client/src/variants/Eightpieces.js

   1 import { ArrayFun } from "@/utils/array";
   2 import { randInt } from "@/utils/alea";
   3 import { ChessRules, PiPo, Move } from "@/base_rules";
   4
   5 export class EightpiecesRules extends ChessRules {
   6   static get JAILER() {
   7     return "j";
   8   }
   9   static get SENTRY() {
  10     return "s";
  11   }
  12   static get LANCER() {
  13     return "l";
  14   }
  15
  16   static get IMAGE_EXTENSION() {
  17     // Temporarily, for the time SVG pieces are being designed:
  18     return ".png";
  19   }
  20
  21   // Lancer directions *from white perspective*
  22   static get LANCER_DIRS() {
  23     return {
  24       'c': [-1, 0], //north
  25       'd': [-1, 1], //N-E
  26       'e': [0, 1], //east
  27       'f': [1, 1], //S-E
  28       'g': [1, 0], //south
  29       'h': [1, -1], //S-W
  30       'm': [0, -1], //west
  31       'o': [-1, -1] //N-W
  32     };
  33   }
  34
  35   static get PIECES() {
  36     return ChessRules.PIECES
  37       .concat([V.JAILER, V.SENTRY])
  38       .concat(Object.keys(V.LANCER_DIRS));
  39   }
  40
  41   getPiece(i, j) {
  42     const piece = this.board[i][j].charAt(1);
  43     // Special lancer case: 8 possible orientations
  44     if (Object.keys(V.LANCER_DIRS).includes(piece)) return V.LANCER;
  45     return piece;
  46   }
  47
  48   getPpath(b, color, score, orientation) {
  49     if ([V.JAILER, V.SENTRY].includes(b[1])) return "Eightpieces/tmp_png/" + b;
  50     if (Object.keys(V.LANCER_DIRS).includes(b[1])) {
  51       if (orientation == 'w') return "Eightpieces/tmp_png/" + b;
  52       // Find opposite direction for adequate display:
  53       let oppDir = '';
  54       switch (b[1]) {
  55         case 'c':
  56           oppDir = 'g';
  57           break;
  58         case 'g':
  59           oppDir = 'c';
  60           break;
  61         case 'd':
  62           oppDir = 'h';
  63           break;
  64         case 'h':
  65           oppDir = 'd';
  66           break;
  67         case 'e':
  68           oppDir = 'm';
  69           break;
  70         case 'm':
  71           oppDir = 'e';
  72           break;
  73         case 'f':
  74           oppDir = 'o';
  75           break;
  76         case 'o':
  77           oppDir = 'f';
  78           break;
  79       }
  80       return "Eightpieces/tmp_png/" + b[0] + oppDir;
  81     }
  82     // TODO: after we have SVG pieces, remove the folder and next prefix:
  83     return "Eightpieces/tmp_png/" + b;
  84   }
  85
  86   getPPpath(b, orientation) {
  87     return this.getPpath(b, null, null, orientation);
  88   }
  89
  90   static ParseFen(fen) {
  91     const fenParts = fen.split(" ");
  92     return Object.assign(
  93       ChessRules.ParseFen(fen),
  94       { sentrypush: fenParts[5] }
  95     );
  96   }
  97
  98   static IsGoodFen(fen) {
  99     if (!ChessRules.IsGoodFen(fen)) return false;
 100     const fenParsed = V.ParseFen(fen);
 101     // 5) Check sentry push (if any)
 102     if (
 103       fenParsed.sentrypush != "-" &&
 104       !fenParsed.sentrypush.match(/^([a-h][1-8],?)+$/)
 105     ) {
 106       return false;
 107     }
 108     return true;
 109   }
 110
 111   getFen() {
 112     return super.getFen() + " " + this.getSentrypushFen();
 113   }
 114
 115   getFenForRepeat() {
 116     return super.getFenForRepeat() + "_" + this.getSentrypushFen();
 117   }
 118
 119   getSentrypushFen() {
 120     const L = this.sentryPush.length;
 121     if (!this.sentryPush[L-1]) return "-";
 122     let res = "";
 123     this.sentryPush[L-1].forEach(coords =>
 124       res += V.CoordsToSquare(coords) + ",");
 125     return res.slice(0, -1);
 126   }
 127
 128   setOtherVariables(fen) {
 129     super.setOtherVariables(fen);
 130     // subTurn == 2 only when a sentry moved, and is about to push something
 131     this.subTurn = 1;
 132     // Sentry position just after a "capture" (subTurn from 1 to 2)
 133     this.sentryPos = null;
 134     // Stack pieces' forbidden squares after a sentry move at each turn
 135     const parsedFen = V.ParseFen(fen);
 136     if (parsedFen.sentrypush == "-") this.sentryPush = [null];
 137     else {
 138       this.sentryPush = [
 139         parsedFen.sentrypush.split(",").map(sq => {
 140           return V.SquareToCoords(sq);
 141         })
 142       ];
 143     }
 144   }
 145
 146   static GenRandInitFen(randomness) {
 147     if (randomness == 0)
 148       // Deterministic:
 149       return "jfsqkbnr/pppppppp/8/8/8/8/PPPPPPPP/JDSQKBNR w 0 ahah - -";
 150
 151     let pieces = { w: new Array(8), b: new Array(8) };
 152     let flags = "";
 153     // Shuffle pieces on first (and last rank if randomness == 2)
 154     for (let c of ["w", "b"]) {
 155       if (c == 'b' && randomness == 1) {
 156         const lancerIdx = pieces['w'].findIndex(p => {
 157           return Object.keys(V.LANCER_DIRS).includes(p);
 158         });
 159         pieces['b'] =
 160           pieces['w'].slice(0, lancerIdx)
 161           .concat(['g'])
 162           .concat(pieces['w'].slice(lancerIdx + 1));
 163         flags += flags;
 164         break;
 165       }
 166
 167       let positions = ArrayFun.range(8);
 168
 169       // Get random squares for bishop and sentry
 170       let randIndex = 2 * randInt(4);
 171       let bishopPos = positions[randIndex];
 172       // The sentry must be on a square of different color
 173       let randIndex_tmp = 2 * randInt(4) + 1;
 174       let sentryPos = positions[randIndex_tmp];
 175       if (c == 'b') {
 176         // Check if white sentry is on the same color as ours.
 177         // If yes: swap bishop and sentry positions.
 178         // NOTE: test % 2 == 1 because there are 7 slashes.
 179         if ((pieces['w'].indexOf('s') - sentryPos) % 2 == 1)
 180           [bishopPos, sentryPos] = [sentryPos, bishopPos];
 181       }
 182       positions.splice(Math.max(randIndex, randIndex_tmp), 1);
 183       positions.splice(Math.min(randIndex, randIndex_tmp), 1);
 184
 185       // Get random squares for knight and lancer
 186       randIndex = randInt(6);
 187       const knightPos = positions[randIndex];
 188       positions.splice(randIndex, 1);
 189       randIndex = randInt(5);
 190       const lancerPos = positions[randIndex];
 191       positions.splice(randIndex, 1);
 192
 193       // Get random square for queen
 194       randIndex = randInt(4);
 195       const queenPos = positions[randIndex];
 196       positions.splice(randIndex, 1);
 197
 198       // Rook, jailer and king positions are now almost fixed,
 199       // only the ordering rook->jailer or jailer->rook must be decided.
 200       let rookPos = positions[0];
 201       let jailerPos = positions[2];
 202       const kingPos = positions[1];
 203       flags += V.CoordToColumn(rookPos) + V.CoordToColumn(jailerPos);
 204       if (Math.random() < 0.5) [rookPos, jailerPos] = [jailerPos, rookPos];
 205
 206       pieces[c][rookPos] = "r";
 207       pieces[c][knightPos] = "n";
 208       pieces[c][bishopPos] = "b";
 209       pieces[c][queenPos] = "q";
 210       pieces[c][kingPos] = "k";
 211       pieces[c][sentryPos] = "s";
 212       // Lancer faces north for white, and south for black:
 213       pieces[c][lancerPos] = c == 'w' ? 'c' : 'g';
 214       pieces[c][jailerPos] = "j";
 215     }
 216     return (
 217       pieces["b"].join("") +
 218       "/pppppppp/8/8/8/8/PPPPPPPP/" +
 219       pieces["w"].join("").toUpperCase() +
 220       " w 0 " + flags + " - -"
 221     );
 222   }
 223
 224   canTake([x1, y1], [x2, y2]) {
 225     if (this.subTurn == 2)
 226       // Only self captures on this subturn:
 227       return this.getColor(x1, y1) == this.getColor(x2, y2);
 228     return super.canTake([x1, y1], [x2, y2]);
 229   }
 230
 231   // Is piece on square (x,y) immobilized?
 232   isImmobilized([x, y]) {
 233     const color = this.getColor(x, y);
 234     const oppCol = V.GetOppCol(color);
 235     for (let step of V.steps[V.ROOK]) {
 236       const [i, j] = [x + step[0], y + step[1]];
 237       if (
 238         V.OnBoard(i, j) &&
 239         this.board[i][j] != V.EMPTY &&
 240         this.getColor(i, j) == oppCol
 241       ) {
 242         if (this.getPiece(i, j) == V.JAILER) return [i, j];
 243       }
 244     }
 245     return null;
 246   }
 247
 248   // Because of the lancers, getPiece() could be wrong:
 249   // use board[x][y][1] instead (always valid).
 250   getBasicMove([sx, sy], [ex, ey], tr) {
 251     const initColor = this.getColor(sx, sy);
 252     const initPiece = this.board[sx][sy].charAt(1);
 253     let mv = new Move({
 254       appear: [
 255         new PiPo({
 256           x: ex,
 257           y: ey,
 258           c: tr ? tr.c : initColor,
 259           p: tr ? tr.p : initPiece
 260         })
 261       ],
 262       vanish: [
 263         new PiPo({
 264           x: sx,
 265           y: sy,
 266           c: initColor,
 267           p: initPiece
 268         })
 269       ]
 270     });
 271
 272     // The opponent piece disappears if we take it
 273     if (this.board[ex][ey] != V.EMPTY) {
 274       mv.vanish.push(
 275         new PiPo({
 276           x: ex,
 277           y: ey,
 278           c: this.getColor(ex, ey),
 279           p: this.board[ex][ey].charAt(1)
 280         })
 281       );
 282     }
 283
 284     return mv;
 285   }
 286
 287   canIplay(side, [x, y]) {
 288     return (
 289       (this.subTurn == 1 && this.turn == side && this.getColor(x, y) == side) ||
 290       (this.subTurn == 2 && x == this.sentryPos.x && y == this.sentryPos.y)
 291     );
 292   }
 293
 294   getPotentialMovesFrom([x, y]) {
 295     // At subTurn == 2, jailers aren't effective (Jeff K)
 296     const piece = this.getPiece(x, y);
 297     const L = this.sentryPush.length;
 298     if (this.subTurn == 1) {
 299       const jsq = this.isImmobilized([x, y]);
 300       if (!!jsq) {
 301         let moves = [];
 302         // Special pass move if king:
 303         if (piece == V.KING) {
 304           moves.push(
 305             new Move({
 306               appear: [],
 307               vanish: [],
 308               start: { x: x, y: y },
 309               end: { x: jsq[0], y: jsq[1] }
 310             })
 311           );
 312         }
 313         else if (piece == V.LANCER && !!this.sentryPush[L-1]) {
 314           // A pushed lancer next to the jailer: reorient
 315           const color = this.getColor(x, y);
 316           const curDir = this.board[x][y].charAt(1);
 317           Object.keys(V.LANCER_DIRS).forEach(k => {
 318             moves.push(
 319               new Move({
 320                 appear: [{ x: x, y: y, c: color, p: k }],
 321                 vanish: [{ x: x, y: y, c: color, p: curDir }],
 322                 start: { x: x, y: y },
 323                 end: { x: jsq[0], y: jsq[1] }
 324               })
 325             );
 326           });
 327         }
 328         return moves;
 329       }
 330     }
 331     let moves = [];
 332     switch (piece) {
 333       case V.JAILER:
 334         moves = this.getPotentialJailerMoves([x, y]);
 335         break;
 336       case V.SENTRY:
 337         moves = this.getPotentialSentryMoves([x, y]);
 338         break;
 339       case V.LANCER:
 340         moves = this.getPotentialLancerMoves([x, y]);
 341         break;
 342       default:
 343         moves = super.getPotentialMovesFrom([x, y]);
 344         break;
 345     }
 346     if (!!this.sentryPush[L-1]) {
 347       // Delete moves walking back on sentry push path,
 348       // only if not a pawn, and the piece is the pushed one.
 349       const pl = this.sentryPush[L-1].length;
 350       const finalPushedSq = this.sentryPush[L-1][pl-1];
 351       moves = moves.filter(m => {
 352         if (
 353           m.vanish[0].p != V.PAWN &&
 354           m.start.x == finalPushedSq.x && m.start.y == finalPushedSq.y &&
 355           this.sentryPush[L-1].some(sq => sq.x == m.end.x && sq.y == m.end.y)
 356         ) {
 357           return false;
 358         }
 359         return true;
 360       });
 361     } else if (this.subTurn == 2) {
 362       // Put back the sentinel on board:
 363       const color = this.turn;
 364       moves.forEach(m => {
 365         m.appear.push({x: x, y: y, p: V.SENTRY, c: color});
 366       });
 367     }
 368     return moves;
 369   }
 370
 371   getPotentialPawnMoves([x, y]) {
 372     const color = this.getColor(x, y);
 373     let moves = [];
 374     const [sizeX, sizeY] = [V.size.x, V.size.y];
 375     let shiftX = (color == "w" ? -1 : 1);
 376     if (this.subTurn == 2) shiftX *= -1;
 377     const firstRank = color == "w" ? sizeX - 1 : 0;
 378     const startRank = color == "w" ? sizeX - 2 : 1;
 379     const lastRank = color == "w" ? 0 : sizeX - 1;
 380
 381     // Pawns might be pushed on 1st rank and attempt to move again:
 382     if (!V.OnBoard(x + shiftX, y)) return [];
 383
 384     const finalPieces =
 385       // A push cannot put a pawn on last rank (it goes backward)
 386       x + shiftX == lastRank
 387         ? Object.keys(V.LANCER_DIRS).concat(
 388           [V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN, V.SENTRY, V.JAILER])
 389         : [V.PAWN];
 390     if (this.board[x + shiftX][y] == V.EMPTY) {
 391       // One square forward
 392       for (let piece of finalPieces) {
 393         moves.push(
 394           this.getBasicMove([x, y], [x + shiftX, y], {
 395             c: color,
 396             p: piece
 397           })
 398         );
 399       }
 400       if (
 401         // 2-squares jumps forbidden if pawn push
 402         this.subTurn == 1 &&
 403         [startRank, firstRank].includes(x) &&
 404         this.board[x + 2 * shiftX][y] == V.EMPTY
 405       ) {
 406         // Two squares jump
 407         moves.push(this.getBasicMove([x, y], [x + 2 * shiftX, y]));
 408       }
 409     }
 410     // Captures
 411     for (let shiftY of [-1, 1]) {
 412       if (
 413         y + shiftY >= 0 &&
 414         y + shiftY < sizeY &&
 415         this.board[x + shiftX][y + shiftY] != V.EMPTY &&
 416         this.canTake([x, y], [x + shiftX, y + shiftY])
 417       ) {
 418         for (let piece of finalPieces) {
 419           moves.push(
 420             this.getBasicMove([x, y], [x + shiftX, y + shiftY], {
 421               c: color,
 422               p: piece
 423             })
 424           );
 425         }
 426       }
 427     }
 428
 429     // En passant: only on subTurn == 1
 430     const Lep = this.epSquares.length;
 431     const epSquare = this.epSquares[Lep - 1];
 432     if (
 433       this.subTurn == 1 &&
 434       !!epSquare &&
 435       epSquare.x == x + shiftX &&
 436       Math.abs(epSquare.y - y) == 1
 437     ) {
 438       let enpassantMove = this.getBasicMove([x, y], [epSquare.x, epSquare.y]);
 439       enpassantMove.vanish.push({
 440         x: x,
 441         y: epSquare.y,
 442         p: "p",
 443         c: this.getColor(x, epSquare.y)
 444       });
 445       moves.push(enpassantMove);
 446     }
 447
 448     return moves;
 449   }
 450
 451   // Obtain all lancer moves in "step" direction
 452   getPotentialLancerMoves_aux([x, y], step, tr) {
 453     let moves = [];
 454     // Add all moves to vacant squares until opponent is met:
 455     const color = this.getColor(x, y);
 456     const oppCol =
 457       this.subTurn == 1
 458         ? V.GetOppCol(color)
 459         // at subTurn == 2, consider own pieces as opponent
 460         : color;
 461     let sq = [x + step[0], y + step[1]];
 462     while (V.OnBoard(sq[0], sq[1]) && this.getColor(sq[0], sq[1]) != oppCol) {
 463       if (this.board[sq[0]][sq[1]] == V.EMPTY)
 464         moves.push(this.getBasicMove([x, y], sq, tr));
 465       sq[0] += step[0];
 466       sq[1] += step[1];
 467     }
 468     if (V.OnBoard(sq[0], sq[1]))
 469       // Add capturing move
 470       moves.push(this.getBasicMove([x, y], sq, tr));
 471     return moves;
 472   }
 473
 474   getPotentialLancerMoves([x, y]) {
 475     let moves = [];
 476     // Add all lancer possible orientations, similar to pawn promotions.
 477     // Except if just after a push: allow all movements from init square then
 478     const L = this.sentryPush.length;
 479     const color = this.getColor(x, y);
 480     if (!!this.sentryPush[L-1]) {
 481       // Maybe I was pushed
 482       const pl = this.sentryPush[L-1].length;
 483       if (
 484         this.sentryPush[L-1][pl-1].x == x &&
 485         this.sentryPush[L-1][pl-1].y == y
 486       ) {
 487         // I was pushed: allow all directions (for this move only), but
 488         // do not change direction after moving, *except* if I keep the
 489         // same orientation in which I was pushed.
 490         const curDir = V.LANCER_DIRS[this.board[x][y].charAt(1)];
 491         Object.values(V.LANCER_DIRS).forEach(step => {
 492           const dirCode = Object.keys(V.LANCER_DIRS).find(k => {
 493             return (
 494               V.LANCER_DIRS[k][0] == step[0] &&
 495               V.LANCER_DIRS[k][1] == step[1]
 496             );
 497           });
 498           const dirMoves =
 499             this.getPotentialLancerMoves_aux(
 500               [x, y],
 501               step,
 502               { p: dirCode, c: color }
 503             );
 504           if (curDir[0] == step[0] && curDir[1] == step[1]) {
 505             // Keeping same orientation: can choose after
 506             let chooseMoves = [];
 507             dirMoves.forEach(m => {
 508               Object.keys(V.LANCER_DIRS).forEach(k => {
 509                 let mk = JSON.parse(JSON.stringify(m));
 510                 mk.appear[0].p = k;
 511                 moves.push(mk);
 512               });
 513             });
 514             Array.prototype.push.apply(moves, chooseMoves);
 515           } else Array.prototype.push.apply(moves, dirMoves);
 516         });
 517         return moves;
 518       }
 519     }
 520     // I wasn't pushed: standard lancer move
 521     const dirCode = this.board[x][y][1];
 522     const monodirMoves =
 523       this.getPotentialLancerMoves_aux([x, y], V.LANCER_DIRS[dirCode]);
 524     // Add all possible orientations aftermove except if I'm being pushed
 525     if (this.subTurn == 1) {
 526       monodirMoves.forEach(m => {
 527         Object.keys(V.LANCER_DIRS).forEach(k => {
 528           let mk = JSON.parse(JSON.stringify(m));
 529           mk.appear[0].p = k;
 530           moves.push(mk);
 531         });
 532       });
 533       return moves;
 534     } else {
 535       // I'm pushed: add potential nudges
 536       let potentialNudges = [];
 537       for (let step of V.steps[V.ROOK].concat(V.steps[V.BISHOP])) {
 538         if (
 539           V.OnBoard(x + step[0], y + step[1]) &&
 540           this.board[x + step[0]][y + step[1]] == V.EMPTY
 541         ) {
 542           const newDirCode = Object.keys(V.LANCER_DIRS).find(k => {
 543             const codeStep = V.LANCER_DIRS[k];
 544             return (codeStep[0] == step[0] && codeStep[1] == step[1]);
 545           });
 546           potentialNudges.push(
 547             this.getBasicMove(
 548               [x, y],
 549               [x + step[0], y + step[1]],
 550               { c: color, p: newDirCode }
 551             )
 552           );
 553         }
 554       }
 555       return monodirMoves.concat(potentialNudges);
 556     }
 557   }
 558
 559   getPotentialSentryMoves([x, y]) {
 560     // The sentry moves a priori like a bishop:
 561     let moves = super.getPotentialBishopMoves([x, y]);
 562     // ...but captures are replaced by special move, if and only if
 563     // "captured" piece can move now, considered as the capturer unit.
 564     // --> except is subTurn == 2, in this case I don't push anything.
 565     if (this.subTurn == 2) return moves.filter(m => m.vanish.length == 1);
 566     moves.forEach(m => {
 567       if (m.vanish.length == 2) {
 568         // Temporarily cancel the sentry capture:
 569         m.appear.pop();
 570         m.vanish.pop();
 571       }
 572     });
 573     const color = this.getColor(x, y);
 574     const fMoves = moves.filter(m => {
 575       // Can the pushed unit make any move? ...resulting in a non-self-check?
 576       if (m.appear.length == 0) {
 577         let res = false;
 578         this.play(m);
 579         let moves2 = this.getPotentialMovesFrom([m.end.x, m.end.y]);
 580         for (let m2 of moves2) {
 581           this.play(m2);
 582           res = !this.underCheck(color);
 583           this.undo(m2);
 584           if (res) break;
 585         }
 586         this.undo(m);
 587         return res;
 588       }
 589       return true;
 590     });
 591     return fMoves;
 592   }
 593
 594   getPotentialJailerMoves([x, y]) {
 595     return super.getPotentialRookMoves([x, y]).filter(m => {
 596       // Remove jailer captures
 597       return m.vanish[0].p != V.JAILER || m.vanish.length == 1;
 598     });
 599   }
 600
 601   getPotentialKingMoves(sq) {
 602     const moves = this.getSlideNJumpMoves(
 603       sq,
 604       V.steps[V.ROOK].concat(V.steps[V.BISHOP]),
 605       "oneStep"
 606     );
 607     return (
 608       this.subTurn == 1
 609         ? moves.concat(this.getCastleMoves(sq))
 610         : moves
 611     );
 612   }
 613
 614   atLeastOneMove() {
 615     // If in second-half of a move, we already know that a move is possible
 616     if (this.subTurn == 2) return true;
 617     return super.atLeastOneMove();
 618   }
 619
 620   filterValid(moves) {
 621     if (moves.length == 0) return [];
 622     const basicFilter = (m, c) => {
 623       this.play(m);
 624       const res = !this.underCheck(c);
 625       this.undo(m);
 626       return res;
 627     };
 628     // Disable check tests for sentry pushes,
 629     // because in this case the move isn't finished
 630     let movesWithoutSentryPushes = [];
 631     let movesWithSentryPushes = [];
 632     moves.forEach(m => {
 633       // Second condition below for special king "pass" moves
 634       if (m.appear.length > 0 || m.vanish.length == 0)
 635         movesWithoutSentryPushes.push(m);
 636       else movesWithSentryPushes.push(m);
 637     });
 638     const color = this.turn;
 639     const oppCol = V.GetOppCol(color);
 640     const filteredMoves =
 641       movesWithoutSentryPushes.filter(m => basicFilter(m, color));
 642     // If at least one full move made, everything is allowed.
 643     // Else: forbid checks and captures.
 644     return (
 645       this.movesCount >= 2
 646         ? filteredMoves
 647         : filteredMoves.filter(m => {
 648           return (m.vanish.length <= 1 && basicFilter(m, oppCol));
 649         })
 650     ).concat(movesWithSentryPushes);
 651   }
 652
 653   getAllValidMoves() {
 654     if (this.subTurn == 1) return super.getAllValidMoves();
 655     // Sentry push:
 656     const sentrySq = [this.sentryPos.x, this.sentryPos.y];
 657     return this.filterValid(this.getPotentialMovesFrom(sentrySq));
 658   }
 659
 660   isAttacked(sq, color) {
 661     return (
 662       super.isAttacked(sq, color) ||
 663       this.isAttackedByLancer(sq, color) ||
 664       this.isAttackedBySentry(sq, color)
 665       // The jailer doesn't capture.
 666     );
 667   }
 668
 669   isAttackedBySlideNJump([x, y], color, piece, steps, oneStep) {
 670     for (let step of steps) {
 671       let rx = x + step[0],
 672           ry = y + step[1];
 673       while (V.OnBoard(rx, ry) && this.board[rx][ry] == V.EMPTY && !oneStep) {
 674         rx += step[0];
 675         ry += step[1];
 676       }
 677       if (
 678         V.OnBoard(rx, ry) &&
 679         this.getPiece(rx, ry) == piece &&
 680         this.getColor(rx, ry) == color &&
 681         !this.isImmobilized([rx, ry])
 682       ) {
 683         return true;
 684       }
 685     }
 686     return false;
 687   }
 688
 689   isAttackedByPawn([x, y], color) {
 690     const pawnShift = (color == "w" ? 1 : -1);
 691     if (x + pawnShift >= 0 && x + pawnShift < V.size.x) {
 692       for (let i of [-1, 1]) {
 693         if (
 694           y + i >= 0 &&
 695           y + i < V.size.y &&
 696           this.getPiece(x + pawnShift, y + i) == V.PAWN &&
 697           this.getColor(x + pawnShift, y + i) == color &&
 698           !this.isImmobilized([x + pawnShift, y + i])
 699         ) {
 700           return true;
 701         }
 702       }
 703     }
 704     return false;
 705   }
 706
 707   isAttackedByLancer([x, y], color) {
 708     for (let step of V.steps[V.ROOK].concat(V.steps[V.BISHOP])) {
 709       // If in this direction there are only enemy pieces and empty squares,
 710       // and we meet a lancer: can he reach us?
 711       // NOTE: do not stop at first lancer, there might be several!
 712       let coord = { x: x + step[0], y: y + step[1] };
 713       let lancerPos = [];
 714       while (
 715         V.OnBoard(coord.x, coord.y) &&
 716         (
 717           this.board[coord.x][coord.y] == V.EMPTY ||
 718           this.getColor(coord.x, coord.y) == color
 719         )
 720       ) {
 721         if (
 722           this.getPiece(coord.x, coord.y) == V.LANCER &&
 723           !this.isImmobilized([coord.x, coord.y])
 724         ) {
 725           lancerPos.push({x: coord.x, y: coord.y});
 726         }
 727         coord.x += step[0];
 728         coord.y += step[1];
 729       }
 730       for (let xy of lancerPos) {
 731         const dir = V.LANCER_DIRS[this.board[xy.x][xy.y].charAt(1)];
 732         if (dir[0] == -step[0] && dir[1] == -step[1]) return true;
 733       }
 734     }
 735     return false;
 736   }
 737
 738   // Helper to check sentries attacks:
 739   selfAttack([x1, y1], [x2, y2]) {
 740     const color = this.getColor(x1, y1);
 741     const oppCol = V.GetOppCol(color);
 742     const sliderAttack = (allowedSteps, lancer) => {
 743       const deltaX = x2 - x1,
 744             absDeltaX = Math.abs(deltaX);
 745       const deltaY = y2 - y1,
 746             absDeltaY = Math.abs(deltaY);
 747       const step = [ deltaX / absDeltaX || 0, deltaY / absDeltaY || 0 ];
 748       if (
 749         // Check that the step is a priori valid:
 750         (absDeltaX != absDeltaY && deltaX != 0 && deltaY != 0) ||
 751         allowedSteps.every(st => st[0] != step[0] || st[1] != step[1])
 752       ) {
 753         return false;
 754       }
 755       let sq = [ x1 + step[0], y1 + step[1] ];
 756       while (sq[0] != x2 || sq[1] != y2) {
 757         if (
 758           // NOTE: no need to check OnBoard in this special case
 759           (!lancer && this.board[sq[0]][sq[1]] != V.EMPTY) ||
 760           (!!lancer && this.getColor(sq[0], sq[1]) == oppCol)
 761         ) {
 762           return false;
 763         }
 764         sq[0] += step[0];
 765         sq[1] += step[1];
 766       }
 767       return true;
 768     };
 769     switch (this.getPiece(x1, y1)) {
 770       case V.PAWN: {
 771         // Pushed pawns move as enemy pawns
 772         const shift = (color == 'w' ? 1 : -1);
 773         return (x1 + shift == x2 && Math.abs(y1 - y2) == 1);
 774       }
 775       case V.KNIGHT: {
 776         const deltaX = Math.abs(x1 - x2);
 777         const deltaY = Math.abs(y1 - y2);
 778         return (
 779           deltaX + deltaY == 3 &&
 780           [1, 2].includes(deltaX) &&
 781           [1, 2].includes(deltaY)
 782         );
 783       }
 784       case V.ROOK:
 785         return sliderAttack(V.steps[V.ROOK]);
 786       case V.BISHOP:
 787         return sliderAttack(V.steps[V.BISHOP]);
 788       case V.QUEEN:
 789         return sliderAttack(V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
 790       case V.LANCER: {
 791         // Special case: as long as no enemy units stands in-between, it attacks
 792         // (if it points toward the king).
 793         const allowedStep = V.LANCER_DIRS[this.board[x1][y1].charAt(1)];
 794         return sliderAttack([allowedStep], "lancer");
 795       }
 796       // No sentries or jailer tests: they cannot self-capture
 797     }
 798     return false;
 799   }
 800
 801   isAttackedBySentry([x, y], color) {
 802     // Attacked by sentry means it can self-take our king.
 803     // Just check diagonals of enemy sentry(ies), and if it reaches
 804     // one of our pieces: can I self-take?
 805     const myColor = V.GetOppCol(color);
 806     let candidates = [];
 807     for (let i=0; i<V.size.x; i++) {
 808       for (let j=0; j<V.size.y; j++) {
 809         if (
 810           this.getPiece(i,j) == V.SENTRY &&
 811           this.getColor(i,j) == color &&
 812           !this.isImmobilized([i, j])
 813         ) {
 814           for (let step of V.steps[V.BISHOP]) {
 815             let sq = [ i + step[0], j + step[1] ];
 816             while (
 817               V.OnBoard(sq[0], sq[1]) &&
 818               this.board[sq[0]][sq[1]] == V.EMPTY
 819             ) {
 820               sq[0] += step[0];
 821               sq[1] += step[1];
 822             }
 823             if (
 824               V.OnBoard(sq[0], sq[1]) &&
 825               this.getColor(sq[0], sq[1]) == myColor
 826             ) {
 827               candidates.push([ sq[0], sq[1] ]);
 828             }
 829           }
 830         }
 831       }
 832     }
 833     for (let c of candidates)
 834       if (this.selfAttack(c, [x, y])) return true;
 835     return false;
 836   }
 837
 838   // Jailer doesn't capture or give check
 839
 840   prePlay(move) {
 841     if (move.appear.length == 0 && move.vanish.length == 1)
 842       // The sentry is about to push a piece: subTurn goes from 1 to 2
 843       this.sentryPos = { x: move.end.x, y: move.end.y };
 844     if (this.subTurn == 2 && move.vanish[0].p != V.PAWN) {
 845       // A piece is pushed: forbid array of squares between start and end
 846       // of move, included (except if it's a pawn)
 847       let squares = [];
 848       if ([V.KNIGHT,V.KING].includes(move.vanish[0].p))
 849         // short-range pieces: just forbid initial square
 850         squares.push({ x: move.start.x, y: move.start.y });
 851       else {
 852         const deltaX = move.end.x - move.start.x;
 853         const deltaY = move.end.y - move.start.y;
 854         const step = [
 855           deltaX / Math.abs(deltaX) || 0,
 856           deltaY / Math.abs(deltaY) || 0
 857         ];
 858         for (
 859           let sq = {x: move.start.x, y: move.start.y};
 860           sq.x != move.end.x || sq.y != move.end.y;
 861           sq.x += step[0], sq.y += step[1]
 862         ) {
 863           squares.push({ x: sq.x, y: sq.y });
 864         }
 865       }
 866       // Add end square as well, to know if I was pushed (useful for lancers)
 867       squares.push({ x: move.end.x, y: move.end.y });
 868       this.sentryPush.push(squares);
 869     } else this.sentryPush.push(null);
 870   }
 871
 872   play(move) {
 873     this.prePlay(move);
 874     move.flags = JSON.stringify(this.aggregateFlags());
 875     this.epSquares.push(this.getEpSquare(move));
 876     V.PlayOnBoard(this.board, move);
 877     // Is it a sentry push? (useful for undo)
 878     move.sentryPush = (this.subTurn == 2);
 879     if (this.subTurn == 1) this.movesCount++;
 880     if (move.appear.length == 0 && move.vanish.length == 1) this.subTurn = 2;
 881     else {
 882       // Turn changes only if not a sentry "pre-push"
 883       this.turn = V.GetOppCol(this.turn);
 884       this.subTurn = 1;
 885     }
 886     this.postPlay(move);
 887   }
 888
 889   postPlay(move) {
 890     if (move.vanish.length == 0 || this.subTurn == 2)
 891       // Special pass move of the king, or sentry pre-push: nothing to update
 892       return;
 893     const c = move.vanish[0].c;
 894     const piece = move.vanish[0].p;
 895     const firstRank = c == "w" ? V.size.x - 1 : 0;
 896
 897     if (piece == V.KING) {
 898       this.kingPos[c][0] = move.appear[0].x;
 899       this.kingPos[c][1] = move.appear[0].y;
 900       this.castleFlags[c] = [V.size.y, V.size.y];
 901       return;
 902     }
 903     // Update castling flags if rooks are moved
 904     const oppCol = V.GetOppCol(c);
 905     const oppFirstRank = V.size.x - 1 - firstRank;
 906     if (
 907       move.start.x == firstRank && //our rook moves?
 908       this.castleFlags[c].includes(move.start.y)
 909     ) {
 910       const flagIdx = (move.start.y == this.castleFlags[c][0] ? 0 : 1);
 911       this.castleFlags[c][flagIdx] = V.size.y;
 912     } else if (
 913       move.end.x == oppFirstRank && //we took opponent rook?
 914       this.castleFlags[oppCol].includes(move.end.y)
 915     ) {
 916       const flagIdx = (move.end.y == this.castleFlags[oppCol][0] ? 0 : 1);
 917       this.castleFlags[oppCol][flagIdx] = V.size.y;
 918     }
 919   }
 920
 921   undo(move) {
 922     this.epSquares.pop();
 923     this.disaggregateFlags(JSON.parse(move.flags));
 924     V.UndoOnBoard(this.board, move);
 925     // Decrement movesCount except if the move is a sentry push
 926     if (!move.sentryPush) this.movesCount--;
 927     if (this.subTurn == 2) this.subTurn = 1;
 928     else {
 929       this.turn = V.GetOppCol(this.turn);
 930       if (move.sentryPush) this.subTurn = 2;
 931     }
 932     this.postUndo(move);
 933   }
 934
 935   postUndo(move) {
 936     super.postUndo(move);
 937     this.sentryPush.pop();
 938   }
 939
 940   static get VALUES() {
 941     return Object.assign(
 942       { l: 4.8, s: 2.8, j: 3.8 }, //Jeff K. estimations
 943       ChessRules.VALUES
 944     );
 945   }
 946
 947   getComputerMove() {
 948     const maxeval = V.INFINITY;
 949     const color = this.turn;
 950     let moves1 = this.getAllValidMoves();
 951
 952     if (moves1.length == 0)
 953       // TODO: this situation should not happen
 954       return null;
 955
 956     const setEval = (move, next) => {
 957       const score = this.getCurrentScore();
 958       const curEval = move.eval;
 959       if (score != "*") {
 960         move.eval =
 961           score == "1/2"
 962             ? 0
 963             : (score == "1-0" ? 1 : -1) * maxeval;
 964       } else move.eval = this.evalPosition();
 965       if (
 966         // "next" is defined after sentry pushes
 967         !!next && (
 968           !curEval ||
 969           color == 'w' && move.eval > curEval ||
 970           color == 'b' && move.eval < curEval
 971         )
 972       ) {
 973         move.second = next;
 974       }
 975     };
 976
 977     // Just search_depth == 1 (because of sentries. TODO: can do better...)
 978     moves1.forEach(m1 => {
 979       this.play(m1);
 980       if (this.subTurn == 1) setEval(m1);
 981       else {
 982         // Need to play every pushes and count:
 983         const moves2 = this.getAllValidMoves();
 984         moves2.forEach(m2 => {
 985           this.play(m2);
 986           setEval(m1, m2);
 987           this.undo(m2);
 988         });
 989       }
 990       this.undo(m1);
 991     });
 992
 993     moves1.sort((a, b) => {
 994       return (color == "w" ? 1 : -1) * (b.eval - a.eval);
 995     });
 996     let candidates = [0];
 997     for (let j = 1; j < moves1.length && moves1[j].eval == moves1[0].eval; j++)
 998       candidates.push(j);
 999     const choice = moves1[candidates[randInt(candidates.length)]];
1000     return (!choice.second ? choice : [choice, choice.second]);
1001   }
1002
1003   // For moves notation:
1004   static get LANCER_DIRNAMES() {
1005     return {
1006       'c': "N",
1007       'd': "NE",
1008       'e': "E",
1009       'f': "SE",
1010       'g': "S",
1011       'h': "SW",
1012       'm': "W",
1013       'o': "NW"
1014     };
1015   }
1016
1017   getNotation(move) {
1018     // Special case "king takes jailer" is a pass move
1019     if (move.appear.length == 0 && move.vanish.length == 0) return "pass";
1020     let notation = undefined;
1021     if (this.subTurn == 2) {
1022       // Do not consider appear[1] (sentry) for sentry pushes
1023       const simpleMove = {
1024         appear: [move.appear[0]],
1025         vanish: move.vanish,
1026         start: move.start,
1027         end: move.end
1028       };
1029       notation = super.getNotation(simpleMove);
1030     } else notation = super.getNotation(move);
1031     if (Object.keys(V.LANCER_DIRNAMES).includes(move.vanish[0].p))
1032       // Lancer: add direction info
1033       notation += "=" + V.LANCER_DIRNAMES[move.appear[0].p];
1034     else if (
1035       move.vanish[0].p == V.PAWN &&
1036       Object.keys(V.LANCER_DIRNAMES).includes(move.appear[0].p)
1037     ) {
1038       // Fix promotions in lancer:
1039       notation = notation.slice(0, -1) + "L:" + V.LANCER_DIRNAMES[move.appear[0].p];
1040     }
1041     return notation;
1042   }
1043 };