client/src/variants/Marseille.js

   1 import { ChessRules } from "@/base_rules";
   2 import { randInt } from "@/utils/alea";
   3
   4 export 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   // 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   play(move) {
  83     move.flags = JSON.stringify(this.aggregateFlags());
  84     move.turn = this.turn + this.subTurn;
  85     V.PlayOnBoard(this.board, move);
  86     const epSq = this.getEpSquare(move);
  87     if (this.movesCount == 0) {
  88       // First move in game
  89       this.turn = "b";
  90       this.epSquares.push([epSq]);
  91       this.movesCount = 1;
  92     }
  93     // Does this move give check on subturn 1? If yes, skip subturn 2
  94     else if (this.subTurn == 1 && this.underCheck(V.GetOppCol(this.turn))) {
  95       this.turn = V.GetOppCol(this.turn);
  96       this.epSquares.push([epSq]);
  97       move.checkOnSubturn1 = true;
  98       this.movesCount++;
  99     } else {
 100       if (this.subTurn == 2) {
 101         this.turn = V.GetOppCol(this.turn);
 102         let lastEpsq = this.epSquares[this.epSquares.length - 1];
 103         lastEpsq.push(epSq);
 104       } else {
 105         this.epSquares.push([epSq]);
 106         this.movesCount++;
 107       }
 108       this.subTurn = 3 - this.subTurn;
 109     }
 110     this.postPlay(move);
 111   }
 112
 113   postPlay(move) {
 114     const c = move.turn.charAt(0);
 115     const piece = move.vanish[0].p;
 116     const firstRank = c == "w" ? V.size.x - 1 : 0;
 117
 118     if (piece == V.KING && move.appear.length > 0) {
 119       this.kingPos[c][0] = move.appear[0].x;
 120       this.kingPos[c][1] = move.appear[0].y;
 121       this.castleFlags[c] = [V.size.y, V.size.y];
 122       return;
 123     }
 124     const oppCol = V.GetOppCol(c);
 125     const oppFirstRank = V.size.x - 1 - firstRank;
 126     if (
 127       move.start.x == firstRank && //our rook moves?
 128       this.castleFlags[c].includes(move.start.y)
 129     ) {
 130       const flagIdx = (move.start.y == this.castleFlags[c][0] ? 0 : 1);
 131       this.castleFlags[c][flagIdx] = V.size.y;
 132     } else if (
 133       move.end.x == oppFirstRank && //we took opponent rook?
 134       this.castleFlags[oppCol].includes(move.end.y)
 135     ) {
 136       const flagIdx = (move.end.y == this.castleFlags[oppCol][0] ? 0 : 1);
 137       this.castleFlags[oppCol][flagIdx] = V.size.y;
 138     }
 139   }
 140
 141   undo(move) {
 142     this.disaggregateFlags(JSON.parse(move.flags));
 143     V.UndoOnBoard(this.board, move);
 144     if (this.movesCount == 1 || !!move.checkOnSubturn1 || this.subTurn == 2) {
 145       // The move may not be full, but is fully undone:
 146       this.epSquares.pop();
 147       // Moves counter was just incremented:
 148       this.movesCount--;
 149     } else {
 150       // Undo the second half of a move
 151       let lastEpsq = this.epSquares[this.epSquares.length - 1];
 152       lastEpsq.pop();
 153     }
 154     this.turn = move.turn[0];
 155     this.subTurn = parseInt(move.turn[1]);
 156     super.postUndo(move);
 157   }
 158
 159   // NOTE:  GenRandInitFen() is OK,
 160   // since at first move turn indicator is just "w"
 161
 162   static get VALUES() {
 163     return {
 164       p: 1,
 165       r: 5,
 166       n: 3,
 167       b: 3,
 168       q: 7, //slightly less than in orthodox game
 169       k: 1000
 170     };
 171   }
 172
 173   // No alpha-beta here, just adapted min-max at depth 2(+1)
 174   getComputerMove() {
 175     const maxeval = V.INFINITY;
 176     const color = this.turn;
 177     const oppCol = V.GetOppCol(this.turn);
 178
 179     // Search best (half) move for opponent turn
 180     const getBestMoveEval = () => {
 181       let score = this.getCurrentScore();
 182       if (score != "*") {
 183         if (score == "1/2") return 0;
 184         return maxeval * (score == "1-0" ? 1 : -1);
 185       }
 186       let moves = this.getAllValidMoves();
 187       let res = oppCol == "w" ? -maxeval : maxeval;
 188       for (let m of moves) {
 189         this.play(m);
 190         score = this.getCurrentScore();
 191         // Now turn is oppCol,2 if m doesn't give check
 192         // Otherwise it's color,1. In both cases the next test makes sense
 193         if (score != "*") {
 194           if (score == "1/2")
 195             res = oppCol == "w" ? Math.max(res, 0) : Math.min(res, 0);
 196           else {
 197             // Found a mate
 198             this.undo(m);
 199             return maxeval * (score == "1-0" ? 1 : -1);
 200           }
 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     let moves11 = this.getAllValidMoves();
 210     let doubleMoves = [];
 211     // Rank moves using a min-max at depth 2
 212     for (let i = 0; i < moves11.length; i++) {
 213       this.play(moves11[i]);
 214       if (this.turn != color) {
 215         // We gave check with last move: search the best opponent move
 216         doubleMoves.push({ moves: [moves11[i]], eval: getBestMoveEval() });
 217       } else {
 218         let moves12 = this.getAllValidMoves();
 219         for (let j = 0; j < moves12.length; j++) {
 220           this.play(moves12[j]);
 221           doubleMoves.push({
 222             moves: [moves11[i], moves12[j]],
 223             eval: getBestMoveEval()
 224           });
 225           this.undo(moves12[j]);
 226         }
 227       }
 228       this.undo(moves11[i]);
 229     }
 230
 231     doubleMoves.sort((a, b) => {
 232       return (color == "w" ? 1 : -1) * (b.eval - a.eval);
 233     });
 234     let candidates = [0]; //indices of candidates moves
 235     for (
 236       let i = 1;
 237       i < doubleMoves.length && doubleMoves[i].eval == doubleMoves[0].eval;
 238       i++
 239     ) {
 240       candidates.push(i);
 241     }
 242
 243     const selected = doubleMoves[randInt(candidates.length)].moves;
 244     if (selected.length == 1) return selected[0];
 245     return selected;
 246   }
 247 };