decode method

dynamic decode(dynamic id)

Given an ID, returns the starting position's arrangement of pieces.

see {link https://en.wikipedia.org/wiki/Fischer_Random_Chess_numbering_scheme}

param id An ID of a starting position returns The starting position's arrangement, or false if invalid ID

Implementation

dynamic decode(id) {
    if (!FischerRandomValidators().isValidID(id)) return false;

    var arrangement = ['0', '1', '2', '3', '4', '5', '6', '7'];

    // Directly place first bishop on the derived square
    var q2b1 = divide(id, 4);
    arrangement[q2b1[1] * 2 + 1] = 'B';

    // Directly place second bishop on the derived square
    var q3b2 = divide(q2b1[0], 4);
    arrangement[q3b2[1] * 2] = 'B';

    // Place queen and knights on the remaining free squares
    var q4q = divide(q3b2[0], 6);
    arrangement = getPlace('Q', q4q[1], arrangement);
    arrangement =
        getPlace('N', q4q[0] > 3 ? ((q4q[0] -= 3) > 3 ? ((q4q[0] -= 2) > 3 ? (q4q[0] = 3) : 2) : 1) : 0, arrangement); // Credit to ugoren for this
    arrangement = getPlace('N', q4q[0], arrangement); // q4 has been modified by the above ternary operators

    // Place king and rooks on the remaining free squares
    arrangement = getPlace('R', 0, arrangement);
    arrangement = getPlace('K', 0, arrangement);
    arrangement = getPlace('R', 0, arrangement);

    return arrangement;
  }