Merge branch 'wip-mdl-48190-m27' of https://github.com/rajeshtaneja/moodle into MOODL...

[moodle.git] / lib / grade / grade_category.php

<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * Definition of a class to represent a grade category
 *
 * @package   core_grades
 * @copyright 2006 Nicolas Connault
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die();

require_once('grade_object.php');

/**
 * grade_category is an object mapped to DB table {prefix}grade_categories
 *
 * @package   core_grades
 * @category  grade
 * @copyright 2007 Nicolas Connault
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class grade_category extends grade_object {
    /**
     * The DB table.
     * @var string $table
     */
    public $table = 'grade_categories';

    /**
     * Array of required table fields, must start with 'id'.
     * @var array $required_fields
     */
    public $required_fields = array('id', 'courseid', 'parent', 'depth', 'path', 'fullname', 'aggregation',
                                 'keephigh', 'droplow', 'aggregateonlygraded', 'aggregateoutcomes',
                                 'aggregatesubcats', 'timecreated', 'timemodified', 'hidden');

    /**
     * The course this category belongs to.
     * @var int $courseid
     */
    public $courseid;

    /**
     * The category this category belongs to (optional).
     * @var int $parent
     */
    public $parent;

    /**
     * The grade_category object referenced by $this->parent (PK).
     * @var grade_category $parent_category
     */
    public $parent_category;

    /**
     * The number of parents this category has.
     * @var int $depth
     */
    public $depth = 0;

    /**
     * Shows the hierarchical path for this category as /1/2/3/ (like course_categories), the last number being
     * this category's autoincrement ID number.
     * @var string $path
     */
    public $path;

    /**
     * The name of this category.
     * @var string $fullname
     */
    public $fullname;

    /**
     * A constant pointing to one of the predefined aggregation strategies (none, mean, median, sum etc) .
     * @var int $aggregation
     */
    public $aggregation = GRADE_AGGREGATE_MEAN;

    /**
     * Keep only the X highest items.
     * @var int $keephigh
     */
    public $keephigh = 0;

    /**
     * Drop the X lowest items.
     * @var int $droplow
     */
    public $droplow = 0;

    /**
     * Aggregate only graded items
     * @var int $aggregateonlygraded
     */
    public $aggregateonlygraded = 0;

    /**
     * Aggregate outcomes together with normal items
     * @var int $aggregateoutcomes
     */
    public $aggregateoutcomes = 0;

    /**
     * Ignore subcategories when aggregating
     * @var int $aggregatesubcats
     */
    public $aggregatesubcats = 0;

    /**
     * Array of grade_items or grade_categories nested exactly 1 level below this category
     * @var array $children
     */
    public $children;

    /**
     * A hierarchical array of all children below this category. This is stored separately from
     * $children because it is more memory-intensive and may not be used as often.
     * @var array $all_children
     */
    public $all_children;

    /**
     * An associated grade_item object, with itemtype=category, used to calculate and cache a set of grade values
     * for this category.
     * @var grade_item $grade_item
     */
    public $grade_item;

    /**
     * Temporary sortorder for speedup of children resorting
     * @var int $sortorder
     */
    public $sortorder;

    /**
     * List of options which can be "forced" from site settings.
     * @var array $forceable
     */
    public $forceable = array('aggregation', 'keephigh', 'droplow', 'aggregateonlygraded', 'aggregateoutcomes', 'aggregatesubcats');

    /**
     * String representing the aggregation coefficient. Variable is used as cache.
     * @var string $coefstring
     */
    public $coefstring = null;

    /**
     * Builds this category's path string based on its parents (if any) and its own id number.
     * This is typically done just before inserting this object in the DB for the first time,
     * or when a new parent is added or changed. It is a recursive function: once the calling
     * object no longer has a parent, the path is complete.
     *
     * @param grade_category $grade_category A Grade_Category object
     * @return string The category's path string
     */
    public static function build_path($grade_category) {
        global $DB;

        if (empty($grade_category->parent)) {
            return '/'.$grade_category->id.'/';

        } else {
            $parent = $DB->get_record('grade_categories', array('id' => $grade_category->parent));
            return grade_category::build_path($parent).$grade_category->id.'/';
        }
    }

    /**
     * Finds and returns a grade_category instance based on params.
     *
     * @param array $params associative arrays varname=>value
     * @return grade_category The retrieved grade_category instance or false if none found.
     */
    public static function fetch($params) {
        return grade_object::fetch_helper('grade_categories', 'grade_category', $params);
    }

    /**
     * Finds and returns all grade_category instances based on params.
     *
     * @param array $params associative arrays varname=>value
     * @return array array of grade_category insatnces or false if none found.
     */
    public static function fetch_all($params) {
        return grade_object::fetch_all_helper('grade_categories', 'grade_category', $params);
    }

    /**
     * In addition to update() as defined in grade_object, call force_regrading of parent categories, if applicable.
     *
     * @param string $source from where was the object updated (mod/forum, manual, etc.)
     * @return bool success
     */
    public function update($source=null) {
        // load the grade item or create a new one
        $this->load_grade_item();

        // force recalculation of path;
        if (empty($this->path)) {
            $this->path  = grade_category::build_path($this);
            $this->depth = substr_count($this->path, '/') - 1;
            $updatechildren = true;

        } else {
            $updatechildren = false;
        }

        $this->apply_forced_settings();

        // these are exclusive
        if ($this->droplow > 0) {
            $this->keephigh = 0;

        } else if ($this->keephigh > 0) {
            $this->droplow = 0;
        }

        // Recalculate grades if needed
        if ($this->qualifies_for_regrading()) {
            $this->force_regrading();
        }

        $this->timemodified = time();

        $result = parent::update($source);

        // now update paths in all child categories
        if ($result and $updatechildren) {

            if ($children = grade_category::fetch_all(array('parent'=>$this->id))) {

                foreach ($children as $child) {
                    $child->path  = null;
                    $child->depth = 0;
                    $child->update($source);
                }
            }
        }

        return $result;
    }

    /**
     * If parent::delete() is successful, send force_regrading message to parent category.
     *
     * @param string $source from where was the object deleted (mod/forum, manual, etc.)
     * @return bool success
     */
    public function delete($source=null) {
        $grade_item = $this->load_grade_item();

        if ($this->is_course_category()) {

            if ($categories = grade_category::fetch_all(array('courseid'=>$this->courseid))) {

                foreach ($categories as $category) {

                    if ($category->id == $this->id) {
                        continue; // do not delete course category yet
                    }
                    $category->delete($source);
                }
            }

            if ($items = grade_item::fetch_all(array('courseid'=>$this->courseid))) {

                foreach ($items as $item) {

                    if ($item->id == $grade_item->id) {
                        continue; // do not delete course item yet
                    }
                    $item->delete($source);
                }
            }

        } else {
            $this->force_regrading();

            $parent = $this->load_parent_category();

            // Update children's categoryid/parent field first
            if ($children = grade_item::fetch_all(array('categoryid'=>$this->id))) {
                foreach ($children as $child) {
                    $child->set_parent($parent->id);
                }
            }

            if ($children = grade_category::fetch_all(array('parent'=>$this->id))) {
                foreach ($children as $child) {
                    $child->set_parent($parent->id);
                }
            }
        }

        // first delete the attached grade item and grades
        $grade_item->delete($source);

        // delete category itself
        return parent::delete($source);
    }

    /**
     * In addition to the normal insert() defined in grade_object, this method sets the depth
     * and path for this object, and update the record accordingly.
     *
     * We do this here instead of in the constructor as they both need to know the record's
     * ID number, which only gets created at insertion time.
     * This method also creates an associated grade_item if this wasn't done during construction.
     *
     * @param string $source from where was the object inserted (mod/forum, manual, etc.)
     * @return int PK ID if successful, false otherwise
     */
    public function insert($source=null) {

        if (empty($this->courseid)) {
            print_error('cannotinsertgrade');
        }

        if (empty($this->parent)) {
            $course_category = grade_category::fetch_course_category($this->courseid);
            $this->parent = $course_category->id;
        }

        $this->path = null;

        $this->timecreated = $this->timemodified = time();

        if (!parent::insert($source)) {
            debugging("Could not insert this category: " . print_r($this, true));
            return false;
        }

        $this->force_regrading();

        // build path and depth
        $this->update($source);

        return $this->id;
    }

    /**
     * Internal function - used only from fetch_course_category()
     * Normal insert() can not be used for course category
     *
     * @param int $courseid The course ID
     * @return int The ID of the new course category
     */
    public function insert_course_category($courseid) {
        $this->courseid    = $courseid;
        $this->fullname    = '?';
        $this->path        = null;
        $this->parent      = null;
        $this->aggregation = GRADE_AGGREGATE_WEIGHTED_MEAN2;

        $this->apply_default_settings();
        $this->apply_forced_settings();

        $this->timecreated = $this->timemodified = time();

        if (!parent::insert('system')) {
            debugging("Could not insert this category: " . print_r($this, true));
            return false;
        }

        // build path and depth
        $this->update('system');

        return $this->id;
    }

    /**
     * Compares the values held by this object with those of the matching record in DB, and returns
     * whether or not these differences are sufficient to justify an update of all parent objects.
     * This assumes that this object has an ID number and a matching record in DB. If not, it will return false.
     *
     * @return bool
     */
    public function qualifies_for_regrading() {
        if (empty($this->id)) {
            debugging("Can not regrade non existing category");
            return false;
        }

        $db_item = grade_category::fetch(array('id'=>$this->id));

        $aggregationdiff = $db_item->aggregation         != $this->aggregation;
        $keephighdiff    = $db_item->keephigh            != $this->keephigh;
        $droplowdiff     = $db_item->droplow             != $this->droplow;
        $aggonlygrddiff  = $db_item->aggregateonlygraded != $this->aggregateonlygraded;
        $aggoutcomesdiff = $db_item->aggregateoutcomes   != $this->aggregateoutcomes;
        $aggsubcatsdiff  = $db_item->aggregatesubcats    != $this->aggregatesubcats;

        return ($aggregationdiff || $keephighdiff || $droplowdiff || $aggonlygrddiff || $aggoutcomesdiff || $aggsubcatsdiff);
    }

    /**
     * Marks this grade categories' associated grade item as needing regrading
     */
    public function force_regrading() {
        $grade_item = $this->load_grade_item();
        $grade_item->force_regrading();
    }

    /**
     * Generates and saves final grades in associated category grade item.
     * These immediate children must already have their own final grades.
     * The category's aggregation method is used to generate final grades.
     *
     * Please note that category grade is either calculated or aggregated, not both at the same time.
     *
     * This method must be used ONLY from grade_item::regrade_final_grades(),
     * because the calculation must be done in correct order!
     *
     * Steps to follow:
     *  1. Get final grades from immediate children
     *  3. Aggregate these grades
     *  4. Save them in final grades of associated category grade item
     *
     * @param int $userid The user ID if final grade generation should be limited to a single user
     * @return bool
     */
    public function generate_grades($userid=null) {
        global $CFG, $DB;

        $this->load_grade_item();

        if ($this->grade_item->is_locked()) {
            return true; // no need to recalculate locked items
        }

        // find grade items of immediate children (category or grade items) and force site settings
        $depends_on = $this->grade_item->depends_on();

        if (empty($depends_on)) {
            $items = false;

        } else {
            list($usql, $params) = $DB->get_in_or_equal($depends_on);
            $sql = "SELECT *
                      FROM {grade_items}
                     WHERE id $usql";
            $items = $DB->get_records_sql($sql, $params);
        }

        // needed mostly for SUM agg type
        $this->auto_update_max($items);

        $grade_inst = new grade_grade();
        $fields = 'g.'.implode(',g.', $grade_inst->required_fields);

        // where to look for final grades - include grade of this item too, we will store the results there
        $gis = array_merge($depends_on, array($this->grade_item->id));
        list($usql, $params) = $DB->get_in_or_equal($gis);

        if ($userid) {
            $usersql = "AND g.userid=?";
            $params[] = $userid;

        } else {
            $usersql = "";
        }

        $sql = "SELECT $fields
                  FROM {grade_grades} g, {grade_items} gi
                 WHERE gi.id = g.itemid AND gi.id $usql $usersql
              ORDER BY g.userid";

        // group the results by userid and aggregate the grades for this user
        $rs = $DB->get_recordset_sql($sql, $params);
        if ($rs->valid()) {
            $prevuser = 0;
            $grade_values = array();
            $excluded     = array();
            $oldgrade     = null;

            foreach ($rs as $used) {

                if ($used->userid != $prevuser) {
                    $this->aggregate_grades($prevuser, $items, $grade_values, $oldgrade, $excluded);
                    $prevuser = $used->userid;
                    $grade_values = array();
                    $excluded     = array();
                    $oldgrade     = null;
                }
                $grade_values[$used->itemid] = $used->finalgrade;

                if ($used->excluded) {
                    $excluded[] = $used->itemid;
                }

                if ($this->grade_item->id == $used->itemid) {
                    $oldgrade = $used;
                }
            }
            $this->aggregate_grades($prevuser, $items, $grade_values, $oldgrade, $excluded);//the last one
        }
        $rs->close();

        return true;
    }

    /**
     * Internal function for grade category grade aggregation
     *
     * @param int    $userid The User ID
     * @param array  $items Grade items
     * @param array  $grade_values Array of grade values
     * @param object $oldgrade Old grade
     * @param array  $excluded Excluded
     */
    private function aggregate_grades($userid, $items, $grade_values, $oldgrade, $excluded) {
        global $CFG;
        if (empty($userid)) {
            //ignore first call
            return;
        }

        if ($oldgrade) {
            $oldfinalgrade = $oldgrade->finalgrade;
            $grade = new grade_grade($oldgrade, false);
            $grade->grade_item =& $this->grade_item;

        } else {
            // insert final grade - it will be needed later anyway
            $grade = new grade_grade(array('itemid'=>$this->grade_item->id, 'userid'=>$userid), false);
            $grade->grade_item =& $this->grade_item;
            $grade->insert('system');
            $oldfinalgrade = null;
        }

        // no need to recalculate locked or overridden grades
        if ($grade->is_locked() or $grade->is_overridden()) {
            return;
        }

        // can not use own final category grade in calculation
        unset($grade_values[$this->grade_item->id]);


        // sum is a special aggregation types - it adjusts the min max, does not use relative values
        if ($this->aggregation == GRADE_AGGREGATE_SUM) {
            $this->sum_grades($grade, $oldfinalgrade, $items, $grade_values, $excluded);
            return;
        }

        // if no grades calculation possible or grading not allowed clear final grade
        if (empty($grade_values) or empty($items) or ($this->grade_item->gradetype != GRADE_TYPE_VALUE and $this->grade_item->gradetype != GRADE_TYPE_SCALE)) {
            $grade->finalgrade = null;

            if (!is_null($oldfinalgrade)) {
                $grade->timemodified = time();
                $grade->update('aggregation');
            }
            return;
        }

        // normalize the grades first - all will have value 0...1
        // ungraded items are not used in aggregation
        foreach ($grade_values as $itemid=>$v) {

            if (is_null($v)) {
                // null means no grade
                unset($grade_values[$itemid]);
                continue;

            } else if (in_array($itemid, $excluded)) {
                unset($grade_values[$itemid]);
                continue;
            }
            $grade_values[$itemid] = grade_grade::standardise_score($v, $items[$itemid]->grademin, $items[$itemid]->grademax, 0, 1);
        }

        // use min grade if grade missing for these types
        if (!$this->aggregateonlygraded) {

            foreach ($items as $itemid=>$value) {

                if (!isset($grade_values[$itemid]) and !in_array($itemid, $excluded)) {
                    $grade_values[$itemid] = 0;
                }
            }
        }

        // limit and sort
        $this->apply_limit_rules($grade_values, $items);
        asort($grade_values, SORT_NUMERIC);

        // let's see we have still enough grades to do any statistics
        if (count($grade_values) == 0) {
            // not enough attempts yet
            $grade->finalgrade = null;

            if (!is_null($oldfinalgrade)) {
                $grade->timemodified = time();
                $grade->update('aggregation');
            }
            return;
        }

        // do the maths
        $result = $this->aggregate_values_and_adjust_bounds($grade_values, $items);
        $agg_grade = $result['grade'];

        // recalculate the grade back to requested range
        $finalgrade = grade_grade::standardise_score($agg_grade, 0, 1, $result['grademin'], $result['grademax']);

        $grade->finalgrade = $this->grade_item->bounded_grade($finalgrade);

        // update in db if changed
        if (grade_floats_different($grade->finalgrade, $oldfinalgrade)) {
            $grade->timemodified = time();
            $grade->update('aggregation');
        }

        return;
    }

    /**
     * Internal function that calculates the aggregated grade and new min/max for this grade category
     *
     * Must be public as it is used by grade_grade::get_hiding_affected()
     *
     * @param array $grade_values An array of values to be aggregated
     * @param array $items The array of grade_items
     * @since Moodle 2.6.5, 2.7.2
     * @return array containing values for:
     *                'grade' => the new calculated grade
     *                'grademin' => the new calculated min grade for the category
     *                'grademax' => the new calculated max grade for the category
     */
    public function aggregate_values_and_adjust_bounds($grade_values, $items) {
        $category_item = $this->get_grade_item();
        $grademin = $category_item->grademin;
        $grademax = $category_item->grademax;

        switch ($this->aggregation) {

            case GRADE_AGGREGATE_MEDIAN: // Middle point value in the set: ignores frequencies
                $num = count($grade_values);
                $grades = array_values($grade_values);

                if ($num % 2 == 0) {
                    $agg_grade = ($grades[intval($num/2)-1] + $grades[intval($num/2)]) / 2;

                } else {
                    $agg_grade = $grades[intval(($num/2)-0.5)];
                }
                break;

            case GRADE_AGGREGATE_MIN:
                $agg_grade = reset($grade_values);
                break;

            case GRADE_AGGREGATE_MAX:
                $agg_grade = array_pop($grade_values);
                break;

            case GRADE_AGGREGATE_MODE:       // the most common value, average used if multimode
                // array_count_values only counts INT and STRING, so if grades are floats we must convert them to string
                $converted_grade_values = array();

                foreach ($grade_values as $k => $gv) {

                    if (!is_int($gv) && !is_string($gv)) {
                        $converted_grade_values[$k] = (string) $gv;

                    } else {
                        $converted_grade_values[$k] = $gv;
                    }
                }

                $freq = array_count_values($converted_grade_values);
                arsort($freq);                      // sort by frequency keeping keys
                $top = reset($freq);               // highest frequency count
                $modes = array_keys($freq, $top);  // search for all modes (have the same highest count)
                rsort($modes, SORT_NUMERIC);       // get highest mode
                $agg_grade = reset($modes);
                break;

            case GRADE_AGGREGATE_WEIGHTED_MEAN: // Weighted average of all existing final grades, weight specified in coef
                $weightsum = 0;
                $sum       = 0;

                foreach ($grade_values as $itemid=>$grade_value) {

                    if ($items[$itemid]->aggregationcoef <= 0) {
                        continue;
                    }
                    $weightsum += $items[$itemid]->aggregationcoef;
                    $sum       += $items[$itemid]->aggregationcoef * $grade_value;
                }

                if ($weightsum == 0) {
                    $agg_grade = null;

                } else {
                    $agg_grade = $sum / $weightsum;
                }
                break;

            case GRADE_AGGREGATE_WEIGHTED_MEAN2:
                // Weighted average of all existing final grades with optional extra credit flag,
                // weight is the range of grade (usually grademax)
                $weightsum = 0;
                $sum       = null;

                foreach ($grade_values as $itemid=>$grade_value) {
                    $weight = $items[$itemid]->grademax - $items[$itemid]->grademin;

                    if ($weight <= 0) {
                        continue;
                    }

                    if ($items[$itemid]->aggregationcoef == 0) {
                        $weightsum += $weight;
                    }
                    $sum += $weight * $grade_value;
                }

                if ($weightsum == 0) {
                    $agg_grade = $sum; // only extra credits

                } else {
                    $agg_grade = $sum / $weightsum;
                }
                break;

            case GRADE_AGGREGATE_EXTRACREDIT_MEAN: // special average
                $num = 0;
                $sum = null;

                foreach ($grade_values as $itemid=>$grade_value) {

                    if ($items[$itemid]->aggregationcoef == 0) {
                        $num += 1;
                        $sum += $grade_value;

                    } else if ($items[$itemid]->aggregationcoef > 0) {
                        $sum += $items[$itemid]->aggregationcoef * $grade_value;
                    }
                }

                if ($num == 0) {
                    $agg_grade = $sum; // only extra credits or wrong coefs

                } else {
                    $agg_grade = $sum / $num;
                }
                break;

            case GRADE_AGGREGATE_SUM:    // Add up all the items.
                $num = count($grade_values);
                // Excluded items can affect the grademax for this grade_item.
                $grademin = 0;
                $grademax = 0;
                $sum = 0;
                foreach ($grade_values as $itemid => $grade_value) {
                    $sum += $grade_value * ($items[$itemid]->grademax - $items[$itemid]->grademin);
                    if ($items[$itemid]->aggregationcoef == 0) {
                        $grademin += $items[$itemid]->grademin;
                        $grademax += $items[$itemid]->grademax;
                    }
                }

                $agg_grade = $sum / ($grademax - $grademin);
                break;

            case GRADE_AGGREGATE_MEAN:    // Arithmetic average of all grade items (if ungraded aggregated, NULL counted as minimum)
            default:
                $num = count($grade_values);
                $sum = array_sum($grade_values);
                $agg_grade = $sum / $num;
                break;
        }

        return array('grade' => $agg_grade, 'grademin' => $grademin, 'grademax' => $grademax);
    }

    /**
     * Internal function that calculates the aggregated grade for this grade category
     *
     * Must be public as it is used by grade_grade::get_hiding_affected()
     *
     * Will be deprecated in Moodle 2.8
     * @param array $grade_values An array of values to be aggregated
     * @param array $items The array of grade_items
     * @return float The aggregate grade for this grade category
     */
    public function aggregate_values($grade_values, $items) {
        $result = $this->aggregate_values_and_adjust_bounds($grade_values, $items);
        return $result['grade'];
    }

    /**
     * Some aggregation types may automatically update max grade
     *
     * @param array $items sub items
     */
    private function auto_update_max($items) {
        if ($this->aggregation != GRADE_AGGREGATE_SUM) {
            // not needed at all
            return;
        }

        if (!$items) {

            if ($this->grade_item->grademax != 0 or $this->grade_item->gradetype != GRADE_TYPE_VALUE) {
                $this->grade_item->grademax  = 0;
                $this->grade_item->grademin  = 0;
                $this->grade_item->gradetype = GRADE_TYPE_VALUE;
                $this->grade_item->update('aggregation');
            }
            return;
        }

        //find max grade possible
        $maxes = array();

        foreach ($items as $item) {

            if ($item->aggregationcoef > 0) {
                // extra credit from this activity - does not affect total
                continue;
            }

            if ($item->gradetype == GRADE_TYPE_VALUE) {
                $maxes[$item->id] = $item->grademax;

            } else if ($item->gradetype == GRADE_TYPE_SCALE) {
                $maxes[$item->id] = $item->grademax; // 0 = nograde, 1 = first scale item, 2 = second scale item
            }
        }
        // apply droplow and keephigh
        $this->apply_limit_rules($maxes, $items);
        $max = array_sum($maxes);

        // update db if anything changed
        if ($this->grade_item->grademax != $max or $this->grade_item->grademin != 0 or $this->grade_item->gradetype != GRADE_TYPE_VALUE) {
            $this->grade_item->grademax  = $max;
            $this->grade_item->grademin  = 0;
            $this->grade_item->gradetype = GRADE_TYPE_VALUE;
            $this->grade_item->update('aggregation');
        }
    }

    /**
     * Internal function for category grades summing
     *
     * @param grade_grade $grade The grade item
     * @param float $oldfinalgrade Old Final grade
     * @param array $items Grade items
     * @param array $grade_values Grade values
     * @param array $excluded Excluded
     */
    private function sum_grades(&$grade, $oldfinalgrade, $items, $grade_values, $excluded) {
        if (empty($items)) {
            return null;
        }

        // ungraded and excluded items are not used in aggregation
        foreach ($grade_values as $itemid=>$v) {

            if (is_null($v)) {
                unset($grade_values[$itemid]);

            } else if (in_array($itemid, $excluded)) {
                unset($grade_values[$itemid]);
            }
        }

        // use 0 if grade missing, droplow used and aggregating all items
        if (!$this->aggregateonlygraded and !empty($this->droplow)) {

            foreach ($items as $itemid=>$value) {

                if (!isset($grade_values[$itemid]) and !in_array($itemid, $excluded)) {
                    $grade_values[$itemid] = 0;
                }
            }
        }

        $this->apply_limit_rules($grade_values, $items);

        $sum = array_sum($grade_values);
        $grade->finalgrade = $this->grade_item->bounded_grade($sum);

        // update in db if changed
        if (grade_floats_different($grade->finalgrade, $oldfinalgrade)) {
            $grade->timemodified = time();
            $grade->update('aggregation');
        }

        return;
    }

    /**
     * Given an array of grade values (numerical indices) applies droplow or keephigh rules to limit the final array.
     *
     * @param array $grade_values itemid=>$grade_value float
     * @param array $items grade item objects
     * @return array Limited grades.
     */
    public function apply_limit_rules(&$grade_values, $items) {
        $extraused = $this->is_extracredit_used();

        if (!empty($this->droplow)) {
            asort($grade_values, SORT_NUMERIC);
            $dropped = 0;

            // If we have fewer grade items available to drop than $this->droplow, use this flag to escape the loop
            // May occur because of "extra credit" or if droplow is higher than the number of grade items
            $droppedsomething = true;

            while ($dropped < $this->droplow && $droppedsomething) {
                $droppedsomething = false;

                $grade_keys = array_keys($grade_values);
                $gradekeycount = count($grade_keys);

                if ($gradekeycount === 0) {
                    //We've dropped all grade items
                    break;
                }

                $originalindex = $founditemid = $foundmax = null;

                // Find the first remaining grade item that is available to be dropped
                foreach ($grade_keys as $gradekeyindex=>$gradekey) {
                    if (!$extraused || $items[$gradekey]->aggregationcoef <= 0) {
                        // Found a non-extra credit grade item that is eligible to be dropped
                        $originalindex = $gradekeyindex;
                        $founditemid = $grade_keys[$originalindex];
                        $foundmax = $items[$founditemid]->grademax;
                        break;
                    }
                }

                if (empty($founditemid)) {
                    // No grade items available to drop
                    break;
                }

                // Now iterate over the remaining grade items
                // We're looking for other grade items with the same grade value but a higher grademax
                $i = 1;
                while ($originalindex + $i < $gradekeycount) {

                    $possibleitemid = $grade_keys[$originalindex+$i];
                    $i++;

                    if ($grade_values[$founditemid] != $grade_values[$possibleitemid]) {
                        // The next grade item has a different grade value. Stop looking.
                        break;
                    }

                    if ($extraused && $items[$possibleitemid]->aggregationcoef > 0) {
                        // Don't drop extra credit grade items. Continue the search.
                        continue;
                    }

                    if ($foundmax < $items[$possibleitemid]->grademax) {
                        // Found a grade item with the same grade value and a higher grademax
                        $foundmax = $items[$possibleitemid]->grademax;
                        $founditemid = $possibleitemid;
                        // Continue searching to see if there is an even higher grademax
                    }
                }

                // Now drop whatever grade item we have found
                unset($grade_values[$founditemid]);
                $dropped++;
                $droppedsomething = true;
            }

        } else if (!empty($this->keephigh)) {
            arsort($grade_values, SORT_NUMERIC);
            $kept = 0;

            foreach ($grade_values as $itemid=>$value) {

                if ($extraused and $items[$itemid]->aggregationcoef > 0) {
                    // we keep all extra credits

                } else if ($kept < $this->keephigh) {
                    $kept++;

                } else {
                    unset($grade_values[$itemid]);
                }
            }
        }
    }

    /**
     * Returns true if category uses extra credit of any kind
     *
     * @return bool True if extra credit used
     */
    public function is_extracredit_used() {
        return self::aggregation_uses_extracredit($this->aggregation);
    }

    /**
     * Returns true if aggregation passed is using extracredit.
     *
     * @param int $aggregation Aggregation const.
     * @return bool True if extra credit used
     */
    public static function aggregation_uses_extracredit($aggregation) {
        return ($aggregation == GRADE_AGGREGATE_WEIGHTED_MEAN2
             or $aggregation == GRADE_AGGREGATE_EXTRACREDIT_MEAN
             or $aggregation == GRADE_AGGREGATE_SUM);
    }

    /**
     * Returns true if category uses special aggregation coefficient
     *
     * @return bool True if an aggregation coefficient is being used
     */
    public function is_aggregationcoef_used() {
        return self::aggregation_uses_aggregationcoef($this->aggregation);

    }

    /**
     * Returns true if aggregation uses aggregationcoef
     *
     * @param int $aggregation Aggregation const.
     * @return bool True if an aggregation coefficient is being used
     */
    public static function aggregation_uses_aggregationcoef($aggregation) {
        return ($aggregation == GRADE_AGGREGATE_WEIGHTED_MEAN
             or $aggregation == GRADE_AGGREGATE_WEIGHTED_MEAN2
             or $aggregation == GRADE_AGGREGATE_EXTRACREDIT_MEAN
             or $aggregation == GRADE_AGGREGATE_SUM);

    }

    /**
     * Recursive function to find which weight/extra credit field to use in the grade item form.
     *
     * Inherits from a parent category if that category has aggregatesubcats set to true.
     *
     * @param string $first Whether or not this is the first item in the recursion
     * @return string
     */
    public function get_coefstring($first=true) {
        if (!is_null($this->coefstring)) {
            return $this->coefstring;
        }

        $overriding_coefstring = null;

        // Stop recursing upwards if this category aggregates subcats or has no parent
        if (!$first && !$this->aggregatesubcats) {

            if ($parent_category = $this->load_parent_category()) {
                return $parent_category->get_coefstring(false);

            } else {
                return null;
            }

        } else if ($first) {

            if (!$this->aggregatesubcats) {

                if ($parent_category = $this->load_parent_category()) {
                    $overriding_coefstring = $parent_category->get_coefstring(false);
                }
            }
        }

        // If an overriding coefstring has trickled down from one of the parent categories, return it. Otherwise, return self.
        if (!is_null($overriding_coefstring)) {
            return $overriding_coefstring;
        }

        // No parent category is overriding this category's aggregation, return its string
        if ($this->aggregation == GRADE_AGGREGATE_WEIGHTED_MEAN) {
            $this->coefstring = 'aggregationcoefweight';

        } else if ($this->aggregation == GRADE_AGGREGATE_WEIGHTED_MEAN2) {
            $this->coefstring = 'aggregationcoefextrasum';

        } else if ($this->aggregation == GRADE_AGGREGATE_EXTRACREDIT_MEAN) {
            $this->coefstring = 'aggregationcoefextraweight';

        } else if ($this->aggregation == GRADE_AGGREGATE_SUM) {
            $this->coefstring = 'aggregationcoefextrasum';

        } else {
            $this->coefstring = 'aggregationcoef';
        }
        return $this->coefstring;
    }

    /**
     * Returns tree with all grade_items and categories as elements
     *
     * @param int $courseid The course ID
     * @param bool $include_category_items as category children
     * @return array
     */
    public static function fetch_course_tree($courseid, $include_category_items=false) {
        $course_category = grade_category::fetch_course_category($courseid);
        $category_array = array('object'=>$course_category, 'type'=>'category', 'depth'=>1,
                                'children'=>$course_category->get_children($include_category_items));

        $course_category->sortorder = $course_category->get_sortorder();
        $sortorder = $course_category->get_sortorder();
        return grade_category::_fetch_course_tree_recursion($category_array, $sortorder);
    }

    /**
     * An internal function that recursively sorts grade categories within a course
     *
     * @param array $category_array The seed of the recursion
     * @param int   $sortorder The current sortorder
     * @return array An array containing 'object', 'type', 'depth' and optionally 'children'
     */
    static private function _fetch_course_tree_recursion($category_array, &$sortorder) {
        // update the sortorder in db if needed
        //NOTE: This leads to us resetting sort orders every time the categories and items page is viewed :(
        //if ($category_array['object']->sortorder != $sortorder) {
            //$category_array['object']->set_sortorder($sortorder);
        //}

        if (isset($category_array['object']->gradetype) && $category_array['object']->gradetype==GRADE_TYPE_NONE) {
            return null;
        }

        // store the grade_item or grade_category instance with extra info
        $result = array('object'=>$category_array['object'], 'type'=>$category_array['type'], 'depth'=>$category_array['depth']);

        // reuse final grades if there
        if (array_key_exists('finalgrades', $category_array)) {
            $result['finalgrades'] = $category_array['finalgrades'];
        }

        // recursively resort children
        if (!empty($category_array['children'])) {
            $result['children'] = array();
            //process the category item first
            $child = null;

            foreach ($category_array['children'] as $oldorder=>$child_array) {

                if ($child_array['type'] == 'courseitem' or $child_array['type'] == 'categoryitem') {
                    $child = grade_category::_fetch_course_tree_recursion($child_array, $sortorder);
                    if (!empty($child)) {
                        $result['children'][$sortorder] = $child;
                    }
                }
            }

            foreach ($category_array['children'] as $oldorder=>$child_array) {

                if ($child_array['type'] != 'courseitem' and $child_array['type'] != 'categoryitem') {
                    $child = grade_category::_fetch_course_tree_recursion($child_array, $sortorder);
                    if (!empty($child)) {
                        $result['children'][++$sortorder] = $child;
                    }
                }
            }
        }

        return $result;
    }

    /**
     * Fetches and returns all the children categories and/or grade_items belonging to this category.
     * By default only returns the immediate children (depth=1), but deeper levels can be requested,
     * as well as all levels (0). The elements are indexed by sort order.
     *
     * @param bool $include_category_items Whether or not to include category grade_items in the children array
     * @return array Array of child objects (grade_category and grade_item).
     */
    public function get_children($include_category_items=false) {
        global $DB;

        // This function must be as fast as possible ;-)
        // fetch all course grade items and categories into memory - we do not expect hundreds of these in course
        // we have to limit the number of queries though, because it will be used often in grade reports

        $cats  = $DB->get_records('grade_categories', array('courseid' => $this->courseid));
        $items = $DB->get_records('grade_items', array('courseid' => $this->courseid));

        // init children array first
        foreach ($cats as $catid=>$cat) {
            $cats[$catid]->children = array();
        }

        //first attach items to cats and add category sortorder
        foreach ($items as $item) {

            if ($item->itemtype == 'course' or $item->itemtype == 'category') {
                $cats[$item->iteminstance]->sortorder = $item->sortorder;

                if (!$include_category_items) {
                    continue;
                }
                $categoryid = $item->iteminstance;

            } else {
                $categoryid = $item->categoryid;
                if (empty($categoryid)) {
                    debugging('Found a grade item that isnt in a category');
                }
            }

            // prevent problems with duplicate sortorders in db
            $sortorder = $item->sortorder;

            while (array_key_exists($categoryid, $cats)
                && array_key_exists($sortorder, $cats[$categoryid]->children)) {

                $sortorder++;
            }

            $cats[$categoryid]->children[$sortorder] = $item;

        }

        // now find the requested category and connect categories as children
        $category = false;

        foreach ($cats as $catid=>$cat) {

            if (empty($cat->parent)) {

                if ($cat->path !== '/'.$cat->id.'/') {
                    $grade_category = new grade_category($cat, false);
                    $grade_category->path  = '/'.$cat->id.'/';
                    $grade_category->depth = 1;
                    $grade_category->update('system');
                    return $this->get_children($include_category_items);
                }

            } else {

                if (empty($cat->path) or !preg_match('|/'.$cat->parent.'/'.$cat->id.'/$|', $cat->path)) {
                    //fix paths and depts
                    static $recursioncounter = 0; // prevents infinite recursion
                    $recursioncounter++;

                    if ($recursioncounter < 5) {
                        // fix paths and depths!
                        $grade_category = new grade_category($cat, false);
                        $grade_category->depth = 0;
                        $grade_category->path  = null;
                        $grade_category->update('system');
                        return $this->get_children($include_category_items);
                    }
                }
                // prevent problems with duplicate sortorders in db
                $sortorder = $cat->sortorder;

                while (array_key_exists($sortorder, $cats[$cat->parent]->children)) {
                    //debugging("$sortorder exists in cat loop");
                    $sortorder++;
                }

                $cats[$cat->parent]->children[$sortorder] = &$cats[$catid];
            }

            if ($catid == $this->id) {
                $category = &$cats[$catid];
            }
        }

        unset($items); // not needed
        unset($cats); // not needed

        $children_array = grade_category::_get_children_recursion($category);

        ksort($children_array);

        return $children_array;

    }

    /**
     * Private method used to retrieve all children of this category recursively
     *
     * @param grade_category $category Source of current recursion
     * @return array An array of child grade categories
     */
    private static function _get_children_recursion($category) {

        $children_array = array();
        foreach ($category->children as $sortorder=>$child) {

            if (array_key_exists('itemtype', $child)) {
                $grade_item = new grade_item($child, false);

                if (in_array($grade_item->itemtype, array('course', 'category'))) {
                    $type  = $grade_item->itemtype.'item';
                    $depth = $category->depth;

                } else {
                    $type  = 'item';
                    $depth = $category->depth; // we use this to set the same colour
                }
                $children_array[$sortorder] = array('object'=>$grade_item, 'type'=>$type, 'depth'=>$depth);

            } else {
                $children = grade_category::_get_children_recursion($child);
                $grade_category = new grade_category($child, false);

                if (empty($children)) {
                    $children = array();
                }
                $children_array[$sortorder] = array('object'=>$grade_category, 'type'=>'category', 'depth'=>$grade_category->depth, 'children'=>$children);
            }
        }

        // sort the array
        ksort($children_array);

        return $children_array;
    }

    /**
     * Uses {@link get_grade_item()} to load or create a grade_item, then saves it as $this->grade_item.
     *
     * @return grade_item
     */
    public function load_grade_item() {
        if (empty($this->grade_item)) {
            $this->grade_item = $this->get_grade_item();
        }
        return $this->grade_item;
    }

    /**
     * Retrieves this grade categories' associated grade_item from the database
     *
     * If no grade_item exists yet, creates one.
     *
     * @return grade_item
     */
    public function get_grade_item() {
        if (empty($this->id)) {
            debugging("Attempt to obtain a grade_category's associated grade_item without the category's ID being set.");
            return false;
        }

        if (empty($this->parent)) {
            $params = array('courseid'=>$this->courseid, 'itemtype'=>'course', 'iteminstance'=>$this->id);

        } else {
            $params = array('courseid'=>$this->courseid, 'itemtype'=>'category', 'iteminstance'=>$this->id);
        }

        if (!$grade_items = grade_item::fetch_all($params)) {
            // create a new one
            $grade_item = new grade_item($params, false);
            $grade_item->gradetype = GRADE_TYPE_VALUE;
            $grade_item->insert('system');

        } else if (count($grade_items) == 1) {
            // found existing one
            $grade_item = reset($grade_items);

        } else {
            debugging("Found more than one grade_item attached to category id:".$this->id);
            // return first one
            $grade_item = reset($grade_items);
        }

        return $grade_item;
    }

    /**
     * Uses $this->parent to instantiate $this->parent_category based on the referenced record in the DB
     *
     * @return grade_category The parent category
     */
    public function load_parent_category() {
        if (empty($this->parent_category) && !empty($this->parent)) {
            $this->parent_category = $this->get_parent_category();
        }
        return $this->parent_category;
    }

    /**
     * Uses $this->parent to instantiate and return a grade_category object
     *
     * @return grade_category Returns the parent category or null if this category has no parent
     */
    public function get_parent_category() {
        if (!empty($this->parent)) {
            $parent_category = new grade_category(array('id' => $this->parent));
            return $parent_category;
        } else {
            return null;
        }
    }

    /**
     * Returns the most descriptive field for this grade category
     *
     * @return string name
     */
    public function get_name() {
        global $DB;
        // For a course category, we return the course name if the fullname is set to '?' in the DB (empty in the category edit form)
        if (empty($this->parent) && $this->fullname == '?') {
            $course = $DB->get_record('course', array('id'=> $this->courseid));
            return format_string($course->fullname);

        } else {
            return $this->fullname;
        }
    }

    /**
     * Sets this category's parent id
     *
     * @param int $parentid The ID of the category that is the new parent to $this
     * @param string $source From where was the object updated (mod/forum, manual, etc.)
     * @return bool success
     */
    public function set_parent($parentid, $source=null) {
        if ($this->parent == $parentid) {
            return true;
        }

        if ($parentid == $this->id) {
            print_error('cannotassignselfasparent');
        }

        if (empty($this->parent) and $this->is_course_category()) {
            print_error('cannothaveparentcate');
        }

        // find parent and check course id
        if (!$parent_category = grade_category::fetch(array('id'=>$parentid, 'courseid'=>$this->courseid))) {
            return false;
        }

        $this->force_regrading();

        // set new parent category
        $this->parent          = $parent_category->id;
        $this->parent_category =& $parent_category;
        $this->path            = null;       // remove old path and depth - will be recalculated in update()
        $this->depth           = 0;          // remove old path and depth - will be recalculated in update()
        $this->update($source);

        return $this->update($source);
    }

    /**
     * Returns the final grade values for this grade category.
     *
     * @param int $userid Optional user ID to retrieve a single user's final grade
     * @return mixed An array of all final_grades (stdClass objects) for this grade_item, or a single final_grade.
     */
    public function get_final($userid=null) {
        $this->load_grade_item();
        return $this->grade_item->get_final($userid);
    }

    /**
     * Returns the sortorder of the grade categories' associated grade_item
     *
     * This method is also available in grade_item for cases where the object type is not known.
     *
     * @return int Sort order
     */
    public function get_sortorder() {
        $this->load_grade_item();
        return $this->grade_item->get_sortorder();
    }

    /**
     * Returns the idnumber of the grade categories' associated grade_item.
     *
     * This method is also available in grade_item for cases where the object type is not known.
     *
     * @return string idnumber
     */
    public function get_idnumber() {
        $this->load_grade_item();
        return $this->grade_item->get_idnumber();
    }

    /**
     * Sets the sortorder variable for this category.
     *
     * This method is also available in grade_item, for cases where the object type is not know.
     *
     * @param int $sortorder The sortorder to assign to this category
     */
    public function set_sortorder($sortorder) {
        $this->load_grade_item();
        $this->grade_item->set_sortorder($sortorder);
    }

    /**
     * Move this category after the given sortorder
     *
     * Does not change the parent
     *
     * @param int $sortorder to place after.
     * @return void
     */
    public function move_after_sortorder($sortorder) {
        $this->load_grade_item();
        $this->grade_item->move_after_sortorder($sortorder);
    }

    /**
     * Return true if this is the top most category that represents the total course grade.
     *
     * @return bool
     */
    public function is_course_category() {
        $this->load_grade_item();
        return $this->grade_item->is_course_item();
    }

    /**
     * Return the course level grade_category object
     *
     * @param int $courseid The Course ID
     * @return grade_category Returns the course level grade_category instance
     */
    public static function fetch_course_category($courseid) {
        if (empty($courseid)) {
            debugging('Missing course id!');
            return false;
        }

        // course category has no parent
        if ($course_category = grade_category::fetch(array('courseid'=>$courseid, 'parent'=>null))) {
            return $course_category;
        }

        // create a new one
        $course_category = new grade_category();
        $course_category->insert_course_category($courseid);

        return $course_category;
    }

    /**
     * Is grading object editable?
     *
     * @return bool
     */
    public function is_editable() {
        return true;
    }

    /**
     * Returns the locked state/date of the grade categories' associated grade_item.
     *
     * This method is also available in grade_item, for cases where the object type is not known.
     *
     * @return bool
     */
    public function is_locked() {
        $this->load_grade_item();
        return $this->grade_item->is_locked();
    }

    /**
     * Sets the grade_item's locked variable and updates the grade_item.
     *
     * Calls set_locked() on the categories' grade_item
     *
     * @param int  $lockedstate 0, 1 or a timestamp int(10) after which date the item will be locked.
     * @param bool $cascade lock/unlock child objects too
     * @param bool $refresh refresh grades when unlocking
     * @return bool success if category locked (not all children mayb be locked though)
     */
    public function set_locked($lockedstate, $cascade=false, $refresh=true) {
        $this->load_grade_item();

        $result = $this->grade_item->set_locked($lockedstate, $cascade, true);

        if ($cascade) {
            //process all children - items and categories
            if ($children = grade_item::fetch_all(array('categoryid'=>$this->id))) {

                foreach ($children as $child) {
                    $child->set_locked($lockedstate, true, false);

                    if (empty($lockedstate) and $refresh) {
                        //refresh when unlocking
                        $child->refresh_grades();
                    }
                }
            }

            if ($children = grade_category::fetch_all(array('parent'=>$this->id))) {

                foreach ($children as $child) {
                    $child->set_locked($lockedstate, true, true);
                }
            }
        }

        return $result;
    }

    /**
     * Overrides grade_object::set_properties() to add special handling for changes to category aggregation types
     *
     * @param stdClass $instance the object to set the properties on
     * @param array|stdClass $params Either an associative array or an object containing property name, property value pairs
     */
    public static function set_properties(&$instance, $params) {
        global $DB;

        parent::set_properties($instance, $params);

        //if they've changed aggregation type we made need to do some fiddling to provide appropriate defaults
        if (!empty($params->aggregation)) {

            //weight and extra credit share a column :( Would like a default of 1 for weight and 0 for extra credit
            //Flip from the default of 0 to 1 (or vice versa) if ALL items in the category are still set to the old default.
            if (self::aggregation_uses_aggregationcoef($params->aggregation)) {
                $sql = $defaultaggregationcoef = null;

                if (!self::aggregation_uses_extracredit($params->aggregation)) {
                    //if all items in this category have aggregation coefficient of 0 we can change it to 1 ie evenly weighted
                    $sql = "select count(id) from {grade_items} where categoryid=:categoryid and aggregationcoef!=0";
                    $defaultaggregationcoef = 1;
                } else {
                    //if all items in this category have aggregation coefficient of 1 we can change it to 0 ie no extra credit
                    $sql = "select count(id) from {grade_items} where categoryid=:categoryid and aggregationcoef!=1";
                    $defaultaggregationcoef = 0;
                }

                $params = array('categoryid'=>$instance->id);
                $count = $DB->count_records_sql($sql, $params);
                if ($count===0) { //category is either empty or all items are set to a default value so we can switch defaults
                    $params['aggregationcoef'] = $defaultaggregationcoef;
                    $DB->execute("update {grade_items} set aggregationcoef=:aggregationcoef where categoryid=:categoryid",$params);
                }
            }
        }
    }

    /**
     * Sets the grade_item's hidden variable and updates the grade_item.
     *
     * Overrides grade_item::set_hidden() to add cascading of the hidden value to grade items in this grade category
     *
     * @param int $hidden 0 mean always visible, 1 means always hidden and a number > 1 is a timestamp to hide until
     * @param bool $cascade apply to child objects too
     */
    public function set_hidden($hidden, $cascade=false) {
        $this->load_grade_item();
        //this hides the associated grade item (the course total)
        $this->grade_item->set_hidden($hidden, $cascade);
        //this hides the category itself and everything it contains
        parent::set_hidden($hidden, $cascade);

        if ($cascade) {

            if ($children = grade_item::fetch_all(array('categoryid'=>$this->id))) {

                foreach ($children as $child) {
                    if ($child->can_control_visibility()) {
                        $child->set_hidden($hidden, $cascade);
                    }
                }
            }

            if ($children = grade_category::fetch_all(array('parent'=>$this->id))) {

                foreach ($children as $child) {
                    $child->set_hidden($hidden, $cascade);
                }
            }
        }

        //if marking category visible make sure parent category is visible MDL-21367
        if( !$hidden ) {
            $category_array = grade_category::fetch_all(array('id'=>$this->parent));
            if ($category_array && array_key_exists($this->parent, $category_array)) {
                $category = $category_array[$this->parent];
                //call set_hidden on the category regardless of whether it is hidden as its parent might be hidden
                //if($category->is_hidden()) {
                    $category->set_hidden($hidden, false);
                //}
            }
        }
    }

    /**
     * Applies default settings on this category
     *
     * @return bool True if anything changed
     */
    public function apply_default_settings() {
        global $CFG;

        foreach ($this->forceable as $property) {

            if (isset($CFG->{"grade_$property"})) {

                if ($CFG->{"grade_$property"} == -1) {
                    continue; //temporary bc before version bump
                }
                $this->$property = $CFG->{"grade_$property"};
            }
        }
    }

    /**
     * Applies forced settings on this category
     *
     * @return bool True if anything changed
     */
    public function apply_forced_settings() {
        global $CFG;

        $updated = false;

        foreach ($this->forceable as $property) {

            if (isset($CFG->{"grade_$property"}) and isset($CFG->{"grade_{$property}_flag"}) and
                                                    ((int) $CFG->{"grade_{$property}_flag"} & 1)) {

                if ($CFG->{"grade_$property"} == -1) {
                    continue; //temporary bc before version bump
                }
                $this->$property = $CFG->{"grade_$property"};
                $updated = true;
            }
        }

        return $updated;
    }

    /**
     * Notification of change in forced category settings.
     *
     * Causes all course and category grade items to be marked as needing to be updated
     */
    public static function updated_forced_settings() {
        global $CFG, $DB;
        $params = array(1, 'course', 'category');
        $sql = "UPDATE {grade_items} SET needsupdate=? WHERE itemtype=? or itemtype=?";
        $DB->execute($sql, $params);
    }
}