/lib/modinfolib.php

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<?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/>.

/**
 * modinfolib.php - Functions/classes relating to cached information about module instances on
 * a course.
 * @package    core
 * @subpackage lib
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 * @author     sam marshall
 */


// Maximum number of modinfo items to keep in memory cache. Do not increase this to a large
// number because:
// a) modinfo can be big (megabyte range) for some courses
// b) performance of cache will deteriorate if there are very many items in it
if (!defined('MAX_MODINFO_CACHE_SIZE')) {
    define('MAX_MODINFO_CACHE_SIZE', 10);
}


/**
 * Information about a course that is cached in the course table 'modinfo' field (and then in
 * memory) in order to reduce the need for other database queries.
 *
 * This includes information about the course-modules and the sections on the course. It can also
 * include dynamic data that has been updated for the current user.
 *
 * Use {@link get_fast_modinfo()} to retrieve the instance of the object for particular course
 * and particular user.
 *
 * @property-read int $courseid Course ID
 * @property-read int $userid User ID
 * @property-read array $sections Array from section number (e.g. 0) to array of course-module IDs in that
 *     section; this only includes sections that contain at least one course-module
 * @property-read cm_info[] $cms Array from course-module instance to cm_info object within this course, in
 *     order of appearance
 * @property-read cm_info[][] $instances Array from string (modname) => int (instance id) => cm_info object
 * @property-read array $groups Groups that the current user belongs to. Calculated on the first request.
 *     Is an array of grouping id => array of group id => group id. Includes grouping id 0 for 'all groups'
 */
class course_modinfo {
    /** @var int Maximum time the course cache building lock can be held */
    const COURSE_CACHE_LOCK_EXPIRY = 180;

    /** @var int Time to wait for the course cache building lock before throwing an exception */
    const COURSE_CACHE_LOCK_WAIT = 60;

    /**
     * List of fields from DB table 'course' that are cached in MUC and are always present in course_modinfo::$course
     * @var array
     */
    public static $cachedfields = array('shortname', 'fullname', 'format',
            'enablecompletion', 'groupmode', 'groupmodeforce', 'cacherev');

    /**
     * For convenience we store the course object here as it is needed in other parts of code
     * @var stdClass
     */
    private $course;

    /**
     * Array of section data from cache
     * @var section_info[]
     */
    private $sectioninfo;

    /**
     * User ID
     * @var int
     */
    private $userid;

    /**
     * Array from int (section num, e.g. 0) => array of int (course-module id); this list only
     * includes sections that actually contain at least one course-module
     * @var array
     */
    private $sections;

    /**
     * Array from int (cm id) => cm_info object
     * @var cm_info[]
     */
    private $cms;

    /**
     * Array from string (modname) => int (instance id) => cm_info object
     * @var cm_info[][]
     */
    private $instances;

    /**
     * Groups that the current user belongs to. This value is calculated on first
     * request to the property or function.
     * When set, it is an array of grouping id => array of group id => group id.
     * Includes grouping id 0 for 'all groups'.
     * @var int[][]
     */
    private $groups;

    /**
     * List of class read-only properties and their getter methods.
     * Used by magic functions __get(), __isset(), __empty()
     * @var array
     */
    private static $standardproperties = array(
        'courseid' => 'get_course_id',
        'userid' => 'get_user_id',
        'sections' => 'get_sections',
        'cms' => 'get_cms',
        'instances' => 'get_instances',
        'groups' => 'get_groups_all',
    );

    /**
     * Magic method getter
     *
     * @param string $name
     * @return mixed
     */
    public function __get($name) {
        if (isset(self::$standardproperties[$name])) {
            $method = self::$standardproperties[$name];
            return $this->$method();
        } else {
            debugging('Invalid course_modinfo property accessed: '.$name);
            return null;
        }
    }

    /**
     * Magic method for function isset()
     *
     * @param string $name
     * @return bool
     */
    public function __isset($name) {
        if (isset(self::$standardproperties[$name])) {
            $value = $this->__get($name);
            return isset($value);
        }
        return false;
    }

    /**
     * Magic method for function empty()
     *
     * @param string $name
     * @return bool
     */
    public function __empty($name) {
        if (isset(self::$standardproperties[$name])) {
            $value = $this->__get($name);
            return empty($value);
        }
        return true;
    }

    /**
     * Magic method setter
     *
     * Will display the developer warning when trying to set/overwrite existing property.
     *
     * @param string $name
     * @param mixed $value
     */
    public function __set($name, $value) {
        debugging("It is not allowed to set the property course_modinfo::\${$name}", DEBUG_DEVELOPER);
    }

    /**
     * Returns course object that was used in the first {@link get_fast_modinfo()} call.
     *
     * It may not contain all fields from DB table {course} but always has at least the following:
     * id,shortname,fullname,format,enablecompletion,groupmode,groupmodeforce,cacherev
     *
     * @return stdClass
     */
    public function get_course() {
        return $this->course;
    }

    /**
     * @return int Course ID
     */
    public function get_course_id() {
        return $this->course->id;
    }

    /**
     * @return int User ID
     */
    public function get_user_id() {
        return $this->userid;
    }

    /**
     * @return array Array from section number (e.g. 0) to array of course-module IDs in that
     *   section; this only includes sections that contain at least one course-module
     */
    public function get_sections() {
        return $this->sections;
    }

    /**
     * @return cm_info[] Array from course-module instance to cm_info object within this course, in
     *   order of appearance
     */
    public function get_cms() {
        return $this->cms;
    }

    /**
     * Obtains a single course-module object (for a course-module that is on this course).
     * @param int $cmid Course-module ID
     * @return cm_info Information about that course-module
     * @throws moodle_exception If the course-module does not exist
     */
    public function get_cm($cmid) {
        if (empty($this->cms[$cmid])) {
            throw new moodle_exception('invalidcoursemodule', 'error');
        }
        return $this->cms[$cmid];
    }

    /**
     * Obtains all module instances on this course.
     * @return cm_info[][] Array from module name => array from instance id => cm_info
     */
    public function get_instances() {
        return $this->instances;
    }

    /**
     * Returns array of localised human-readable module names used in this course
     *
     * @param bool $plural if true returns the plural form of modules names
     * @return array
     */
    public function get_used_module_names($plural = false) {
        $modnames = get_module_types_names($plural);
        $modnamesused = array();
        foreach ($this->get_cms() as $cmid => $mod) {
            if (!isset($modnamesused[$mod->modname]) && isset($modnames[$mod->modname]) && $mod->uservisible) {
                $modnamesused[$mod->modname] = $modnames[$mod->modname];
            }
        }
        return $modnamesused;
    }

    /**
     * Obtains all instances of a particular module on this course.
     * @param $modname Name of module (not full frankenstyle) e.g. 'label'
     * @return cm_info[] Array from instance id => cm_info for modules on this course; empty if none
     */
    public function get_instances_of($modname) {
        if (empty($this->instances[$modname])) {
            return array();
        }
        return $this->instances[$modname];
    }

    /**
     * Groups that the current user belongs to organised by grouping id. Calculated on the first request.
     * @return int[][] array of grouping id => array of group id => group id. Includes grouping id 0 for 'all groups'
     */
    private function get_groups_all() {
        if (is_null($this->groups)) {
            // NOTE: Performance could be improved here. The system caches user groups
            // in $USER->groupmember[$courseid] => array of groupid=>groupid. Unfortunately this
            // structure does not include grouping information. It probably could be changed to
            // do so, without a significant performance hit on login, thus saving this one query
            // each request.
            $this->groups = groups_get_user_groups($this->course->id, $this->userid);
        }
        return $this->groups;
    }

    /**
     * Returns groups that the current user belongs to on the course. Note: If not already
     * available, this may make a database query.
     * @param int $groupingid Grouping ID or 0 (default) for all groups
     * @return int[] Array of int (group id) => int (same group id again); empty array if none
     */
    public function get_groups($groupingid = 0) {
        $allgroups = $this->get_groups_all();
        if (!isset($allgroups[$groupingid])) {
            return array();
        }
        return $allgroups[$groupingid];
    }

    /**
     * Gets all sections as array from section number => data about section.
     * @return section_info[] Array of section_info objects organised by section number
     */
    public function get_section_info_all() {
        return $this->sectioninfo;
    }

    /**
     * Gets data about specific numbered section.
     * @param int $sectionnumber Number (not id) of section
     * @param int $strictness Use MUST_EXIST to throw exception if it doesn't
     * @return section_info Information for numbered section or null if not found
     */
    public function get_section_info($sectionnumber, $strictness = IGNORE_MISSING) {
        if (!array_key_exists($sectionnumber, $this->sectioninfo)) {
            if ($strictness === MUST_EXIST) {
                throw new moodle_exception('sectionnotexist');
            } else {
                return null;
            }
        }
        return $this->sectioninfo[$sectionnumber];
    }

    /**
     * Static cache for generated course_modinfo instances
     *
     * @see course_modinfo::instance()
     * @see course_modinfo::clear_instance_cache()
     * @var course_modinfo[]
     */
    protected static $instancecache = array();

    /**
     * Timestamps (microtime) when the course_modinfo instances were last accessed
     *
     * It is used to remove the least recent accessed instances when static cache is full
     *
     * @var float[]
     */
    protected static $cacheaccessed = array();

    /**
     * Clears the cache used in course_modinfo::instance()
     *
     * Used in {@link get_fast_modinfo()} when called with argument $reset = true
     * and in {@link rebuild_course_cache()}
     *
     * @param null|int|stdClass $courseorid if specified removes only cached value for this course
     */
    public static function clear_instance_cache($courseorid = null) {
        if (empty($courseorid)) {
            self::$instancecache = array();
            self::$cacheaccessed = array();
            return;
        }
        if (is_object($courseorid)) {
            $courseorid = $courseorid->id;
        }
        if (isset(self::$instancecache[$courseorid])) {
            // Unsetting static variable in PHP is peculiar, it removes the reference,
            // but data remain in memory. Prior to unsetting, the varable needs to be
            // set to empty to remove its remains from memory.
            self::$instancecache[$courseorid] = '';
            unset(self::$instancecache[$courseorid]);
            unset(self::$cacheaccessed[$courseorid]);
        }
    }

    /**
     * Returns the instance of course_modinfo for the specified course and specified user
     *
     * This function uses static cache for the retrieved instances. The cache
     * size is limited by MAX_MODINFO_CACHE_SIZE. If instance is not found in
     * the static cache or it was created for another user or the cacherev validation
     * failed - a new instance is constructed and returned.
     *
     * Used in {@link get_fast_modinfo()}
     *
     * @param int|stdClass $courseorid object from DB table 'course' (must have field 'id'
     *     and recommended to have field 'cacherev') or just a course id
     * @param int $userid User id to populate 'availble' and 'uservisible' attributes of modules and sections.
     *     Set to 0 for current user (default). Set to -1 to avoid calculation of dynamic user-depended data.
     * @return course_modinfo
     */
    public static function instance($courseorid, $userid = 0) {
        global $USER;
        if (is_object($courseorid)) {
            $course = $courseorid;
        } else {
            $course = (object)array('id' => $courseorid);
        }
        if (empty($userid)) {
            $userid = $USER->id;
        }

        if (!empty(self::$instancecache[$course->id])) {
            if (self::$instancecache[$course->id]->userid == $userid &&
                    (!isset($course->cacherev) ||
                    $course->cacherev == self::$instancecache[$course->id]->get_course()->cacherev)) {
                // This course's modinfo for the same user was recently retrieved, return cached.
                self::$cacheaccessed[$course->id] = microtime(true);
                return self::$instancecache[$course->id];
            } else {
                // Prevent potential reference problems when switching users.
                self::clear_instance_cache($course->id);
            }
        }
        $modinfo = new course_modinfo($course, $userid);

        // We have a limit of MAX_MODINFO_CACHE_SIZE entries to store in static variable.
        if (count(self::$instancecache) >= MAX_MODINFO_CACHE_SIZE) {
            // Find the course that was the least recently accessed.
            asort(self::$cacheaccessed, SORT_NUMERIC);
            $courseidtoremove = key(array_reverse(self::$cacheaccessed, true));
            self::clear_instance_cache($courseidtoremove);
        }

        // Add modinfo to the static cache.
        self::$instancecache[$course->id] = $modinfo;
        self::$cacheaccessed[$course->id] = microtime(true);

        return $modinfo;
    }

    /**
     * Constructs based on course.
     * Note: This constructor should not usually be called directly.
     * Use get_fast_modinfo($course) instead as this maintains a cache.
     * @param stdClass $course course object, only property id is required.
     * @param int $userid User ID
     * @throws moodle_exception if course is not found
     */
    public function __construct($course, $userid) {
        global $CFG, $COURSE, $SITE, $DB;

        if (!isset($course->cacherev)) {
            // We require presence of property cacherev to validate the course cache.
            // No need to clone the $COURSE or $SITE object here because we clone it below anyway.
            $course = get_course($course->id, false);
        }

        $cachecoursemodinfo = cache::make('core', 'coursemodinfo');

        // Retrieve modinfo from cache. If not present or cacherev mismatches, call rebuild and retrieve again.
        $coursemodinfo = $cachecoursemodinfo->get($course->id);
        if ($coursemodinfo === false || ($course->cacherev != $coursemodinfo->cacherev)) {
            $lock = self::get_course_cache_lock($course->id);
            try {
                // Only actually do the build if it's still needed after getting the lock (not if
                // somebody else, who might have been holding the lock, built it already).
                $coursemodinfo = $cachecoursemodinfo->get($course->id);
                if ($coursemodinfo === false || ($course->cacherev != $coursemodinfo->cacherev)) {
                    $coursemodinfo = self::inner_build_course_cache($course, $lock);
                }
            } finally {
                $lock->release();
            }
        }

        // Set initial values
        $this->userid = $userid;
        $this->sections = array();
        $this->cms = array();
        $this->instances = array();
        $this->groups = null;

        // If we haven't already preloaded contexts for the course, do it now
        // Modules are also cached here as long as it's the first time this course has been preloaded.
        context_helper::preload_course($course->id);

        // Quick integrity check: as a result of race conditions modinfo may not be regenerated after the change.
        // It is especially dangerous if modinfo contains the deleted course module, as it results in fatal error.
        // We can check it very cheap by validating the existence of module context.
        if ($course->id == $COURSE->id || $course->id == $SITE->id) {
            // Only verify current course (or frontpage) as pages with many courses may not have module contexts cached.
            // (Uncached modules will result in a very slow verification).
            foreach ($coursemodinfo->modinfo as $mod) {
                if (!context_module::instance($mod->cm, IGNORE_MISSING)) {
                    debugging('Course cache integrity check failed: course module with id '. $mod->cm.
                            ' does not have context. Rebuilding cache for course '. $course->id);
                    // Re-request the course record from DB as well, don't use get_course() here.
                    $course = $DB->get_record('course', array('id' => $course->id), '*', MUST_EXIST);
                    $coursemodinfo = self::build_course_cache($course);
                    break;
                }
            }
        }

        // Overwrite unset fields in $course object with cached values, store the course object.
        $this->course = fullclone($course);
        foreach ($coursemodinfo as $key => $value) {
            if ($key !== 'modinfo' && $key !== 'sectioncache' &&
                    (!isset($this->course->$key) || $key === 'cacherev')) {
                $this->course->$key = $value;
            }
        }

        // Loop through each piece of module data, constructing it
        static $modexists = array();
        foreach ($coursemodinfo->modinfo as $mod) {
            if (!isset($mod->name) || strval($mod->name) === '') {
                // something is wrong here
                continue;
            }

            // Skip modules which don't exist
            if (!array_key_exists($mod->mod, $modexists)) {
                $modexists[$mod->mod] = file_exists("$CFG->dirroot/mod/$mod->mod/lib.php");
            }
            if (!$modexists[$mod->mod]) {
                continue;
            }

            // Construct info for this module
            $cm = new cm_info($this, null, $mod, null);

            // Store module in instances and cms array
            if (!isset($this->instances[$cm->modname])) {
                $this->instances[$cm->modname] = array();
            }
            $this->instances[$cm->modname][$cm->instance] = $cm;
            $this->cms[$cm->id] = $cm;

            // Reconstruct sections. This works because modules are stored in order
            if (!isset($this->sections[$cm->sectionnum])) {
                $this->sections[$cm->sectionnum] = array();
            }
            $this->sections[$cm->sectionnum][] = $cm->id;
        }

        // Expand section objects
        $this->sectioninfo = array();
        foreach ($coursemodinfo->sectioncache as $number => $data) {
            $this->sectioninfo[$number] = new section_info($data, $number, null, null,
                    $this, null);
        }
    }

    /**
     * This method can not be used anymore.
     *
     * @see course_modinfo::build_course_cache()
     * @deprecated since 2.6
     */
    public static function build_section_cache($courseid) {
        throw new coding_exception('Function course_modinfo::build_section_cache() can not be used anymore.' .
            ' Please use course_modinfo::build_course_cache() whenever applicable.');
    }

    /**
     * Builds a list of information about sections on a course to be stored in
     * the course cache. (Does not include information that is already cached
     * in some other way.)
     *
     * @param stdClass $course Course object (must contain fields
     * @return array Information about sections, indexed by section number (not id)
     */
    protected static function build_course_section_cache($course) {
        global $DB;

        // Get section data
        $sections = $DB->get_records('course_sections', array('course' => $course->id), 'section',
                'section, id, course, name, summary, summaryformat, sequence, visible, availability');
        $compressedsections = array();

        $formatoptionsdef = course_get_format($course)->section_format_options();
        // Remove unnecessary data and add availability
        foreach ($sections as $number => $section) {
            // Add cached options from course format to $section object
            foreach ($formatoptionsdef as $key => $option) {
                if (!empty($option['cache'])) {
                    $formatoptions = course_get_format($course)->get_format_options($section);
                    if (!array_key_exists('cachedefault', $option) || $option['cachedefault'] !== $formatoptions[$key]) {
                        $section->$key = $formatoptions[$key];
                    }
                }
            }
            // Clone just in case it is reused elsewhere
            $compressedsections[$number] = clone($section);
            section_info::convert_for_section_cache($compressedsections[$number]);
        }

        return $compressedsections;
    }

    /**
     * Gets a lock for rebuilding the cache of a single course.
     *
     * Caller must release the returned lock.
     *
     * This is used to ensure that the cache rebuild doesn't happen multiple times in parallel.
     * This function will wait up to 1 minute for the lock to be obtained. If the lock cannot
     * be obtained, it throws an exception.
     *
     * @param int $courseid Course id
     * @return \core\lock\lock Lock (must be released!)
     * @throws moodle_exception If the lock cannot be obtained
     */
    protected static function get_course_cache_lock($courseid) {
        // Get database lock to ensure this doesn't happen multiple times in parallel. Wait a
        // reasonable time for the lock to be released, so we can give a suitable error message.
        // In case the system crashes while building the course cache, the lock will automatically
        // expire after a (slightly longer) period.
        $lockfactory = \core\lock\lock_config::get_lock_factory('core_modinfo');
        $lock = $lockfactory->get_lock('build_course_cache_' . $courseid,
                self::COURSE_CACHE_LOCK_WAIT, self::COURSE_CACHE_LOCK_EXPIRY);
        if (!$lock) {
            throw new moodle_exception('locktimeout', '', '', null,
                    'core_modinfo/build_course_cache_' . $courseid);
        }
        return $lock;
    }

    /**
     * Builds and stores in MUC object containing information about course
     * modules and sections together with cached fields from table course.
     *
     * @param stdClass $course object from DB table course. Must have property 'id'
     *     but preferably should have all cached fields.
     * @return stdClass object with all cached keys of the course plus fields modinfo and sectioncache.
     *     The same object is stored in MUC
     * @throws moodle_exception if course is not found (if $course object misses some of the
     *     necessary fields it is re-requested from database)
     */
    public static function build_course_cache($course) {
        if (empty($course->id)) {
            throw new coding_exception('Object $course is missing required property \id\'');
        }

        $lock = self::get_course_cache_lock($course->id);
        try {
            return self::inner_build_course_cache($course, $lock);
        } finally {
            $lock->release();
        }
    }

    /**
     * Called to build course cache when there is already a lock obtained.
     *
     * @param stdClass $course object from DB table course
     * @param \core\lock\lock $lock Lock object - not actually used, just there to indicate you have a lock
     * @return stdClass Course object that has been stored in MUC
     */
    protected static function inner_build_course_cache($course, \core\lock\lock $lock) {
        global $DB, $CFG;
        require_once("{$CFG->dirroot}/course/lib.php");

        // Ensure object has all necessary fields.
        foreach (self::$cachedfields as $key) {
            if (!isset($course->$key)) {
                $course = $DB->get_record('course', array('id' => $course->id),
                        implode(',', array_merge(array('id'), self::$cachedfields)), MUST_EXIST);
                break;
            }
        }
        // Retrieve all information about activities and sections.
        // This may take time on large courses and it is possible that another user modifies the same course during this process.
        // Field cacherev stored in both DB and cache will ensure that cached data matches the current course state.
        $coursemodinfo = new stdClass();
        $coursemodinfo->modinfo = get_array_of_activities($course->id);
        $coursemodinfo->sectioncache = self::build_course_section_cache($course);
        foreach (self::$cachedfields as $key) {
            $coursemodinfo->$key = $course->$key;
        }
        // Set the accumulated activities and sections information in cache, together with cacherev.
        $cachecoursemodinfo = cache::make('core', 'coursemodinfo');
        $cachecoursemodinfo->set($course->id, $coursemodinfo);
        return $coursemodinfo;
    }
}


/**
 * Data about a single module on a course. This contains most of the fields in the course_modules
 * table, plus additional data when required.
 *
 * The object can be accessed by core or any plugin (i.e. course format, block, filter, etc.) as
 * get_fast_modinfo($courseorid)->cms[$coursemoduleid]
 * or
 * get_fast_modinfo($courseorid)->instances[$moduletype][$instanceid]
 *
 * There are three stages when activity module can add/modify data in this object:
 *
 * <b>Stage 1 - during building the cache.</b>
 * Allows to add to the course cache static user-independent information about the module.
 * Modules should try to include only absolutely necessary information that may be required
 * when displaying course view page. The information is stored in application-level cache
 * and reset when {@link rebuild_course_cache()} is called or cache is purged by admin.
 *
 * Modules can implement callback XXX_get_coursemodule_info() returning instance of object
 * {@link cached_cm_info}
 *
 * <b>Stage 2 - dynamic data.</b>
 * Dynamic data is user-dependend, it is stored in request-level cache. To reset this cache
 * {@link get_fast_modinfo()} with $reset argument may be called.
 *
 * Dynamic data is obtained when any of the following properties/methods is requested:
 * - {@link cm_info::$url}
 * - {@link cm_info::$name}
 * - {@link cm_info::$onclick}
 * - {@link cm_info::get_icon_url()}
 * - {@link cm_info::$uservisible}
 * - {@link cm_info::$available}
 * - {@link cm_info::$availableinfo}
 * - plus any of the properties listed in Stage 3.
 *
 * Modules can implement callback <b>XXX_cm_info_dynamic()</b> and inside this callback they
 * are allowed to use any of the following set methods:
 * - {@link cm_info::set_available()}
 * - {@link cm_info::set_name()}
 * - {@link cm_info::set_no_view_link()}
 * - {@link cm_info::set_user_visible()}
 * - {@link cm_info::set_on_click()}
 * - {@link cm_info::set_icon_url()}
 * Any methods affecting view elements can also be set in this callback.
 *
 * <b>Stage 3 (view data).</b>
 * Also user-dependend data stored in request-level cache. Second stage is created
 * because populating the view data can be expensive as it may access much more
 * Moodle APIs such as filters, user information, output renderers and we
 * don't want to request it until necessary.
 * View data is obtained when any of the following properties/methods is requested:
 * - {@link cm_info::$afterediticons}
 * - {@link cm_info::$content}
 * - {@link cm_info::get_formatted_content()}
 * - {@link cm_info::$extraclasses}
 * - {@link cm_info::$afterlink}
 *
 * Modules can implement callback <b>XXX_cm_info_view()</b> and inside this callback they
 * are allowed to use any of the following set methods:
 * - {@link cm_info::set_after_edit_icons()}
 * - {@link cm_info::set_after_link()}
 * - {@link cm_info::set_content()}
 * - {@link cm_info::set_extra_classes()}
 *
 * @property-read int $id Course-module ID - from course_modules table
 * @property-read int $instance Module instance (ID within module table) - from course_modules table
 * @property-read int $course Course ID - from course_modules table
 * @property-read string $idnumber 'ID number' from course-modules table (arbitrary text set by user) - from
 *    course_modules table
 * @property-read int $added Time that this course-module was added (unix time) - from course_modules table
 * @property-read int $visible Visible setting (0 or 1; if this is 0, students cannot see/access the activity) - from
 *    course_modules table
 * @property-read int $visibleoncoursepage Visible on course page setting - from course_modules table, adjusted to
 *    whether course format allows this module to have the "stealth" mode
 * @property-read int $visibleold Old visible setting (if the entire section is hidden, the previous value for
 *    visible is stored in this field) - from course_modules table
 * @property-read int $groupmode Group mode (one of the constants NOGROUPS, SEPARATEGROUPS, or VISIBLEGROUPS) - from
 *    course_modules table. Use {@link cm_info::$effectivegroupmode} to find the actual group mode that may be forced by course.
 * @property-read int $groupingid Grouping ID (0 = all groupings)
 * @property-read bool $coursegroupmodeforce Indicates whether the course containing the module has forced the groupmode
 *    This means that cm_info::$groupmode should be ignored and cm_info::$coursegroupmode be used instead
 * @property-read int $coursegroupmode Group mode (one of the constants NOGROUPS, SEPARATEGROUPS, or VISIBLEGROUPS) - from
 *    course table - as specified for the course containing the module
 *    Effective only if {@link cm_info::$coursegroupmodeforce} is set
 * @property-read int $effectivegroupmode Effective group mode for this module (one of the constants NOGROUPS, SEPARATEGROUPS,
 *    or VISIBLEGROUPS). This can be different from groupmode set for the module if the groupmode is forced for the course.
 *    This value will always be NOGROUPS if module type does not support group mode.
 * @property-read int $indent Indent level on course page (0 = no indent) - from course_modules table
 * @property-read int $completion Activity completion setting for this activity, COMPLETION_TRACKING_xx constant - from
 *    course_modules table
 * @property-read mixed $completiongradeitemnumber Set to the item number (usually 0) if completion depends on a particular
 *    grade of this activity, or null if completion does not depend on a grade - from course_modules table
 * @property-read int $completionview 1 if 'on view' completion is enabled, 0 otherwise - from course_modules table
 * @property-read int $completionexpected Set to a unix time if completion of this activity is expected at a
 *    particular time, 0 if no time set - from course_modules table
 * @property-read string $availability Availability information as JSON string or null if none -
 *    from course_modules table
 * @property-read int $showdescription Controls whether the description of the activity displays on the course main page (in
 *    addition to anywhere it might display within the activity itself). 0 = do not show
 *    on main page, 1 = show on main page.
 * @property-read string $extra (deprecated) Extra HTML that is put in an unhelpful part of the HTML when displaying this module in
 *    course page - from cached data in modinfo field. Deprecated, replaced by ->extraclasses and ->onclick
 * @property-read string $icon Name of icon to use - from cached data in modinfo field
 * @property-read string $iconcomponent Component that contains icon - from cached data in modinfo field
 * @property-read string $modname Name of module e.g. 'forum' (this is the same name as the module's main database
 *    table) - from cached data in modinfo field
 * @property-read int $module ID of module type - from course_modules table
 * @property-read string $name Name of module instance for display on page e.g. 'General discussion forum' - from cached
 *    data in modinfo field
 * @property-read int $sectionnum Section number that this course-module is in (section 0 = above the calendar, section 1
 *    = week/topic 1, etc) - from cached data in modinfo field
 * @property-read int $section Section id - from course_modules table
 * @property-read array $conditionscompletion Availability conditions for this course-module based on the completion of other
 *    course-modules (array from other course-module id to required completion state for that
 *    module) - from cached data in modinfo field
 * @property-read array $conditionsgrade Availability conditions for this course-module based on course grades (array from
 *    grade item id to object with ->min, ->max fields) - from cached data in modinfo field
 * @property-read array $conditionsfield Availability conditions for this course-module based on user fields
 * @property-read bool $available True if this course-module is available to students i.e. if all availability conditions
 *    are met - obtained dynamically
 * @property-read string $availableinfo If course-module is not available to students, this string gives information about
 *    availability which can be displayed to students and/or staff (e.g. 'Available from 3
 *    January 2010') for display on main page - obtained dynamically
 * @property-read bool $uservisible True if this course-module is available to the CURRENT user (for example, if current user
 *    has viewhiddenactivities capability, they can access the course-module even if it is not
 *    visible or not available, so this would be true in that case)
 * @property-read context_module $context Module context
 * @property-read string $modfullname Returns a localised human-readable name of the module type - calculated on request
 * @property-read string $modplural Returns a localised human-readable name of the module type in plural form - calculated on request
 * @property-read string $content Content to display on main (view) page - calculated on request
 * @property-read moodle_url $url URL to link to for this module, or null if it doesn't have a view page - calculated on request
 * @property-read string $extraclasses Extra CSS classes to add to html output for this activity on main page - calculated on request
 * @property-read string $onclick Content of HTML on-click attribute already escaped - calculated on request
 * @property-read mixed $customdata Optional custom data stored in modinfo cache for this activity, or null if none
 * @property-read string $afterlink Extra HTML code to display after link - calculated on request
 * @property-read string $afterediticons Extra HTML code to display after editing icons (e.g. more icons) - calculated on request
 * @property-read bool $deletioninprogress True if this course module is scheduled for deletion, false otherwise.
 */
class cm_info implements IteratorAggregate {
    /**
     * State: Only basic data from modinfo cache is available.
     */
    const STATE_BASIC = 0;

    /**
     * State: In the process of building dynamic data (to avoid recursive calls to obtain_dynamic_data())
     */
    const STATE_BUILDING_DYNAMIC = 1;

    /**
     * State: Dynamic data is available too.
     */
    const STATE_DYNAMIC = 2;

    /**
     * State: In the process of building view data (to avoid recursive calls to obtain_view_data())
     */
    const STATE_BUILDING_VIEW = 3;

    /**
     * State: View data (for course page) is available.
     */
    const STATE_VIEW = 4;

    /**
     * Parent object
     * @var course_modinfo
     */
    private $modinfo;

    /**
     * Level of information stored inside this object (STATE_xx constant)
     * @var int
     */
    private $state;

    /**
     * Course-module ID - from course_modules table
     * @var int
     */
    private $id;

    /**
     * Module instance (ID within module table) - from course_modules table
     * @var int
     */
    private $instance;

    /**
     * 'ID number' from course-modules table (arbitrary text set by user) - from
     * course_modules table
     * @var string
     */
    private $idnumber;

    /**
     * Time that this course-module was added (unix time) - from course_modules table
     * @var int
     */
    private $added;

    /**
     * This variable is not used and is included here only so it can be documented.
     * Once the database entry is removed from course_modules, it should be deleted
     * here too.
     * @var int
     * @deprecated Do not use this variable
     */
    private $score;

    /**
     * Visible setting (0 or 1; if this is 0, students cannot see/access the activity) - from
     * course_modules table
     * @var int
     */
    private $visible;

    /**
     * Visible on course page setting - from course_modules table
     * @var int
     */
    private $visibleoncoursepage;

    /**
     * Old visible setting (if the entire section is hidden, the previous value for
     * visible is stored in this field) - from course_modules table
     * @var int
     */
    private $visibleold;

    /**
     * Group mode (one of the constants NONE, SEPARATEGROUPS, or VISIBLEGROUPS) - from
     * course_modules table
     * @var int
     */
    private $groupmode;

    /**
     * Grouping ID (0 = all groupings)
     * @var int
     */
    private $groupingid;

    /**
     * Indent level on course page (0 = no indent) - from course_modules table
     * @var int
     */
    private $indent;

    /**
     * Activity completion setting for this activity, COMPLETION_TRACKING_xx constant - from
     * course_modules table
     * @var int
     */
    private $completion;

    /**
     * Set to the item number (usually 0) if completion depends on a particular
     * grade of this activity, or null if completion does not depend on a grade - from
     * course_modules table
     * @var mixed
     */
    private $completiongradeitemnumber;

    /**
     * 1 if 'on view' completion is enabled, 0 otherwise - from course_modules table
     * @var int
     */
    private $completionview;

    /**
     * Set to a unix time if completion of this activity is expected at a
     * particular time, 0 if no time set - from course_modules table
     * @var int
     */
    private $completionexpected;

    /**
     * Availability information as JSON string or null if none - from course_modules table
     * @var string
     */
    private $availability;

    /**
     * Controls whether the description of the activity displays on the course main page (in
     * addition to anywhere it might display within the activity itself). 0 = do not show
     * on main page, 1 = show on main page.
     * @var int
     */
    private $showdescription;

    /**
     * Extra HTML that is put in an unhelpful part of the HTML when displaying this module in
     * course page - from cached data in modinfo field
     * @deprecated This is crazy, don't use it. Replaced by ->extraclasses and ->onclick
     * @var string
     */
    private $extra;

    /**
     * Name of icon to use - from cached data in modinfo field
     * @var string
     */
    private $icon;

    /**
     * Component that contains icon - from cached data in modinfo field
     * @var string
     */
    private $iconcomponent;

    /**
     * Name of module e.g. 'forum' (this is the same name as the module's main database
     * table) - from cached data in modinfo field
     * @var string
     */
    private $modname;

    /**
     * ID of module - from course_modules table
     * @var int
     */
    private $module;

    /**
     * Name of module instance for display on page e.g. 'General discussion forum' - from cached
     * data in modinfo field
     * @var string
     */
    private $name;

    /**
     * Section number that this course-module is in (section 0 = above the calendar, section 1
     * = week/topic 1, etc) - from cached data in modinfo field
     * @var int
     */
    private $sectionnum;

    /**
     * Section id - from course_modules table
     * @var int
     */
    private $section;

    /**
     * Availability conditions for this course-module based on the completion of other
     * course-modules (array from other course-module id to required completion state for that
     * module) - from cached data in modinfo field
     * @var array
     */
    private $conditionscompletion;

    /**
     * Availability conditions for this course-module based on course grades (array from
     * grade item id to object with ->min, ->max fields) - from cached data in modinfo field
     * @var array
     */
    private $conditionsgrade;

    /**
     * Availability conditions for this course-module based on user fields
     * @var array
     */
    private $conditionsfield;

    /**
     * True if this course-module is available to students i.e. if all availability conditions
     * are met - obtained dynamically
     * @var bool
     */
    private $available;

    /**
     * If course-module is not available to students, this string gives information about
     * availability which can be displayed to students and/or staff (e.g. 'Available from 3
     * January 2010') for display on main page - obtained dynamically
     * @var string
     */
    private $availableinfo;

    /**
     * True if this course-module is available to the CURRENT user (for example, if current user
     * has viewhiddenactivities capability, they can access the course-module even if it is not
     * visible or not available, so this would be true in that case)
     * @var bool
     */
    private $uservisible;

    /**
     * True if this course-module is visible to the CURRENT user on the course page
     * @var bool
     */
    private $uservisibleoncoursepage;

    /**
     * @var moodle_url
     */
    private $url;

    /**
     * @var string
     */
    private $content;

    /**
     * @var bool
     */
    private $contentisformatted;

    /**
     * @var string
     */
    private $extraclasses;

    /**
     * @var moodle_url full external url pointing to icon image for activity
     */
    private $iconurl;

    /**
     * @var string
     */
    private $onclick;

    /**
     * @var mixed
     */
    private $customdata;

    /**
     * @var string
     */
    private $afterlink;

    /**
     * @var string
     */
    private $afterediticons;

    /**
     * @var bool representing the deletion state of the module. True if the mod is scheduled for deletion.
     */
    private $deletioninprogress;

    /**
     * List of class read-only properties and their getter methods.
     * Used by magic functions __get(), __isset(), __empty()
     * @var array
     */
    private static $standardproperties = array(
        'url' => 'get_url',
        'content' => 'get_content',
        'extraclasses' => 'get_extra_classes',
        'onclick' => 'get_on_click',
        'customdata' => 'get_custom_data',
        'afterlink' => 'get_after_link',
        'afterediticons' => 'get_after_edit_icons',
        'modfullname' => 'get_module_type_name',
        'modplural' => 'get_module_type_name_plural',
        'id' => false,
        'added' => false,
        'availability' => false,
        'available' => 'get_available',
        'availableinfo' => 'get_available_info',
        'completion' => false,
        'completionexpected' => false,
        'completiongradeitemnumber' => false,
        'completionview' => false,
        'conditionscompletion' => false,
        'conditionsfield' => false,
        'conditionsgrade' => false,
        'context' => 'get_context',
        'course' => 'get_course_id',
        'coursegroupmode' => 'get_course_groupmode',
        'coursegroupmodeforce' => 'get_course_groupmodeforce',
        'effectivegroupmode' => 'get_effective_groupmode',
        'extra' => false,
        'groupingid' => false,
        'groupmembersonly' => 'get_deprecated_group_members_only',
        'groupmode' => false,
        'icon' => false,
        'iconcomponent' => false,
        'idnumber' => false,
        'indent' => false,
        'instance' => false,
        'modname' => false,
        'module' => false,
        'name' => 'get_name',
        'score' => false,
        'section' => false,
        'sectionnum' => false,
        'showdescription' => false,
        'uservisible' => 'get_user_visible',
        'visible' => false,
        'visibleoncoursepage' => false,
        'visibleold' => false,
        'deletioninprogress' => false
    );

    /**
     * List of methods with no arguments that were public prior to Moodle 2.6.
     *
     * They can still be accessed publicly via magic __call() function with no warnings
     * but are not listed in the class methods list.
     * For the consistency of the code it is better to use corresponding properties.
     *
     * These methods be deprecated completely in later versions.
     *
     * @var array $standardmethods
     */
    private static $standardmethods = array(
        // Following methods are not recommended to use because there have associated read-only properties.
        'get_url',
        'get_content',
        'get_extra_classes',
        'get_on_click',
        'get_custom_data',
        'get_after_link',
        'get_after_edit_icons',
        // Method obtain_dynamic_data() should not be called from outside of this class but it was public before Moodle 2.6.
        'obtain_dynamic_data',
    );

    /**
     * Magic method to call functions that are now declared as private but were public in Moodle before 2.6.
     * These private methods can not be used anymore.
     *
     * @param string $name
     * @param array $arguments
     * @return mixed
     * @throws coding_exception
     */
    public function __call($name, $arguments) {
        if (in_array($name, self::$standardmethods)) {
            $message = "cm_info::$name() can not be used anymore.";
            if ($alternative = array_search($name, self::$standardproperties)) {
                $message .= " Please use the property cm_info->$alternative instead.";
            }
            throw new coding_exception($message);
        }
        throw new coding_exception("Method cm_info::{$name}() does not exist");
    }

    /**
     * Magic method getter
     *
     * @param string $name
     * @return mixed
     */
    public function __get($name) {
        if (isset(self::$standardproperties[$name])) {
            if ($method = self::$standardproperties[$name]) {
                return $this->$method();
            } else {
                return $this->$name;
            }
        } else {
            debugging('Invalid cm_info property accessed: '.$name);
            return null;
        }
    }

    /**
     * Implementation of IteratorAggregate::getIterator(), allows to cycle through properties
     * and use {@link convert_to_array()}
     *
     * @return ArrayIterator
     */
    public function getIterator() {
        // Make sure dynamic properties are retrieved prior to view properties.
        $this->obtain_dynamic_data();
        $ret = array();

        // Do not iterate over deprecated properties.
        $props = self::$standardproperties;
        unset($props['groupmembersonly']);

        foreach ($props as $key => $unused) {
            $ret[$key] = $this->__get($key);
        }
        return new ArrayIterator($ret);
    }

    /**
     * Magic method for function isset()
     *
     * @param string $name
     * @return bool
     */
    public function __isset($name) {
        if (isset(self::$standardproperties[$name])) {
            $value = $this->__get($name);
            return isset($value);
        }
        return false;
    }

    /**
     * Magic method for function empty()
     *
     * @param string $name
     * @return bool
     */
    public function __empty($name) {
        if (isset(self::$standardproperties[$name])) {
            $value = $this->__get($name);
 …

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