ? o.end : {x:o.appear[0].x, y:o.appear[0].y};
28 }
29 }
30
31 // NOTE: x coords = top to bottom; y = left to right (from white player perspective)
32 class ChessRules
33 {
34 // Path to pieces
35 static getPpath(b)
36 {
37 return b; //usual pieces in pieces/ folder
38 }
39 // Turn "wb" into "B" (for FEN)
40 static board2fen(b)
41 {
42 return b[0]=='w' ? b[1].toUpperCase() : b[1];
43 }
44 // Turn "p" into "bp" (for board)
45 static fen2board(f)
46 {
47 return f.charCodeAt()<=90 ? "w"+f.toLowerCase() : "b"+f;
48 }
49
50 /////////////////
51 // INITIALIZATION
52
53 // fen == "position flags"
54 constructor(fen, moves)
55 {
56 this.moves = moves;
57 // Use fen string to initialize variables, flags and board
58 this.board = VariantRules.GetBoard(fen);
59 this.setFlags(fen);
60 this.initVariables(fen);
61 }
62
63 initVariables(fen)
64 {
65 this.INIT_COL_KING = {'w':-1, 'b':-1};
66 this.INIT_COL_ROOK = {'w':[-1,-1], 'b':[-1,-1]};
67 this.kingPos = {'w':[-1,-1], 'b':[-1,-1]}; //squares of white and black king
68 const fenParts = fen.split(" ");
69 const position = fenParts[0].split("/");
70 for (let i=0; i<position.length; i++)
71 {
72 let k = 0; //column index on board
73 for (let j=0; j<position[i].length; j++)
74 {
75 switch (position[i].charAt(j))
76 {
77 case 'k':
78 this.kingPos['b'] = [i,k];
79 this.INIT_COL_KING['b'] = k;
80 break;
81 case 'K':
82 this.kingPos['w'] = [i,k];
83 this.INIT_COL_KING['w'] = k;
84 break;
85 case 'r':
86 if (this.INIT_COL_ROOK['b'][0] < 0)
87 this.INIT_COL_ROOK['b'][0] = k;
88 else
89 this.INIT_COL_ROOK['b'][1] = k;
90 break;
91 case 'R':
92 if (this.INIT_COL_ROOK['w'][0] < 0)
93 this.INIT_COL_ROOK['w'][0] = k;
94 else
95 this.INIT_COL_ROOK['w'][1] = k;
96 break;
97 default:
98 let num = parseInt(position[i].charAt(j));
99 if (!isNaN(num))
100 k += (num-1);
101 }
102 k++;
103 }
104 }
105 const epSq = this.moves.length > 0 ? this.getEpSquare(this.lastMove) : undefined;
106 this.epSquares = [ epSq ];
107 }
108
109 // Turn diagram fen into double array ["wb","wp","bk",...]
110 static GetBoard(fen)
111 {
112 let rows = fen.split(" ")[0].split("/");
113 const [sizeX,sizeY] = VariantRules.size;
114 let board = doubleArray(sizeX, sizeY, "");
115 for (let i=0; i<rows.length; i++)
116 {
117 let j = 0;
118 for (let indexInRow = 0; indexInRow < rows[i].length; indexInRow++)
119 {
120 let character = rows[i][indexInRow];
121 let num = parseInt(character);
122 if (!isNaN(num))
123 j += num; //just shift j
124 else //something at position i,j
125 board[i][j++] = VariantRules.fen2board(character);
126 }
127 }
128 return board;
129 }
130
131 // Extract (relevant) flags from fen
132 setFlags(fen)
133 {
134 // white a-castle, h-castle, black a-castle, h-castle
135 this.castleFlags = {'w': new Array(2), 'b': new Array(2)};
136 let flags = fen.split(" ")[1]; //flags right after position
137 for (let i=0; i<4; i++)
138 this.castleFlags[i < 2 ? 'w' : 'b'][i%2] = (flags.charAt(i) == '1');
139 }
140
141 ///////////////////
142 // GETTERS, SETTERS
143
144 static get size() { return [8,8]; }
145 // Two next functions return 'undefined' if called on empty square
146 getColor(i,j) { return this.board[i][j].charAt(0); }
147 getPiece(i,j) { return this.board[i][j].charAt(1); }
148
149 // Color
150 getOppCol(color) { return color=="w" ? "b" : "w"; }
151
152 get lastMove() {
153 const L = this.moves.length;
154 return L>0 ? this.moves[L-1] : null;
155 }
156 get turn() {
157 return this.moves.length%2==0 ? 'w' : 'b';
158 }
159
160 // Pieces codes
161 static get PAWN() { return 'p'; }
162 static get ROOK() { return 'r'; }
163 static get KNIGHT() { return 'n'; }
164 static get BISHOP() { return 'b'; }
165 static get QUEEN() { return 'q'; }
166 static get KING() { return 'k'; }
167
168 // Empty square
169 static get EMPTY() { return ''; }
170
171 // Some pieces movements
172 static get steps() {
173 return {
174 'r': [ [-1,0],[1,0],[0,-1],[0,1] ],
175 'n': [ [-1,-2],[-1,2],[1,-2],[1,2],[-2,-1],[-2,1],[2,-1],[2,1] ],
176 'b': [ [-1,-1],[-1,1],[1,-1],[1,1] ],
177 };
178 }
179
180 // Aggregates flags into one object
181 get flags() {
182 return this.castleFlags;
183 }
184
185 // Reverse operation
186 parseFlags(flags)
187 {
188 this.castleFlags = flags;
189 }
190
191 // En-passant square, if any
192 getEpSquare(move)
193 {
194 const [sx,sy,ex] = [move.start.x,move.start.y,move.end.x];
195 if (this.getPiece(sx,sy) == VariantRules.PAWN && Math.abs(sx - ex) == 2)
196 {
197 return {
198 x: (sx + ex)/2,
199 y: sy
200 };
201 }
202 return undefined; //default
203 }
204
205 // Can thing on square1 take thing on square2
206 canTake([x1,y1], [x2,y2])
207 {
208 return this.getColor(x1,y1) != this.getColor(x2,y2);
209 }
210
211 ///////////////////
212 // MOVES GENERATION
213
214 // All possible moves from selected square (assumption: color is OK)
215 getPotentialMovesFrom([x,y])
216 {
217 switch (this.getPiece(x,y))
218 {
219 case VariantRules.PAWN:
220 return this.getPotentialPawnMoves([x,y]);
221 case VariantRules.ROOK:
222 return this.getPotentialRookMoves([x,y]);
223 case VariantRules.KNIGHT:
224 return this.getPotentialKnightMoves([x,y]);
225 case VariantRules.BISHOP:
226 return this.getPotentialBishopMoves([x,y]);
227 case VariantRules.QUEEN:
228 return this.getPotentialQueenMoves([x,y]);
229 case VariantRules.KING:
230 return this.getPotentialKingMoves([x,y]);
231 }
232 }
233
234 // Build a regular move from its initial and destination squares; tr: transformation
235 getBasicMove([sx,sy], [ex,ey], tr)
236 {
237 let mv = new Move({
238 appear: [
239 new PiPo({
240 x: ex,
241 y: ey,
242 c: !!tr ? tr.c : this.getColor(sx,sy),
243 p: !!tr ? tr.p : this.getPiece(sx,sy)
244 })
245 ],
246 vanish: [
247 new PiPo({
248 x: sx,
249 y: sy,
250 c: this.getColor(sx,sy),
251 p: this.getPiece(sx,sy)
252 })
253 ]
254 });
255
256 // The opponent piece disappears if we take it
257 if (this.board[ex][ey] != VariantRules.EMPTY)
258 {
259 mv.vanish.push(
260 new PiPo({
261 x: ex,
262 y: ey,
263 c: this.getColor(ex,ey),
264 p: this.getPiece(ex,ey)
265 })
266 );
267 }
268 return mv;
269 }
270
271 // Generic method to find possible moves of non-pawn pieces ("sliding or jumping")
272 getSlideNJumpMoves([x,y], steps, oneStep)
273 {
274 const color = this.getColor(x,y);
275 let moves = [];
276 const [sizeX,sizeY] = VariantRules.size;
277 outerLoop:
278 for (let step of steps)
279 {
280 let i = x + step[0];
281 let j = y + step[1];
282 while (i>=0 && i<sizeX && j>=0 && j<sizeY
283 && this.board[i][j] == VariantRules.EMPTY)
284 {
285 moves.push(this.getBasicMove([x,y], [i,j]));
286 if (oneStep !== undefined)
287 continue outerLoop;
288 i += step[0];
289 j += step[1];
290 }
291 if (i>=0 && i<sizeX && j>=0 && j<sizeY && this.canTake([x,y], [i,j]))
292 moves.push(this.getBasicMove([x,y], [i,j]));
293 }
294 return moves;
295 }
296
297 // What are the pawn moves from square x,y ?
298 getPotentialPawnMoves([x,y])
299 {
300 const color = this.turn;
301 let moves = [];
302 const V = VariantRules;
303 const [sizeX,sizeY] = V.size;
304 const shift = (color == "w" ? -1 : 1);
305 const firstRank = (color == 'w' ? sizeX-1 : 0);
306 const startRank = (color == "w" ? sizeX-2 : 1);
307 const lastRank = (color == "w" ? 0 : sizeX-1);
308
309 if (x+shift >= 0 && x+shift < sizeX && x+shift != lastRank)
310 {
311 // Normal moves
312 if (this.board[x+shift][y] == V.EMPTY)
313 {
314 moves.push(this.getBasicMove([x,y], [x+shift,y]));
315 // Next condition because variants with pawns on 1st rank allow them to jump
316 if ([startRank,firstRank].includes(x) && this.board[x+2*shift][y] == V.EMPTY)
317 {
318 // Two squares jump
319 moves.push(this.getBasicMove([x,y], [x+2*shift,y]));
320 }
321 }
322 // Captures
323 if (y>0 && this.canTake([x,y], [x+shift,y-1])
324 && this.board[x+shift][y-1] != V.EMPTY)
325 {
326 moves.push(this.getBasicMove([x,y], [x+shift,y-1]));
327 }
328 if (y<sizeY-1 && this.canTake([x,y], [x+shift,y+1])
329 && this.board[x+shift][y+1] != V.EMPTY)
330 {
331 moves.push(this.getBasicMove([x,y], [x+shift,y+1]));
332 }
333 }
334
335 if (x+shift == lastRank)
336 {
337 // Promotion
338 const pawnColor = this.getColor(x,y); //can be different for checkered
339 let promotionPieces = [V.ROOK,V.KNIGHT,V.BISHOP,V.QUEEN];
340 promotionPieces.forEach(p => {
341 // Normal move
342 if (this.board[x+shift][y] == V.EMPTY)
343 moves.push(this.getBasicMove([x,y], [x+shift,y], {c:pawnColor,p:p}));
344 // Captures
345 if (y>0 && this.canTake([x,y], [x+shift,y-1])
346 && this.board[x+shift][y-1] != V.EMPTY)
347 {
348 moves.push(this.getBasicMove([x,y], [x+shift,y-1], {c:pawnColor,p:p}));
349 }
350 if (y<sizeY-1 && this.canTake([x,y], [x+shift,y+1])
351 && this.board[x+shift][y+1] != V.EMPTY)
352 {
353 moves.push(this.getBasicMove([x,y], [x+shift,y+1], {c:pawnColor,p:p}));
354 }
355 });
356 }
357
358 // En passant
359 const Lep = this.epSquares.length;
360 const epSquare = Lep>0 ? this.epSquares[Lep-1] : undefined;
361 if (!!epSquare && epSquare.x == x+shift && Math.abs(epSquare.y - y) == 1)
362 {
363 let epStep = epSquare.y - y;
364 var enpassantMove = this.getBasicMove([x,y], [x+shift,y+epStep]);
365 enpassantMove.vanish.push({
366 x: x,
367 y: y+epStep,
368 p: 'p',
369 c: this.getColor(x,y+epStep)
370 });
371 moves.push(enpassantMove);
372 }
373
374 return moves;
375 }
376
377 // What are the rook moves from square x,y ?
378 getPotentialRookMoves(sq)
379 {
380 return this.getSlideNJumpMoves(sq, VariantRules.steps[VariantRules.ROOK]);
381 }
382
383 // What are the knight moves from square x,y ?
384 getPotentialKnightMoves(sq)
385 {
386 return this.getSlideNJumpMoves(
387 sq, VariantRules.steps[VariantRules.KNIGHT], "oneStep");
388 }
389
390 // What are the bishop moves from square x,y ?
391 getPotentialBishopMoves(sq)
392 {
393 return this.getSlideNJumpMoves(sq, VariantRules.steps[VariantRules.BISHOP]);
394 }
395
396 // What are the queen moves from square x,y ?
397 getPotentialQueenMoves(sq)
398 {
399 const V = VariantRules;
400 return this.getSlideNJumpMoves(sq, V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
401 }
402
403 // What are the king moves from square x,y ?
404 getPotentialKingMoves(sq)
405 {
406 const V = VariantRules;
407 // Initialize with normal moves
408 let moves = this.getSlideNJumpMoves(sq,
409 V.steps[V.ROOK].concat(V.steps[V.BISHOP]), "oneStep");
410 return moves.concat(this.getCastleMoves(sq));
411 }
412
413 getCastleMoves([x,y])
414 {
415 const c = this.getColor(x,y);
416 const [sizeX,sizeY] = VariantRules.size;
417 if (x != (c=="w" ? sizeX-1 : 0) || y != this.INIT_COL_KING[c])
418 return []; //x isn't first rank, or king has moved (shortcut)
419
420 const V = VariantRules;
421
422 // Castling ?
423 const oppCol = this.getOppCol(c);
424 let moves = [];
425 let i = 0;
426 const finalSquares = [ [2,3], [sizeY-2,sizeY-3] ]; //king, then rook
427 castlingCheck:
428 for (let castleSide=0; castleSide < 2; castleSide++) //large, then small
429 {
430 if (!this.castleFlags[c][castleSide])
431 continue;
432 // If this code is reached, rooks and king are on initial position
433
434 // Nothing on the path of the king (and no checks; OK also if y==finalSquare)?
435 let step = finalSquares[castleSide][0] < y ? -1 : 1;
436 for (i=y; i!=finalSquares[castleSide][0]; i+=step)
437 {
438 if (this.isAttacked([x,i], [oppCol]) || (this.board[x][i] != V.EMPTY &&
439 // NOTE: next check is enough, because of chessboard constraints
440 (this.getColor(x,i) != c || ![V.KING,V.ROOK].includes(this.getPiece(x,i)))))
441 {
442 continue castlingCheck;
443 }
444 }
445
446 // Nothing on the path to the rook?
447 step = castleSide == 0 ? -1 : 1;
448 for (i = y + step; i != this.INIT_COL_ROOK[c][castleSide]; i += step)
449 {
450 if (this.board[x][i] != V.EMPTY)
451 continue castlingCheck;
452 }
453 const rookPos = this.INIT_COL_ROOK[c][castleSide];
454
455 // Nothing on final squares, except maybe king and castling rook?
456 for (i=0; i<2; i++)
457 {
458 if (this.board[x][finalSquares[castleSide][i]] != V.EMPTY &&
459 this.getPiece(x,finalSquares[castleSide][i]) != V.KING &&
460 finalSquares[castleSide][i] != rookPos)
461 {
462 continue castlingCheck;
463 }
464 }
465
466 // If this code is reached, castle is valid
467 moves.push( new Move({
468 appear: [
469 new PiPo({x:x,y:finalSquares[castleSide][0],p:V.KING,c:c}),
470 new PiPo({x:x,y:finalSquares[castleSide][1],p:V.ROOK,c:c})],
471 vanish: [
472 new PiPo({x:x,y:y,p:V.KING,c:c}),
473 new PiPo({x:x,y:rookPos,p:V.ROOK,c:c})],
474 end: Math.abs(y - rookPos) <= 2
475 ? {x:x, y:rookPos}
476 : {x:x, y:y + 2 * (castleSide==0 ? -1 : 1)}
477 }) );
478 }
479
480 return moves;
481 }
482
483 ///////////////////
484 // MOVES VALIDATION
485
486 canIplay(side, [x,y])
487 {
488 return ((side=='w' && this.moves.length%2==0)
489 || (side=='b' && this.moves.length%2==1))
490 && this.getColor(x,y) == side;
491 }
492
493 getPossibleMovesFrom(sq)
494 {
495 // Assuming color is right (already checked)
496 return this.filterValid( this.getPotentialMovesFrom(sq) );
497 }
498
499 // TODO: promotions (into R,B,N,Q) should be filtered only once
500 filterValid(moves)
501 {
502 if (moves.length == 0)
503 return [];
504 return moves.filter(m => { return !this.underCheck(m); });
505 }
506
507 // Search for all valid moves considering current turn (for engine and game end)
508 getAllValidMoves()
509 {
510 const color = this.turn;
511 const oppCol = this.getOppCol(color);
512 let potentialMoves = [];
513 const [sizeX,sizeY] = VariantRules.size;
514 for (let i=0; i<sizeX; i++)
515 {
516 for (let j=0; j<sizeY; j++)
517 {
518 // Next condition "!= oppCol" = harmless hack to work with checkered variant
519 if (this.board[i][j] != VariantRules.EMPTY && this.getColor(i,j) != oppCol)
520 Array.prototype.push.apply(potentialMoves, this.getPotentialMovesFrom([i,j]));
521 }
522 }
523 // NOTE: prefer lazy undercheck tests, letting the king being taken?
524 // No: if happen on last 1/2 move, could lead to forbidden moves, wrong evals
525 return this.filterValid(potentialMoves);
526 }
527
528 // Stop at the first move found
529 atLeastOneMove()
530 {
531 const color = this.turn;
532 const oppCol = this.getOppCol(color);
533 const [sizeX,sizeY] = VariantRules.size;
534 for (let i=0; i<sizeX; i++)
535 {
536 for (let j=0; j<sizeY; j++)
537 {
538 if (this.board[i][j] != VariantRules.EMPTY && this.getColor(i,j) != oppCol)
539 {
540 const moves = this.getPotentialMovesFrom([i,j]);
541 if (moves.length > 0)
542 {
543 for (let k=0; k<moves.length; k++)
544 {
545 if (this.filterValid([moves[k]]).length > 0)
546 return true;
547 }
548 }
549 }
550 }
551 }
552 return false;
553 }
554
555 // Check if pieces of color in array 'colors' are attacking square x,y
556 isAttacked(sq, colors)
557 {
558 return (this.isAttackedByPawn(sq, colors)
559 || this.isAttackedByRook(sq, colors)
560 || this.isAttackedByKnight(sq, colors)
561 || this.isAttackedByBishop(sq, colors)
562 || this.isAttackedByQueen(sq, colors)
563 || this.isAttackedByKing(sq, colors));
564 }
565
566 // Is square x,y attacked by 'colors' pawns ?
567 isAttackedByPawn([x,y], colors)
568 {
569 const [sizeX,sizeY] = VariantRules.size;
570 for (let c of colors)
571 {
572 let pawnShift = (c=="w" ? 1 : -1);
573 if (x+pawnShift>=0 && x+pawnShift<sizeX)
574 {
575 for (let i of [-1,1])
576 {
577 if (y+i>=0 && y+i<sizeY && this.getPiece(x+pawnShift,y+i)==VariantRules.PAWN
578 && this.getColor(x+pawnShift,y+i)==c)
579 {
580 return true;
581 }
582 }
583 }
584 }
585 return false;
586 }
587
588 // Is square x,y attacked by 'colors' rooks ?
589 isAttackedByRook(sq, colors)
590 {
591 return this.isAttackedBySlideNJump(sq, colors,
592 VariantRules.ROOK, VariantRules.steps[VariantRules.ROOK]);
593 }
594
595 // Is square x,y attacked by 'colors' knights ?
596 isAttackedByKnight(sq, colors)
597 {
598 return this.isAttackedBySlideNJump(sq, colors,
599 VariantRules.KNIGHT, VariantRules.steps[VariantRules.KNIGHT], "oneStep");
600 }
601
602 // Is square x,y attacked by 'colors' bishops ?
603 isAttackedByBishop(sq, colors)
604 {
605 return this.isAttackedBySlideNJump(sq, colors,
606 VariantRules.BISHOP, VariantRules.steps[VariantRules.BISHOP]);
607 }
608
609 // Is square x,y attacked by 'colors' queens ?
610 isAttackedByQueen(sq, colors)
611 {
612 const V = VariantRules;
613 return this.isAttackedBySlideNJump(sq, colors, V.QUEEN,
614 V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
615 }
616
617 // Is square x,y attacked by 'colors' king(s) ?
618 isAttackedByKing(sq, colors)
619 {
620 const V = VariantRules;
621 return this.isAttackedBySlideNJump(sq, colors, V.KING,
622 V.steps[V.ROOK].concat(V.steps[V.BISHOP]), "oneStep");
623 }
624
625 // Generic method for non-pawn pieces ("sliding or jumping"):
626 // is x,y attacked by a piece of color in array 'colors' ?
627 isAttackedBySlideNJump([x,y], colors, piece, steps, oneStep)
628 {
629 const [sizeX,sizeY] = VariantRules.size;
630 for (let step of steps)
631 {
632 let rx = x+step[0], ry = y+step[1];
633 while (rx>=0 && rx<sizeX && ry>=0 && ry<sizeY
634 && this.board[rx][ry] == VariantRules.EMPTY && !oneStep)
635 {
636 rx += step[0];
637 ry += step[1];
638 }
639 if (rx>=0 && rx<sizeX && ry>=0 && ry<sizeY
640 && this.board[rx][ry] != VariantRules.EMPTY
641 && this.getPiece(rx,ry) == piece && colors.includes(this.getColor(rx,ry)))
642 {
643 return true;
644 }
645 }
646 return false;
647 }
648
649 // Is current player under check after his move ?
650 underCheck(move)
651 {
652 const color = this.turn;
653 this.play(move);
654 let res = this.isAttacked(this.kingPos[color], [this.getOppCol(color)]);
655 this.undo(move);
656 return res;
657 }
658
659 // On which squares is opponent under check after our move ?
660 getCheckSquares(move)
661 {
662 this.play(move);
663 const color = this.turn; //opponent
664 let res = this.isAttacked(this.kingPos[color], [this.getOppCol(color)])
665 ? [ JSON.parse(JSON.stringify(this.kingPos[color])) ] //need to duplicate!
666 : [ ];
667 this.undo(move);
668 return res;
669 }
670
671 // Apply a move on board
672 static PlayOnBoard(board, move)
673 {
674 for (let psq of move.vanish)
675 board[psq.x][psq.y] = VariantRules.EMPTY;
676 for (let psq of move.appear)
677 board[psq.x][psq.y] = psq.c + psq.p;
678 }
679 // Un-apply the played move
680 static UndoOnBoard(board, move)
681 {
682 for (let psq of move.appear)
683 board[psq.x][psq.y] = VariantRules.EMPTY;
684 for (let psq of move.vanish)
685 board[psq.x][psq.y] = psq.c + psq.p;
686 }
687
688 // Before move is played, update variables + flags
689 updateVariables(move)
690 {
691 const piece = this.getPiece(move.start.x,move.start.y);
692 const c = this.getColor(move.start.x,move.start.y);
693 const [sizeX,sizeY] = VariantRules.size;
694 const firstRank = (c == "w" ? sizeX-1 : 0);
695
696 // Update king position + flags
697 if (piece == VariantRules.KING && move.appear.length > 0)
698 {
699 this.kingPos[c][0] = move.appear[0].x;
700 this.kingPos[c][1] = move.appear[0].y;
701 this.castleFlags[c] = [false,false];
702 return;
703 }
704 const oppCol = this.getOppCol(c);
705 const oppFirstRank = (sizeX-1) - firstRank;
706 if (move.start.x == firstRank //our rook moves?
707 && this.INIT_COL_ROOK[c].includes(move.start.y))
708 {
709 const flagIdx = (move.start.y == this.INIT_COL_ROOK[c][0] ? 0 : 1);
710 this.castleFlags[c][flagIdx] = false;
711 }
712 else if (move.end.x == oppFirstRank //we took opponent rook?
713 && this.INIT_COL_ROOK[oppCol].includes(move.end.y))
714 {
715 const flagIdx = (move.end.y == this.INIT_COL_ROOK[oppCol][0] ? 0 : 1);
716 this.castleFlags[oppCol][flagIdx] = false;
717 }
718 }
719
720 // After move is undo-ed, un-update variables (flags are reset)
721 // TODO: more symmetry, by storing flags increment in move...
722 unupdateVariables(move)
723 {
724 // (Potentially) Reset king position
725 const c = this.getColor(move.start.x,move.start.y);
726 if (this.getPiece(move.start.x,move.start.y) == VariantRules.KING)
727 this.kingPos[c] = [move.start.x, move.start.y];
728 }
729
730 play(move, ingame)
731 {
732 if (!!ingame)
733 move.notation = [this.getNotation(move), this.getLongNotation(move)];
734
735 move.flags = JSON.stringify(this.flags); //save flags (for undo)
736 this.updateVariables(move);
737 this.moves.push(move);
738 this.epSquares.push( this.getEpSquare(move) );
739 VariantRules.PlayOnBoard(this.board, move);
740 }
741
742 undo(move)
743 {
744 VariantRules.UndoOnBoard(this.board, move);
745 this.epSquares.pop();
746 this.moves.pop();
747 this.unupdateVariables(move);
748 this.parseFlags(JSON.parse(move.flags));
749 }
750
751 //////////////
752 // END OF GAME
753
754 // Basic check for 3 repetitions (in the last moves only)
755 checkRepetition()
756 {
757 if (this.moves.length >= 8)
758 {
759 const L = this.moves.length;
760 if (_.isEqual(this.moves[L-1], this.moves[L-5]) &&
761 _.isEqual(this.moves[L-2], this.moves[L-6]) &&
762 _.isEqual(this.moves[L-3], this.moves[L-7]) &&
763 _.isEqual(this.moves[L-4], this.moves[L-8]))
764 {
765 return true;
766 }
767 }
768 return false;
769 }
770
771 // Is game over ? And if yes, what is the score ?
772 checkGameOver()
773 {
774 if (this.checkRepetition())
775 return "1/2";
776
777 if (this.atLeastOneMove()) // game not over
778 return "*";
779
780 // Game over
781 return this.checkGameEnd();
782 }
783
784 // No moves are possible: compute score
785 checkGameEnd()
786 {
787 const color = this.turn;
788 // No valid move: stalemate or checkmate?
789 if (!this.isAttacked(this.kingPos[color], [this.getOppCol(color)]))
790 return "1/2";
791 // OK, checkmate
792 return color == "w" ? "0-1" : "1-0";
793 }
794
795 ////////
796 //ENGINE
797
798 // Pieces values
799 static get VALUES() {
800 return {
801 'p': 1,
802 'r': 5,
803 'n': 3,
804 'b': 3,
805 'q': 9,
806 'k': 1000
807 };
808 }
809
810 static get INFINITY() {
811 return 9999; //"checkmate" (unreachable eval)
812 }
813
814 static get THRESHOLD_MATE() {
815 // At this value or above, the game is over
816 return VariantRules.INFINITY;
817 }
818
819 static get SEARCH_DEPTH() {
820 return 3; //2 for high branching factor, 4 for small (Loser chess)
821 }
822
823 // Assumption: at least one legal move
824 // NOTE: works also for extinction chess because depth is 3...
825 getComputerMove()
826 {
827 this.shouldReturn = false;
828 const maxeval = VariantRules.INFINITY;
829 const color = this.turn;
830 // Some variants may show a bigger moves list to the human (Switching),
831 // thus the argument "computer" below (which is generally ignored)
832 let moves1 = this.getAllValidMoves("computer");
833
834 // Can I mate in 1 ? (for Magnetic & Extinction)
835 for (let i of _.shuffle(_.range(moves1.length)))
836 {
837 this.play(moves1[i]);
838 const finish = (Math.abs(this.evalPosition()) >= VariantRules.THRESHOLD_MATE);
839 this.undo(moves1[i]);
840 if (finish)
841 return moves1[i];
842 }
843
844 // Rank moves using a min-max at depth 2
845 for (let i=0; i<moves1.length; i++)
846 {
847 moves1[i].eval = (color=="w" ? -1 : 1) * maxeval; //very low, I'm checkmated
848 this.play(moves1[i]);
849 let eval2 = undefined;
850 if (this.atLeastOneMove())
851 {
852 eval2 = (color=="w" ? 1 : -1) * maxeval; //initialized with checkmate value
853 // Second half-move:
854 let moves2 = this.getAllValidMoves("computer");
855 for (let j=0; j<moves2.length; j++)
856 {
857 this.play(moves2[j]);
858 let evalPos = undefined;
859 if (this.atLeastOneMove())
860 evalPos = this.evalPosition()
861 else
862 {
863 // Work with scores for Loser variant
864 const score = this.checkGameEnd();
865 evalPos = (score=="1/2" ? 0 : (score=="1-0" ? 1 : -1) * maxeval);
866 }
867 if ((color == "w" && evalPos < eval2) || (color=="b" && evalPos > eval2))
868 eval2 = evalPos;
869 this.undo(moves2[j]);
870 }
871 }
872 else
873 {
874 const score = this.checkGameEnd();
875 eval2 = (score=="1/2" ? 0 : (score=="1-0" ? 1 : -1) * maxeval);
876 }
877 if ((color=="w" && eval2 > moves1[i].eval)
878 || (color=="b" && eval2 < moves1[i].eval))
879 {
880 moves1[i].eval = eval2;
881 }
882 this.undo(moves1[i]);
883 }
884 moves1.sort( (a,b) => { return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
885 //console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
886
887 let candidates = [0]; //indices of candidates moves
888 for (let j=1; j<moves1.length && moves1[j].eval == moves1[0].eval; j++)
889 candidates.push(j);
890 let currentBest = moves1[_.sample(candidates, 1)];
891
892 // Skip depth 3+ if we found a checkmate (or if we are checkmated in 1...)
893 if (VariantRules.SEARCH_DEPTH >= 3
894 && Math.abs(moves1[0].eval) < VariantRules.THRESHOLD_MATE)
895 {
896 for (let i=0; i<moves1.length; i++)
897 {
898 if (this.shouldReturn)
899 return currentBest; //depth-2, minimum
900 this.play(moves1[i]);
901 // 0.1 * oldEval : heuristic to avoid some bad moves (not all...)
902 moves1[i].eval = 0.1*moves1[i].eval +
903 this.alphabeta(VariantRules.SEARCH_DEPTH-1, -maxeval, maxeval);
904 this.undo(moves1[i]);
905 }
906 moves1.sort( (a,b) => { return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
907 }
908 else
909 return currentBest;
910 //console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
911
912 candidates = [0];
913 for (let j=1; j<moves1.length && moves1[j].eval == moves1[0].eval; j++)
914 candidates.push(j);
915 return moves1[_.sample(candidates, 1)];
916 }
917
918 alphabeta(depth, alpha, beta)
919 {
920 const maxeval = VariantRules.INFINITY;
921 const color = this.turn;
922 if (!this.atLeastOneMove())
923 {
924 switch (this.checkGameEnd())
925 {
926 case "1/2":
927 return 0;
928 default:
929 const score = this.checkGameEnd();
930 return (score=="1/2" ? 0 : (score=="1-0" ? 1 : -1) * maxeval);
931 }
932 }
933 if (depth == 0)
934 return this.evalPosition();
935 const moves = this.getAllValidMoves("computer");
936 let v = color=="w" ? -maxeval : maxeval;
937 if (color == "w")
938 {
939 for (let i=0; i<moves.length; i++)
940 {
941 this.play(moves[i]);
942 v = Math.max(v, this.alphabeta(depth-1, alpha, beta));
943 this.undo(moves[i]);
944 alpha = Math.max(alpha, v);
945 if (alpha >= beta)
946 break; //beta cutoff
947 }
948 }
949 else //color=="b"
950 {
951 for (let i=0; i<moves.length; i++)
952 {
953 this.play(moves[i]);
954 v = Math.min(v, this.alphabeta(depth-1, alpha, beta));
955 this.undo(moves[i]);
956 beta = Math.min(beta, v);
957 if (alpha >= beta)
958 break; //alpha cutoff
959 }
960 }
961 return v;
962 }
963
964 evalPosition()
965 {
966 const [sizeX,sizeY] = VariantRules.size;
967 let evaluation = 0;
968 // Just count material for now
969 for (let i=0; i<sizeX; i++)
970 {
971 for (let j=0; j<sizeY; j++)
972 {
973 if (this.board[i][j] != VariantRules.EMPTY)
974 {
975 const sign = this.getColor(i,j) == "w" ? 1 : -1;
976 evaluation += sign * VariantRules.VALUES[this.getPiece(i,j)];
977 }
978 }
979 }
980 return evaluation;
981 }
982
983 ////////////
984 // FEN utils
985
986 // Setup the initial random (assymetric) position
987 static GenRandInitFen()
988 {
989 let pieces = [new Array(8), new Array(8)];
990 // Shuffle pieces on first and last rank
991 for (let c = 0; c <= 1; c++)
992 {
993 let positions = _.range(8);
994
995 // Get random squares for bishops
996 let randIndex = 2 * _.random(3);
997 let bishop1Pos = positions[randIndex];
998 // The second bishop must be on a square of different color
999 let randIndex_tmp = 2 * _.random(3) + 1;
1000 let bishop2Pos = positions[randIndex_tmp];
1001 // Remove chosen squares
1002 positions.splice(Math.max(randIndex,randIndex_tmp), 1);
1003 positions.splice(Math.min(randIndex,randIndex_tmp), 1);
1004
1005 // Get random squares for knights
1006 randIndex = _.random(5);
1007 let knight1Pos = positions[randIndex];
1008 positions.splice(randIndex, 1);
1009 randIndex = _.random(4);
1010 let knight2Pos = positions[randIndex];
1011 positions.splice(randIndex, 1);
1012
1013 // Get random square for queen
1014 randIndex = _.random(3);
1015 let queenPos = positions[randIndex];
1016 positions.splice(randIndex, 1);
1017
1018 // Rooks and king positions are now fixed, because of the ordering rook-king-rook
1019 let rook1Pos = positions[0];
1020 let kingPos = positions[1];
1021 let rook2Pos = positions[2];
1022
1023 // Finally put the shuffled pieces in the board array
1024 pieces[c][rook1Pos] = 'r';
1025 pieces[c][knight1Pos] = 'n';
1026 pieces[c][bishop1Pos] = 'b';
1027 pieces[c][queenPos] = 'q';
1028 pieces[c][kingPos] = 'k';
1029 pieces[c][bishop2Pos] = 'b';
1030 pieces[c][knight2Pos] = 'n';
1031 pieces[c][rook2Pos] = 'r';
1032 }
1033 let fen = pieces[0].join("") +
1034 "/pppppppp/8/8/8/8/PPPPPPPP/" +
1035 pieces[1].join("").toUpperCase() +
1036 " 1111"; //add flags
1037 return fen;
1038 }
1039
1040 // Return current fen according to pieces+colors state
1041 getFen()
1042 {
1043 return this.getBaseFen() + " " + this.getFlagsFen();
1044 }
1045
1046 // Position part of the FEN string
1047 getBaseFen()
1048 {
1049 let fen = "";
1050 let [sizeX,sizeY] = VariantRules.size;
1051 for (let i=0; i<sizeX; i++)
1052 {
1053 let emptyCount = 0;
1054 for (let j=0; j<sizeY; j++)
1055 {
1056 if (this.board[i][j] == VariantRules.EMPTY)
1057 emptyCount++;
1058 else
1059 {
1060 if (emptyCount > 0)
1061 {
1062 // Add empty squares in-between
1063 fen += emptyCount;
1064 emptyCount = 0;
1065 }
1066 fen += VariantRules.board2fen(this.board[i][j]);
1067 }
1068 }
1069 if (emptyCount > 0)
1070 {
1071 // "Flush remainder"
1072 fen += emptyCount;
1073 }
1074 if (i < sizeX - 1)
1075 fen += "/"; //separate rows
1076 }
1077 return fen;
1078 }
1079
1080 // Flags part of the FEN string
1081 getFlagsFen()
1082 {
1083 let fen = "";
1084 // Add castling flags
1085 for (let i of ['w','b'])
1086 {
1087 for (let j=0; j<2; j++)
1088 fen += (this.castleFlags[i][j] ? '1' : '0');
1089 }
1090 return fen;
1091 }
1092
1093 // Context: just before move is played, turn hasn't changed
1094 getNotation(move)
1095 {
1096 if (move.appear.length == 2 && move.appear[0].p == VariantRules.KING) //castle
1097 return (move.end.y < move.start.y ? "0-0-0" : "0-0");
1098
1099 // Translate final square
1100 const finalSquare =
1101 String.fromCharCode(97 + move.end.y) + (VariantRules.size[0]-move.end.x);
1102
1103 const piece = this.getPiece(move.start.x, move.start.y);
1104 if (piece == VariantRules.PAWN)
1105 {
1106 // Pawn move
1107 let notation = "";
1108 if (move.vanish.length > move.appear.length)
1109 {
1110 // Capture
1111 const startColumn = String.fromCharCode(97 + move.start.y);
1112 notation = startColumn + "x" + finalSquare;
1113 }
1114 else //no capture
1115 notation = finalSquare;
1116 if (move.appear.length > 0 && piece != move.appear[0].p) //promotion
1117 notation += "=" + move.appear[0].p.toUpperCase();
1118 return notation;
1119 }
1120
1121 else
1122 {
1123 // Piece movement
1124 return piece.toUpperCase() +
1125 (move.vanish.length > move.appear.length ? "x" : "") + finalSquare;
1126 }
1127 }
1128
1129 // Complete the usual notation, may be required for de-ambiguification
1130 getLongNotation(move)
1131 {
1132 const startSquare =
1133 String.fromCharCode(97 + move.start.y) + (VariantRules.size[0]-move.start.x);
1134 const finalSquare =
1135 String.fromCharCode(97 + move.end.y) + (VariantRules.size[0]-move.end.x);
1136 return startSquare + finalSquare; //not encoding move. But short+long is enough
1137 }
1138
1139 // The score is already computed when calling this function
1140 getPGN(mycolor, score, fenStart, mode)
1141 {
1142 const zeroPad = x => { return (x<10 ? "0" : "") + x; };
1143 let pgn = "";
1144 pgn += '[Site "vchess.club"]<br>';
1145 const d = new Date();
1146 const opponent = mode=="human" ? "Anonymous" : "Computer";
1147 pgn += '[Variant "' + variant + '"]<br>';
1148 pgn += '[Date "' + d.getFullYear() + '-' + (d.getMonth()+1) +
1149 '-' + zeroPad(d.getDate()) + '"]<br>';
1150 pgn += '[White "' + (mycolor=='w'?'Myself':opponent) + '"]<br>';
1151 pgn += '[Black "' + (mycolor=='b'?'Myself':opponent) + '"]<br>';
1152 pgn += '[FenStart "' + fenStart + '"]<br>';
1153 pgn += '[Fen "' + this.getFen() + '"]<br>';
1154 pgn += '[Result "' + score + '"]<br><br>';
1155
1156 // Standard PGN
1157 for (let i=0; i<this.moves.length; i++)
1158 {
1159 if (i % 2 == 0)
1160 pgn += ((i/2)+1) + ".";
1161 pgn += this.moves[i].notation[0] + " ";
1162 }
1163 pgn += "<br><br>";
1164
1165 // "Complete moves" PGN (helping in ambiguous cases)
1166 for (let i=0; i<this.moves.length; i++)
1167 {
1168 if (i % 2 == 0)
1169 pgn += ((i/2)+1) + ".";
1170 pgn += this.moves[i].notation[1] + " ";
1171 }
1172
1173 return pgn;
1174 }
1175 }
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