Horde_Ldap_Filter::_parseCombination PHP Method

    protected static function _parseCombination($filter)
    {
        // Extract logical operator and filter arguments.
        $operator = substr($filter, 0, 1);
        $filter = substr($filter, 1);
        // Split $filter into individual subfilters. We cannot use split() for
        // this, because we do not know the complexiness of the
        // subfilter. Thus, we look trough the filter string and just recognize
        // ending filters at the first level. We record the index number of the
        // char and use that information later to split the string.
        $sub_index_pos = array();
        // Previous character looked at.
        $prev_char = '';
        // Denotes the current bracket level we are, >1 is too deep, 1 is ok, 0
        // is outside any subcomponent.
        $level = 0;
        for ($curpos = 0, $len = strlen($filter); $curpos < $len; $curpos++) {
            $cur_char = $filter[$curpos];
            // Rise/lower bracket level.
            if ($cur_char == '(' && $prev_char != '\\') {
                $level++;
            } elseif ($cur_char == ')' && $prev_char != '\\') {
                $level--;
            }
            if ($cur_char == '(' && $prev_char == ')' && $level == 1) {
                // Mark the position for splitting.
                $sub_index_pos[] = $curpos;
            }
            $prev_char = $cur_char;
        }
        // Now perform the splits. To get the last part too, we need to add the
        // "END" index to the split array.
        $sub_index_pos[] = strlen($filter);
        $subfilters = array();
        $oldpos = 0;
        foreach ($sub_index_pos as $s_pos) {
            $str_part = substr($filter, $oldpos, $s_pos - $oldpos);
            $subfilters[] = $str_part;
            $oldpos = $s_pos;
        }
        if (count($subfilters) > 1) {
            // Several subfilters found.
            if ($operator == '!') {
                throw new Horde_Ldap_Exception('Invalid filter syntax: NOT operator detected but several arguments given');
            }
        } elseif (!count($subfilters)) {
            // This should not happen unless the user specified a wrong filter.
            throw new Horde_Ldap_Exception('Invalid filter syntax: got operator ' . $operator . ' but no argument');
        }
        // Now parse the subfilters into objects and combine them using the
        // operator.
        $subfilters_o = array();
        foreach ($subfilters as $s_s) {
            $subfilters_o[] = self::parse($s_s);
        }
        if (count($subfilters_o) == 1) {
            $subfilters_o = $subfilters_o[0];
        }
        return self::combine($operator, $subfilters_o);
    }