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