client/src/variants/Enpassant.js

   1 import { ChessRules, PiPo, Move } from "@/base_rules";
   2
   3 export class EnpassantRules extends ChessRules {
   4   static IsGoodEnpassant(enpassant) {
   5     if (enpassant != "-") {
   6       const squares = enpassant.split(",");
   7       for (let sq of squares) {
   8         const ep = V.SquareToCoords(sq);
   9         if (isNaN(ep.x) || !V.OnBoard(ep)) return false;
  10       }
  11     }
  12     return true;
  13   }
  14
  15   getEpSquare(moveOrSquare) {
  16     if (!moveOrSquare) return undefined;
  17     if (typeof moveOrSquare === "string") {
  18       const square = moveOrSquare;
  19       if (square == "-") return undefined;
  20       let res = [];
  21       square.split(",").forEach(sq => {
  22         res.push(V.SquareToCoords(sq));
  23       });
  24       return res;
  25     }
  26     // Argument is a move: all intermediate squares are en-passant candidates,
  27     // except if the moving piece is a king.
  28     const move = moveOrSquare;
  29     const piece = move.appear[0].p;
  30     if (piece == V.KING ||
  31       (
  32         Math.abs(move.end.x-move.start.x) <= 1 &&
  33         Math.abs(move.end.y-move.start.y) <= 1
  34       )
  35     ) {
  36       return undefined;
  37     }
  38     const delta = [move.end.x-move.start.x, move.end.y-move.start.y];
  39     let step = undefined;
  40     if (piece == V.KNIGHT) {
  41       const divisor = Math.min(Math.abs(delta[0]), Math.abs(delta[1]));
  42       step = [delta[0]/divisor || 0, delta[1]/divisor || 0];
  43     } else {
  44       step = [delta[0]/Math.abs(delta[0]) || 0, delta[1]/Math.abs(delta[1]) || 0];
  45     }
  46     let res = [];
  47     for (
  48       let [x,y] = [move.start.x+step[0],move.start.y+step[1]];
  49       x != move.end.x || y != move.end.y;
  50       x += step[0], y += step[1]
  51     ) {
  52       res.push({x:x, y:y});
  53     }
  54     // Add final square to know which piece is taken en passant:
  55     res.push(move.end);
  56     return res;
  57   }
  58
  59   getEnpassantFen() {
  60     const L = this.epSquares.length;
  61     if (!this.epSquares[L - 1]) return "-"; //no en-passant
  62     let res = "";
  63     this.epSquares[L - 1].forEach(sq => {
  64       res += V.CoordsToSquare(sq) + ",";
  65     });
  66     return res.slice(0, -1); //remove last comma
  67   }
  68
  69   getPotentialMovesFrom([x, y]) {
  70     let moves = super.getPotentialMovesFrom([x,y]);
  71     // Add en-passant captures from this square:
  72     const L = this.epSquares.length;
  73     if (!this.epSquares[L - 1]) return moves;
  74     const squares = this.epSquares[L - 1];
  75     const S = squares.length;
  76     // Object describing the removed opponent's piece:
  77     const pipoV = new PiPo({
  78       x: squares[S-1].x,
  79       y: squares[S-1].y,
  80       c: V.GetOppCol(this.turn),
  81       p: this.getPiece(squares[S-1].x, squares[S-1].y)
  82     });
  83     // Check if existing non-capturing moves could also capture en passant
  84     moves.forEach(m => {
  85       if (
  86         m.appear[0].p != V.PAWN && //special pawn case is handled elsewhere
  87         m.vanish.length <= 1 &&
  88         [...Array(S-1).keys()].some(i => {
  89           return m.end.x == squares[i].x && m.end.y == squares[i].y;
  90         })
  91       ) {
  92         m.vanish.push(pipoV);
  93       }
  94     });
  95     // Special case of the king knight's movement:
  96     if (this.getPiece(x, y) == V.KING) {
  97       V.steps[V.KNIGHT].forEach(step => {
  98         const endX = x + step[0];
  99         const endY = y + step[1];
 100         if (
 101           V.OnBoard(endX, endY) &&
 102           [...Array(S-1).keys()].some(i => {
 103             return endX == squares[i].x && endY == squares[i].y;
 104           })
 105         ) {
 106           let enpassantMove = this.getBasicMove([x, y], [endX, endY]);
 107           enpassantMove.vanish.push(pipoV);
 108           moves.push(enpassantMove);
 109         }
 110       });
 111     }
 112     return moves;
 113   }
 114
 115   getEnpassantCaptures([x, y], shiftX) {
 116     const Lep = this.epSquares.length;
 117     const squares = this.epSquares[Lep - 1];
 118     let moves = [];
 119     if (!!squares) {
 120       const S = squares.length;
 121       const taken = squares[S-1];
 122       const pipoV = new PiPo({
 123         x: taken.x,
 124         y: taken.y,
 125         p: this.getPiece(taken.x, taken.y),
 126         c: this.getColor(taken.x, taken.y)
 127       });
 128       [...Array(S-1).keys()].forEach(i => {
 129         const sq = squares[i];
 130         if (sq.x == x + shiftX && Math.abs(sq.y - y) == 1) {
 131           let enpassantMove = this.getBasicMove([x, y], [sq.x, sq.y]);
 132           enpassantMove.vanish.push(pipoV);
 133           moves.push(enpassantMove);
 134         }
 135       });
 136     }
 137     return moves;
 138   }
 139
 140   // Remove the "onestep" condition: knight promote to knightrider:
 141   getPotentialKnightMoves(sq) {
 142     return this.getSlideNJumpMoves(sq, V.steps[V.KNIGHT]);
 143   }
 144
 145   filterValid(moves) {
 146     const filteredMoves = super.filterValid(moves);
 147     // If at least one full move made, everything is allowed:
 148     if (this.movesCount >= 2)
 149       return filteredMoves;
 150     // Else, forbid captures:
 151     return filteredMoves.filter(m => m.vanish.length == 1);
 152   }
 153
 154   isAttackedByKnight(sq, color) {
 155     return this.isAttackedBySlideNJump(
 156       sq,
 157       color,
 158       V.KNIGHT,
 159       V.steps[V.KNIGHT]
 160     );
 161   }
 162
 163   static get SEARCH_DEPTH() {
 164     return 2;
 165   }
 166
 167   static get VALUES() {
 168     return {
 169       p: 1,
 170       r: 5,
 171       n: 4,
 172       b: 3,
 173       q: 9,
 174       k: 1000
 175     };
 176   }
 177 };