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
   6   static IsGoodEnpassant(enpassant) {
   7     const squares = enpassant.split(",");
   8     if (squares.length > 2) return false;
   9     for (let sq of squares) {
  10       if (sq != "-") {
  11         const ep = V.SquareToCoords(sq);
  12         if (isNaN(ep.x) || !V.OnBoard(ep)) return false;
  13       }
  14     }
  15     return true;
  16   }
  17
  18   // There may be 2 enPassant squares (if 2 pawns jump 2 squares in same turn)
  19   getEnpassantFen() {
  20     return this.epSquares[this.epSquares.length - 1].map(
  21       epsq => epsq === undefined
  22         ? "-" //no en-passant
  23         : V.CoordsToSquare(epsq)
  24     ).join(",");
  25   }
  26
  27   setOtherVariables(fen) {
  28     const parsedFen = V.ParseFen(fen);
  29     this.setFlags(parsedFen.flags);
  30     this.epSquares = [parsedFen.enpassant.split(",").map(sq => {
  31       if (sq != "-") return V.SquareToCoords(sq);
  32       return undefined;
  33     })];
  34     this.scanKings(fen);
  35     // Extract subTurn from turn indicator: "w" (first move), or
  36     // "w1" or "w2" white subturn 1 or 2, and same for black
  37     this.turn = parsedFen.turn;
  38     this.subTurn = 1;
  39   }
  40
  41   getEnpassantCaptures([x, y], shiftX) {
  42     let moves = [];
  43     // En passant: always OK if subturn 1,
  44     // OK on subturn 2 only if enPassant was played at subturn 1
  45     // (and if there are two e.p. squares available).
  46     const Lep = this.epSquares.length;
  47     const epSquares = this.epSquares[Lep - 1]; //always at least one element
  48     let epSqs = [];
  49     epSquares.forEach(sq => {
  50       if (sq) epSqs.push(sq);
  51     });
  52     if (epSqs.length == 0) return moves;
  53     const oppCol = V.GetOppCol(this.getColor(x, y));
  54     for (let sq of epSqs) {
  55       if (
  56         this.subTurn == 1 ||
  57         (epSqs.length == 2 &&
  58           // Was this en-passant capture already played at subturn 1 ?
  59           // (Or maybe the opponent filled the en-passant square with a piece)
  60           this.board[epSqs[0].x][epSqs[0].y] != V.EMPTY)
  61       ) {
  62         if (
  63           sq.x == x + shiftX &&
  64           Math.abs(sq.y - y) == 1 &&
  65           // Add condition "enemy pawn must be present"
  66           this.getPiece(x, sq.y) == V.PAWN &&
  67           this.getColor(x, sq.y) == oppCol
  68         ) {
  69           let epMove = this.getBasicMove([x, y], [sq.x, sq.y]);
  70           epMove.vanish.push({
  71             x: x,
  72             y: sq.y,
  73             p: "p",
  74             c: oppCol
  75           });
  76           moves.push(epMove);
  77         }
  78       }
  79     }
  80     return moves;
  81   }
  82
  83   isAttacked() {
  84     // Goal is king capture => no checks
  85     return false;
  86   }
  87
  88   filterValid(moves) {
  89     return moves;
  90   }
  91
  92   getCheckSquares() {
  93     return [];
  94   }
  95
  96   getCurrentScore() {
  97     const color = this.turn;
  98     if (this.kingPos[color][0] < 0) return (color == 'w' ? "0-1" : "1-0");
  99     return "*";
 100   }
 101
 102   play(move) {
 103     move.flags = JSON.stringify(this.aggregateFlags());
 104     V.PlayOnBoard(this.board, move);
 105     const epSq = this.getEpSquare(move);
 106     if (this.subTurn == 2) {
 107       let lastEpsq = this.epSquares[this.epSquares.length - 1];
 108       lastEpsq.push(epSq);
 109       this.turn = V.GetOppCol(this.turn);
 110     }
 111     else {
 112       this.epSquares.push([epSq]);
 113       this.movesCount++;
 114       if (
 115         this.movesCount == 1 ||
 116         // King is captured at subTurn 1?
 117         (move.vanish.length == 2 && move.vanish[1].p == V.KING)
 118       ) {
 119         this.turn = "b";
 120       }
 121     }
 122     if (this.movesCount > 1) this.subTurn = 3 - this.subTurn;
 123     this.postPlay(move);
 124   }
 125
 126   postPlay(move) {
 127     const c = move.vanish[0].c;
 128     const piece = move.vanish[0].p;
 129     const firstRank = c == "w" ? V.size.x - 1 : 0;
 130
 131     if (piece == V.KING) {
 132       this.kingPos[c] = [move.appear[0].x, move.appear[0].y];
 133       this.castleFlags[c] = [V.size.y, V.size.y];
 134       return;
 135     }
 136     const oppCol = V.GetOppCol(c);
 137     if (move.vanish.length == 2 && move.vanish[1].p == V.KING) {
 138       // Opponent's king is captured, game over
 139       this.kingPos[oppCol] = [-1, -1];
 140       move.captureKing = true; //for undo
 141     }
 142     const oppFirstRank = V.size.x - 1 - firstRank;
 143     if (
 144       move.start.x == firstRank && //our rook moves?
 145       this.castleFlags[c].includes(move.start.y)
 146     ) {
 147       const flagIdx = (move.start.y == this.castleFlags[c][0] ? 0 : 1);
 148       this.castleFlags[c][flagIdx] = V.size.y;
 149     }
 150     if (
 151       move.end.x == oppFirstRank && //we took opponent rook?
 152       this.castleFlags[oppCol].includes(move.end.y)
 153     ) {
 154       const flagIdx = (move.end.y == this.castleFlags[oppCol][0] ? 0 : 1);
 155       this.castleFlags[oppCol][flagIdx] = V.size.y;
 156     }
 157   }
 158
 159   undo(move) {
 160     this.disaggregateFlags(JSON.parse(move.flags));
 161     V.UndoOnBoard(this.board, move);
 162     if (this.subTurn == 2 || this.movesCount == 1 || !!move.captureKing) {
 163       this.epSquares.pop();
 164       this.movesCount--;
 165       if (this.movesCount == 0) this.turn = "w";
 166     }
 167     else {
 168       let lastEpsq = this.epSquares[this.epSquares.length - 1];
 169       lastEpsq.pop();
 170       this.turn = V.GetOppCol(this.turn);
 171     }
 172     if (this.movesCount > 0) this.subTurn = 3 - this.subTurn;
 173     this.postUndo(move);
 174   }
 175
 176   postUndo(move) {
 177     if (move.vanish.length == 2 && move.vanish[1].p == V.KING)
 178       // Opponent's king was captured
 179       this.kingPos[move.vanish[1].c] = [move.vanish[1].x, move.vanish[1].y];
 180     super.postUndo(move);
 181   }
 182
 183   // No alpha-beta here, just adapted min-max at depth 2(+1)
 184   getComputerMove() {
 185     const maxeval = V.INFINITY;
 186     const color = this.turn;
 187     const oppCol = V.GetOppCol(this.turn);
 188
 189     // Search best (half) move for opponent turn
 190     const getBestMoveEval = () => {
 191       let score = this.getCurrentScore();
 192       if (score != "*") return maxeval * (score == "1-0" ? 1 : -1);
 193       let moves = this.getAllValidMoves();
 194       let res = oppCol == "w" ? -maxeval : maxeval;
 195       for (let m of moves) {
 196         this.play(m);
 197         score = this.getCurrentScore();
 198         if (score != "*") {
 199           // King captured
 200           this.undo(m);
 201           return maxeval * (score == "1-0" ? 1 : -1);
 202         }
 203         const evalPos = this.evalPosition();
 204         res = oppCol == "w" ? Math.max(res, evalPos) : Math.min(res, evalPos);
 205         this.undo(m);
 206       }
 207       return res;
 208     };
 209
 210     const moves11 = this.getAllValidMoves();
 211     if (this.movesCount == 0)
 212       // First white move at random:
 213       return moves11[randInt(moves11.length)];
 214     let doubleMove = null;
 215     let bestEval = Number.POSITIVE_INFINITY * (color == 'w' ? -1 : 1);
 216     // Rank moves using a min-max at depth 2
 217     for (let i = 0; i < moves11.length; i++) {
 218       this.play(moves11[i]);
 219       const moves12 = this.getAllValidMoves();
 220       for (let j = 0; j < moves12.length; j++) {
 221         this.play(moves12[j]);
 222         // Small fluctuations to uniformize play a little
 223         const evalM = getBestMoveEval() + 0.05 - Math.random() / 10
 224         if (
 225           (color == 'w' && evalM > bestEval) ||
 226           (color == 'b' && evalM < bestEval)
 227         ) {
 228           doubleMove = [moves11[i],  moves12[j]];
 229           bestEval = evalM;
 230         }
 231         this.undo(moves12[j]);
 232       }
 233       this.undo(moves11[i]);
 234     }
 235     // TODO: not always the best move played (why ???)
 236     return doubleMove;
 237   }
 238
 239 };