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[vchess.git] / client / src / variants / Marseille.js

import { ChessRules } from "@/base_rules";
import { randInt } from "@/utils/alea";

export const VariantRules = class MarseilleRules extends ChessRules {
  static IsGoodEnpassant(enpassant) {
    const squares = enpassant.split(",");
    if (squares.length > 2) return false;
    for (let sq of squares) {
      if (sq != "-") {
        const ep = V.SquareToCoords(sq);
        if (isNaN(ep.x) || !V.OnBoard(ep)) return false;
      }
    }
    return true;
  }

  getTurnFen() {
    return this.turn + this.subTurn;
  }

  // There may be 2 enPassant squares (if 2 pawns jump 2 squares in same turn)
  getEnpassantFen() {
    return this.epSquares[this.epSquares.length - 1].map(
      epsq => epsq === undefined
        ? "-" //no en-passant
        : V.CoordsToSquare(epsq)
    ).join(",");
  }

  setOtherVariables(fen) {
    const parsedFen = V.ParseFen(fen);
    this.setFlags(parsedFen.flags);
    this.epSquares = [parsedFen.enpassant.split(",").map(sq => {
      if (sq != "-") return V.SquareToCoords(sq);
      return undefined;
    })];
    this.scanKingsRooks(fen);
    // Extract subTurn from turn indicator: "w" (first move), or
    // "w1" or "w2" white subturn 1 or 2, and same for black
    const fullTurn = V.ParseFen(fen).turn;
    this.turn = fullTurn[0];
    // At move 1, the subTurn doesn't need to be specified:
    this.subTurn = fullTurn[1] || 1;
  }

  getPotentialPawnMoves([x, y]) {
    const color = this.turn;
    let moves = [];
    const [sizeX, sizeY] = [V.size.x, V.size.y];
    const shiftX = color == "w" ? -1 : 1;
    const firstRank = color == "w" ? sizeX - 1 : 0;
    const startRank = color == "w" ? sizeX - 2 : 1;
    const lastRank = color == "w" ? 0 : sizeX - 1;
    const finalPieces =
      x + shiftX == lastRank ? [V.ROOK, V.KNIGHT, V.BISHOP, V.QUEEN] : [V.PAWN];

    // One square forward
    if (this.board[x + shiftX][y] == V.EMPTY) {
      for (let piece of finalPieces) {
        moves.push(
          this.getBasicMove([x, y], [x + shiftX, y], { c: color, p: piece })
        );
      }
      // Next condition because pawns on 1st rank can generally jump
      if (
        [startRank, firstRank].includes(x) &&
        this.board[x + 2 * shiftX][y] == V.EMPTY
      ) {
        // Two squares jump
        moves.push(this.getBasicMove([x, y], [x + 2 * shiftX, y]));
      }
    }
    // Captures
    for (let shiftY of [-1, 1]) {
      if (
        y + shiftY >= 0 &&
        y + shiftY < sizeY &&
        this.board[x + shiftX][y + shiftY] != V.EMPTY &&
        this.canTake([x, y], [x + shiftX, y + shiftY])
      ) {
        for (let piece of finalPieces) {
          moves.push(
            this.getBasicMove([x, y], [x + shiftX, y + shiftY], {
              c: color,
              p: piece
            })
          );
        }
      }
    }

    // En passant: always OK if subturn 1,
    // OK on subturn 2 only if enPassant was played at subturn 1
    // (and if there are two e.p. squares available).
    const Lep = this.epSquares.length;
    const epSquares = this.epSquares[Lep - 1]; //always at least one element
    let epSqs = [];
    epSquares.forEach(sq => {
      if (sq) epSqs.push(sq);
    });
    if (epSqs.length == 0) return moves;
    const oppCol = V.GetOppCol(color);
    for (let sq of epSqs) {
      if (
        this.subTurn == 1 ||
        (epSqs.length == 2 &&
          // Was this en-passant capture already played at subturn 1 ?
          // (Or maybe the opponent filled the en-passant square with a piece)
          this.board[epSqs[0].x][epSqs[0].y] != V.EMPTY)
      ) {
        if (
          sq.x == x + shiftX &&
          Math.abs(sq.y - y) == 1 &&
          // Add condition "enemy pawn must be present"
          this.getPiece(x, sq.y) == V.PAWN &&
          this.getColor(x, sq.y) == oppCol
        ) {
          let epMove = this.getBasicMove([x, y], [sq.x, sq.y]);
          epMove.vanish.push({
            x: x,
            y: sq.y,
            p: "p",
            c: oppCol
          });
          moves.push(epMove);
        }
      }
    }

    return moves;
  }

  play(move) {
    move.flags = JSON.stringify(this.aggregateFlags());
    move.turn = this.turn + this.subTurn;
    V.PlayOnBoard(this.board, move);
    const epSq = this.getEpSquare(move);
    if (this.movesCount == 0) {
      // First move in game
      this.turn = "b";
      this.epSquares.push([epSq]);
      this.movesCount = 1;
    }
    // Does this move give check on subturn 1? If yes, skip subturn 2
    else if (this.subTurn == 1 && this.underCheck(V.GetOppCol(this.turn))) {
      this.turn = V.GetOppCol(this.turn);
      this.epSquares.push([epSq]);
      move.checkOnSubturn1 = true;
      this.movesCount++;
    } else {
      if (this.subTurn == 2) {
        this.turn = V.GetOppCol(this.turn);
        let lastEpsq = this.epSquares[this.epSquares.length - 1];
        lastEpsq.push(epSq);
      } else {
        this.epSquares.push([epSq]);
        this.movesCount++;
      }
      this.subTurn = 3 - this.subTurn;
    }
    this.updateVariables(move);
  }

  undo(move) {
    this.disaggregateFlags(JSON.parse(move.flags));
    V.UndoOnBoard(this.board, move);
    if (this.movesCount == 1 || !!move.checkOnSubturn1 || this.subTurn == 2) {
      // The move may not be full, but is fully undone:
      this.epSquares.pop();
      // Moves counter was just incremented:
      this.movesCount--;
    } else {
      // Undo the second half of a move
      let lastEpsq = this.epSquares[this.epSquares.length - 1];
      lastEpsq.pop();
    }
    this.turn = move.turn[0];
    this.subTurn = parseInt(move.turn[1]);
    this.unupdateVariables(move);
  }

  // NOTE:  GenRandInitFen() is OK,
  // since at first move turn indicator is just "w"

  static get VALUES() {
    return {
      p: 1,
      r: 5,
      n: 3,
      b: 3,
      q: 7, //slightly less than in orthodox game
      k: 1000
    };
  }

  // No alpha-beta here, just adapted min-max at depth 2(+1)
  getComputerMove() {
    const maxeval = V.INFINITY;
    const color = this.turn;
    const oppCol = V.GetOppCol(this.turn);

    // Search best (half) move for opponent turn
    const getBestMoveEval = () => {
      let score = this.getCurrentScore();
      if (score != "*") {
        if (score == "1/2") return 0;
        return maxeval * (score == "1-0" ? 1 : -1);
      }
      let moves = this.getAllValidMoves();
      let res = oppCol == "w" ? -maxeval : maxeval;
      for (let m of moves) {
        this.play(m);
        score = this.getCurrentScore();
        // Now turn is oppCol,2 if m doesn't give check
        // Otherwise it's color,1. In both cases the next test makes sense
        if (score != "*") {
          if (score == "1/2")
            res = oppCol == "w" ? Math.max(res, 0) : Math.min(res, 0);
          else {
            // Found a mate
            this.undo(m);
            return maxeval * (score == "1-0" ? 1 : -1);
          }
        }
        const evalPos = this.evalPosition();
        res = oppCol == "w" ? Math.max(res, evalPos) : Math.min(res, evalPos);
        this.undo(m);
      }
      return res;
    };

    let moves11 = this.getAllValidMoves();
    let doubleMoves = [];
    // Rank moves using a min-max at depth 2
    for (let i = 0; i < moves11.length; i++) {
      this.play(moves11[i]);
      if (this.turn != color) {
        // We gave check with last move: search the best opponent move
        doubleMoves.push({ moves: [moves11[i]], eval: getBestMoveEval() });
      } else {
        let moves12 = this.getAllValidMoves();
        for (let j = 0; j < moves12.length; j++) {
          this.play(moves12[j]);
          doubleMoves.push({
            moves: [moves11[i], moves12[j]],
            eval: getBestMoveEval()
          });
          this.undo(moves12[j]);
        }
      }
      this.undo(moves11[i]);
    }

    doubleMoves.sort((a, b) => {
      return (color == "w" ? 1 : -1) * (b.eval - a.eval);
    });
    let candidates = [0]; //indices of candidates moves
    for (
      let i = 1;
      i < doubleMoves.length && doubleMoves[i].eval == doubleMoves[0].eval;
      i++
    ) {
      candidates.push(i);
    }

    const selected = doubleMoves[randInt(candidates.length)].moves;
    if (selected.length == 1) return selected[0];
    return selected;
  }
};