client/src/variants/Doublemove1.js

   1 import { ChessRules } from "@/base_rules";
   2 import { randInt } from "@/utils/alea";
   3
   4 export class Doublemove1Rules 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     this.turn = parsedFen.turn;
  35     this.subTurn = 1;
  36   }
  37
  38   getEnpassantCaptures([x, y], shiftX) {
  39     let moves = [];
  40     // En passant: always OK if subturn 1,
  41     // OK on subturn 2 only if enPassant was played at subturn 1
  42     // (and if there are two e.p. squares available).
  43     const Lep = this.epSquares.length;
  44     const epSquares = this.epSquares[Lep - 1]; //always at least one element
  45     let epSqs = [];
  46     epSquares.forEach(sq => {
  47       if (sq) epSqs.push(sq);
  48     });
  49     if (epSqs.length == 0) return moves;
  50     const oppCol = V.GetOppCol(this.getColor(x, y));
  51     for (let sq of epSqs) {
  52       if (
  53         this.subTurn == 1 ||
  54         (epSqs.length == 2 &&
  55           // Was this en-passant capture already played at subturn 1 ?
  56           // (Or maybe the opponent filled the en-passant square with a piece)
  57           this.board[epSqs[0].x][epSqs[0].y] != V.EMPTY)
  58       ) {
  59         if (
  60           sq.x == x + shiftX &&
  61           Math.abs(sq.y - y) == 1 &&
  62           // Add condition "enemy pawn must be present"
  63           this.getPiece(x, sq.y) == V.PAWN &&
  64           this.getColor(x, sq.y) == oppCol
  65         ) {
  66           let epMove = this.getBasicMove([x, y], [sq.x, sq.y]);
  67           epMove.vanish.push({
  68             x: x,
  69             y: sq.y,
  70             p: "p",
  71             c: oppCol
  72           });
  73           moves.push(epMove);
  74         }
  75       }
  76     }
  77     return moves;
  78   }
  79
  80   play(move) {
  81     move.flags = JSON.stringify(this.aggregateFlags());
  82     move.turn = [this.turn, this.subTurn];
  83     V.PlayOnBoard(this.board, move);
  84     const epSq = this.getEpSquare(move);
  85     if (this.movesCount == 0) {
  86       // First move in game
  87       this.turn = "b";
  88       this.epSquares.push([epSq]);
  89       this.movesCount = 1;
  90     }
  91     // Does this move give check on subturn 1? If yes, skip subturn 2
  92     else if (this.subTurn == 1 && this.underCheck(V.GetOppCol(this.turn))) {
  93       this.turn = V.GetOppCol(this.turn);
  94       this.epSquares.push([epSq]);
  95       move.checkOnSubturn1 = true;
  96       this.movesCount++;
  97     }
  98     else {
  99       if (this.subTurn == 2) {
 100         this.turn = V.GetOppCol(this.turn);
 101         let lastEpsq = this.epSquares[this.epSquares.length - 1];
 102         lastEpsq.push(epSq);
 103       }
 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[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     }
 133     else if (
 134       move.end.x == oppFirstRank && //we took opponent rook?
 135       this.castleFlags[oppCol].includes(move.end.y)
 136     ) {
 137       const flagIdx = (move.end.y == this.castleFlags[oppCol][0] ? 0 : 1);
 138       this.castleFlags[oppCol][flagIdx] = V.size.y;
 139     }
 140   }
 141
 142   undo(move) {
 143     this.disaggregateFlags(JSON.parse(move.flags));
 144     V.UndoOnBoard(this.board, move);
 145     if (this.movesCount == 1 || !!move.checkOnSubturn1 || this.subTurn == 2) {
 146       // The move may not be full, but is fully undone:
 147       this.epSquares.pop();
 148       // Moves counter was just incremented:
 149       this.movesCount--;
 150     }
 151     else {
 152       // Undo the second half of a move
 153       let lastEpsq = this.epSquares[this.epSquares.length - 1];
 154       lastEpsq.pop();
 155     }
 156     this.turn = move.turn[0];
 157     this.subTurn = move.turn[1];
 158     super.postUndo(move);
 159   }
 160
 161   static get VALUES() {
 162     return {
 163       p: 1,
 164       r: 5,
 165       n: 3,
 166       b: 3,
 167       q: 7, //slightly less than in orthodox game
 168       k: 1000
 169     };
 170   }
 171
 172   // No alpha-beta here, just adapted min-max at depth 2(+1)
 173   getComputerMove() {
 174     const maxeval = V.INFINITY;
 175     const color = this.turn;
 176     const oppCol = V.GetOppCol(this.turn);
 177
 178     // Search best (half) move for opponent turn
 179     const getBestMoveEval = () => {
 180       let score = this.getCurrentScore();
 181       if (score != "*") {
 182         if (score == "1/2") return 0;
 183         return maxeval * (score == "1-0" ? 1 : -1);
 184       }
 185       let moves = this.getAllValidMoves();
 186       let res = oppCol == "w" ? -maxeval : maxeval;
 187       for (let m of moves) {
 188         this.play(m);
 189         score = this.getCurrentScore();
 190         // Now turn is oppCol,2 if m doesn't give check
 191         // Otherwise it's color,1. In both cases the next test makes sense
 192         if (score != "*") {
 193           if (score == "1/2")
 194             res = oppCol == "w" ? Math.max(res, 0) : Math.min(res, 0);
 195           else {
 196             // Found a mate
 197             this.undo(m);
 198             return maxeval * (score == "1-0" ? 1 : -1);
 199           }
 200         }
 201         const evalPos = this.evalPosition();
 202         res = oppCol == "w" ? Math.max(res, evalPos) : Math.min(res, evalPos);
 203         this.undo(m);
 204       }
 205       return res;
 206     };
 207
 208     const moves11 = this.getAllValidMoves();
 209     let doubleMoves = [];
 210     // Rank moves using a min-max at depth 2
 211     for (let i = 0; i < moves11.length; i++) {
 212       this.play(moves11[i]);
 213       if (this.turn != color) {
 214         // We gave check with last move: search the best opponent move
 215         doubleMoves.push({ moves: [moves11[i]], eval: getBestMoveEval() });
 216       }
 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() + 0.05 - Math.random() / 10
 224           });
 225           this.undo(moves12[j]);
 226         }
 227       }
 228       this.undo(moves11[i]);
 229     }
 230
 231     // TODO: array + sort + candidates logic not required when adding small
 232     // fluctuations to the eval function (could also be generalized).
 233     doubleMoves.sort((a, b) => {
 234       return (color == "w" ? 1 : -1) * (b.eval - a.eval);
 235     });
 236     let candidates = [0]; //indices of candidates moves
 237     for (
 238       let i = 1;
 239       i < doubleMoves.length && doubleMoves[i].eval == doubleMoves[0].eval;
 240       i++
 241     ) {
 242       candidates.push(i);
 243     }
 244     const selected = doubleMoves[randInt(candidates.length)].moves;
 245     if (selected.length == 1) return selected[0];
 246     return selected;
 247   }
 248 };