$this->select_db_handle($type, $sql);
    }
 
    /**
     * This should be called immediately after each db query. It does a clean up of resources.
     *
     * @param mixed $result The db specific result obtained from running a query.
     * @return void
     */
    protected function query_end($result) {
        if ($this->written) {
            // Adjust the written time.
            array_walk($this->written, function (&$val) {
                if ($val === true) {
                    $val = microtime(true);
                }
            });
        }
 
        parent::query_end($result);
    }
 
    /**
     * Select appropriate db handle - readwrite or readonly
     * @param int $type type of query
     * @param string $sql
     * @return void
     */
    protected function select_db_handle(int $type, string $sql): void {
        if ($this->dbhreadonly && $this->can_use_readonly($type, $sql)) {
            $this->readsslave++;
            $this->set_db_handle($this->dbhreadonly);
            return;
        }
        $this->set_dbhwrite();
    }
 
    /**
     * Check if The query qualifies for readonly connection execution
     * Logging queries are exempt, those are write operations that circumvent

     * @param int $type type of query
     * @param mixed $extrainfo driver specific extra information
     * @return void
     */
    protected function query_start($sql, ?array $params, $type, $extrainfo=null) {
        $this->read_slave_query_start($sql, $params, $type, $extrainfo);
        // pgsql driver tends to send debug to output, we do not need that.
        $this->last_error_reporting = error_reporting(0);
    }
 
    /**
     * Called immediately after each db query.
     * @param mixed db specific result
     * @return void
     */
    protected function query_end($result) {
        // reset original debug level
        error_reporting($this->last_error_reporting);
        try {
            $this->read_slave_query_end($result);
            if ($this->savepointpresent &&
                    !in_array(
                        $this->last_type,
                        [SQL_QUERY_AUX, SQL_QUERY_AUX_READONLY, SQL_QUERY_SELECT],
                        true
                    )) {
                $res = @pg_query($this->pgsql, "RELEASE SAVEPOINT moodle_pg_savepoint; SAVEPOINT moodle_pg_savepoint");
                if ($res) {
                    pg_free_result($res);
                }
            }
        } catch (Exception $e) {
            if ($this->savepointpresent) {
                $res = @pg_query($this->pgsql, "ROLLBACK TO SAVEPOINT moodle_pg_savepoint; SAVEPOINT moodle_pg_savepoint");
                if ($res) {
                    pg_free_result($res);
                }
            }
            throw $e;
        }

     * @param array $params array of sql parameters
     * @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).
     * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
     * @return array of objects, or empty array if no records were found
     * @throws dml_exception A DML specific exception is thrown for any errors.
     */
    public function get_records_sql($sql, ?array $params = null, $limitfrom = 0, $limitnum = 0) {
        list($limitfrom, $limitnum) = $this->normalise_limit_from_num($limitfrom, $limitnum);
 
        if ($limitnum) {
            $sql .= " LIMIT $limitnum";
        }
        if ($limitfrom) {
            $sql .= " OFFSET $limitfrom";
        }
 
        list($sql, $params, $type) = $this->fix_sql_params($sql, $params);
        $this->query_start($sql, $params, SQL_QUERY_SELECT);
        $result = pg_query_params($this->pgsql, $sql, $params);
        $this->query_end($result);
 
        // find out if there are any blobs
        $numfields = pg_num_fields($result);
        $blobs = array();
        for ($i = 0; $i < $numfields; $i++) {
            $type = $this->pg_field_type($result, $i);
            if ($type == 'bytea') {
                $blobs[] = pg_field_name($result, $i);
            }
        }
 
        $return = [];
        while ($row = pg_fetch_assoc($result)) {
            $id = reset($row);
            if ($blobs) {
                foreach ($blobs as $blob) {
                    $row[$blob] = ($row[$blob] !== null ? pg_unescape_bytea($row[$blob]) : null);
                }
            }
            if (isset($return[$id])) {

        }
        return $menu;
    }
 
    /**
     * Get the first two columns from a number of records as an associative array using a SQL statement.
     *
     * Arguments are like {@link function get_recordset_sql}.
     * Return value is like {@link function get_records_menu}.
     *
     * @param string $sql The SQL string you wish to be executed.
     * @param array $params array of sql parameters
     * @param int $limitfrom return a subset of records, starting at this point (optional).
     * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
     * @return array an associative array
     * @throws dml_exception A DML specific exception is thrown for any errors.
     */
    public function get_records_sql_menu($sql, ?array $params=null, $limitfrom=0, $limitnum=0) {
        $menu = array();
        if ($records = $this->get_records_sql($sql, $params, $limitfrom, $limitnum)) {
            foreach ($records as $record) {
                $record = (array)$record;
                $key   = array_shift($record);
                $value = array_shift($record);
                $menu[$key] = $value;
            }
        }
        return $menu;
    }
 
    /**
     * Get a single database record as an object where all the given conditions met.
     *
     * @param string $table The table to select from.
     * @param array $conditions optional array $fieldname=>requestedvalue with AND in between
     * @param string $fields A comma separated list of fields to be returned from the chosen table.
     * @param int $strictness IGNORE_MISSING means compatible mode, false returned if record not found, debug message if more found;
     *                        IGNORE_MULTIPLE means return first, ignore multiple records found(not recommended);
     *                        MUST_EXIST means we will throw an exception if no record or multiple records found.
     *

        }
        return $info;
    }
    
    public static function get_faculties($courseids=array()) {
        global $DB;
        
        $where = null;
        $params = array();
        if ($courseids) {
            list($courseidsql, $courseidparams) = $DB->get_in_or_equal($courseids, SQL_PARAMS_NAMED, 'courseid');  
            $where = " AND l.course $courseidsql";
            $params = $params + $courseidparams;
        }
        $sql = "SELECT DISTINCT(sr.userid), CONCAT(u.firstname,' ', u.lastname) as fullname
            FROM {lecture_session_roles} sr, {user} u 
            WHERE sr.roleid= ".self::facultyroleid." AND sr.sessionid in ( 
                select ls.id from {lecture_sessions} ls join {lecture} l on l.id=ls.lecture $where
                ) AND u.id=sr.userid ORDER BY u.firstname, u.lastname";
        return $DB->get_records_sql_menu($sql, $params);
    }
    
    public static function get_lecture_type_menu($categoryid, $subcategoryid, $courseids=array()) {
        global $CFG, $DB;
        
        require_once $CFG->dirroot.'/course/modlib.php';
        include_modulelib('lecture');
        
        $coursecatcache = cache::make('core', 'coursecat');
        $types = false;
        $cachekey = 'ltype-cat-'. $categoryid.'-subcat-'.$subcategoryid;
        $types = $coursecatcache->get($cachekey);
        if ($types !== false) {
            return $types;
        }
        
        $menu = array();
        if ($sessionfield = $DB->get_record('lecture_session_field', array('shortname'=>'lecturetype'))) {
            $where = array();
            $where[] = "lsd.fieldid = :fieldid";

        }  
        
        $catid = $options['categoryid'];
        $subcatid = $options['subcategoryid'];
        $courseids = $options['courseids'];
        $courseid = $options['courseid'];
        $courseoptions = array('recursive'=>true, 'idonly'=>true);
        $programoptions = teaching_schedule::get_program_options();
        $semesteroptions = teaching_schedule::get_program_semesters($catid);
        $subjectoptions = array();
       
        if ($subcatid) {
            $subjectoptions = teaching_schedule::get_subject_options($subcatid);
        }
        $groupoptions = array();
        if ($courseid) {
            $groupoptions = teaching_schedule::get_course_group_options($courseid);
        }
       
        $facultyoptions = teaching_schedule::get_faculties($courseids);
       
      
        $lecturetypeoptions = teaching_schedule::get_lecture_type_menu($catid, $subcatid, $courseids);
      
        $content = '';
        // Program selector
        $content .= html_writer::start_tag('div', array('class' => 'teachingschedule-filter-course mt-4 mb-4'));
        $content .= html_writer::label(get_string('course'), 'menucategoryid', true);
        $content .= html_writer::select($programoptions, "categoryid", $options['categoryid'], array(0 => $this->strings->all), array('name' => 'categoryid', 'data-role'=>"filter"));
        $content .= html_writer::end_tag('div');
        
        $content .= html_writer::start_tag('div', array('class' => 'teachingschedule-filter'));
        $content .= html_writer::tag('span', $this->strings->searchby, array('class' => 'searchby'));        
        // Faculty search
        $content .= html_writer::start_tag('label', array('class' => 'filterfaculty'));
        $content .= $this->strings->faculty.' ';
        $content .= html_writer::select($facultyoptions, 'facultyid', $options['facultyid'], array(0 => $this->strings->all), array('class'=>'custom-select', 'data-role'=>"filter"));
        $content .= html_writer::end_tag('label');        
        // Year search        
        $fileryears = html_writer::select(teaching_schedule::get_year_options(), "year", $options['year'], array(0 => $this->strings->all), array('data-role'=>"filter"));

    $options['year'] = 0;
    $sessionsdata = teaching_schedule::get_sessions($options);
}
 
$renderer = $PAGE->get_renderer('block_teaching_schedule');
echo $OUTPUT->header();
echo html_writer::start_tag('div', array('class' => 'row no-gutters page-heading-box'));
echo html_writer::start_tag('div', array('class' => 'col-9'));
echo html_writer::tag('h3', get_string('pluginname', 'block_teaching_schedule'));
echo html_writer::end_tag('div');
echo html_writer::start_tag('div', array('class' => 'col-3 text-right'));
if(is_siteadmin()){
    echo html_writer::link($CFG->wwwroot . '/admin/tool/uploadcourselecture/index.php#uploadcourselecture', 'Add course lecture', array('class' => 'btn btn-primary mx-2', 'alt' => 'Add course lecture', 'title' => 'Add course lecture'));
}
echo html_writer::link('#', 'Go Back', array('onclick' => 'goBack()', 'class' => 'btn btn-primary', 'alt' => 'Go Back', 'title' => 'Go Back'));
echo html_writer::end_tag('div');
echo html_writer::end_tag('div');
 
echo html_writer::start_div('', array('id'=> 'teaching-schedule-filter-main'));
echo $renderer->render_teaching_schedule_filters($options);
echo html_writer::end_div();
echo html_writer::start_div('', array('id'=> 'teaching-schedule-table-main'));
echo $renderer->render_teaching_schedule_table($sessionsdata['sessions']);
echo $renderer->paging_bar($sessionsdata['total'], $page, $perpage, $PAGE->url);
echo html_writer::end_div();
$PAGE->requires->js_call_amd('block_teaching_schedule/filters', 'init', array($context->id));
$PAGE->requires->js_call_amd('core/form-autocomplete', 'enhance', $params = array(
            '#menufacultyid',
            false,
            '',
            get_string('enterfacultyname', 'block_teaching_schedule'),
            false,
            true,
            get_string('noselection', 'form')
        )
    );
echo $OUTPUT->footer();