client/src/variants/Rococo.js

   1 import { ChessRules, PiPo, Move } from "@/base_rules";
   2 import { ArrayFun } from "@/utils/array";
   3 import { shuffle } from "@/utils/alea";
   4
   5 export class RococoRules extends ChessRules {
   6   static get HasFlags() {
   7     return false;
   8   }
   9
  10   static get HasEnpassant() {
  11     return false;
  12   }
  13
  14   static get PIECES() {
  15     return ChessRules.PIECES.concat([V.IMMOBILIZER]);
  16   }
  17
  18   static get Lines() {
  19     return [
  20       [[1, 1], [1, 9]],
  21       [[1, 9], [9, 9]],
  22       [[9, 9], [9, 1]],
  23       [[9, 1], [1, 1]]
  24     ];
  25   }
  26
  27   getPpath(b) {
  28     if (b[1] == "m")
  29       //'m' for Immobilizer (I is too similar to 1)
  30       return "Rococo/" + b;
  31     return b; //usual piece
  32   }
  33
  34   getPPpath(m) {
  35     // The only "choice" case is between a swap and a mutual destruction:
  36     // show empty square in case of mutual destruction.
  37     if (m.appear.length == 0) return "Rococo/empty";
  38     return m.appear[0].c + m.appear[0].p;
  39   }
  40
  41   setOtherVariables(fen) {
  42     // No castling, but checks, so keep track of kings
  43     this.kingPos = { w: [-1, -1], b: [-1, -1] };
  44     const fenParts = fen.split(" ");
  45     const position = fenParts[0].split("/");
  46     for (let i = 0; i < position.length; i++) {
  47       let k = 0;
  48       for (let j = 0; j < position[i].length; j++) {
  49         switch (position[i].charAt(j)) {
  50           case "k":
  51             this.kingPos["b"] = [i, k];
  52             break;
  53           case "K":
  54             this.kingPos["w"] = [i, k];
  55             break;
  56           default: {
  57             const num = parseInt(position[i].charAt(j), 10);
  58             if (!isNaN(num)) k += num - 1;
  59           }
  60         }
  61         k++;
  62       }
  63     }
  64     // Local stack of swaps:
  65     this.smoves = [];
  66     const smove = V.ParseFen(fen).smove;
  67     if (smove == "-") this.smoves.push(null);
  68     else {
  69       this.smoves.push({
  70         start: ChessRules.SquareToCoords(smove.substr(0, 2)),
  71         end: ChessRules.SquareToCoords(smove.substr(2))
  72       });
  73     }
  74   }
  75
  76   static ParseFen(fen) {
  77     return Object.assign(
  78       ChessRules.ParseFen(fen),
  79       { smove: fen.split(" ")[3] }
  80     );
  81   }
  82
  83   static IsGoodFen(fen) {
  84     if (!ChessRules.IsGoodFen(fen)) return false;
  85     const fenParts = fen.split(" ");
  86     if (fenParts.length != 4) return false;
  87     if (fenParts[3] != "-" && !fenParts[3].match(/^([a-h][1-8]){2}$/))
  88       return false;
  89     return true;
  90   }
  91
  92   getSmove(move) {
  93     if (move.appear.length == 2)
  94       return { start: move.start, end: move.end };
  95     return null;
  96   }
  97
  98   static get size() {
  99     // Add the "capturing edge"
 100     return { x: 10, y: 10 };
 101   }
 102
 103   static get IMMOBILIZER() {
 104     return "m";
 105   }
 106   // Although other pieces keep their names here for coding simplicity,
 107   // keep in mind that:
 108   //  - a "rook" is a swapper, exchanging positions and "capturing" by
 109   //             mutual destruction only.
 110   //  - a "knight" is a long-leaper, capturing as in draughts
 111   //  - a "bishop" is a chameleon, capturing as its prey
 112   //  - a "queen" is a withdrawer+advancer, capturing by moving away from
 113   //              pieces or advancing in front of them.
 114
 115   // Is piece on square (x,y) immobilized?
 116   isImmobilized([x, y]) {
 117     const piece = this.getPiece(x, y);
 118     const oppCol = V.GetOppCol(this.getColor(x, y));
 119     const adjacentSteps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 120     for (let step of adjacentSteps) {
 121       const [i, j] = [x + step[0], y + step[1]];
 122       if (
 123         V.OnBoard(i, j) &&
 124         this.board[i][j] != V.EMPTY &&
 125         this.getColor(i, j) == oppCol
 126       ) {
 127         const oppPiece = this.getPiece(i, j);
 128         if (oppPiece == V.IMMOBILIZER) return [i, j];
 129         // Only immobilizers are immobilized by chameleons:
 130         if (oppPiece == V.BISHOP && piece == V.IMMOBILIZER) return [i, j];
 131       }
 132     }
 133     return null;
 134   }
 135
 136   static OnEdge(x, y) {
 137     return x == 0 || y == 0 || x == V.size.x - 1 || y == V.size.y - 1;
 138   }
 139
 140   getPotentialMovesFrom([x, y]) {
 141     // Pre-check: is thing on this square immobilized?
 142     const imSq = this.isImmobilized([x, y]);
 143     const piece = this.getPiece(x, y);
 144     if (!!imSq && piece != V.KING) {
 145       // Only option is suicide, if I'm not a king:
 146       return [
 147         new Move({
 148           start: { x: x, y: y },
 149           end: { x: imSq[0], y: imSq[1] },
 150           appear: [],
 151           vanish: [
 152             new PiPo({
 153               x: x,
 154               y: y,
 155               c: this.getColor(x, y),
 156               p: this.getPiece(x, y)
 157             })
 158           ]
 159         })
 160       ];
 161     }
 162     let moves = [];
 163     switch (piece) {
 164       case V.IMMOBILIZER:
 165         moves = this.getPotentialImmobilizerMoves([x, y]);
 166         break;
 167       default:
 168         moves = super.getPotentialMovesFrom([x, y]);
 169     }
 170     // Post-processing: prune redundant non-minimal capturing moves,
 171     // and non-capturing moves ending on the edge:
 172     moves.forEach(m => {
 173       // Useful precomputation
 174       m.dist = Math.abs(m.end.x - m.start.x) + Math.abs(m.end.y - m.start.y);
 175     });
 176     return moves.filter(m => {
 177       if (!V.OnEdge(m.end.x, m.end.y)) return true;
 178       // End on the edge:
 179       if (m.vanish.length == 1) return false;
 180       // Capture or swap: only captures get filtered
 181       if (m.appear.length == 2) return true;
 182       // Can we find other moves with a shorter path to achieve the same
 183       // capture? Apply to queens and knights.
 184       if (
 185         moves.some(mv => {
 186           return (
 187             mv.dist < m.dist &&
 188             mv.vanish.length == m.vanish.length &&
 189             mv.vanish.every(v => {
 190               return m.vanish.some(vv => {
 191                 return (
 192                   vv.x == v.x && vv.y == v.y && vv.c == v.c && vv.p == v.p
 193                 );
 194               });
 195             })
 196           );
 197         })
 198       ) {
 199         return false;
 200       }
 201       return true;
 202     });
 203     // NOTE: not removing "dist" field; shouldn't matter much...
 204   }
 205
 206   getSlideNJumpMoves([x, y], steps, oneStep) {
 207     const piece = this.getPiece(x, y);
 208     let moves = [];
 209     outerLoop: for (let step of steps) {
 210       let i = x + step[0];
 211       let j = y + step[1];
 212       while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 213         moves.push(this.getBasicMove([x, y], [i, j]));
 214         if (oneStep !== undefined) continue outerLoop;
 215         i += step[0];
 216         j += step[1];
 217       }
 218       // Only king can take on occupied square:
 219       if (piece == V.KING && V.OnBoard(i, j) && this.canTake([x, y], [i, j]))
 220         moves.push(this.getBasicMove([x, y], [i, j]));
 221     }
 222     return moves;
 223   }
 224
 225   // "Cannon/grasshopper pawn"
 226   getPotentialPawnMoves([x, y]) {
 227     const oppCol = V.GetOppCol(this.turn);
 228     let moves = [];
 229     const adjacentSteps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 230     adjacentSteps.forEach(step => {
 231       const [i, j] = [x + step[0], y + step[1]];
 232       if (V.OnBoard(i, j)) {
 233         if (this.board[i][j] == V.EMPTY)
 234           moves.push(this.getBasicMove([x, y], [i, j]));
 235         else {
 236           // Try to leap over:
 237           const [ii, jj] = [i + step[0], j + step[1]];
 238           if (V.OnBoard(ii, jj) && this.getColor(ii, jj) == oppCol)
 239             moves.push(this.getBasicMove([x, y], [ii, jj]));
 240         }
 241       }
 242     });
 243     return moves;
 244   }
 245
 246   // NOTE: not really captures, but let's keep the name
 247   getRookCaptures([x, y], byChameleon) {
 248     let moves = [];
 249     const oppCol = V.GetOppCol(this.turn);
 250     // Simple: if something is visible, we can swap
 251     V.steps[V.ROOK].concat(V.steps[V.BISHOP]).forEach(step => {
 252       let [i, j] = [x + step[0], y + step[1]];
 253       while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 254         i += step[0];
 255         j += step[1];
 256       }
 257       if (V.OnBoard(i, j) && this.getColor(i, j) == oppCol) {
 258         const oppPiece = this.getPiece(i, j);
 259         if (!byChameleon || oppPiece == V.ROOK) {
 260           let m = this.getBasicMove([x, y], [i, j]);
 261           m.appear.push(
 262             new PiPo({
 263               x: x,
 264               y: y,
 265               c: oppCol,
 266               p: this.getPiece(i, j)
 267             })
 268           );
 269           moves.push(m);
 270           if (i == x + step[0] && j == y + step[1]) {
 271             // Add mutual destruction option:
 272             m = new Move({
 273               start: { x: x, y: y},
 274               end: { x: i, y: j },
 275               appear: [],
 276               // TODO: is copying necessary here?
 277               vanish: JSON.parse(JSON.stringify(m.vanish))
 278             });
 279             moves.push(m);
 280           }
 281         }
 282       }
 283     });
 284     return moves;
 285   }
 286
 287   // Swapper
 288   getPotentialRookMoves(sq) {
 289     return super.getPotentialQueenMoves(sq).concat(this.getRookCaptures(sq));
 290   }
 291
 292   getKnightCaptures(startSquare, byChameleon) {
 293     // Look in every direction for captures
 294     const steps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 295     const color = this.turn;
 296     const oppCol = V.GetOppCol(color);
 297     let moves = [];
 298     const [x, y] = [startSquare[0], startSquare[1]];
 299     const piece = this.getPiece(x, y); //might be a chameleon!
 300     outerLoop: for (let step of steps) {
 301       let [i, j] = [x + step[0], y + step[1]];
 302       while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 303         i += step[0];
 304         j += step[1];
 305       }
 306       if (
 307         !V.OnBoard(i, j) ||
 308         this.getColor(i, j) == color ||
 309         (!!byChameleon && this.getPiece(i, j) != V.KNIGHT)
 310       ) {
 311         continue;
 312       }
 313       // last(thing), cur(thing) : stop if "cur" is our color,
 314       // or beyond board limits, or if "last" isn't empty and cur neither.
 315       // Otherwise, if cur is empty then add move until cur square;
 316       // if cur is occupied then stop if !!byChameleon and the square not
 317       // occupied by a leaper.
 318       let last = [i, j];
 319       let cur = [i + step[0], j + step[1]];
 320       let vanished = [new PiPo({ x: x, y: y, c: color, p: piece })];
 321       while (V.OnBoard(cur[0], cur[1])) {
 322         if (this.board[last[0]][last[1]] != V.EMPTY) {
 323           const oppPiece = this.getPiece(last[0], last[1]);
 324           if (!!byChameleon && oppPiece != V.KNIGHT) continue outerLoop;
 325           // Something to eat:
 326           vanished.push(
 327             new PiPo({ x: last[0], y: last[1], c: oppCol, p: oppPiece })
 328           );
 329         }
 330         if (this.board[cur[0]][cur[1]] != V.EMPTY) {
 331           if (
 332             this.getColor(cur[0], cur[1]) == color ||
 333             this.board[last[0]][last[1]] != V.EMPTY
 334           ) {
 335             //TODO: redundant test
 336             continue outerLoop;
 337           }
 338         } else {
 339           moves.push(
 340             new Move({
 341               appear: [new PiPo({ x: cur[0], y: cur[1], c: color, p: piece })],
 342               vanish: JSON.parse(JSON.stringify(vanished)), //TODO: required?
 343               start: { x: x, y: y },
 344               end: { x: cur[0], y: cur[1] }
 345             })
 346           );
 347         }
 348         last = [last[0] + step[0], last[1] + step[1]];
 349         cur = [cur[0] + step[0], cur[1] + step[1]];
 350       }
 351     }
 352     return moves;
 353   }
 354
 355   // Long-leaper
 356   getPotentialKnightMoves(sq) {
 357     return super.getPotentialQueenMoves(sq).concat(this.getKnightCaptures(sq));
 358   }
 359
 360   // Chameleon
 361   getPotentialBishopMoves([x, y]) {
 362     const oppCol = V.GetOppCol(this.turn);
 363     let moves = super
 364       .getPotentialQueenMoves([x, y])
 365       .concat(this.getKnightCaptures([x, y], "asChameleon"))
 366       .concat(this.getRookCaptures([x, y], "asChameleon"));
 367     // No "king capture" because king cannot remain under check
 368     this.addQueenCaptures(moves, "asChameleon");
 369     // Also add pawn captures (as a pawn):
 370     const adjacentSteps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 371     adjacentSteps.forEach(step => {
 372       const [i, j] = [x + step[0], y + step[1]];
 373       const [ii, jj] = [i + step[0], j + step[1]];
 374       // Try to leap over (i,j):
 375       if (
 376         V.OnBoard(ii, jj) &&
 377         this.board[i][j] != V.EMPTY &&
 378         this.board[ii][jj] != V.EMPTY &&
 379         this.getColor(ii, jj) == oppCol &&
 380         this.getPiece(ii, jj) == V.PAWN
 381       ) {
 382         moves.push(this.getBasicMove([x, y], [ii, jj]));
 383       }
 384     });
 385     // Post-processing: merge similar moves, concatenating vanish arrays
 386     let mergedMoves = {};
 387     moves.forEach(m => {
 388       const key = m.end.x + V.size.x * m.end.y;
 389       if (!mergedMoves[key]) mergedMoves[key] = m;
 390       else {
 391         for (let i = 1; i < m.vanish.length; i++)
 392           mergedMoves[key].vanish.push(m.vanish[i]);
 393       }
 394     });
 395     return Object.values(mergedMoves);
 396   }
 397
 398   addQueenCaptures(moves, byChameleon) {
 399     if (moves.length == 0) return;
 400     const [x, y] = [moves[0].start.x, moves[0].start.y];
 401     const adjacentSteps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 402     let capturingDirStart = {};
 403     const oppCol = V.GetOppCol(this.turn);
 404     // Useful precomputation:
 405     adjacentSteps.forEach(step => {
 406       const [i, j] = [x + step[0], y + step[1]];
 407       if (
 408         V.OnBoard(i, j) &&
 409         this.board[i][j] != V.EMPTY &&
 410         this.getColor(i, j) == oppCol &&
 411         (!byChameleon || this.getPiece(i, j) == V.QUEEN)
 412       ) {
 413         capturingDirStart[step[0] + "_" + step[1]] = this.getPiece(i, j);
 414       }
 415     });
 416     moves.forEach(m => {
 417       const step = [
 418         m.end.x != x ? (m.end.x - x) / Math.abs(m.end.x - x) : 0,
 419         m.end.y != y ? (m.end.y - y) / Math.abs(m.end.y - y) : 0
 420       ];
 421       // TODO: this test should be done only once per direction
 422       const capture = capturingDirStart[(-step[0]) + "_" + (-step[1])];
 423       if (!!capture) {
 424         const [i, j] = [x - step[0], y - step[1]];
 425         m.vanish.push(
 426           new PiPo({
 427             x: i,
 428             y: j,
 429             p: capture,
 430             c: oppCol
 431           })
 432         );
 433       }
 434       // Also test the end (advancer effect)
 435       const [i, j] = [m.end.x + step[0], m.end.y + step[1]];
 436       if (
 437         V.OnBoard(i, j) &&
 438         this.board[i][j] != V.EMPTY &&
 439         this.getColor(i, j) == oppCol &&
 440         (!byChameleon || this.getPiece(i, j) == V.QUEEN)
 441       ) {
 442         m.vanish.push(
 443           new PiPo({
 444             x: i,
 445             y: j,
 446             p: this.getPiece(i, j),
 447             c: oppCol
 448           })
 449         );
 450       }
 451     });
 452   }
 453
 454   // Withdrawer + advancer: "pushme-pullyu"
 455   getPotentialQueenMoves(sq) {
 456     let moves = super.getPotentialQueenMoves(sq);
 457     this.addQueenCaptures(moves);
 458     return moves;
 459   }
 460
 461   getPotentialImmobilizerMoves(sq) {
 462     // Immobilizer doesn't capture
 463     return super.getPotentialQueenMoves(sq);
 464   }
 465
 466   // Does m2 un-do m1 ? (to disallow undoing swaps)
 467   oppositeMoves(m1, m2) {
 468     return (
 469       !!m1 &&
 470       m2.appear.length == 2 &&
 471       m1.start.x == m2.start.x &&
 472       m1.end.x == m2.end.x &&
 473       m1.start.y == m2.start.y &&
 474       m1.end.y == m2.end.y
 475     );
 476   }
 477
 478   filterValid(moves) {
 479     if (moves.length == 0) return [];
 480     const color = this.turn;
 481     return (
 482       super.filterValid(
 483         moves.filter(m => {
 484           const L = this.smoves.length; //at least 1: init from FEN
 485           return !this.oppositeMoves(this.smoves[L - 1], m);
 486         })
 487       )
 488     );
 489   }
 490
 491   // isAttacked() is OK because the immobilizer doesn't take
 492
 493   isAttackedByPawn([x, y], color) {
 494     // Attacked if an enemy pawn stands just behind an immediate obstacle:
 495     const adjacentSteps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 496     for (let step of adjacentSteps) {
 497       const [i, j] = [x + step[0], y + step[1]];
 498       const [ii, jj] = [i + step[0], j + step[1]];
 499       if (
 500         V.OnBoard(ii, jj) &&
 501         this.board[i][j] != V.EMPTY &&
 502         this.board[ii][jj] != V.EMPTY &&
 503         this.getColor(ii, jj) == color &&
 504         this.getPiece(ii, jj) == V.PAWN &&
 505         !this.isImmobilized([ii, jj])
 506       ) {
 507         return true;
 508       }
 509     }
 510     return false;
 511   }
 512
 513   isAttackedByRook([x, y], color) {
 514     // The only way a swapper can take is by mutual destruction when the
 515     // enemy piece stands just next:
 516     const adjacentSteps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 517     for (let step of adjacentSteps) {
 518       const [i, j] = [x + step[0], y + step[1]];
 519       if (
 520         V.OnBoard(i, j) &&
 521         this.board[i][j] != V.EMPTY &&
 522         this.getColor(i, j) == color &&
 523         this.getPiece(i, j) == V.ROOK &&
 524         !this.isImmobilized([i, j])
 525       ) {
 526         return true;
 527       }
 528     }
 529     return false;
 530   }
 531
 532   isAttackedByKnight([x, y], color) {
 533     // Square (x,y) must be on same line as a knight,
 534     // and there must be empty square(s) behind.
 535     const steps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 536     outerLoop: for (let step of steps) {
 537       const [i0, j0] = [x + step[0], y + step[1]];
 538       if (V.OnBoard(i0, j0) && this.board[i0][j0] == V.EMPTY) {
 539         // Try in opposite direction:
 540         let [i, j] = [x - step[0], y - step[1]];
 541         while (V.OnBoard(i, j)) {
 542           while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 543             i -= step[0];
 544             j -= step[1];
 545           }
 546           if (V.OnBoard(i, j)) {
 547             if (this.getColor(i, j) == color) {
 548               if (
 549                 this.getPiece(i, j) == V.KNIGHT &&
 550                 !this.isImmobilized([i, j])
 551               )
 552                 return true;
 553               continue outerLoop;
 554             }
 555             // [else] Our color,
 556             // could be captured *if there was an empty space*
 557             if (this.board[i + step[0]][j + step[1]] != V.EMPTY)
 558               continue outerLoop;
 559             i -= step[0];
 560             j -= step[1];
 561           }
 562         }
 563       }
 564     }
 565     return false;
 566   }
 567
 568   isAttackedByBishop([x, y], color) {
 569     // We cheat a little here: since this function is used exclusively for
 570     // the king, it's enough to check the immediate surrounding of the square.
 571     const adjacentSteps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 572     for (let step of adjacentSteps) {
 573       const [i, j] = [x + step[0], y + step[1]];
 574       if (
 575         V.OnBoard(i, j) &&
 576         this.board[i][j] != V.EMPTY &&
 577         this.getColor(i, j) == color &&
 578         this.getPiece(i, j) == V.BISHOP &&
 579         !this.isImmobilized([i, j])
 580       ) {
 581         return true;
 582       }
 583     }
 584     return false;
 585   }
 586
 587   isAttackedByQueen([x, y], color) {
 588     // Is there a queen in view?
 589     const adjacentSteps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 590     for (let step of adjacentSteps) {
 591       let [i, j] = [x + step[0], y + step[1]];
 592       while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 593         i += step[0];
 594         j += step[1];
 595       }
 596       if (
 597         V.OnBoard(i, j) &&
 598         this.getColor(i, j) == color &&
 599         this.getPiece(i, j) == V.QUEEN
 600       ) {
 601         // Two cases: the queen is at 2 steps at least, or just close
 602         // but maybe with enough space behind to withdraw.
 603         let attacked = false;
 604         if (i == x + step[0] && j == y + step[1]) {
 605           const [ii, jj] = [i + step[0], j + step[1]];
 606           if (V.OnBoard(ii, jj) && this.board[ii][jj] == V.EMPTY)
 607             attacked = true;
 608         }
 609         else attacked = true;
 610         if (attacked && !this.isImmobilized([i, j])) return true;
 611       }
 612     }
 613     return false;
 614   }
 615
 616   isAttackedByKing([x, y], color) {
 617     const steps = V.steps[V.ROOK].concat(V.steps[V.BISHOP]);
 618     for (let step of steps) {
 619       let rx = x + step[0],
 620           ry = y + step[1];
 621       if (
 622         V.OnBoard(rx, ry) &&
 623         this.getPiece(rx, ry) === V.KING &&
 624         this.getColor(rx, ry) == color &&
 625         !this.isImmobilized([rx, ry])
 626       ) {
 627         return true;
 628       }
 629     }
 630     return false;
 631   }
 632
 633   static GenRandInitFen(randomness) {
 634     if (randomness == 0) {
 635       return (
 636         "91/1rqnbknqm1/1pppppppp1/91/91/91/91/1PPPPPPPP1/1MQNBKNQR1/91 w 0 -"
 637       );
 638     }
 639
 640     let pieces = { w: new Array(8), b: new Array(8) };
 641     // Shuffle pieces on first and last rank
 642     for (let c of ["w", "b"]) {
 643       if (c == 'b' && randomness == 1) {
 644         pieces['b'] = pieces['w'];
 645         break;
 646       }
 647
 648       // Get random squares for every piece, totally freely
 649       let positions = shuffle(ArrayFun.range(8));
 650       const composition = ['r', 'm', 'n', 'n', 'q', 'q', 'b', 'k'];
 651       for (let i = 0; i < 8; i++) pieces[c][positions[i]] = composition[i];
 652     }
 653     return (
 654       "91/1" + pieces["b"].join("") +
 655       "1/1pppppppp1/91/91/91/91/1PPPPPPPP1/1" +
 656       pieces["w"].join("").toUpperCase() + "1/91 w 0 -"
 657     );
 658   }
 659
 660   getSmoveFen() {
 661     const L = this.smoves.length;
 662     return (
 663       !this.smoves[L - 1]
 664         ? "-"
 665         : ChessRules.CoordsToSquare(this.smoves[L - 1].start) +
 666           ChessRules.CoordsToSquare(this.smoves[L - 1].end)
 667     );
 668   }
 669
 670   getFen() {
 671     return super.getFen() + " " + this.getSmoveFen();
 672   }
 673
 674   getFenForRepeat() {
 675     return super.getFenForRepeat() + "_" + this.getSmoveFen();
 676   }
 677
 678   postPlay(move) {
 679     super.postPlay(move);
 680     this.smoves.push(this.getSmove(move));
 681   }
 682
 683   postUndo(move) {
 684     super.postUndo(move);
 685     this.smoves.pop();
 686   }
 687
 688   static get VALUES() {
 689     return {
 690       p: 1,
 691       r: 2,
 692       n: 5,
 693       b: 3,
 694       q: 5,
 695       m: 5,
 696       k: 1000
 697     };
 698   }
 699
 700   static get SEARCH_DEPTH() {
 701     return 2;
 702   }
 703
 704   getNotation(move) {
 705     const initialSquare = V.CoordsToSquare(move.start);
 706     const finalSquare = V.CoordsToSquare(move.end);
 707     if (move.appear.length == 0) {
 708       // Suicide 'S' or mutual destruction 'D':
 709       return (
 710         initialSquare + (move.vanish.length == 1 ? "S" : "D" + finalSquare)
 711       );
 712     }
 713     let notation = undefined;
 714     if (move.appear[0].p == V.PAWN) {
 715       // Pawn: generally ambiguous short notation, so we use full description
 716       notation = "P" + initialSquare + finalSquare;
 717     } else if (move.appear[0].p == V.KING)
 718       notation = "K" + (move.vanish.length > 1 ? "x" : "") + finalSquare;
 719     else notation = move.appear[0].p.toUpperCase() + finalSquare;
 720     // Add a capture mark (not describing what is captured...):
 721     if (move.vanish.length > 1 && move.appear[0].p != V.KING) notation += "X";
 722     return notation;
 723   }
 724 };