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 {
   6   static IsGoodEnpassant(enpassant)
   7   {
   8     if (enpassant != "-")
   9     {
  10       const squares = enpassant.split(",");
  11       if (squares.length > 2)
  12         return false;
  13       for (let sq of squares)
  14       {
  15         const ep = V.SquareToCoords(sq);
  16         if (isNaN(ep.x) || !V.OnBoard(ep))
  17           return false;
  18       }
  19     }
  20     return true;
  21   }
  22
  23   getTurnFen()
  24   {
  25     return this.turn + this.subTurn;
  26   }
  27
  28   // There may be 2 enPassant squares (if 2 pawns jump 2 squares in same turn)
  29   getEnpassantFen()
  30   {
  31     const L = this.epSquares.length;
  32     if (this.epSquares[L-1].every(epsq => epsq === undefined))
  33       return "-"; //no en-passant
  34     let res = "";
  35     this.epSquares[L-1].forEach(epsq => {
  36       if (!!epsq)
  37         res += V.CoordsToSquare(epsq) + ",";
  38     });
  39     return res.slice(0,-1); //remove last comma
  40   }
  41
  42   setOtherVariables(fen)
  43   {
  44     const parsedFen = V.ParseFen(fen);
  45     this.setFlags(parsedFen.flags);
  46     if (parsedFen.enpassant == "-")
  47       this.epSquares = [ [undefined] ];
  48     else
  49     {
  50       let res = [];
  51       const squares = parsedFen.enpassant.split(",");
  52       for (let sq of squares)
  53         res.push(V.SquareToCoords(sq));
  54       this.epSquares = [ res ];
  55     }
  56     this.scanKingsRooks(fen);
  57     // Extract subTurn from turn indicator: "w" (first move), or
  58     // "w1" or "w2" white subturn 1 or 2, and same for black
  59     const fullTurn = V.ParseFen(fen).turn;
  60     this.turn = fullTurn[0];
  61     this.subTurn = (fullTurn[1] || 0); //"w0" = special code for first move in game
  62   }
  63
  64   getPotentialPawnMoves([x,y])
  65   {
  66     const color = this.turn;
  67     let moves = [];
  68     const [sizeX,sizeY] = [V.size.x,V.size.y];
  69     const shiftX = (color == "w" ? -1 : 1);
  70     const firstRank = (color == 'w' ? sizeX-1 : 0);
  71     const startRank = (color == "w" ? sizeX-2 : 1);
  72     const lastRank = (color == "w" ? 0 : sizeX-1);
  73     const finalPieces = x + shiftX == lastRank
  74       ? [V.ROOK,V.KNIGHT,V.BISHOP,V.QUEEN]
  75       : [V.PAWN];
  76
  77     // One square forward
  78     if (this.board[x+shiftX][y] == V.EMPTY)
  79     {
  80       for (let piece of finalPieces)
  81       {
  82         moves.push(this.getBasicMove([x,y], [x+shiftX,y],
  83           {c:color,p:piece}));
  84       }
  85       // Next condition because pawns on 1st rank can generally jump
  86       if ([startRank,firstRank].includes(x)
  87         && this.board[x+2*shiftX][y] == V.EMPTY)
  88       {
  89         // Two squares jump
  90         moves.push(this.getBasicMove([x,y], [x+2*shiftX,y]));
  91       }
  92     }
  93     // Captures
  94     for (let shiftY of [-1,1])
  95     {
  96       if (y + shiftY >= 0 && y + shiftY < sizeY
  97         && this.board[x+shiftX][y+shiftY] != V.EMPTY
  98         && this.canTake([x,y], [x+shiftX,y+shiftY]))
  99       {
 100         for (let piece of finalPieces)
 101         {
 102           moves.push(this.getBasicMove([x,y], [x+shiftX,y+shiftY],
 103             {c:color,p:piece}));
 104         }
 105       }
 106     }
 107
 108     // En passant: always OK if subturn 1,
 109     // OK on subturn 2 only if enPassant was played at subturn 1
 110     // (and if there are two e.p. squares available).
 111     const Lep = this.epSquares.length;
 112     const epSquares = this.epSquares[Lep-1]; //always at least one element
 113     let epSqs = [];
 114     epSquares.forEach(sq => {
 115       if (!!sq)
 116         epSqs.push(sq);
 117     });
 118     if (epSqs.length == 0)
 119       return moves;
 120     const oppCol = V.GetOppCol(color);
 121     for (let sq of epSqs)
 122     {
 123       if (this.subTurn == 1 || (epSqs.length == 2 &&
 124         // Was this en-passant capture already played at subturn 1 ?
 125         // (Or maybe the opponent filled the en-passant square with a piece)
 126         this.board[epSqs[0].x][epSqs[0].y] != V.EMPTY))
 127       {
 128         if (sq.x == x+shiftX && Math.abs(sq.y - y) == 1
 129           // Add condition "enemy pawn must be present"
 130           && this.getPiece(x,sq.y) == V.PAWN && this.getColor(x,sq.y) == oppCol)
 131         {
 132           let epMove = this.getBasicMove([x,y], [sq.x,sq.y]);
 133           epMove.vanish.push({
 134             x: x,
 135             y: sq.y,
 136             p: 'p',
 137             c: oppCol
 138           });
 139           moves.push(epMove);
 140         }
 141       }
 142     }
 143
 144     return moves;
 145   }
 146
 147   play(move)
 148   {
 149     move.flags = JSON.stringify(this.aggregateFlags());
 150     move.turn = this.turn + this.subTurn;
 151     V.PlayOnBoard(this.board, move);
 152     const epSq = this.getEpSquare(move);
 153     if (this.subTurn == 0) //first move in game
 154     {
 155       this.turn = "b";
 156       this.subTurn = 1;
 157       this.epSquares.push([epSq]);
 158     }
 159     // Does this move give check on subturn 1? If yes, skip subturn 2
 160     else if (this.subTurn==1 && this.underCheck(V.GetOppCol(this.turn)))
 161     {
 162       this.turn = V.GetOppCol(this.turn);
 163       this.epSquares.push([epSq]);
 164       move.checkOnSubturn1 = true;
 165     }
 166     else
 167     {
 168       if (this.subTurn == 2)
 169       {
 170         this.turn = V.GetOppCol(this.turn);
 171         let lastEpsq = this.epSquares[this.epSquares.length-1];
 172         lastEpsq.push(epSq);
 173       }
 174       else
 175         this.epSquares.push([epSq]);
 176       this.subTurn = 3 - this.subTurn;
 177     }
 178     this.updateVariables(move);
 179   }
 180
 181   undo(move)
 182   {
 183     this.disaggregateFlags(JSON.parse(move.flags));
 184     V.UndoOnBoard(this.board, move);
 185     if (move.turn[1] == '0' || move.checkOnSubturn1 || this.subTurn == 2)
 186       this.epSquares.pop();
 187     else //this.subTurn == 1
 188     {
 189       let lastEpsq = this.epSquares[this.epSquares.length-1];
 190       lastEpsq.pop();
 191     }
 192     this.turn = move.turn[0];
 193     this.subTurn = parseInt(move.turn[1]);
 194     this.unupdateVariables(move);
 195   }
 196
 197   // NOTE:  GenRandInitFen() is OK,
 198   // since at first move turn indicator is just "w"
 199
 200   static get VALUES()
 201   {
 202     return {
 203       'p': 1,
 204       'r': 5,
 205       'n': 3,
 206       'b': 3,
 207       'q': 7, //slightly less than in orthodox game
 208       'k': 1000
 209     };
 210   }
 211
 212   // No alpha-beta here, just adapted min-max at depth 2(+1)
 213   getComputerMove()
 214   {
 215     if (this.subTurn == 2)
 216       return null; //TODO: imperfect interface setup
 217
 218     const maxeval = V.INFINITY;
 219     const color = this.turn;
 220     const oppCol = V.GetOppCol(this.turn);
 221
 222     // Search best (half) move for opponent turn
 223     const getBestMoveEval = () => {
 224       const turnBefore = this.turn + this.subTurn;
 225       let score = this.getCurrentScore();
 226       if (score != "*")
 227       {
 228         if (score == "1/2")
 229           return 0;
 230         return maxeval * (score == "1-0" ? 1 : -1);
 231       }
 232       let moves = this.getAllValidMoves();
 233       let res = (oppCol == "w" ? -maxeval : maxeval);
 234       for (let m of moves)
 235       {
 236         this.play(m);
 237         score = this.getCurrentScore();
 238         // Now turn is oppCol,2 if m doesn't give check
 239         // Otherwise it's color,1. In both cases the next test makes sense
 240         if (score != "*")
 241         {
 242           if (score == "1/2")
 243             res = (oppCol == "w" ? Math.max(res, 0) : Math.min(res, 0));
 244           else
 245           {
 246             // Found a mate
 247             this.undo(m);
 248             return maxeval * (score == "1-0" ? 1 : -1);
 249           }
 250         }
 251         const evalPos = this.evalPosition();
 252         res = (oppCol == "w" ? Math.max(res, evalPos) : Math.min(res, evalPos));
 253         this.undo(m);
 254       }
 255       return res;
 256     };
 257
 258     let moves11 = this.getAllValidMoves();
 259     let doubleMoves = [];
 260     // Rank moves using a min-max at depth 2
 261     for (let i=0; i<moves11.length; i++)
 262     {
 263       this.play(moves11[i]);
 264       if (this.turn != color)
 265       {
 266         // We gave check with last move: search the best opponent move
 267         doubleMoves.push({moves:[moves11[i]], eval:getBestMoveEval()});
 268       }
 269       else
 270       {
 271         let moves12 = this.getAllValidMoves();
 272         for (let j=0; j<moves12.length; j++)
 273         {
 274           this.play(moves12[j]);
 275           doubleMoves.push({
 276             moves:[moves11[i],moves12[j]],
 277             eval:getBestMoveEval()});
 278           this.undo(moves12[j]);
 279         }
 280       }
 281       this.undo(moves11[i]);
 282     }
 283
 284     doubleMoves.sort( (a,b) => {
 285       return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
 286     let candidates = [0]; //indices of candidates moves
 287     for (let i=1;
 288       i<doubleMoves.length && doubleMoves[i].eval == doubleMoves[0].eval;
 289       i++)
 290     {
 291       candidates.push(i);
 292     }
 293
 294     const selected = doubleMoves[randInt(candidates.length)].moves;
 295     if (selected.length == 1)
 296       return selected[0];
 297     return selected;
 298   }
 299 }