client/src/variants/Doublemove2.js

   1 import { ChessRules } from "@/base_rules";
   2 import { randInt } from "@/utils/alea";
   3
   4 export class Doublemove2Rules 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   // There may be 2 enPassant squares (if 2 pawns jump 2 squares in same turn)
  18   getEnpassantFen() {
  19     return this.epSquares[this.epSquares.length - 1].map(
  20       epsq => epsq === undefined
  21         ? "-" //no en-passant
  22         : V.CoordsToSquare(epsq)
  23     ).join(",");
  24   }
  25
  26   setOtherVariables(fen) {
  27     const parsedFen = V.ParseFen(fen);
  28     this.setFlags(parsedFen.flags);
  29     this.epSquares = [parsedFen.enpassant.split(",").map(sq => {
  30       if (sq != "-") return V.SquareToCoords(sq);
  31       return undefined;
  32     })];
  33     this.scanKings(fen);
  34     // Extract subTurn from turn indicator: "w" (first move), or
  35     // "w1" or "w2" white subturn 1 or 2, and same for black
  36     this.turn = parsedFen.turn;
  37     this.subTurn = 1;
  38   }
  39
  40   getEnpassantCaptures([x, y], shiftX) {
  41     let moves = [];
  42     // En passant: always OK if subturn 1,
  43     // OK on subturn 2 only if enPassant was played at subturn 1
  44     // (and if there are two e.p. squares available).
  45     const Lep = this.epSquares.length;
  46     const epSquares = this.epSquares[Lep - 1]; //always at least one element
  47     let epSqs = [];
  48     epSquares.forEach(sq => {
  49       if (sq) epSqs.push(sq);
  50     });
  51     if (epSqs.length == 0) return moves;
  52     const oppCol = V.GetOppCol(this.getColor(x, y));
  53     for (let sq of epSqs) {
  54       if (
  55         this.subTurn == 1 ||
  56         (epSqs.length == 2 &&
  57           // Was this en-passant capture already played at subturn 1 ?
  58           // (Or maybe the opponent filled the en-passant square with a piece)
  59           this.board[epSqs[0].x][epSqs[0].y] != V.EMPTY)
  60       ) {
  61         if (
  62           sq.x == x + shiftX &&
  63           Math.abs(sq.y - y) == 1 &&
  64           // Add condition "enemy pawn must be present"
  65           this.getPiece(x, sq.y) == V.PAWN &&
  66           this.getColor(x, sq.y) == oppCol
  67         ) {
  68           let epMove = this.getBasicMove([x, y], [sq.x, sq.y]);
  69           epMove.vanish.push({
  70             x: x,
  71             y: sq.y,
  72             p: "p",
  73             c: oppCol
  74           });
  75           moves.push(epMove);
  76         }
  77       }
  78     }
  79     return moves;
  80   }
  81
  82   isAttacked() {
  83     // Goal is king capture => no checks
  84     return false;
  85   }
  86
  87   filterValid(moves) {
  88     return moves;
  89   }
  90
  91   getCheckSquares() {
  92     return [];
  93   }
  94
  95   getCurrentScore() {
  96     const color = this.turn;
  97     if (this.kingPos[color][0] < 0) return (color == 'w' ? "0-1" : "1-0");
  98     return "*";
  99   }
 100
 101   play(move) {
 102     move.flags = JSON.stringify(this.aggregateFlags());
 103     V.PlayOnBoard(this.board, move);
 104     const epSq = this.getEpSquare(move);
 105     if (this.subTurn == 2) {
 106       let lastEpsq = this.epSquares[this.epSquares.length - 1];
 107       lastEpsq.push(epSq);
 108       this.turn = V.GetOppCol(this.turn);
 109     }
 110     else {
 111       this.epSquares.push([epSq]);
 112       this.movesCount++;
 113       if (
 114         this.movesCount == 1 ||
 115         // King is captured at subTurn 1?
 116         (move.vanish.length == 2 && move.vanish[1].p == V.KING)
 117       ) {
 118         this.turn = "b";
 119       }
 120     }
 121     if (this.movesCount > 1) this.subTurn = 3 - this.subTurn;
 122     this.postPlay(move);
 123   }
 124
 125   postPlay(move) {
 126     const c = move.vanish[0].c;
 127     const piece = move.vanish[0].p;
 128     const firstRank = c == "w" ? V.size.x - 1 : 0;
 129
 130     if (piece == V.KING && move.appear.length > 0) {
 131       this.kingPos[c] = [move.appear[0].x, move.appear[0].y];
 132       this.castleFlags[c] = [V.size.y, V.size.y];
 133       return;
 134     }
 135     const oppCol = V.GetOppCol(c);
 136     if (move.vanish.length == 2 && move.vanish[1].p == V.KING) {
 137       // Opponent's king is captured, game over
 138       this.kingPos[oppCol] = [-1, -1];
 139       move.captureKing = true; //for undo
 140     }
 141     const oppFirstRank = V.size.x - 1 - firstRank;
 142     if (
 143       move.start.x == firstRank && //our rook moves?
 144       this.castleFlags[c].includes(move.start.y)
 145     ) {
 146       const flagIdx = (move.start.y == this.castleFlags[c][0] ? 0 : 1);
 147       this.castleFlags[c][flagIdx] = V.size.y;
 148     }
 149     else if (
 150       move.end.x == oppFirstRank && //we took opponent rook?
 151       this.castleFlags[oppCol].includes(move.end.y)
 152     ) {
 153       const flagIdx = (move.end.y == this.castleFlags[oppCol][0] ? 0 : 1);
 154       this.castleFlags[oppCol][flagIdx] = V.size.y;
 155     }
 156   }
 157
 158   undo(move) {
 159     this.disaggregateFlags(JSON.parse(move.flags));
 160     V.UndoOnBoard(this.board, move);
 161     if (this.subTurn == 2 || this.movesCount == 1 || !!move.captureKing) {
 162       this.epSquares.pop();
 163       this.movesCount--;
 164       if (this.movesCount == 0) this.turn = "w";
 165     }
 166     else {
 167       let lastEpsq = this.epSquares[this.epSquares.length - 1];
 168       lastEpsq.pop();
 169       this.turn = V.GetOppCol(this.turn);
 170     }
 171     if (this.movesCount > 0) this.subTurn = 3 - this.subTurn;
 172     this.postUndo(move);
 173   }
 174
 175   postUndo(move) {
 176     if (move.vanish.length == 2 && move.vanish[1].p == V.KING)
 177       // Opponent's king was captured
 178       this.kingPos[move.vanish[1].c] = [move.vanish[1].x, move.vanish[1].y];
 179     super.postUndo(move);
 180   }
 181
 182   // No alpha-beta here, just adapted min-max at depth 2(+1)
 183   getComputerMove() {
 184     const maxeval = V.INFINITY;
 185     const color = this.turn;
 186     const oppCol = V.GetOppCol(this.turn);
 187
 188     // Search best (half) move for opponent turn
 189     const getBestMoveEval = () => {
 190       let score = this.getCurrentScore();
 191       if (score != "*") return maxeval * (score == "1-0" ? 1 : -1);
 192       let moves = this.getAllValidMoves();
 193       let res = oppCol == "w" ? -maxeval : maxeval;
 194       for (let m of moves) {
 195         this.play(m);
 196         score = this.getCurrentScore();
 197         if (score != "*") {
 198           // King captured
 199           this.undo(m);
 200           return maxeval * (score == "1-0" ? 1 : -1);
 201         }
 202         const evalPos = this.evalPosition();
 203         res = oppCol == "w" ? Math.max(res, evalPos) : Math.min(res, evalPos);
 204         this.undo(m);
 205       }
 206       return res;
 207     };
 208
 209     const moves11 = this.getAllValidMoves();
 210     if (this.movesCount == 0)
 211       // First white move at random:
 212       return moves11[randInt(moves11.length)];
 213     let doubleMoves = [];
 214     // Rank moves using a min-max at depth 2
 215     for (let i = 0; i < moves11.length; i++) {
 216       this.play(moves11[i]);
 217       const moves12 = this.getAllValidMoves();
 218       for (let j = 0; j < moves12.length; j++) {
 219         this.play(moves12[j]);
 220         doubleMoves.push({
 221           moves: [moves11[i], moves12[j]],
 222           // Small fluctuations to uniformize play a little
 223           eval: getBestMoveEval() + 0.05 - Math.random() / 10
 224         });
 225         this.undo(moves12[j]);
 226       }
 227       this.undo(moves11[i]);
 228     }
 229
 230     doubleMoves.sort((a, b) => {
 231       return (color == "w" ? 1 : -1) * (b.eval - a.eval);
 232     });
 233     let candidates = [0]; //indices of candidates moves
 234     for (
 235       let i = 1;
 236       i < doubleMoves.length && doubleMoves[i].eval == doubleMoves[0].eval;
 237       i++
 238     ) {
 239       candidates.push(i);
 240     }
 241     return doubleMoves[randInt(candidates.length)].moves;
 242   }
 243 };