client/src/variants/Berolina.js

   1 import { ChessRules } from "@/base_rules";
   2
   3 export const VariantRules = class BerolinaRules extends ChessRules {
   4   // En-passant after 2-sq jump
   5   getEpSquare(moveOrSquare) {
   6     if (!moveOrSquare) return undefined;
   7     if (typeof moveOrSquare === "string") {
   8       const square = moveOrSquare;
   9       if (square == "-") return undefined;
  10       // Enemy pawn initial column must be given too:
  11       let res = [];
  12       const epParts = square.split(",");
  13       res.push(V.SquareToCoords(epParts[0]));
  14       res.push(V.ColumnToCoord(epParts[1]));
  15       return res;
  16     }
  17     // Argument is a move:
  18     const move = moveOrSquare;
  19     const [sx, ex, sy] = [move.start.x, move.end.x, move.start.y];
  20     if (this.getPiece(sx, sy) == V.PAWN && Math.abs(sx - ex) == 2) {
  21       return [
  22         {
  23           x: (ex + sx) / 2,
  24           y: (move.end.y + sy) / 2
  25         },
  26         // The arrival column must be remembered, because
  27         // potentially two pawns could be candidates to be captured:
  28         // one on our left, and one on our right.
  29         move.end.y
  30       ];
  31     }
  32     return undefined; //default
  33   }
  34
  35   static IsGoodEnpassant(enpassant) {
  36     if (enpassant != "-") {
  37       const epParts = enpassant.split(",");
  38       const epSq = V.SquareToCoords(epParts[0]);
  39       if (isNaN(epSq.x) || isNaN(epSq.y) || !V.OnBoard(epSq)) return false;
  40       const arrCol = V.ColumnToCoord(epParts[1]);
  41       if (isNaN(arrCol) || arrCol < 0 || arrCol >= V.size.y) return false;
  42     }
  43     return true;
  44   }
  45
  46   getEnpassantFen() {
  47     const L = this.epSquares.length;
  48     if (!this.epSquares[L - 1]) return "-"; //no en-passant
  49     return (
  50       V.CoordsToSquare(this.epSquares[L - 1][0]) +
  51       "," +
  52       V.CoordToColumn(this.epSquares[L - 1][1])
  53     );
  54   }
  55
  56   // Special pawns movements
  57   getPotentialPawnMoves([x, y]) {
  58     const color = this.turn;
  59     let moves = [];
  60     const [sizeX, sizeY] = [V.size.x, V.size.y];
  61     const shiftX = color == "w" ? -1 : 1;
  62     const startRank = color == "w" ? sizeX - 2 : 1;
  63     const lastRank = color == "w" ? 0 : sizeX - 1;
  64     const finalPieces =
  65       x + shiftX == lastRank ? [V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN] : [V.PAWN];
  66
  67     // One square diagonally
  68     for (let shiftY of [-1, 1]) {
  69       if (this.board[x + shiftX][y + shiftY] == V.EMPTY) {
  70         for (let piece of finalPieces) {
  71           moves.push(
  72             this.getBasicMove([x, y], [x + shiftX, y + shiftY], {
  73               c: color,
  74               p: piece
  75             })
  76           );
  77         }
  78         if (
  79           x == startRank &&
  80           y + 2 * shiftY >= 0 &&
  81           y + 2 * shiftY < sizeY &&
  82           this.board[x + 2 * shiftX][y + 2 * shiftY] == V.EMPTY
  83         ) {
  84           // Two squares jump
  85           moves.push(
  86             this.getBasicMove([x, y], [x + 2 * shiftX, y + 2 * shiftY])
  87           );
  88         }
  89       }
  90     }
  91     // Capture
  92     if (
  93       this.board[x + shiftX][y] != V.EMPTY &&
  94       this.canTake([x, y], [x + shiftX, y])
  95     ) {
  96       for (let piece of finalPieces)
  97         moves.push(
  98           this.getBasicMove([x, y], [x + shiftX, y], { c: color, p: piece })
  99         );
 100     }
 101
 102     // En passant
 103     const Lep = this.epSquares.length;
 104     const epSquare = this.epSquares[Lep - 1]; //always at least one element
 105     if (
 106       !!epSquare &&
 107       epSquare[0].x == x + shiftX &&
 108       epSquare[0].y == y
 109     ) {
 110       let enpassantMove = this.getBasicMove([x, y], [x + shiftX, y]);
 111       enpassantMove.vanish.push({
 112         x: x,
 113         y: epSquare[1],
 114         p: "p",
 115         c: this.getColor(x, epSquare[1])
 116       });
 117       moves.push(enpassantMove);
 118     }
 119
 120     return moves;
 121   }
 122
 123   isAttackedByPawn([x, y], colors) {
 124     for (let c of colors) {
 125       let pawnShift = c == "w" ? 1 : -1;
 126       if (x + pawnShift >= 0 && x + pawnShift < V.size.x) {
 127         if (
 128           this.getPiece(x + pawnShift, y) == V.PAWN &&
 129           this.getColor(x + pawnShift, y) == c
 130         ) {
 131           return true;
 132         }
 133       }
 134     }
 135     return false;
 136   }
 137
 138   getNotation(move) {
 139     const piece = this.getPiece(move.start.x, move.start.y);
 140     if (piece == V.PAWN) {
 141       // Pawn move
 142       const finalSquare = V.CoordsToSquare(move.end);
 143       let notation = "";
 144       if (move.vanish.length == 2)
 145         //capture
 146         notation = "Px" + finalSquare;
 147       else {
 148         // No capture: indicate the initial square for potential ambiguity
 149         const startSquare = V.CoordsToSquare(move.start);
 150         notation = startSquare + finalSquare;
 151       }
 152       if (move.appear[0].p != V.PAWN)
 153         //promotion
 154         notation += "=" + move.appear[0].p.toUpperCase();
 155       return notation;
 156     }
 157     return super.getNotation(move); //all other pieces are orthodox
 158   }
 159 };