First draft of Magnetic chess

[vchess.git] / public / javascripts / variants / Magnetic.js

class MagneticRules
{
    getEpSquare(move)
    {
        return undefined; //no en-passant
    }

    // Complete a move with magnetic actions
    applyMagneticLaws([x,y], move)
    {
        // TODO
    }

    getBasicMove([sx,sy], [ex,ey], tr)
    {
        var mv = new Move({
            appear: [
                new PiPo({
                    x: ex,
                    y: ey,
                    c: !!tr ? tr.c : this.getColor(sx,sy),
                    p: !!tr ? tr.p : this.getPiece(sx,sy)
                })
            ],
            vanish: [
                new PiPo({
                    x: sx,
                    y: sy,
                    c: this.getColor(sx,sy),
                    p: this.getPiece(sx,sy)
                })
            ]
        });

        if (this.board[ex][ey] != VariantRules.EMPTY)
        {
            mv.vanish.push(
                new PiPo({
                    x: ex,
                    y: ey,
                    c: this.getColor(ex,ey),
                    p: this.getPiece(ex,ey)
                })
            );
        }
        this.applyMagneticLaws([ex,ey], mv);
        return mv;
    }

    getCastleMoves([x,y])
    {
        const c = this.getColor(x,y);
        if (x != (c=="w" ? 7 : 0) || y != this.INIT_COL_KING[c])
            return []; //x isn't first rank, or king has moved (shortcut)

        const V = VariantRules;

        // Castling ?
        const oppCol = this.getOppCol(c);
        let moves = [];
        let i = 0;
        const finalSquares = [ [2,3], [6,5] ]; //king, then rook
        castlingCheck:
        for (let castleSide=0; castleSide < 2; castleSide++) //large, then small
        {
            if (!this.flags[c][castleSide])
                continue;
            // If this code is reached, rooks and king are on initial position

            // Nothing on the path of the king (and no checks; OK also if y==finalSquare)?
            let step = finalSquares[castleSide][0] < y ? -1 : 1;
            for (i=y; i!=finalSquares[castleSide][0]; i+=step)
            {
                if (this.isAttacked([x,i], oppCol) || (this.board[x][i] != V.EMPTY &&
                    // NOTE: next check is enough, because of chessboard constraints
                    (this.getColor(x,i) != c || ![V.KING,V.ROOK].includes(this.getPiece(x,i)))))
                {
                    continue castlingCheck;
                }
            }

            // Nothing on the path to the rook?
            step = castleSide == 0 ? -1 : 1;
            for (i = y + step; i != this.INIT_COL_ROOK[c][castleSide]; i += step)
            {
                if (this.board[x][i] != V.EMPTY)
                    continue castlingCheck;
            }
            const rookPos = this.INIT_COL_ROOK[c][castleSide];

            // Nothing on final squares, except maybe king and castling rook?
            for (i=0; i<2; i++)
            {
                if (this.board[x][finalSquares[castleSide][i]] != V.EMPTY &&
                    this.getPiece(x,finalSquares[castleSide][i]) != V.KING &&
                    finalSquares[castleSide][i] != rookPos)
                {
                    continue castlingCheck;
                }
            }

            // If this code is reached, castle is valid
            let cmove = new Move({
                appear: [
                    new PiPo({x:x,y:finalSquares[castleSide][0],p:V.KING,c:c}),
                    new PiPo({x:x,y:finalSquares[castleSide][1],p:V.ROOK,c:c})],
                vanish: [
                    new PiPo({x:x,y:y,p:V.KING,c:c}),
                    new PiPo({x:x,y:rookPos,p:V.ROOK,c:c})],
                end: Math.abs(y - rookPos) <= 2
                    ? {x:x, y:rookPos}
                    : {x:x, y:y + 2 * (castleSide==0 ? -1 : 1)}
            });
            this.applyMagneticLaws([x,finalSquares[castleSide][1]], cmove);
            moves.push(cmove);
        }

        return moves;
    }

    // TODO: verify this assertion
//  atLeastOneMove()
//  {
//      return true; //always at least one possible move
//  }

    underCheck(move)
    {
        return false; //there is no check
    }

    getCheckSquares(move)
    {
        const c = this.getOppCol(this.turn); //opponent
        const saveKingPos = this.kingPos[c]; //king might be taken
        this.play(move);
        // The only way to be "under check" is to have lost the king (thus game over)
        let res = this.kingPos[c][0] < 0;
            ? [ JSON.parse(JSON.stringify(saveKingPos)) ]
            : [ ];
        this.undo(move);
        return res;
    }

    updateVariables(move)
    {
        super.updateVariables(move);
        const c = this.getColor(move.start.x,move.start.y);
        if (c != this.getColor(move.end.x,move.end.y)
            && this.board[move.end.x][move.end.y] != VariantRules.EMPTY
            && this.getPiece(move.end.x,move.end.y) == VariantRules.KING)
        {
            // We took opponent king !
            const oppCol = this.getOppCol(c);
            this.kingPos[oppCol] = [-1,-1];
            this.flags[oppCol] = [false,false];
        }
    }

    unupdateVariables(move)
    {
        super.unupdateVariables(move);
        const c = this.getColor(move.start.x,move.start.y);
        const oppCol = this.getOppCol(c);
        if (this.kingPos[oppCol][0] < 0)
        {
            // Last move took opponent's king
            for (let psq of move.vanish)
            {
                if (psq.p == 'k')
                {
                    this.kingPos[oppCol] = [psq.x, psq.y];
                    break;
                }
            }
        }
    }

    checkGameOver()
    {
        if (this.checkRepetition())
            return "1/2";

        const color = this.turn;
        // TODO: do we need "atLeastOneMove()"?
        if (this.atLeastOneMove() && this.kingPos[color][0] >= 0)
            return "*";

        return this.checkGameEnd();
    }

    checkGameEnd()
    {
        // No valid move: our king disappeared
        return this.turn == "w" ? "0-1" : "1-0";
    }
}