如何在DataTable多级分组中获取组用于设置组行的样式？

function groupRowCallback(row, level, data) {
    if (level === 0) {
        $(row).addClass('group-level-0');
    } else if (level === 1) {
        $(row).addClass('group-level-1');
    } else if (level === 2) {
        $(row).addClass('group-level-2');
    }
}

$(document).ready(function() {
    $('#example').DataTable({
        // 配置多级分组
        "columns": [
            {"data": "group1"},
            {"data": "group2"},
            {"data": "value"}
        ],
        "columnDefs": [
            {"visible": false, "targets": [0, 1]},  // 隐藏分组列
            {"orderable": false, "targets": [0, 1]}  // 禁止排序分组列
        ],
        "order": [[0, 'asc'], [1, 'asc']],  // 按第一列和第二列升序排序

        // 调用自定义函数设置组行样式
        "drawCallback": function(settings) {
            var api = this.api();
            var rows = api.rows({page:'current'}).nodes();
            var lastGroup = null;
            api.column(0, {page:'current'}).data().each(function(group, i) {
                if (lastGroup !== group) {
                    $(rows).eq(i).before(
                        '<tr class="group-row"><td colspan="3">' + group + '</td></tr>'
                    );
                    lastGroup = group;
                }
            });
        },
        "rowCallback": function(row, data, index) {
            // 根据级别调用自定义函数设置组行样式
            var level = $(row).prevAll('.group-row').length;
            groupRowCallback(row, level, data);
        }
    });
});