fn generateMoves(self: @This(), color: Colors) void {
        var source_square: BoardType = undefined;
        var target_square: BoardType = undefined;
        const pieces = switch (color) {
            .white => &[_]PE{ .P, .N, .B, .R, .Q, .K },
            .black => &[_]PE{ .p, .n, .b, .r, .q, .k },
        };
        for (pieces) |piece| {
            var board = @bitCast(BoardType, self.bitboards[piece.int()]);
            // generate pawn and castling moves
            switch (piece) {
                .P, .p => {
                    while (board != 0) {
                        const s = @intCast(u6, @ctz(board));
                        source_square = @as(BoardType, 1) << s;
                        std.debug.print("pawn: {any}\n", .{@intToEnum(Square, s)});
                        // early exit on underflow/overflow
                        switch (piece) {
                            .P => if (@subWithOverflow(BoardType, source_square, 8, &target_square)) continue,
                            .p => if (@addWithOverflow(BoardType, source_square, 8, &target_square)) continue,
                            else => unreachable,
                        }
                        // generate quiet pawn moves
                        if (self.occupBoth() & target_square == 0) {
                            const promote_condition = switch (piece) {
                                .P => source_square >= @enumToInt(Square.a7) and
                                    source_square <= @enumToInt(Square.h7),
                                .p => source_square >= @enumToInt(Square.a2) and
                                    source_square <= @enumToInt(Square.h2),
                                else => unreachable,
                            };
                            const double_step_condition = switch (piece) {
                                .P => source_square >= @enumToInt(Square.a2) and
                                    source_square <= @enumToInt(Square.h2) and
                                    self.occupBoth() & (target_square - 8) == 0,
                                .p => source_square >= @enumToInt(Square.a7) and
                                    source_square <= @enumToInt(Square.h7) and
                                    self.occupBoth() & (target_square + 8) == 0,
                                else => unreachable,
                            };
                            if (promote_condition) {
                                // TODO: add move to move list
                            } else {
                                // TODO: single step
                                // TODO: double step
                                // FIXME: if single step is no-go, double can not work
                                if (double_step_condition) {}
                            }
                        }
                        // pop least significant bit
                        board ^= source_square;
                    }
                },
                else => {},
            }
        }
        // generate move for rest of pieces
    }

test "generateMoves" {
    var game = Game{ .attacks = Attacks.init() };
    try game.parseFEN("r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq - 0 1");
    game.show();
    game.generateMoves(game.side);
}