public function readGroups(string $before, string $start, string $end, string $after)
    {
        // init
        $groups = [];
        $group = [];
        $position = 'before_search';

        foreach ($this->parsedfile as $edi_row) {
            // search before group segment
            if ($position == 'before_search' && $edi_row[0] == $before) {
                $position = 'before_is';
                continue;
            }

            if ($position == 'before_search') {
                continue;
            }

            if ($position == 'before_is' && $edi_row[0] == $before) {
                continue;
            }

            // after before search start
            if ($position == 'before_is' && $edi_row[0] == $start) {
                $position = 'group_is';
                $group[] = $edi_row;
                continue;
            }

            // if after before segment no start segment, search again before segment
            if ($position == 'before_is') {
                $position = 'before_search';
                continue;
            }

            // get group element
            if ($position == 'group_is' && $edi_row[0] != $end) {
                $group[] = $edi_row;
                continue;
            }

            // found end of group
            if ($position == 'group_is' && $edi_row[0] == $end) {
                $position = 'group_finish';
                $group[] = $edi_row;
                $groups[] = $group;
                $group = [];
                continue;
            }

            // next group start
            if ($position == 'group_finish' && $edi_row[0] == $start) {
                $group[] = $edi_row;
                $position = 'group_is';
                continue;
            }

            // finish
            if ($position == 'group_finish' && $edi_row[0] == $after) {
                break;
            }

            $this->errors[] = 'Reading group ' . $before . '/' . $start . '/' . $end . '/' . $after
                              . '. Error on position: ' . $position;

            return false;
        }

        return $groups;
    }