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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 export const PiPo = class PiPo //Piece+Position
8 {
9 // o: {piece[p], color[c], posX[x], posY[y]}
10 constructor(o)
11 {
12 this.p = o.p;
13 this.c = o.c;
14 this.x = o.x;
15 this.y = o.y;
16 }
17 }
18
19 // TODO: for animation, moves should contains "moving" and "fading" maybe...
20 export const Move = class Move
21 {
22 // o: {appear, vanish, [start,] [end,]}
23 // appear,vanish = arrays of PiPo
24 // start,end = coordinates to apply to trigger move visually (think castle)
25 constructor(o)
26 {
27 this.appear = o.appear;
28 this.vanish = o.vanish;
29 this.start = !!o.start ? o.start : {x:o.vanish[0].x, y:o.vanish[0].y};
30 this.end = !!o.end ? o.end : {x:o.appear[0].x, y:o.appear[0].y};
31 }
32 }
33
34 // NOTE: x coords = top to bottom; y = left to right (from white player perspective)
35 export const ChessRules = class ChessRules
36 {
37 //////////////
38 // MISC UTILS
39
40 static get HasFlags() { return true; } //some variants don't have flags
41
42 static get HasEnpassant() { return true; } //some variants don't have ep.
43
44 // Path to pieces
45 static getPpath(b)
46 {
47 return b; //usual pieces in pieces/ folder
48 }
49
50 // Turn "wb" into "B" (for FEN)
51 static board2fen(b)
52 {
53 return (b[0]=='w' ? b[1].toUpperCase() : b[1]);
54 }
55
56 // Turn "p" into "bp" (for board)
57 static fen2board(f)
58 {
59 return (f.charCodeAt()<=90 ? "w"+f.toLowerCase() : "b"+f);
60 }
61
62 // Check if FEN describe a position
63 static IsGoodFen(fen)
64 {
65 const fenParsed = V.ParseFen(fen);
66 // 1) Check position
67 if (!V.IsGoodPosition(fenParsed.position))
68 return false;
69 // 2) Check turn
70 if (!fenParsed.turn || !V.IsGoodTurn(fenParsed.turn))
71 return false;
72 // 3) Check moves count
73 if (!fenParsed.movesCount || !(parseInt(fenParsed.movesCount) >= 0))
74 return false;
75 // 4) Check flags
76 if (V.HasFlags && (!fenParsed.flags || !V.IsGoodFlags(fenParsed.flags)))
77 return false;
78 // 5) Check enpassant
79 if (V.HasEnpassant &&
80 (!fenParsed.enpassant || !V.IsGoodEnpassant(fenParsed.enpassant)))
81 {
82 return false;
83 }
84 return true;
85 }
86
87 // Is position part of the FEN a priori correct?
88 static IsGoodPosition(position)
89 {
90 if (position.length == 0)
91 return false;
92 const rows = position.split("/");
93 if (rows.length != V.size.x)
94 return false;
95 for (let row of rows)
96 {
97 let sumElts = 0;
98 for (let i=0; i<row.length; i++)
99 {
100 if (V.PIECES.includes(row[i].toLowerCase()))
101 sumElts++;
102 else
103 {
104 const num = parseInt(row[i]);
105 if (isNaN(num))
106 return false;
107 sumElts += num;
108 }
109 }
110 if (sumElts != V.size.y)
111 return false;
112 }
113 return true;
114 }
115
116 // For FEN checking
117 static IsGoodTurn(turn)
118 {
119 return ["w","b"].includes(turn);
120 }
121
122 // For FEN checking
123 static IsGoodFlags(flags)
124 {
125 return !!flags.match(/^[01]{4,4}$/);
126 }
127
128 static IsGoodEnpassant(enpassant)
129 {
130 if (enpassant != "-")
131 {
132 const ep = V.SquareToCoords(fenParsed.enpassant);
133 if (isNaN(ep.x) || !V.OnBoard(ep))
134 return false;
135 }
136 return true;
137 }
138
139 // 3 --> d (column number to letter)
140 static CoordToColumn(colnum)
141 {
142 return String.fromCharCode(97 + colnum);
143 }
144
145 // d --> 3 (column letter to number)
146 static ColumnToCoord(column)
147 {
148 return column.charCodeAt(0) - 97;
149 }
150
151 // a4 --> {x:3,y:0}
152 static SquareToCoords(sq)
153 {
154 return {
155 // NOTE: column is always one char => max 26 columns
156 // row is counted from black side => subtraction
157 x: V.size.x - parseInt(sq.substr(1)),
158 y: sq[0].charCodeAt() - 97
159 };
160 }
161
162 // {x:0,y:4} --> e8
163 static CoordsToSquare(coords)
164 {
165 return V.CoordToColumn(coords.y) + (V.size.x - coords.x);
166 }
167
168 // Aggregates flags into one object
169 aggregateFlags()
170 {
171 return this.castleFlags;
172 }
173
174 // Reverse operation
175 disaggregateFlags(flags)
176 {
177 this.castleFlags = flags;
178 }
179
180 // En-passant square, if any
181 getEpSquare(moveOrSquare)
182 {
183 if (!moveOrSquare)
184 return undefined;
185 if (typeof moveOrSquare === "string")
186 {
187 const square = moveOrSquare;
188 if (square == "-")
189 return undefined;
190 return V.SquareToCoords(square);
191 }
192 // Argument is a move:
193 const move = moveOrSquare;
194 const [sx,sy,ex] = [move.start.x,move.start.y,move.end.x];
195 // NOTE: next conditions are first for Atomic, and last for Checkered
196 if (move.appear.length > 0 && Math.abs(sx - ex) == 2
197 && move.appear[0].p == V.PAWN && ["w","b"].includes(move.appear[0].c))
198 {
199 return {
200 x: (sx + ex)/2,
201 y: sy
202 };
203 }
204 return undefined; //default
205 }
206
207 // Can thing on square1 take thing on square2
208 canTake([x1,y1], [x2,y2])
209 {
210 return this.getColor(x1,y1) !== this.getColor(x2,y2);
211 }
212
213 // Is (x,y) on the chessboard?
214 static OnBoard(x,y)
215 {
216 return (x>=0 && x<V.size.x && y>=0 && y<V.size.y);
217 }
218
219 // Used in interface: 'side' arg == player color
220 canIplay(side, [x,y])
221 {
222 return (this.turn == side && this.getColor(x,y) == side);
223 }
224
225 // On which squares is color under check ? (for interface)
226 getCheckSquares(color)
227 {
228 return this.isAttacked(this.kingPos[color], [V.GetOppCol(color)])
229 ? [JSON.parse(JSON.stringify(this.kingPos[color]))] //need to duplicate!
230 : [];
231 }
232
233 /////////////
234 // FEN UTILS
235
236 // Setup the initial random (assymetric) position
237 static GenRandInitFen()
238 {
239 let pieces = { "w": new Array(8), "b": new Array(8) };
240 // Shuffle pieces on first and last rank
241 for (let c of ["w","b"])
242 {
243 let positions = ArrayFun.range(8);
244
245 // Get random squares for bishops
246 let randIndex = 2 * randInt(4);
247 const bishop1Pos = positions[randIndex];
248 // The second bishop must be on a square of different color
249 let randIndex_tmp = 2 * randInt(4) + 1;
250 const bishop2Pos = positions[randIndex_tmp];
251 // Remove chosen squares
252 positions.splice(Math.max(randIndex,randIndex_tmp), 1);
253 positions.splice(Math.min(randIndex,randIndex_tmp), 1);
254
255 // Get random squares for knights
256 randIndex = randInt(6);
257 const knight1Pos = positions[randIndex];
258 positions.splice(randIndex, 1);
259 randIndex = randInt(5);
260 const knight2Pos = positions[randIndex];
261 positions.splice(randIndex, 1);
262
263 // Get random square for queen
264 randIndex = randInt(4);
265 const queenPos = positions[randIndex];
266 positions.splice(randIndex, 1);
267
268 // Rooks and king positions are now fixed,
269 // because of the ordering rook-king-rook
270 const rook1Pos = positions[0];
271 const kingPos = positions[1];
272 const rook2Pos = positions[2];
273
274 // Finally put the shuffled pieces in the board array
275 pieces[c][rook1Pos] = 'r';
276 pieces[c][knight1Pos] = 'n';
277 pieces[c][bishop1Pos] = 'b';
278 pieces[c][queenPos] = 'q';
279 pieces[c][kingPos] = 'k';
280 pieces[c][bishop2Pos] = 'b';
281 pieces[c][knight2Pos] = 'n';
282 pieces[c][rook2Pos] = 'r';
283 }
284 return pieces["b"].join("") +
285 "/pppppppp/8/8/8/8/PPPPPPPP/" +
286 pieces["w"].join("").toUpperCase() +
287 " w 0 1111 -"; //add turn + flags + enpassant
288 }
289
290 // "Parse" FEN: just return untransformed string data
291 static ParseFen(fen)
292 {
293 const fenParts = fen.split(" ");
294 let res =
295 {
296 position: fenParts[0],
297 turn: fenParts[1],
298 movesCount: fenParts[2],
299 };
300 let nextIdx = 3;
301 if (V.HasFlags)
302 Object.assign(res, {flags: fenParts[nextIdx++]});
303 if (V.HasEnpassant)
304 Object.assign(res, {enpassant: fenParts[nextIdx]});
305 return res;
306 }
307
308 // Return current fen (game state)
309 getFen()
310 {
311 return this.getBaseFen() + " " +
312 this.getTurnFen() + " " + this.movesCount +
313 (V.HasFlags ? (" " + this.getFlagsFen()) : "") +
314 (V.HasEnpassant ? (" " + this.getEnpassantFen()) : "");
315 }
316
317 // Position part of the FEN string
318 getBaseFen()
319 {
320 let position = "";
321 for (let i=0; i<V.size.x; i++)
322 {
323 let emptyCount = 0;
324 for (let j=0; j<V.size.y; j++)
325 {
326 if (this.board[i][j] == V.EMPTY)
327 emptyCount++;
328 else
329 {
330 if (emptyCount > 0)
331 {
332 // Add empty squares in-between
333 position += emptyCount;
334 emptyCount = 0;
335 }
336 position += V.board2fen(this.board[i][j]);
337 }
338 }
339 if (emptyCount > 0)
340 {
341 // "Flush remainder"
342 position += emptyCount;
343 }
344 if (i < V.size.x - 1)
345 position += "/"; //separate rows
346 }
347 return position;
348 }
349
350 getTurnFen()
351 {
352 return this.turn;
353 }
354
355 // Flags part of the FEN string
356 getFlagsFen()
357 {
358 let flags = "";
359 // Add castling flags
360 for (let i of ['w','b'])
361 {
362 for (let j=0; j<2; j++)
363 flags += (this.castleFlags[i][j] ? '1' : '0');
364 }
365 return flags;
366 }
367
368 // Enpassant part of the FEN string
369 getEnpassantFen()
370 {
371 const L = this.epSquares.length;
372 if (!this.epSquares[L-1])
373 return "-"; //no en-passant
374 return V.CoordsToSquare(this.epSquares[L-1]);
375 }
376
377 // Turn position fen into double array ["wb","wp","bk",...]
378 static GetBoard(position)
379 {
380 const rows = position.split("/");
381 let board = ArrayFun.init(V.size.x, V.size.y, "");
382 for (let i=0; i<rows.length; i++)
383 {
384 let j = 0;
385 for (let indexInRow = 0; indexInRow < rows[i].length; indexInRow++)
386 {
387 const character = rows[i][indexInRow];
388 const num = parseInt(character);
389 if (!isNaN(num))
390 j += num; //just shift j
391 else //something at position i,j
392 board[i][j++] = V.fen2board(character);
393 }
394 }
395 return board;
396 }
397
398 // Extract (relevant) flags from fen
399 setFlags(fenflags)
400 {
401 // white a-castle, h-castle, black a-castle, h-castle
402 this.castleFlags = {'w': [true,true], 'b': [true,true]};
403 if (!fenflags)
404 return;
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 constructor(fen)
413 {
414 this.re_init(fen);
415 }
416
417 // Fen string fully describes the game state
418 re_init(fen)
419 {
420 const fenParsed = V.ParseFen(fen);
421 this.board = V.GetBoard(fenParsed.position);
422 this.turn = fenParsed.turn[0]; //[0] to work with MarseilleRules
423 this.movesCount = parseInt(fenParsed.movesCount);
424 this.setOtherVariables(fen);
425 }
426
427 // Scan board for kings and rooks positions
428 scanKingsRooks(fen)
429 {
430 this.INIT_COL_KING = {'w':-1, 'b':-1};
431 this.INIT_COL_ROOK = {'w':[-1,-1], 'b':[-1,-1]};
432 this.kingPos = {'w':[-1,-1], 'b':[-1,-1]}; //squares of white and black king
433 const fenRows = V.ParseFen(fen).position.split("/");
434 for (let i=0; i<fenRows.length; i++)
435 {
436 let k = 0; //column index on board
437 for (let j=0; j<fenRows[i].length; j++)
438 {
439 switch (fenRows[i].charAt(j))
440 {
441 case 'k':
442 this.kingPos['b'] = [i,k];
443 this.INIT_COL_KING['b'] = k;
444 break;
445 case 'K':
446 this.kingPos['w'] = [i,k];
447 this.INIT_COL_KING['w'] = k;
448 break;
449 case 'r':
450 if (this.INIT_COL_ROOK['b'][0] < 0)
451 this.INIT_COL_ROOK['b'][0] = k;
452 else
453 this.INIT_COL_ROOK['b'][1] = k;
454 break;
455 case 'R':
456 if (this.INIT_COL_ROOK['w'][0] < 0)
457 this.INIT_COL_ROOK['w'][0] = k;
458 else
459 this.INIT_COL_ROOK['w'][1] = k;
460 break;
461 default:
462 const num = parseInt(fenRows[i].charAt(j));
463 if (!isNaN(num))
464 k += (num-1);
465 }
466 k++;
467 }
468 }
469 }
470
471 // Some additional variables from FEN (variant dependant)
472 setOtherVariables(fen)
473 {
474 // Set flags and enpassant:
475 const parsedFen = V.ParseFen(fen);
476 if (V.HasFlags)
477 this.setFlags(parsedFen.flags);
478 if (V.HasEnpassant)
479 {
480 const epSq = parsedFen.enpassant != "-"
481 ? V.SquareToCoords(parsedFen.enpassant)
482 : undefined;
483 this.epSquares = [ epSq ];
484 }
485 // Search for king and rooks positions:
486 this.scanKingsRooks(fen);
487 }
488
489 /////////////////////
490 // GETTERS & SETTERS
491
492 static get size()
493 {
494 return {x:8, y:8};
495 }
496
497 // Color of thing on suqare (i,j). 'undefined' if square is empty
498 getColor(i,j)
499 {
500 return this.board[i][j].charAt(0);
501 }
502
503 // Piece type on square (i,j). 'undefined' if square is empty
504 getPiece(i,j)
505 {
506 return this.board[i][j].charAt(1);
507 }
508
509 // Get opponent color
510 static GetOppCol(color)
511 {
512 return (color=="w" ? "b" : "w");
513 }
514
515 // Pieces codes (for a clearer code)
516 static get PAWN() { return 'p'; }
517 static get ROOK() { return 'r'; }
518 static get KNIGHT() { return 'n'; }
519 static get BISHOP() { return 'b'; }
520 static get QUEEN() { return 'q'; }
521 static get KING() { return 'k'; }
522
523 // For FEN checking:
524 static get PIECES()
525 {
526 return [V.PAWN,V.ROOK,V.KNIGHT,V.BISHOP,V.QUEEN,V.KING];
527 }
528
529 // Empty square
530 static get EMPTY() { return ""; }
531
532 // Some pieces movements
533 static get steps()
534 {
535 return {
536 'r': [ [-1,0],[1,0],[0,-1],[0,1] ],
537 'n': [ [-1,-2],[-1,2],[1,-2],[1,2],[-2,-1],[-2,1],[2,-1],[2,1] ],
538 'b': [ [-1,-1],[-1,1],[1,-1],[1,1] ],
539 };
540 }
541
542 ////////////////////
543 // MOVES GENERATION
544
545 // All possible moves from selected square (assumption: color is OK)
546 getPotentialMovesFrom([x,y])
547 {
548 switch (this.getPiece(x,y))
549 {
550 case V.PAWN:
551 return this.getPotentialPawnMoves([x,y]);
552 case V.ROOK:
553 return this.getPotentialRookMoves([x,y]);
554 case V.KNIGHT:
555 return this.getPotentialKnightMoves([x,y]);
556 case V.BISHOP:
557 return this.getPotentialBishopMoves([x,y]);
558 case V.QUEEN:
559 return this.getPotentialQueenMoves([x,y]);
560 case V.KING:
561 return this.getPotentialKingMoves([x,y]);
562 }
563 }
564
565 // Build a regular move from its initial and destination squares.
566 // tr: transformation
567 getBasicMove([sx,sy], [ex,ey], tr)
568 {
569 let mv = new Move({
570 appear: [
571 new PiPo({
572 x: ex,
573 y: ey,
574 c: !!tr ? tr.c : this.getColor(sx,sy),
575 p: !!tr ? tr.p : this.getPiece(sx,sy)
576 })
577 ],
578 vanish: [
579 new PiPo({
580 x: sx,
581 y: sy,
582 c: this.getColor(sx,sy),
583 p: this.getPiece(sx,sy)
584 })
585 ]
586 });
587
588 // The opponent piece disappears if we take it
589 if (this.board[ex][ey] != V.EMPTY)
590 {
591 mv.vanish.push(
592 new PiPo({
593 x: ex,
594 y: ey,
595 c: this.getColor(ex,ey),
596 p: this.getPiece(ex,ey)
597 })
598 );
599 }
600 return mv;
601 }
602
603 // Generic method to find possible moves of non-pawn pieces:
604 // "sliding or jumping"
605 getSlideNJumpMoves([x,y], steps, oneStep)
606 {
607 const color = this.getColor(x,y);
608 let moves = [];
609 outerLoop:
610 for (let step of steps)
611 {
612 let i = x + step[0];
613 let j = y + step[1];
614 while (V.OnBoard(i,j) && this.board[i][j] == V.EMPTY)
615 {
616 moves.push(this.getBasicMove([x,y], [i,j]));
617 if (oneStep !== undefined)
618 continue outerLoop;
619 i += step[0];
620 j += step[1];
621 }
622 if (V.OnBoard(i,j) && this.canTake([x,y], [i,j]))
623 moves.push(this.getBasicMove([x,y], [i,j]));
624 }
625 return moves;
626 }
627
628 // What are the pawn moves from square x,y ?
629 getPotentialPawnMoves([x,y])
630 {
631 const color = this.turn;
632 let moves = [];
633 const [sizeX,sizeY] = [V.size.x,V.size.y];
634 const shiftX = (color == "w" ? -1 : 1);
635 const firstRank = (color == 'w' ? sizeX-1 : 0);
636 const startRank = (color == "w" ? sizeX-2 : 1);
637 const lastRank = (color == "w" ? 0 : sizeX-1);
638 const pawnColor = this.getColor(x,y); //can be different for checkered
639
640 // NOTE: next condition is generally true (no pawn on last rank)
641 if (x+shiftX >= 0 && x+shiftX < sizeX)
642 {
643 const finalPieces = x + shiftX == lastRank
644 ? [V.ROOK,V.KNIGHT,V.BISHOP,V.QUEEN]
645 : [V.PAWN]
646 // One square forward
647 if (this.board[x+shiftX][y] == V.EMPTY)
648 {
649 for (let piece of finalPieces)
650 {
651 moves.push(this.getBasicMove([x,y], [x+shiftX,y],
652 {c:pawnColor,p:piece}));
653 }
654 // Next condition because pawns on 1st rank can generally jump
655 if ([startRank,firstRank].includes(x)
656 && this.board[x+2*shiftX][y] == V.EMPTY)
657 {
658 // Two squares jump
659 moves.push(this.getBasicMove([x,y], [x+2*shiftX,y]));
660 }
661 }
662 // Captures
663 for (let shiftY of [-1,1])
664 {
665 if (y + shiftY >= 0 && y + shiftY < sizeY
666 && this.board[x+shiftX][y+shiftY] != V.EMPTY
667 && this.canTake([x,y], [x+shiftX,y+shiftY]))
668 {
669 for (let piece of finalPieces)
670 {
671 moves.push(this.getBasicMove([x,y], [x+shiftX,y+shiftY],
672 {c:pawnColor,p:piece}));
673 }
674 }
675 }
676 }
677
678 if (V.HasEnpassant)
679 {
680 // En passant
681 const Lep = this.epSquares.length;
682 const epSquare = this.epSquares[Lep-1]; //always at least one element
683 if (!!epSquare && epSquare.x == x+shiftX && Math.abs(epSquare.y - y) == 1)
684 {
685 let enpassantMove = this.getBasicMove([x,y], [epSquare.x,epSquare.y]);
686 enpassantMove.vanish.push({
687 x: x,
688 y: epSquare.y,
689 p: 'p',
690 c: this.getColor(x,epSquare.y)
691 });
692 moves.push(enpassantMove);
693 }
694 }
695
696 return moves;
697 }
698
699 // What are the rook moves from square x,y ?
700 getPotentialRookMoves(sq)
701 {
702 return this.getSlideNJumpMoves(sq, V.steps[V.ROOK]);
703 }
704
705 // What are the knight moves from square x,y ?
706 getPotentialKnightMoves(sq)
707 {
708 return this.getSlideNJumpMoves(sq, V.steps[V.KNIGHT], "oneStep");
709 }
710
711 // What are the bishop moves from square x,y ?
712 getPotentialBishopMoves(sq)
713 {
714 return this.getSlideNJumpMoves(sq, V.steps[V.BISHOP]);
715 }
716
717 // What are the queen moves from square x,y ?
718 getPotentialQueenMoves(sq)
719 {
720 return this.getSlideNJumpMoves(sq,
721 V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
722 }
723
724 // What are the king moves from square x,y ?
725 getPotentialKingMoves(sq)
726 {
727 // Initialize with normal moves
728 let moves = this.getSlideNJumpMoves(sq,
729 V.steps[V.ROOK].concat(V.steps[V.BISHOP]), "oneStep");
730 return moves.concat(this.getCastleMoves(sq));
731 }
732
733 getCastleMoves([x,y])
734 {
735 const c = this.getColor(x,y);
736 if (x != (c=="w" ? V.size.x-1 : 0) || y != this.INIT_COL_KING[c])
737 return []; //x isn't first rank, or king has moved (shortcut)
738
739 // Castling ?
740 const oppCol = V.GetOppCol(c);
741 let moves = [];
742 let i = 0;
743 const finalSquares = [ [2,3], [V.size.y-2,V.size.y-3] ]; //king, then rook
744 castlingCheck:
745 for (let castleSide=0; castleSide < 2; castleSide++) //large, then small
746 {
747 if (!this.castleFlags[c][castleSide])
748 continue;
749 // If this code is reached, rooks and king are on initial position
750
751 // Nothing on the path of the king ?
752 // (And no checks; OK also if y==finalSquare)
753 let step = finalSquares[castleSide][0] < y ? -1 : 1;
754 for (i=y; i!=finalSquares[castleSide][0]; i+=step)
755 {
756 if (this.isAttacked([x,i], [oppCol]) || (this.board[x][i] != V.EMPTY &&
757 // NOTE: next check is enough, because of chessboard constraints
758 (this.getColor(x,i) != c
759 || ![V.KING,V.ROOK].includes(this.getPiece(x,i)))))
760 {
761 continue castlingCheck;
762 }
763 }
764
765 // Nothing on the path to the rook?
766 step = castleSide == 0 ? -1 : 1;
767 for (i = y + step; i != this.INIT_COL_ROOK[c][castleSide]; i += step)
768 {
769 if (this.board[x][i] != V.EMPTY)
770 continue castlingCheck;
771 }
772 const rookPos = this.INIT_COL_ROOK[c][castleSide];
773
774 // Nothing on final squares, except maybe king and castling rook?
775 for (i=0; i<2; i++)
776 {
777 if (this.board[x][finalSquares[castleSide][i]] != V.EMPTY &&
778 this.getPiece(x,finalSquares[castleSide][i]) != V.KING &&
779 finalSquares[castleSide][i] != rookPos)
780 {
781 continue castlingCheck;
782 }
783 }
784
785 // If this code is reached, castle is valid
786 moves.push( new Move({
787 appear: [
788 new PiPo({x:x,y:finalSquares[castleSide][0],p:V.KING,c:c}),
789 new PiPo({x:x,y:finalSquares[castleSide][1],p:V.ROOK,c:c})],
790 vanish: [
791 new PiPo({x:x,y:y,p:V.KING,c:c}),
792 new PiPo({x:x,y:rookPos,p:V.ROOK,c:c})],
793 end: Math.abs(y - rookPos) <= 2
794 ? {x:x, y:rookPos}
795 : {x:x, y:y + 2 * (castleSide==0 ? -1 : 1)}
796 }) );
797 }
798
799 return moves;
800 }
801
802 ////////////////////
803 // MOVES VALIDATION
804
805 // For the interface: possible moves for the current turn from square sq
806 getPossibleMovesFrom(sq)
807 {
808 return this.filterValid( this.getPotentialMovesFrom(sq) );
809 }
810
811 // TODO: promotions (into R,B,N,Q) should be filtered only once
812 filterValid(moves)
813 {
814 if (moves.length == 0)
815 return [];
816 const color = this.turn;
817 return moves.filter(m => {
818 this.play(m);
819 const res = !this.underCheck(color);
820 this.undo(m);
821 return res;
822 });
823 }
824
825 // Search for all valid moves considering current turn
826 // (for engine and game end)
827 getAllValidMoves()
828 {
829 const color = this.turn;
830 const oppCol = V.GetOppCol(color);
831 let potentialMoves = [];
832 for (let i=0; i<V.size.x; i++)
833 {
834 for (let j=0; j<V.size.y; j++)
835 {
836 // Next condition "!= oppCol" to work with checkered variant
837 if (this.board[i][j] != V.EMPTY && this.getColor(i,j) != oppCol)
838 {
839 Array.prototype.push.apply(potentialMoves,
840 this.getPotentialMovesFrom([i,j]));
841 }
842 }
843 }
844 return this.filterValid(potentialMoves);
845 }
846
847 // Stop at the first move found
848 atLeastOneMove()
849 {
850 const color = this.turn;
851 const oppCol = V.GetOppCol(color);
852 for (let i=0; i<V.size.x; i++)
853 {
854 for (let j=0; j<V.size.y; j++)
855 {
856 if (this.board[i][j] != V.EMPTY && this.getColor(i,j) != oppCol)
857 {
858 const moves = this.getPotentialMovesFrom([i,j]);
859 if (moves.length > 0)
860 {
861 for (let k=0; k<moves.length; k++)
862 {
863 if (this.filterValid([moves[k]]).length > 0)
864 return true;
865 }
866 }
867 }
868 }
869 }
870 return false;
871 }
872
873 // Check if pieces of color in 'colors' are attacking (king) on square x,y
874 isAttacked(sq, colors)
875 {
876 return (this.isAttackedByPawn(sq, colors)
877 || this.isAttackedByRook(sq, colors)
878 || this.isAttackedByKnight(sq, colors)
879 || this.isAttackedByBishop(sq, colors)
880 || this.isAttackedByQueen(sq, colors)
881 || this.isAttackedByKing(sq, colors));
882 }
883
884 // Is square x,y attacked by 'colors' pawns ?
885 isAttackedByPawn([x,y], colors)
886 {
887 for (let c of colors)
888 {
889 let pawnShift = (c=="w" ? 1 : -1);
890 if (x+pawnShift>=0 && x+pawnShift<V.size.x)
891 {
892 for (let i of [-1,1])
893 {
894 if (y+i>=0 && y+i<V.size.y && this.getPiece(x+pawnShift,y+i)==V.PAWN
895 && this.getColor(x+pawnShift,y+i)==c)
896 {
897 return true;
898 }
899 }
900 }
901 }
902 return false;
903 }
904
905 // Is square x,y attacked by 'colors' rooks ?
906 isAttackedByRook(sq, colors)
907 {
908 return this.isAttackedBySlideNJump(sq, colors, V.ROOK, V.steps[V.ROOK]);
909 }
910
911 // Is square x,y attacked by 'colors' knights ?
912 isAttackedByKnight(sq, colors)
913 {
914 return this.isAttackedBySlideNJump(sq, colors,
915 V.KNIGHT, V.steps[V.KNIGHT], "oneStep");
916 }
917
918 // Is square x,y attacked by 'colors' bishops ?
919 isAttackedByBishop(sq, colors)
920 {
921 return this.isAttackedBySlideNJump(sq, colors, V.BISHOP, V.steps[V.BISHOP]);
922 }
923
924 // Is square x,y attacked by 'colors' queens ?
925 isAttackedByQueen(sq, colors)
926 {
927 return this.isAttackedBySlideNJump(sq, colors, V.QUEEN,
928 V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
929 }
930
931 // Is square x,y attacked by 'colors' king(s) ?
932 isAttackedByKing(sq, colors)
933 {
934 return this.isAttackedBySlideNJump(sq, colors, V.KING,
935 V.steps[V.ROOK].concat(V.steps[V.BISHOP]), "oneStep");
936 }
937
938 // Generic method for non-pawn pieces ("sliding or jumping"):
939 // is x,y attacked by a piece of color in array 'colors' ?
940 isAttackedBySlideNJump([x,y], colors, piece, steps, oneStep)
941 {
942 for (let step of steps)
943 {
944 let rx = x+step[0], ry = y+step[1];
945 while (V.OnBoard(rx,ry) && this.board[rx][ry] == V.EMPTY && !oneStep)
946 {
947 rx += step[0];
948 ry += step[1];
949 }
950 if (V.OnBoard(rx,ry) && this.getPiece(rx,ry) === piece
951 && colors.includes(this.getColor(rx,ry)))
952 {
953 return true;
954 }
955 }
956 return false;
957 }
958
959 // Is color under check after his move ?
960 underCheck(color)
961 {
962 return this.isAttacked(this.kingPos[color], [V.GetOppCol(color)]);
963 }
964
965 /////////////////
966 // MOVES PLAYING
967
968 // Apply a move on board
969 static PlayOnBoard(board, move)
970 {
971 for (let psq of move.vanish)
972 board[psq.x][psq.y] = V.EMPTY;
973 for (let psq of move.appear)
974 board[psq.x][psq.y] = psq.c + psq.p;
975 }
976 // Un-apply the played move
977 static UndoOnBoard(board, move)
978 {
979 for (let psq of move.appear)
980 board[psq.x][psq.y] = V.EMPTY;
981 for (let psq of move.vanish)
982 board[psq.x][psq.y] = psq.c + psq.p;
983 }
984
985 // After move is played, update variables + flags
986 updateVariables(move)
987 {
988 let piece = undefined;
989 let c = undefined;
990 if (move.vanish.length >= 1)
991 {
992 // Usual case, something is moved
993 piece = move.vanish[0].p;
994 c = move.vanish[0].c;
995 }
996 else
997 {
998 // Crazyhouse-like variants
999 piece = move.appear[0].p;
1000 c = move.appear[0].c;
1001 }
1002 if (c == "c") //if (!["w","b"].includes(c))
1003 {
1004 // 'c = move.vanish[0].c' doesn't work for Checkered
1005 c = V.GetOppCol(this.turn);
1006 }
1007 const firstRank = (c == "w" ? V.size.x-1 : 0);
1008
1009 // Update king position + flags
1010 if (piece == V.KING && move.appear.length > 0)
1011 {
1012 this.kingPos[c][0] = move.appear[0].x;
1013 this.kingPos[c][1] = move.appear[0].y;
1014 if (V.HasFlags)
1015 this.castleFlags[c] = [false,false];
1016 return;
1017 }
1018 if (V.HasFlags)
1019 {
1020 // Update castling flags if rooks are moved
1021 const oppCol = V.GetOppCol(c);
1022 const oppFirstRank = (V.size.x-1) - firstRank;
1023 if (move.start.x == firstRank //our rook moves?
1024 && this.INIT_COL_ROOK[c].includes(move.start.y))
1025 {
1026 const flagIdx = (move.start.y == this.INIT_COL_ROOK[c][0] ? 0 : 1);
1027 this.castleFlags[c][flagIdx] = false;
1028 }
1029 else if (move.end.x == oppFirstRank //we took opponent rook?
1030 && this.INIT_COL_ROOK[oppCol].includes(move.end.y))
1031 {
1032 const flagIdx = (move.end.y == this.INIT_COL_ROOK[oppCol][0] ? 0 : 1);
1033 this.castleFlags[oppCol][flagIdx] = false;
1034 }
1035 }
1036 }
1037
1038 // After move is undo-ed *and flags resetted*, un-update other variables
1039 // TODO: more symmetry, by storing flags increment in move (?!)
1040 unupdateVariables(move)
1041 {
1042 // (Potentially) Reset king position
1043 const c = this.getColor(move.start.x,move.start.y);
1044 if (this.getPiece(move.start.x,move.start.y) == V.KING)
1045 this.kingPos[c] = [move.start.x, move.start.y];
1046 }
1047
1048 play(move)
1049 {
1050 // DEBUG:
1051 // if (!this.states) this.states = [];
1052 // const stateFen = this.getBaseFen() + this.getTurnFen() + this.getFlagsFen();
1053 // this.states.push(stateFen);
1054
1055 if (V.HasFlags)
1056 move.flags = JSON.stringify(this.aggregateFlags()); //save flags (for undo)
1057 if (V.HasEnpassant)
1058 this.epSquares.push( this.getEpSquare(move) );
1059 V.PlayOnBoard(this.board, move);
1060 this.turn = V.GetOppCol(this.turn);
1061 this.movesCount++;
1062 this.updateVariables(move);
1063 }
1064
1065 undo(move)
1066 {
1067 if (V.HasEnpassant)
1068 this.epSquares.pop();
1069 if (V.HasFlags)
1070 this.disaggregateFlags(JSON.parse(move.flags));
1071 V.UndoOnBoard(this.board, move);
1072 this.turn = V.GetOppCol(this.turn);
1073 this.movesCount--;
1074 this.unupdateVariables(move);
1075
1076 // DEBUG:
1077 // const stateFen = this.getBaseFen() + this.getTurnFen() + this.getFlagsFen();
1078 // if (stateFen != this.states[this.states.length-1]) debugger;
1079 // this.states.pop();
1080 }
1081
1082 ///////////////
1083 // END OF GAME
1084
1085 // What is the score ? (Interesting if game is over)
1086 getCurrentScore()
1087 {
1088 if (this.atLeastOneMove()) // game not over
1089 return "*";
1090
1091 // Game over
1092 const color = this.turn;
1093 // No valid move: stalemate or checkmate?
1094 if (!this.isAttacked(this.kingPos[color], [V.GetOppCol(color)]))
1095 return "1/2";
1096 // OK, checkmate
1097 return (color == "w" ? "0-1" : "1-0");
1098 }
1099
1100 ///////////////
1101 // ENGINE PLAY
1102
1103 // Pieces values
1104 static get VALUES()
1105 {
1106 return {
1107 'p': 1,
1108 'r': 5,
1109 'n': 3,
1110 'b': 3,
1111 'q': 9,
1112 'k': 1000
1113 };
1114 }
1115
1116 // "Checkmate" (unreachable eval)
1117 static get INFINITY() { return 9999; }
1118
1119 // At this value or above, the game is over
1120 static get THRESHOLD_MATE() { return V.INFINITY; }
1121
1122 // Search depth: 2 for high branching factor, 4 for small (Loser chess, eg.)
1123 static get SEARCH_DEPTH() { return 3; }
1124
1125 // NOTE: works also for extinction chess because depth is 3...
1126 getComputerMove()
1127 {
1128 const maxeval = V.INFINITY;
1129 const color = this.turn;
1130 // Some variants may show a bigger moves list to the human (Switching),
1131 // thus the argument "computer" below (which is generally ignored)
1132 let moves1 = this.getAllValidMoves("computer");
1133 if (moves1.length == 0) //TODO: this situation should not happen
1134 return null;
1135
1136 // Can I mate in 1 ? (for Magnetic & Extinction)
1137 for (let i of shuffle(ArrayFun.range(moves1.length)))
1138 {
1139 this.play(moves1[i]);
1140 let finish = (Math.abs(this.evalPosition()) >= V.THRESHOLD_MATE);
1141 if (!finish)
1142 {
1143 const score = this.getCurrentScore();
1144 if (["1-0","0-1"].includes(score))
1145 finish = true;
1146 }
1147 this.undo(moves1[i]);
1148 if (finish)
1149 return moves1[i];
1150 }
1151
1152 // Rank moves using a min-max at depth 2
1153 for (let i=0; i<moves1.length; i++)
1154 {
1155 // Initial self evaluation is very low: "I'm checkmated"
1156 moves1[i].eval = (color=="w" ? -1 : 1) * maxeval;
1157 this.play(moves1[i]);
1158 const score1 = this.getCurrentScore();
1159 let eval2 = undefined;
1160 if (score1 == "*")
1161 {
1162 // Initial enemy evaluation is very low too, for him
1163 eval2 = (color=="w" ? 1 : -1) * maxeval;
1164 // Second half-move:
1165 let moves2 = this.getAllValidMoves("computer");
1166 for (let j=0; j<moves2.length; j++)
1167 {
1168 this.play(moves2[j]);
1169 const score2 = this.getCurrentScore();
1170 const evalPos = score2 == "*"
1171 ? this.evalPosition()
1172 : (score2=="1/2" ? 0 : (score2=="1-0" ? 1 : -1) * maxeval);
1173 if ((color == "w" && evalPos < eval2)
1174 || (color=="b" && evalPos > eval2))
1175 {
1176 eval2 = evalPos;
1177 }
1178 this.undo(moves2[j]);
1179 }
1180 }
1181 else
1182 eval2 = (score1=="1/2" ? 0 : (score1=="1-0" ? 1 : -1) * maxeval);
1183 if ((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) => { return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
1191
1192 let candidates = [0]; //indices of candidates moves
1193 for (let j=1; j<moves1.length && moves1[j].eval == moves1[0].eval; j++)
1194 candidates.push(j);
1195 let currentBest = moves1[candidates[randInt(candidates.length)]];
1196
1197 // Skip depth 3+ if we found a checkmate (or if we are checkmated in 1...)
1198 if (V.SEARCH_DEPTH >= 3 && Math.abs(moves1[0].eval) < V.THRESHOLD_MATE)
1199 {
1200 // From here, depth >= 3: may take a while, so we control time
1201 const timeStart = Date.now();
1202 for (let i=0; i<moves1.length; i++)
1203 {
1204 if (Date.now()-timeStart >= 5000) //more than 5 seconds
1205 return currentBest; //depth 2 at least
1206 this.play(moves1[i]);
1207 // 0.1 * oldEval : heuristic to avoid some bad moves (not all...)
1208 moves1[i].eval = 0.1*moves1[i].eval +
1209 this.alphabeta(V.SEARCH_DEPTH-1, -maxeval, maxeval);
1210 this.undo(moves1[i]);
1211 }
1212 moves1.sort( (a,b) => {
1213 return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
1214 }
1215 else
1216 return currentBest;
1217 // console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
1218
1219 candidates = [0];
1220 for (let j=1; j<moves1.length && moves1[j].eval == moves1[0].eval; j++)
1221 candidates.push(j);
1222 return moves1[candidates[randInt(candidates.length)]];
1223 }
1224
1225 alphabeta(depth, alpha, beta)
1226 {
1227 const maxeval = V.INFINITY;
1228 const color = this.turn;
1229 const score = this.getCurrentScore();
1230 if (score != "*")
1231 return (score=="1/2" ? 0 : (score=="1-0" ? 1 : -1) * maxeval);
1232 if (depth == 0)
1233 return this.evalPosition();
1234 const moves = this.getAllValidMoves("computer");
1235 let v = color=="w" ? -maxeval : maxeval;
1236 if (color == "w")
1237 {
1238 for (let i=0; i<moves.length; i++)
1239 {
1240 this.play(moves[i]);
1241 v = Math.max(v, this.alphabeta(depth-1, alpha, beta));
1242 this.undo(moves[i]);
1243 alpha = Math.max(alpha, v);
1244 if (alpha >= beta)
1245 break; //beta cutoff
1246 }
1247 }
1248 else //color=="b"
1249 {
1250 for (let i=0; i<moves.length; i++)
1251 {
1252 this.play(moves[i]);
1253 v = Math.min(v, this.alphabeta(depth-1, alpha, beta));
1254 this.undo(moves[i]);
1255 beta = Math.min(beta, v);
1256 if (alpha >= beta)
1257 break; //alpha cutoff
1258 }
1259 }
1260 return v;
1261 }
1262
1263 evalPosition()
1264 {
1265 let evaluation = 0;
1266 // Just count material for now
1267 for (let i=0; i<V.size.x; i++)
1268 {
1269 for (let j=0; j<V.size.y; j++)
1270 {
1271 if (this.board[i][j] != V.EMPTY)
1272 {
1273 const sign = this.getColor(i,j) == "w" ? 1 : -1;
1274 evaluation += sign * V.VALUES[this.getPiece(i,j)];
1275 }
1276 }
1277 }
1278 return evaluation;
1279 }
1280
1281 /////////////////////////
1282 // MOVES + GAME NOTATION
1283 /////////////////////////
1284
1285 // Context: just before move is played, turn hasn't changed
1286 // TODO: un-ambiguous notation (switch on piece type, check directions...)
1287 getNotation(move)
1288 {
1289 if (move.appear.length == 2 && move.appear[0].p == V.KING) //castle
1290 return (move.end.y < move.start.y ? "0-0-0" : "0-0");
1291
1292 // Translate final square
1293 const finalSquare = V.CoordsToSquare(move.end);
1294
1295 const piece = this.getPiece(move.start.x, move.start.y);
1296 if (piece == V.PAWN)
1297 {
1298 // Pawn move
1299 let notation = "";
1300 if (move.vanish.length > move.appear.length)
1301 {
1302 // Capture
1303 const startColumn = V.CoordToColumn(move.start.y);
1304 notation = startColumn + "x" + finalSquare;
1305 }
1306 else //no capture
1307 notation = finalSquare;
1308 if (move.appear.length > 0 && move.appear[0].p != V.PAWN) //promotion
1309 notation += "=" + move.appear[0].p.toUpperCase();
1310 return notation;
1311 }
1312
1313 else
1314 {
1315 // Piece movement
1316 return piece.toUpperCase() +
1317 (move.vanish.length > move.appear.length ? "x" : "") + finalSquare;
1318 }
1319 }
1320 }