client/src/variants/Marseille.js

   1 import { ChessRules } from "@/base_rules";
   2 import { randInt } from "@/utils/alea";
   3
   4 export const VariantRules = class MarseilleRules extends ChessRules {
   5   static IsGoodEnpassant(enpassant) {
   6     const squares = enpassant.split(",");
   7     if (squares.length > 2) return false;
   8     for (let sq of squares) {
   9       if (sq != "-") {
  10         const ep = V.SquareToCoords(sq);
  11         if (isNaN(ep.x) || !V.OnBoard(ep)) return false;
  12       }
  13     }
  14     return true;
  15   }
  16
  17   getTurnFen() {
  18     return this.turn + this.subTurn;
  19   }
  20
  21   // There may be 2 enPassant squares (if 2 pawns jump 2 squares in same turn)
  22   getEnpassantFen() {
  23     return this.epSquares[this.epSquares.length - 1].map(
  24       epsq => epsq === undefined
  25         ? "-" //no en-passant
  26         : V.CoordsToSquare(epsq)
  27     ).join(",");
  28   }
  29
  30   setOtherVariables(fen) {
  31     const parsedFen = V.ParseFen(fen);
  32     this.setFlags(parsedFen.flags);
  33     this.epSquares = [parsedFen.enpassant.split(",").map(sq => {
  34       if (sq != "-") return V.SquareToCoords(sq);
  35       return undefined;
  36     })];
  37     this.scanKingsRooks(fen);
  38     // Extract subTurn from turn indicator: "w" (first move), or
  39     // "w1" or "w2" white subturn 1 or 2, and same for black
  40     const fullTurn = V.ParseFen(fen).turn;
  41     this.turn = fullTurn[0];
  42     // At move 1, the subTurn doesn't need to be specified:
  43     this.subTurn = fullTurn[1] || 1;
  44   }
  45
  46   getPotentialPawnMoves([x, y]) {
  47     const color = this.turn;
  48     let moves = [];
  49     const [sizeX, sizeY] = [V.size.x, V.size.y];
  50     const shiftX = color == "w" ? -1 : 1;
  51     const firstRank = color == "w" ? sizeX - 1 : 0;
  52     const startRank = color == "w" ? sizeX - 2 : 1;
  53     const lastRank = color == "w" ? 0 : sizeX - 1;
  54     const finalPieces =
  55       x + shiftX == lastRank ? [V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN] : [V.PAWN];
  56
  57     // One square forward
  58     if (this.board[x + shiftX][y] == V.EMPTY) {
  59       for (let piece of finalPieces) {
  60         moves.push(
  61           this.getBasicMove([x, y], [x + shiftX, y], { c: color, p: piece })
  62         );
  63       }
  64       // Next condition because pawns on 1st rank can generally jump
  65       if (
  66         [startRank, firstRank].includes(x) &&
  67         this.board[x + 2 * shiftX][y] == V.EMPTY
  68       ) {
  69         // Two squares jump
  70         moves.push(this.getBasicMove([x, y], [x + 2 * shiftX, y]));
  71       }
  72     }
  73     // Captures
  74     for (let shiftY of [-1, 1]) {
  75       if (
  76         y + shiftY >= 0 &&
  77         y + shiftY < sizeY &&
  78         this.board[x + shiftX][y + shiftY] != V.EMPTY &&
  79         this.canTake([x, y], [x + shiftX, y + shiftY])
  80       ) {
  81         for (let piece of finalPieces) {
  82           moves.push(
  83             this.getBasicMove([x, y], [x + shiftX, y + shiftY], {
  84               c: color,
  85               p: piece
  86             })
  87           );
  88         }
  89       }
  90     }
  91
  92     // En passant: always OK if subturn 1,
  93     // OK on subturn 2 only if enPassant was played at subturn 1
  94     // (and if there are two e.p. squares available).
  95     const Lep = this.epSquares.length;
  96     const epSquares = this.epSquares[Lep - 1]; //always at least one element
  97     let epSqs = [];
  98     epSquares.forEach(sq => {
  99       if (sq) epSqs.push(sq);
 100     });
 101     if (epSqs.length == 0) return moves;
 102     const oppCol = V.GetOppCol(color);
 103     for (let sq of epSqs) {
 104       if (
 105         this.subTurn == 1 ||
 106         (epSqs.length == 2 &&
 107           // Was this en-passant capture already played at subturn 1 ?
 108           // (Or maybe the opponent filled the en-passant square with a piece)
 109           this.board[epSqs[0].x][epSqs[0].y] != V.EMPTY)
 110       ) {
 111         if (
 112           sq.x == x + shiftX &&
 113           Math.abs(sq.y - y) == 1 &&
 114           // Add condition "enemy pawn must be present"
 115           this.getPiece(x, sq.y) == V.PAWN &&
 116           this.getColor(x, sq.y) == oppCol
 117         ) {
 118           let epMove = this.getBasicMove([x, y], [sq.x, sq.y]);
 119           epMove.vanish.push({
 120             x: x,
 121             y: sq.y,
 122             p: "p",
 123             c: oppCol
 124           });
 125           moves.push(epMove);
 126         }
 127       }
 128     }
 129
 130     return moves;
 131   }
 132
 133   play(move) {
 134     move.flags = JSON.stringify(this.aggregateFlags());
 135     move.turn = this.turn + this.subTurn;
 136     V.PlayOnBoard(this.board, move);
 137     const epSq = this.getEpSquare(move);
 138     if (this.movesCount == 0) {
 139       // First move in game
 140       this.turn = "b";
 141       this.epSquares.push([epSq]);
 142       this.movesCount = 1;
 143     }
 144     // Does this move give check on subturn 1? If yes, skip subturn 2
 145     else if (this.subTurn == 1 && this.underCheck(V.GetOppCol(this.turn))) {
 146       this.turn = V.GetOppCol(this.turn);
 147       this.epSquares.push([epSq]);
 148       move.checkOnSubturn1 = true;
 149       this.movesCount++;
 150     } else {
 151       if (this.subTurn == 2) {
 152         this.turn = V.GetOppCol(this.turn);
 153         let lastEpsq = this.epSquares[this.epSquares.length - 1];
 154         lastEpsq.push(epSq);
 155       } else {
 156         this.epSquares.push([epSq]);
 157         this.movesCount++;
 158       }
 159       this.subTurn = 3 - this.subTurn;
 160     }
 161     this.updateVariables(move);
 162   }
 163
 164   undo(move) {
 165     this.disaggregateFlags(JSON.parse(move.flags));
 166     V.UndoOnBoard(this.board, move);
 167     if (this.movesCount == 1 || !!move.checkOnSubturn1 || this.subTurn == 2) {
 168       // The move may not be full, but is fully undone:
 169       this.epSquares.pop();
 170       // Moves counter was just incremented:
 171       this.movesCount--;
 172     } else {
 173       // Undo the second half of a move
 174       let lastEpsq = this.epSquares[this.epSquares.length - 1];
 175       lastEpsq.pop();
 176     }
 177     this.turn = move.turn[0];
 178     this.subTurn = parseInt(move.turn[1]);
 179     this.unupdateVariables(move);
 180   }
 181
 182   // NOTE:  GenRandInitFen() is OK,
 183   // since at first move turn indicator is just "w"
 184
 185   static get VALUES() {
 186     return {
 187       p: 1,
 188       r: 5,
 189       n: 3,
 190       b: 3,
 191       q: 7, //slightly less than in orthodox game
 192       k: 1000
 193     };
 194   }
 195
 196   // No alpha-beta here, just adapted min-max at depth 2(+1)
 197   getComputerMove() {
 198     const maxeval = V.INFINITY;
 199     const color = this.turn;
 200     const oppCol = V.GetOppCol(this.turn);
 201
 202     // Search best (half) move for opponent turn
 203     const getBestMoveEval = () => {
 204       let score = this.getCurrentScore();
 205       if (score != "*") {
 206         if (score == "1/2") return 0;
 207         return maxeval * (score == "1-0" ? 1 : -1);
 208       }
 209       let moves = this.getAllValidMoves();
 210       let res = oppCol == "w" ? -maxeval : maxeval;
 211       for (let m of moves) {
 212         this.play(m);
 213         score = this.getCurrentScore();
 214         // Now turn is oppCol,2 if m doesn't give check
 215         // Otherwise it's color,1. In both cases the next test makes sense
 216         if (score != "*") {
 217           if (score == "1/2")
 218             res = oppCol == "w" ? Math.max(res, 0) : Math.min(res, 0);
 219           else {
 220             // Found a mate
 221             this.undo(m);
 222             return maxeval * (score == "1-0" ? 1 : -1);
 223           }
 224         }
 225         const evalPos = this.evalPosition();
 226         res = oppCol == "w" ? Math.max(res, evalPos) : Math.min(res, evalPos);
 227         this.undo(m);
 228       }
 229       return res;
 230     };
 231
 232     let moves11 = this.getAllValidMoves();
 233     let doubleMoves = [];
 234     // Rank moves using a min-max at depth 2
 235     for (let i = 0; i < moves11.length; i++) {
 236       this.play(moves11[i]);
 237       if (this.turn != color) {
 238         // We gave check with last move: search the best opponent move
 239         doubleMoves.push({ moves: [moves11[i]], eval: getBestMoveEval() });
 240       } else {
 241         let moves12 = this.getAllValidMoves();
 242         for (let j = 0; j < moves12.length; j++) {
 243           this.play(moves12[j]);
 244           doubleMoves.push({
 245             moves: [moves11[i], moves12[j]],
 246             eval: getBestMoveEval()
 247           });
 248           this.undo(moves12[j]);
 249         }
 250       }
 251       this.undo(moves11[i]);
 252     }
 253
 254     doubleMoves.sort((a, b) => {
 255       return (color == "w" ? 1 : -1) * (b.eval - a.eval);
 256     });
 257     let candidates = [0]; //indices of candidates moves
 258     for (
 259       let i = 1;
 260       i < doubleMoves.length && doubleMoves[i].eval == doubleMoves[0].eval;
 261       i++
 262     ) {
 263       candidates.push(i);
 264     }
 265
 266     const selected = doubleMoves[randInt(candidates.length)].moves;
 267     if (selected.length == 1) return selected[0];
 268     return selected;
 269   }
 270 };