client/src/variants/Grasshopper.js

   1 import { ChessRules } from "@/base_rules";
   2 import { ArrayFun } from "@/utils/array";
   3 import { randInt } from "@/utils/alea";
   4
   5 export const VariantRules = class GrasshopperRules extends ChessRules {
   6   static get HasEnpassant() {
   7     return false;
   8   }
   9
  10   static get GRASSHOPPER() {
  11     return "g";
  12   }
  13
  14   static get PIECES() {
  15     return ChessRules.PIECES.concat([V.GRASSHOPPER]);
  16   }
  17
  18   getPpath(b) {
  19     return (b[1] == V.GRASSHOPPER ? "Grasshopper/" : "") + b;
  20   }
  21
  22   getPotentialMovesFrom([x, y]) {
  23     switch (this.getPiece(x, y)) {
  24       case V.GRASSHOPPER:
  25         return this.getPotentialGrasshopperMoves([x, y]);
  26       default:
  27         return super.getPotentialMovesFrom([x, y]);
  28     }
  29   }
  30
  31   getPotentialPawnMoves([x, y]) {
  32     const color = this.turn;
  33     let moves = [];
  34     const [sizeX, sizeY] = [V.size.x, V.size.y];
  35     const shiftX = color == "w" ? -1 : 1;
  36     const lastRank = color == "w" ? 0 : sizeX - 1;
  37
  38     const finalPieces =
  39       x + shiftX == lastRank
  40         ? [V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN, V.GRASSHOPPER]
  41         : [V.PAWN];
  42     if (this.board[x + shiftX][y] == V.EMPTY) {
  43       // One square forward
  44       for (let piece of finalPieces) {
  45         moves.push(
  46           this.getBasicMove([x, y], [x + shiftX, y], {
  47             c: color,
  48             p: piece
  49           })
  50         );
  51       }
  52       // No 2-squares jump
  53     }
  54     // Captures
  55     for (let shiftY of [-1, 1]) {
  56       if (
  57         y + shiftY >= 0 &&
  58         y + shiftY < sizeY &&
  59         this.board[x + shiftX][y + shiftY] != V.EMPTY &&
  60         this.canTake([x, y], [x + shiftX, y + shiftY])
  61       ) {
  62         for (let piece of finalPieces) {
  63           moves.push(
  64             this.getBasicMove([x, y], [x + shiftX, y + shiftY], {
  65               c: color,
  66               p: piece
  67             })
  68           );
  69         }
  70       }
  71     }
  72
  73     return moves;
  74   }
  75
  76   getPotentialGrasshopperMoves([x, y]) {
  77     let moves = [];
  78     // Look in every direction until an obstacle (to jump) is met
  79     for (const step of V.steps[V.ROOK].concat(V.steps[V.BISHOP])) {
  80       let i = x + step[0];
  81       let j = y + step[1];
  82       while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
  83         i += step[0];
  84         j += step[1];
  85       }
  86       // Move is valid if the next square is empty or occupied by enemy
  87       const nextSq = [i+step[0], j+step[1]];
  88       if (V.OnBoard(nextSq[0], nextSq[1]) && this.canTake([x, y], nextSq))
  89         moves.push(this.getBasicMove([x, y], nextSq));
  90     }
  91     return moves;
  92   }
  93
  94   isAttacked(sq, colors) {
  95     return (
  96       super.isAttacked(sq, colors) ||
  97       this.isAttackedByGrasshopper(sq, colors)
  98     );
  99   }
 100
 101   isAttackedByGrasshopper([x, y], colors) {
 102     // Reversed process: is there an adjacent obstacle,
 103     // and a grasshopper next in the same line?
 104     for (const step of V.steps[V.ROOK].concat(V.steps[V.BISHOP])) {
 105       const nextSq = [x+step[0], y+step[1]];
 106       if (
 107         V.OnBoard(nextSq[0], nextSq[1]) &&
 108         this.board[nextSq[0]][nextSq[1]] != V.EMPTY
 109       ) {
 110         let i = nextSq[0] + step[0];
 111         let j = nextSq[1] + step[1];
 112         while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
 113           i += step[0];
 114           j += step[1];
 115         }
 116         if (
 117           V.OnBoard(i, j) &&
 118           this.getPiece(i, j) == V.GRASSHOPPER &&
 119           colors.includes(this.getColor(i, j))
 120         ) {
 121           return true;
 122         }
 123       }
 124     }
 125     return false;
 126   }
 127
 128   static get VALUES() {
 129     return Object.assign(
 130       // TODO: grasshoppers power decline with less pieces on board...
 131       { g: 2 },
 132       ChessRules.VALUES
 133     );
 134   }
 135
 136   static get SEARCH_DEPTH() {
 137     return 2;
 138   }
 139
 140   static GenRandInitFen(randomness) {
 141     return ChessRules.GenRandInitFen(randomness)
 142       .slice(0, -2)
 143       .replace(
 144         "/pppppppp/8/8/8/8/PPPPPPPP/",
 145         "/gggggggg/pppppppp/8/8/PPPPPPPP/GGGGGGGG/"
 146       );
 147   }
 148 };