Horde_Imap_Client_Socket::_thread PHP Method

    protected function _thread($options)
    {
        $thread_criteria = array(Horde_Imap_Client::THREAD_ORDEREDSUBJECT => 'ORDEREDSUBJECT', Horde_Imap_Client::THREAD_REFERENCES => 'REFERENCES', Horde_Imap_Client::THREAD_REFS => 'REFS');
        $tsort = isset($options['criteria']) ? is_string($options['criteria']) ? Horde_String::upper($options['criteria']) : $thread_criteria[$options['criteria']] : 'ORDEREDSUBJECT';
        if (!$this->_capability('THREAD', $tsort)) {
            switch ($tsort) {
                case 'ORDEREDSUBJECT':
                    if (empty($options['search'])) {
                        $ids = $this->getIdsOb(Horde_Imap_Client_Ids::ALL, !empty($options['sequence']));
                    } else {
                        $search_res = $this->search($this->_selected, $options['search'], array('sequence' => !empty($options['sequence'])));
                        $ids = $search_res['match'];
                    }
                    /* Do client-side ORDEREDSUBJECT threading. */
                    $query = new Horde_Imap_Client_Fetch_Query();
                    $query->envelope();
                    $query->imapDate();
                    $fetch_res = $this->fetch($this->_selected, $query, array('ids' => $ids));
                    if (!isset($this->_temp['clientsort'])) {
                        $this->_temp['clientsort'] = new Horde_Imap_Client_Socket_ClientSort($this);
                    }
                    return $this->_temp['clientsort']->threadOrderedSubject($fetch_res, empty($options['sequence']));
                case 'REFERENCES':
                case 'REFS':
                    throw new Horde_Imap_Client_Exception_NoSupportExtension('THREAD', sprintf('Server does not support "%s" thread sort.', $tsort));
            }
        }
        $cmd = $this->_command(empty($options['sequence']) ? 'UID THREAD' : 'THREAD')->add($tsort);
        /* If UTF-8 support is activated, a client MUST NOT
         * send the charset specification (RFC 6855 [3]; Errata 4029). */
        if (empty($options['search'])) {
            if (!$this->_capability()->isEnabled('UTF8=ACCEPT')) {
                $cmd->add('US-ASCII');
            }
            $cmd->add('ALL');
        } else {
            $search_query = $options['search']->build();
            if (!$this->_capability()->isEnabled('UTF8=ACCEPT')) {
                $cmd->add(is_null($search_query['charset']) ? 'US-ASCII' : $search_query['charset']);
            }
            $cmd->add($search_query['query'], true);
        }
        return new Horde_Imap_Client_Data_Thread($this->_sendCmd($cmd)->data['threadparse'], empty($options['sequence']) ? 'uid' : 'sequence');
    }