function search_users($needle, $type, $relation_type)
{
    global $tbl_user, $tbl_user_rel_access_url, $tbl_group_rel_user, $group_id, $_configuration;
    $xajax_response = new XajaxResponse();
    $return = $return_origin = $return_destination = '';
    $without_user_id = $without_user_id = $condition_relation = '';
    if (!empty($group_id) && !empty($relation_type)) {
        $group_id = intval($group_id);
        $relation_type = intval($relation_type);
        // get user_id from relation type and group id
        $sql = "SELECT user_id FROM {$tbl_group_rel_user}\n\t\t\t\tWHERE group_id = '{$group_id}'\n\t\t\t\tAND relation_type IN (" . GROUP_USER_PERMISSION_ADMIN . "," . GROUP_USER_PERMISSION_READER . "," . GROUP_USER_PERMISSION_PENDING_INVITATION . "," . GROUP_USER_PERMISSION_MODERATOR . ", " . GROUP_USER_PERMISSION_HRM . ") ";
        $res = Database::query($sql);
        $user_ids = array();
        if (Database::num_rows($res) > 0) {
            while ($row = Database::fetch_row($res)) {
                $user_ids[] = $row[0];
            }
            $without_user_id = " AND user.user_id NOT IN(" . implode(',', $user_ids) . ") ";
        }
        if ($relation_type == GROUP_USER_PERMISSION_PENDING_INVITATION) {
            $condition_relation = " AND groups.relation_type IN (" . GROUP_USER_PERMISSION_PENDING_INVITATION . "," . GROUP_USER_PERMISSION_READER . ") ";
        } else {
            $condition_relation = " AND groups.relation_type = '{$relation_type}' ";
        }
        // data for destination user list
        $sql = "SELECT user.user_id, user.username, user.lastname, user.firstname\n\t\t\t\tFROM {$tbl_group_rel_user} groups\n\t\t\t\tINNER JOIN  {$tbl_user} user ON user.user_id = groups.user_id\n\t\t\t\tWHERE groups.group_id = '{$group_id}' {$condition_relation} ";
        $rs_destination = Database::query($sql);
        if (Database::num_rows($rs_destination) > 0) {
            $return_destination .= '<select id="destination_users" name="sessionUsersList[]" multiple="multiple" size="15" style="width:360px;">';
            while ($row = Database::fetch_array($rs_destination)) {
                $person_name = api_get_person_name($row['firstname'], $row['lastname']);
                $return_destination .= '<option value="' . $row['user_id'] . '">' . $person_name . ' (' . $row['username'] . ')</option>';
            }
            $return_destination .= '</select>';
        } else {
            $return_destination .= '<select id="destination_users" name="sessionUsersList[]" multiple="multiple" size="15" style="width:360px;"></select>';
        }
        $xajax_response->addAssign('ajax_destination_list', 'innerHTML', api_utf8_encode($return_destination));
    } else {
        $return_destination .= '<select id="destination_users" name="sessionUsersList[]" multiple="multiple" size="15" style="width:360px;"></select>';
        $xajax_response->addAssign('ajax_destination_list', 'innerHTML', api_utf8_encode($return_destination));
        if ($type == 'single') {
            $return .= '';
            $xajax_response->addAssign('ajax_list_users_single', 'innerHTML', api_utf8_encode($return));
        } else {
            $return_origin .= '<select id="origin_users" name="nosessionUsersList[]" multiple="multiple" size="15" style="width:360px;"></select>';
            $xajax_response->addAssign('ajax_origin_list_multiple', 'innerHTML', api_utf8_encode($return_origin));
        }
    }
    if (!empty($needle) && !empty($type)) {
        // xajax send utf8 datas... datas in db can be non-utf8 datas
        $charset = api_get_system_encoding();
        $needle = Database::escape_string($needle);
        $needle = api_convert_encoding($needle, $charset, 'utf-8');
        $user_anonymous = api_get_anonymous_id();
        $order_clause = api_sort_by_first_name() ? ' ORDER BY firstname, lastname, username' : ' ORDER BY lastname, firstname, username';
        if ($type == 'single') {
            if (!empty($group_id) && !empty($relation_type)) {
                // search users where username or firstname or lastname begins likes $needle
                $sql = "SELECT user_id, username, lastname, firstname FROM {$tbl_user} user\n\t\t\t\t\t\tWHERE (username LIKE '{$needle}%' OR firstname LIKE '{$needle}%' OR lastname LIKE '{$needle}%')\n\t\t\t\t\t\tAND user_id<>'{$user_anonymous}' {$without_user_id} {$order_clause} LIMIT 11";
                if ($_configuration['multiple_access_urls']) {
                    $access_url_id = api_get_current_access_url_id();
                    if ($access_url_id != -1) {
                        $sql = "SELECT user.user_id, username, lastname, firstname FROM {$tbl_user} user\n\t\t\t\t\t\t\t\tINNER JOIN {$tbl_user_rel_access_url} url_user ON (url_user.user_id=user.user_id)\n\t\t\t\t\t\t\t\tWHERE access_url_id = '{$access_url_id}'  AND (username LIKE '{$needle}%' OR firstname LIKE '{$needle}%' OR lastname LIKE '{$needle}%')\n\t\t\t\t\t\t\t\tAND user.user_id<>'{$user_anonymous}' {$without_user_id} {$order_clause} LIMIT 11 ";
                    }
                }
                $rs_single = Database::query($sql);
                $i = 0;
                while ($user = Database::fetch_array($rs_single)) {
                    $i++;
                    if ($i <= 10) {
                        $person_name = api_get_person_name($user['firstname'], $user['lastname']);
                        $return .= '<a href="javascript: void(0);" onclick="javascript: add_user(\'' . $user['user_id'] . '\',\'' . $person_name . ' (' . $user['username'] . ')' . '\')">' . $person_name . ' (' . $user['username'] . ')</a><br />';
                    } else {
                        $return .= '...<br />';
                    }
                }
                $xajax_response->addAssign('ajax_list_users_single', 'innerHTML', api_utf8_encode($return));
            } else {
                $xajax_response->addAlert(get_lang('YouMustChooseARelationType'));
                $xajax_response->addClear('user_to_add', 'value');
            }
        } else {
            // multiple
            if (!empty($group_id) && !empty($relation_type)) {
                $sql = "SELECT user_id, username, lastname, firstname FROM {$tbl_user} user\n\t\t\t\t        WHERE " . (api_sort_by_first_name() ? 'firstname' : 'lastname') . " LIKE '{$needle}%' AND user_id<>'{$user_anonymous}' {$without_user_id} {$order_clause} ";
                if ($_configuration['multiple_access_urls']) {
                    $access_url_id = api_get_current_access_url_id();
                    if ($access_url_id != -1) {
                        $sql = "SELECT user.user_id, username, lastname, firstname FROM {$tbl_user} user\n\t\t\t\t\t\t\t\tINNER JOIN {$tbl_user_rel_access_url} url_user ON (url_user.user_id=user.user_id)\n\t\t\t\t\t\t\t\tWHERE access_url_id = '{$access_url_id}'\n\t\t\t\t\t\t\t\tAND " . (api_sort_by_first_name() ? 'firstname' : 'lastname') . " LIKE '{$needle}%'\n\t\t\t\t\t\t\t\tAND user.user_id<>'{$user_anonymous}' {$without_user_id} {$order_clause} ";
                    }
                }
                $rs_multiple = Database::query($sql);
                $return_origin .= '<select id="origin_users" name="nosessionUsersList[]" multiple="multiple" size="15" style="width:360px;">';
                while ($user = Database::fetch_array($rs_multiple)) {
                    $person_name = api_get_person_name($user['firstname'], $user['lastname']);
                    $return_origin .= '<option value="' . $user['user_id'] . '">' . $person_name . ' (' . $user['username'] . ')</option>';
                }
                $return_origin .= '</select>';
                $xajax_response->addAssign('ajax_origin_list_multiple', 'innerHTML', api_utf8_encode($return_origin));
            }
        }
    }
    return $xajax_response;
}