client/src/variants/Xiangqi.js

   1 import { ChessRules } from "@/base_rules";
   2
   3 export class XiangqiRules extends ChessRules {
   4
   5   // NOTE (TODO?) scanKings() could be more efficient (in Jangqi too)
   6
   7   static get Monochrome() {
   8     return true;
   9   }
  10
  11   static get Notoodark() {
  12     return true;
  13   }
  14
  15   static get Lines() {
  16     let lines = [];
  17     // Draw all inter-squares lines, shifted:
  18     for (let i = 0; i < V.size.x; i++)
  19       lines.push([[i+0.5, 0.5], [i+0.5, V.size.y-0.5]]);
  20     for (let j = 0; j < V.size.y; j++)
  21       lines.push([[0.5, j+0.5], [V.size.x-0.5, j+0.5]]);
  22     // Add palaces:
  23     lines.push([[0.5, 3.5], [2.5, 5.5]]);
  24     lines.push([[0.5, 5.5], [2.5, 3.5]]);
  25     lines.push([[9.5, 3.5], [7.5, 5.5]]);
  26     lines.push([[9.5, 5.5], [7.5, 3.5]]);
  27     // Show river:
  28     lines.push([[4.5, 0.5], [5.5, 8.5]]);
  29     lines.push([[5.5, 0.5], [4.5, 8.5]]);
  30     return lines;
  31   }
  32
  33   static get HasFlags() {
  34     return false;
  35   }
  36
  37   static get HasEnpassant() {
  38     return false;
  39   }
  40
  41   static get LoseOnRepetition() {
  42     return true;
  43   }
  44
  45   static get ELEPHANT() {
  46     return "e";
  47   }
  48
  49   static get CANNON() {
  50     return "c";
  51   }
  52
  53   static get ADVISOR() {
  54     return "a";
  55   }
  56
  57   static get PIECES() {
  58     return [V.PAWN, V.ROOK, V.KNIGHT, V.ELEPHANT, V.ADVISOR, V.KING, V.CANNON];
  59   }
  60
  61   getPpath(b) {
  62     return "Xiangqi/" + b;
  63   }
  64
  65   static get size() {
  66     return { x: 10, y: 9};
  67   }
  68
  69   getPotentialMovesFrom(sq) {
  70     let moves = [];
  71     const piece = this.getPiece(sq[0], sq[1]);
  72     switch (piece) {
  73       case V.PAWN:
  74         moves = this.getPotentialPawnMoves(sq);
  75         break;
  76       case V.ROOK:
  77         moves = super.getPotentialRookMoves(sq);
  78         break;
  79       case V.KNIGHT:
  80         moves = this.getPotentialKnightMoves(sq);
  81         break;
  82       case V.ELEPHANT:
  83         moves = this.getPotentialElephantMoves(sq);
  84         break;
  85       case V.ADVISOR:
  86         moves = this.getPotentialAdvisorMoves(sq);
  87         break;
  88       case V.KING:
  89         moves = this.getPotentialKingMoves(sq);
  90         break;
  91       case V.CANNON:
  92         moves = this.getPotentialCannonMoves(sq);
  93         break;
  94     }
  95     if (piece != V.KING && this.kingPos['w'][1] != this.kingPos['b'][1])
  96       return moves;
  97     if (this.kingPos['w'][1] == this.kingPos['b'][1]) {
  98       const colKing = this.kingPos['w'][1];
  99       let intercept = 0; //count intercepting pieces
 100       for (let i = this.kingPos['b'][0] + 1; i < this.kingPos['w'][0]; i++) {
 101         if (this.board[i][colKing] != V.EMPTY) intercept++;
 102       }
 103       if (intercept >= 2) return moves;
 104       // intercept == 1 (0 is impossible):
 105       // Any move not removing intercept is OK
 106       return moves.filter(m => {
 107         return (
 108           // From another column?
 109           m.start.y != colKing ||
 110           // From behind a king? (including kings themselves!)
 111           m.start.x <= this.kingPos['b'][0] ||
 112           m.start.x >= this.kingPos['w'][0] ||
 113           // Intercept piece moving: must remain in-between
 114           (
 115             m.end.y == colKing &&
 116             m.end.x > this.kingPos['b'][0] &&
 117             m.end.x < this.kingPos['w'][0]
 118           )
 119         );
 120       });
 121     }
 122     // piece == king: check only if move.end.y == enemy king column
 123     const color = this.getColor(sq[0], sq[1]);
 124     const oppCol = V.GetOppCol(color);
 125     // colCheck == -1 if unchecked, 1 if checked and occupied,
 126     //              0 if checked and clear
 127     let colCheck = -1;
 128     return moves.filter(m => {
 129       if (m.end.y != this.kingPos[oppCol][1]) return true;
 130       if (colCheck < 0) {
 131         // Do the check:
 132         colCheck = 0;
 133         for (let i = this.kingPos['b'][0] + 1; i < this.kingPos['w'][0]; i++) {
 134           if (this.board[i][m.end.y] != V.EMPTY) {
 135             colCheck++;
 136             break;
 137           }
 138         }
 139         return colCheck == 1;
 140       }
 141       // Check already done:
 142       return colCheck == 1;
 143     });
 144   }
 145
 146   getPotentialPawnMoves([x, y]) {
 147     const c = this.getColor(x, y);
 148     const shiftX = (c == 'w' ? -1 : 1);
 149     const crossedRiver = (c == 'w' && x <= 4 || c == 'b' && x >= 5);
 150     const lastRank = (c == 'w' && x == 0 || c == 'b' && x == 9);
 151     let steps = [];
 152     if (!lastRank) steps.push([shiftX, 0]);
 153     if (crossedRiver) {
 154       if (y > 0) steps.push([0, -1]);
 155       if (y < 9) steps.push([0, 1]);
 156     }
 157     return super.getSlideNJumpMoves([x, y], steps, "oneStep");
 158   }
 159
 160   knightStepsFromRookStep(step) {
 161     if (step[0] == 0) return [ [1, 2*step[1]], [-1, 2*step[1]] ];
 162     return [ [2*step[0], 1], [2*step[0], -1] ];
 163   }
 164
 165   getPotentialKnightMoves([x, y]) {
 166     let steps = [];
 167     for (let rookStep of ChessRules.steps[V.ROOK]) {
 168       const [i, j] = [x + rookStep[0], y + rookStep[1]];
 169       if (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 170         Array.prototype.push.apply(steps,
 171           // These moves might be impossible, but need to be checked:
 172           this.knightStepsFromRookStep(rookStep));
 173       }
 174     }
 175     return super.getSlideNJumpMoves([x, y], steps, "oneStep");
 176   }
 177
 178   getPotentialElephantMoves([x, y]) {
 179     let steps = [];
 180     const c = this.getColor(x, y);
 181     for (let bishopStep of ChessRules.steps[V.BISHOP]) {
 182       const [i, j] = [x + bishopStep[0], y + bishopStep[1]];
 183       if (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 184         const [newX, newY] = [x + 2*bishopStep[0], y + 2*bishopStep[1]];
 185         if ((c == 'w' && newX >= 5) || (c == 'b' && newX <= 4))
 186           // A priori valid (elephant don't cross the river)
 187           steps.push(bishopStep.map(s => 2*s));
 188           // "out of board" checks delayed to next method
 189       }
 190     }
 191     return super.getSlideNJumpMoves([x, y], steps, "oneStep");
 192   }
 193
 194   getPotentialAdvisorMoves([x, y]) {
 195     // Diagonal steps inside palace
 196     const c = this.getColor(x, y);
 197     if (
 198       y != 4 ||
 199       (c == 'w' && x != V.size.x - 2) ||
 200       (c == 'b' && x != 1)
 201     ) {
 202       // In a corner: only one step available
 203       let step = null;
 204       const direction = (c == 'w' ? -1 : 1);
 205       if ((c == 'w' && x == V.size.x - 1) || (c == 'b' && x == 0)) {
 206         // On first line
 207         if (y == 3) step = [direction, 1];
 208         else step = [direction, -1];
 209       }
 210       else {
 211         // On third line
 212         if (y == 3) step = [-direction, 1];
 213         else step = [-direction, -1];
 214       }
 215       return super.getSlideNJumpMoves([x, y], [step], "oneStep");
 216     }
 217     // In the middle of the palace:
 218     return (
 219       super.getSlideNJumpMoves([x, y], ChessRules.steps[V.BISHOP], "oneStep")
 220     );
 221   }
 222
 223   getPotentialKingMoves([x, y]) {
 224     // Orthogonal steps inside palace
 225     const c = this.getColor(x, y);
 226     if (
 227       y != 4 ||
 228       (c == 'w' && x != V.size.x - 2) ||
 229       (c == 'b' && x != 1)
 230     ) {
 231       // On the edge: only two steps available
 232       let steps = [];
 233       if (x < (c == 'w' ? V.size.x - 1 : 2)) steps.push([1, 0]);
 234       if (x > (c == 'w' ? V.size.x - 3 : 0)) steps.push([-1, 0]);
 235       if (y > 3) steps.push([0, -1]);
 236       if (y < 5) steps.push([0, 1]);
 237       return super.getSlideNJumpMoves([x, y], steps, "oneStep");
 238     }
 239     // In the middle of the palace:
 240     return (
 241       super.getSlideNJumpMoves([x, y], ChessRules.steps[V.ROOK], "oneStep")
 242     );
 243   }
 244
 245   // NOTE: duplicated from Shako (TODO?)
 246   getPotentialCannonMoves([x, y]) {
 247     const oppCol = V.GetOppCol(this.turn);
 248     let moves = [];
 249     // Look in every direction until an obstacle (to jump) is met
 250     for (const step of V.steps[V.ROOK]) {
 251       let i = x + step[0];
 252       let j = y + step[1];
 253       while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 254         moves.push(this.getBasicMove([x, y], [i, j]));
 255         i += step[0];
 256         j += step[1];
 257       }
 258       // Then, search for an enemy
 259       i += step[0];
 260       j += step[1];
 261       while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 262         i += step[0];
 263         j += step[1];
 264       }
 265       if (V.OnBoard(i, j) && this.getColor(i, j) == oppCol)
 266         moves.push(this.getBasicMove([x, y], [i, j]));
 267     }
 268     return moves;
 269   }
 270
 271   // (King) Never attacked by advisor, since it stays in the palace
 272   // Also, never attacked by elephants since they don't cross the river.
 273   isAttacked(sq, color) {
 274     return (
 275       this.isAttackedByPawn(sq, color) ||
 276       super.isAttackedByRook(sq, color) ||
 277       this.isAttackedByKnight(sq, color) ||
 278       this.isAttackedByCannon(sq, color)
 279     );
 280   }
 281
 282   isAttackedByPawn([x, y], color) {
 283     // The pawn necessarily crossed the river (attack on king)
 284     const shiftX = (color == 'w' ? 1 : -1); //shift from king
 285     return super.isAttackedBySlideNJump(
 286       [x, y], color, V.PAWN, [[shiftX, 0], [0, 1], [0, -1]], "oneStep");
 287   }
 288
 289   knightStepsFromBishopStep(step) {
 290     return [ [2*step[0], step[1]], [step[0], 2*step[1]] ];
 291   }
 292
 293   isAttackedByKnight([x, y], color) {
 294     // Check bishop steps: if empty, look continuation knight step
 295     let steps = [];
 296     for (let s of ChessRules.steps[V.BISHOP]) {
 297       const [i, j] = [x + s[0], y + s[1]];
 298       if (
 299         V.OnBoard(i, j) &&
 300         this.board[i][j] == V.EMPTY
 301       ) {
 302         Array.prototype.push.apply(steps, this.knightStepsFromBishopStep(s));
 303       }
 304     }
 305     return (
 306       super.isAttackedBySlideNJump([x, y], color, V.KNIGHT, steps, "oneStep")
 307     );
 308   }
 309
 310   // NOTE: duplicated from Shako (TODO?)
 311   isAttackedByCannon([x, y], color) {
 312     // Reversed process: is there an obstacle in line,
 313     // and a cannon next in the same line?
 314     for (const step of V.steps[V.ROOK]) {
 315       let [i, j] = [x+step[0], y+step[1]];
 316       while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 317         i += step[0];
 318         j += step[1];
 319       }
 320       if (V.OnBoard(i, j)) {
 321         // Keep looking in this direction
 322         i += step[0];
 323         j += step[1];
 324         while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 325           i += step[0];
 326           j += step[1];
 327         }
 328         if (
 329           V.OnBoard(i, j) &&
 330           this.getPiece(i, j) == V.CANNON &&
 331           this.getColor(i, j) == color
 332         ) {
 333           return true;
 334         }
 335       }
 336     }
 337     return false;
 338   }
 339
 340   getCurrentScore() {
 341     if (this.atLeastOneMove()) return "*";
 342     // Game over
 343     const color = this.turn;
 344     // No valid move: I lose!
 345     return (color == "w" ? "0-1" : "1-0");
 346   }
 347
 348   static get VALUES() {
 349     return {
 350       p: 1,
 351       r: 9,
 352       n: 4,
 353       e: 2.5,
 354       a: 2,
 355       c: 4.5,
 356       k: 1000
 357     };
 358   }
 359
 360   evalPosition() {
 361     let evaluation = 0;
 362     for (let i = 0; i < V.size.x; i++) {
 363       for (let j = 0; j < V.size.y; j++) {
 364         if (this.board[i][j] != V.EMPTY) {
 365           const c = this.getColor(i, j);
 366           const sign = (c == 'w' ? 1 : -1);
 367           const piece = this.getPiece(i, j);
 368           let pieceEval = V.VALUES[this.getPiece(i, j)];
 369           if (
 370             piece == V.PAWN &&
 371             (
 372               (c == 'w' && i <= 4) ||
 373               (c == 'b' && i >= 5)
 374             )
 375           ) {
 376             // Pawn crossed the river: higher value
 377             pieceEval++;
 378           }
 379           evaluation += sign * pieceEval;
 380         }
 381       }
 382     }
 383     return evaluation;
 384   }
 385
 386   static get SEARCH_DEPTH() {
 387     return 2;
 388   }
 389
 390   static GenRandInitFen() {
 391     // No randomization here (TODO?)
 392     return "rneakaenr/9/1c5c1/p1p1p1p1p/9/9/P1P1P1P1P/1C5C1/9/RNEAKAENR w 0";
 393   }
 394
 395   getNotation(move) {
 396     let notation = super.getNotation(move);
 397     if (move.vanish.length == 2 && move.vanish[0].p == V.PAWN)
 398       notation = "P" + notation.substr(1);
 399     return notation;
 400   }
 401
 402 };