/lib/accesslib.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/>.

/**
 * This file contains functions for managing user access
 *
 * <b>Public API vs internals</b>
 *
 * General users probably only care about
 *
 * Context handling
 * - context_course::instance($courseid), context_module::instance($cm->id), context_coursecat::instance($catid)
 * - context::instance_by_id($contextid)
 * - $context->get_parent_contexts();
 * - $context->get_child_contexts();
 *
 * Whether the user can do something...
 * - has_capability()
 * - has_any_capability()
 * - has_all_capabilities()
 * - require_capability()
 * - require_login() (from moodlelib)
 * - is_enrolled()
 * - is_viewing()
 * - is_guest()
 * - is_siteadmin()
 * - isguestuser()
 * - isloggedin()
 *
 * What courses has this user access to?
 * - get_enrolled_users()
 *
 * What users can do X in this context?
 * - get_enrolled_users() - at and bellow course context
 * - get_users_by_capability() - above course context
 *
 * Modify roles
 * - role_assign()
 * - role_unassign()
 * - role_unassign_all()
 *
 * Advanced - for internal use only
 * - load_all_capabilities()
 * - reload_all_capabilities()
 * - has_capability_in_accessdata()
 * - get_user_roles_sitewide_accessdata()
 * - etc.
 *
 * <b>Name conventions</b>
 *
 * "ctx" means context
 * "ra" means role assignment
 * "rdef" means role definition
 *
 * <b>accessdata</b>
 *
 * Access control data is held in the "accessdata" array
 * which - for the logged-in user, will be in $USER->access
 *
 * For other users can be generated and passed around (but may also be cached
 * against userid in $ACCESSLIB_PRIVATE->accessdatabyuser).
 *
 * $accessdata is a multidimensional array, holding
 * role assignments (RAs), role switches and initialization time.
 *
 * Things are keyed on "contextpaths" (the path field of
 * the context table) for fast walking up/down the tree.
 * <code>
 * $accessdata['ra'][$contextpath] = array($roleid=>$roleid)
 *                  [$contextpath] = array($roleid=>$roleid)
 *                  [$contextpath] = array($roleid=>$roleid)
 * </code>
 *
 * <b>Stale accessdata</b>
 *
 * For the logged-in user, accessdata is long-lived.
 *
 * On each pageload we load $ACCESSLIB_PRIVATE->dirtycontexts which lists
 * context paths affected by changes. Any check at-or-below
 * a dirty context will trigger a transparent reload of accessdata.
 *
 * Changes at the system level will force the reload for everyone.
 *
 * <b>Default role caps</b>
 * The default role assignment is not in the DB, so we
 * add it manually to accessdata.
 *
 * This means that functions that work directly off the
 * DB need to ensure that the default role caps
 * are dealt with appropriately.
 *
 * @package    core_access
 * @copyright  1999 onwards Martin Dougiamas  http://dougiamas.com
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

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

/** No capability change */
define('CAP_INHERIT', 0);
/** Allow permission, overrides CAP_PREVENT defined in parent contexts */
define('CAP_ALLOW', 1);
/** Prevent permission, overrides CAP_ALLOW defined in parent contexts */
define('CAP_PREVENT', -1);
/** Prohibit permission, overrides everything in current and child contexts */
define('CAP_PROHIBIT', -1000);

/** System context level - only one instance in every system */
define('CONTEXT_SYSTEM', 10);
/** User context level -  one instance for each user describing what others can do to user */
define('CONTEXT_USER', 30);
/** Course category context level - one instance for each category */
define('CONTEXT_COURSECAT', 40);
/** Course context level - one instances for each course */
define('CONTEXT_COURSE', 50);
/** Course module context level - one instance for each course module */
define('CONTEXT_MODULE', 70);
/**
 * Block context level - one instance for each block, sticky blocks are tricky
 * because ppl think they should be able to override them at lower contexts.
 * Any other context level instance can be parent of block context.
 */
define('CONTEXT_BLOCK', 80);

/** Capability allow management of trusts - NOT IMPLEMENTED YET - see {@link http://docs.moodle.org/dev/Hardening_new_Roles_system} */
define('RISK_MANAGETRUST', 0x0001);
/** Capability allows changes in system configuration - see {@link http://docs.moodle.org/dev/Hardening_new_Roles_system} */
define('RISK_CONFIG',      0x0002);
/** Capability allows user to add scripted content - see {@link http://docs.moodle.org/dev/Hardening_new_Roles_system} */
define('RISK_XSS',         0x0004);
/** Capability allows access to personal user information - see {@link http://docs.moodle.org/dev/Hardening_new_Roles_system} */
define('RISK_PERSONAL',    0x0008);
/** Capability allows users to add content others may see - see {@link http://docs.moodle.org/dev/Hardening_new_Roles_system} */
define('RISK_SPAM',        0x0010);
/** capability allows mass delete of data belonging to other users - see {@link http://docs.moodle.org/dev/Hardening_new_Roles_system} */
define('RISK_DATALOSS',    0x0020);

/** rolename displays - the name as defined in the role definition, localised if name empty */
define('ROLENAME_ORIGINAL', 0);
/** rolename displays - the name as defined by a role alias at the course level, falls back to ROLENAME_ORIGINAL if alias not present */
define('ROLENAME_ALIAS', 1);
/** rolename displays - Both, like this:  Role alias (Original) */
define('ROLENAME_BOTH', 2);
/** rolename displays - the name as defined in the role definition and the shortname in brackets */
define('ROLENAME_ORIGINALANDSHORT', 3);
/** rolename displays - the name as defined by a role alias, in raw form suitable for editing */
define('ROLENAME_ALIAS_RAW', 4);
/** rolename displays - the name is simply short role name */
define('ROLENAME_SHORT', 5);

if (!defined('CONTEXT_CACHE_MAX_SIZE')) {
    /** maximum size of context cache - it is possible to tweak this config.php or in any script before inclusion of context.php */
    define('CONTEXT_CACHE_MAX_SIZE', 2500);
}

/**
 * Although this looks like a global variable, it isn't really.
 *
 * It is just a private implementation detail to accesslib that MUST NOT be used elsewhere.
 * It is used to cache various bits of data between function calls for performance reasons.
 * Sadly, a PHP global variable is the only way to implement this, without rewriting everything
 * as methods of a class, instead of functions.
 *
 * @access private
 * @global stdClass $ACCESSLIB_PRIVATE
 * @name $ACCESSLIB_PRIVATE
 */
global $ACCESSLIB_PRIVATE;
$ACCESSLIB_PRIVATE = new stdClass();
$ACCESSLIB_PRIVATE->cacheroledefs    = array(); // Holds site-wide role definitions.
$ACCESSLIB_PRIVATE->dirtycontexts    = null;    // Dirty contexts cache, loaded from DB once per page
$ACCESSLIB_PRIVATE->dirtyusers       = null;    // Dirty users cache, loaded from DB once per $USER->id
$ACCESSLIB_PRIVATE->accessdatabyuser = array(); // Holds the cache of $accessdata structure for users (including $USER)

/**
 * Clears accesslib's private caches. ONLY BE USED BY UNIT TESTS
 *
 * This method should ONLY BE USED BY UNIT TESTS. It clears all of
 * accesslib's private caches. You need to do this before setting up test data,
 * and also at the end of the tests.
 *
 * @access private
 * @return void
 */
function accesslib_clear_all_caches_for_unit_testing() {
    global $USER;
    if (!PHPUNIT_TEST) {
        throw new coding_exception('You must not call clear_all_caches outside of unit tests.');
    }

    accesslib_clear_all_caches(true);
    accesslib_reset_role_cache();

    unset($USER->access);
}

/**
 * Clears accesslib's private caches. ONLY BE USED FROM THIS LIBRARY FILE!
 *
 * This reset does not touch global $USER.
 *
 * @access private
 * @param bool $resetcontexts
 * @return void
 */
function accesslib_clear_all_caches($resetcontexts) {
    global $ACCESSLIB_PRIVATE;

    $ACCESSLIB_PRIVATE->dirtycontexts    = null;
    $ACCESSLIB_PRIVATE->dirtyusers       = null;
    $ACCESSLIB_PRIVATE->accessdatabyuser = array();

    if ($resetcontexts) {
        context_helper::reset_caches();
    }
}

/**
 * Full reset of accesslib's private role cache. ONLY TO BE USED FROM THIS LIBRARY FILE!
 *
 * This reset does not touch global $USER.
 *
 * Note: Only use this when the roles that need a refresh are unknown.
 *
 * @see accesslib_clear_role_cache()
 *
 * @access private
 * @return void
 */
function accesslib_reset_role_cache() {
    global $ACCESSLIB_PRIVATE;

    $ACCESSLIB_PRIVATE->cacheroledefs = array();
    $cache = cache::make('core', 'roledefs');
    $cache->purge();
}

/**
 * Clears accesslib's private cache of a specific role or roles. ONLY BE USED FROM THIS LIBRARY FILE!
 *
 * This reset does not touch global $USER.
 *
 * @access private
 * @param int|array $roles
 * @return void
 */
function accesslib_clear_role_cache($roles) {
    global $ACCESSLIB_PRIVATE;

    if (!is_array($roles)) {
        $roles = [$roles];
    }

    foreach ($roles as $role) {
        if (isset($ACCESSLIB_PRIVATE->cacheroledefs[$role])) {
            unset($ACCESSLIB_PRIVATE->cacheroledefs[$role]);
        }
    }

    $cache = cache::make('core', 'roledefs');
    $cache->delete_many($roles);
}

/**
 * Role is assigned at system context.
 *
 * @access private
 * @param int $roleid
 * @return array
 */
function get_role_access($roleid) {
    $accessdata = get_empty_accessdata();
    $accessdata['ra']['/'.SYSCONTEXTID] = array((int)$roleid => (int)$roleid);
    return $accessdata;
}

/**
 * Fetch raw "site wide" role definitions.
 * Even MUC static acceleration cache appears a bit slow for this.
 * Important as can be hit hundreds of times per page.
 *
 * @param array $roleids List of role ids to fetch definitions for.
 * @return array Complete definition for each requested role.
 */
function get_role_definitions(array $roleids) {
    global $ACCESSLIB_PRIVATE;

    if (empty($roleids)) {
        return array();
    }

    // Grab all keys we have not yet got in our static cache.
    if ($uncached = array_diff($roleids, array_keys($ACCESSLIB_PRIVATE->cacheroledefs))) {
        $cache = cache::make('core', 'roledefs');
        foreach ($cache->get_many($uncached) as $roleid => $cachedroledef) {
            if (is_array($cachedroledef)) {
                $ACCESSLIB_PRIVATE->cacheroledefs[$roleid] = $cachedroledef;
            }
        }

        // Check we have the remaining keys from the MUC.
        if ($uncached = array_diff($roleids, array_keys($ACCESSLIB_PRIVATE->cacheroledefs))) {
            $uncached = get_role_definitions_uncached($uncached);
            $ACCESSLIB_PRIVATE->cacheroledefs += $uncached;
            $cache->set_many($uncached);
        }
    }

    // Return just the roles we need.
    return array_intersect_key($ACCESSLIB_PRIVATE->cacheroledefs, array_flip($roleids));
}

/**
 * Query raw "site wide" role definitions.
 *
 * @param array $roleids List of role ids to fetch definitions for.
 * @return array Complete definition for each requested role.
 */
function get_role_definitions_uncached(array $roleids) {
    global $DB;

    if (empty($roleids)) {
        return array();
    }

    // Create a blank results array: even if a role has no capabilities,
    // we need to ensure it is included in the results to show we have
    // loaded all the capabilities that there are.
    $rdefs = array();
    foreach ($roleids as $roleid) {
        $rdefs[$roleid] = array();
    }

    // Load all the capabilities for these roles in all contexts.
    list($sql, $params) = $DB->get_in_or_equal($roleids);
    $sql = "SELECT ctx.path, rc.roleid, rc.capability, rc.permission
              FROM {role_capabilities} rc
              JOIN {context} ctx ON rc.contextid = ctx.id
              JOIN {capabilities} cap ON rc.capability = cap.name
             WHERE rc.roleid $sql";
    $rs = $DB->get_recordset_sql($sql, $params);

    // Store the capabilities into the expected data structure.
    foreach ($rs as $rd) {
        if (!isset($rdefs[$rd->roleid][$rd->path])) {
            $rdefs[$rd->roleid][$rd->path] = array();
        }
        $rdefs[$rd->roleid][$rd->path][$rd->capability] = (int) $rd->permission;
    }

    $rs->close();

    // Sometimes (e.g. get_user_capability_course_helper::get_capability_info_at_each_context)
    // we process role definitinons in a way that requires we see parent contexts
    // before child contexts. This sort ensures that works (and is faster than
    // sorting in the SQL query).
    foreach ($rdefs as $roleid => $rdef) {
        ksort($rdefs[$roleid]);
    }

    return $rdefs;
}

/**
 * Get the default guest role, this is used for guest account,
 * search engine spiders, etc.
 *
 * @return stdClass role record
 */
function get_guest_role() {
    global $CFG, $DB;

    if (empty($CFG->guestroleid)) {
        if ($roles = $DB->get_records('role', array('archetype'=>'guest'))) {
            $guestrole = array_shift($roles);   // Pick the first one
            set_config('guestroleid', $guestrole->id);
            return $guestrole;
        } else {
            debugging('Can not find any guest role!');
            return false;
        }
    } else {
        if ($guestrole = $DB->get_record('role', array('id'=>$CFG->guestroleid))) {
            return $guestrole;
        } else {
            // somebody is messing with guest roles, remove incorrect setting and try to find a new one
            set_config('guestroleid', '');
            return get_guest_role();
        }
    }
}

/**
 * Check whether a user has a particular capability in a given context.
 *
 * For example:
 *      $context = context_module::instance($cm->id);
 *      has_capability('mod/forum:replypost', $context)
 *
 * By default checks the capabilities of the current user, but you can pass a
 * different userid. By default will return true for admin users, but you can override that with the fourth argument.
 *
 * Guest and not-logged-in users can never get any dangerous capability - that is any write capability
 * or capabilities with XSS, config or data loss risks.
 *
 * @category access
 *
 * @param string $capability the name of the capability to check. For example mod/forum:view
 * @param context $context the context to check the capability in. You normally get this with instance method of a context class.
 * @param integer|stdClass $user A user id or object. By default (null) checks the permissions of the current user.
 * @param boolean $doanything If false, ignores effect of admin role assignment
 * @return boolean true if the user has this capability. Otherwise false.
 */
function has_capability($capability, context $context, $user = null, $doanything = true) {
    global $USER, $CFG, $SCRIPT, $ACCESSLIB_PRIVATE;

    if (during_initial_install()) {
        if ($SCRIPT === "/$CFG->admin/index.php"
                or $SCRIPT === "/$CFG->admin/cli/install.php"
                or $SCRIPT === "/$CFG->admin/cli/install_database.php"
                or (defined('BEHAT_UTIL') and BEHAT_UTIL)
                or (defined('PHPUNIT_UTIL') and PHPUNIT_UTIL)) {
            // we are in an installer - roles can not work yet
            return true;
        } else {
            return false;
        }
    }

    if (strpos($capability, 'moodle/legacy:') === 0) {
        throw new coding_exception('Legacy capabilities can not be used any more!');
    }

    if (!is_bool($doanything)) {
        throw new coding_exception('Capability parameter "doanything" is wierd, only true or false is allowed. This has to be fixed in code.');
    }

    // capability must exist
    if (!$capinfo = get_capability_info($capability)) {
        debugging('Capability "'.$capability.'" was not found! This has to be fixed in code.');
        return false;
    }

    if (!isset($USER->id)) {
        // should never happen
        $USER->id = 0;
        debugging('Capability check being performed on a user with no ID.', DEBUG_DEVELOPER);
    }

    // make sure there is a real user specified
    if ($user === null) {
        $userid = $USER->id;
    } else {
        $userid = is_object($user) ? $user->id : $user;
    }

    // make sure forcelogin cuts off not-logged-in users if enabled
    if (!empty($CFG->forcelogin) and $userid == 0) {
        return false;
    }

    // make sure the guest account and not-logged-in users never get any risky caps no matter what the actual settings are.
    if (($capinfo->captype === 'write') or ($capinfo->riskbitmask & (RISK_XSS | RISK_CONFIG | RISK_DATALOSS))) {
        if (isguestuser($userid) or $userid == 0) {
            return false;
        }
    }

    // Check whether context locking is enabled.
    if (!empty($CFG->contextlocking)) {
        if ($capinfo->captype === 'write' && $context->locked) {
            // Context locking applies to any write capability in a locked context.
            // It does not apply to moodle/site:managecontextlocks - this is to allow context locking to be unlocked.
            if ($capinfo->name !== 'moodle/site:managecontextlocks') {
                // It applies to all users who are not site admins.
                // It also applies to site admins when contextlockappliestoadmin is set.
                if (!is_siteadmin($userid) || !empty($CFG->contextlockappliestoadmin)) {
                    return false;
                }
            }
        }
    }

    // somehow make sure the user is not deleted and actually exists
    if ($userid != 0) {
        if ($userid == $USER->id and isset($USER->deleted)) {
            // this prevents one query per page, it is a bit of cheating,
            // but hopefully session is terminated properly once user is deleted
            if ($USER->deleted) {
                return false;
            }
        } else {
            if (!context_user::instance($userid, IGNORE_MISSING)) {
                // no user context == invalid userid
                return false;
            }
        }
    }

    // context path/depth must be valid
    if (empty($context->path) or $context->depth == 0) {
        // this should not happen often, each upgrade tries to rebuild the context paths
        debugging('Context id '.$context->id.' does not have valid path, please use context_helper::build_all_paths()');
        if (is_siteadmin($userid)) {
            return true;
        } else {
            return false;
        }
    }

    // Find out if user is admin - it is not possible to override the doanything in any way
    // and it is not possible to switch to admin role either.
    if ($doanything) {
        if (is_siteadmin($userid)) {
            if ($userid != $USER->id) {
                return true;
            }
            // make sure switchrole is not used in this context
            if (empty($USER->access['rsw'])) {
                return true;
            }
            $parts = explode('/', trim($context->path, '/'));
            $path = '';
            $switched = false;
            foreach ($parts as $part) {
                $path .= '/' . $part;
                if (!empty($USER->access['rsw'][$path])) {
                    $switched = true;
                    break;
                }
            }
            if (!$switched) {
                return true;
            }
            //ok, admin switched role in this context, let's use normal access control rules
        }
    }

    // Careful check for staleness...
    $context->reload_if_dirty();

    if ($USER->id == $userid) {
        if (!isset($USER->access)) {
            load_all_capabilities();
        }
        $access =& $USER->access;

    } else {
        // make sure user accessdata is really loaded
        get_user_accessdata($userid, true);
        $access =& $ACCESSLIB_PRIVATE->accessdatabyuser[$userid];
    }

    return has_capability_in_accessdata($capability, $context, $access);
}

/**
 * Check if the user has any one of several capabilities from a list.
 *
 * This is just a utility method that calls has_capability in a loop. Try to put
 * the capabilities that most users are likely to have first in the list for best
 * performance.
 *
 * @category access
 * @see has_capability()
 *
 * @param array $capabilities an array of capability names.
 * @param context $context the context to check the capability in. You normally get this with instance method of a context class.
 * @param integer|stdClass $user A user id or object. By default (null) checks the permissions of the current user.
 * @param boolean $doanything If false, ignore effect of admin role assignment
 * @return boolean true if the user has any of these capabilities. Otherwise false.
 */
function has_any_capability(array $capabilities, context $context, $user = null, $doanything = true) {
    foreach ($capabilities as $capability) {
        if (has_capability($capability, $context, $user, $doanything)) {
            return true;
        }
    }
    return false;
}

/**
 * Check if the user has all the capabilities in a list.
 *
 * This is just a utility method that calls has_capability in a loop. Try to put
 * the capabilities that fewest users are likely to have first in the list for best
 * performance.
 *
 * @category access
 * @see has_capability()
 *
 * @param array $capabilities an array of capability names.
 * @param context $context the context to check the capability in. You normally get this with instance method of a context class.
 * @param integer|stdClass $user A user id or object. By default (null) checks the permissions of the current user.
 * @param boolean $doanything If false, ignore effect of admin role assignment
 * @return boolean true if the user has all of these capabilities. Otherwise false.
 */
function has_all_capabilities(array $capabilities, context $context, $user = null, $doanything = true) {
    foreach ($capabilities as $capability) {
        if (!has_capability($capability, $context, $user, $doanything)) {
            return false;
        }
    }
    return true;
}

/**
 * Is course creator going to have capability in a new course?
 *
 * This is intended to be used in enrolment plugins before or during course creation,
 * do not use after the course is fully created.
 *
 * @category access
 *
 * @param string $capability the name of the capability to check.
 * @param context $context course or category context where is course going to be created
 * @param integer|stdClass $user A user id or object. By default (null) checks the permissions of the current user.
 * @return boolean true if the user will have this capability.
 *
 * @throws coding_exception if different type of context submitted
 */
function guess_if_creator_will_have_course_capability($capability, context $context, $user = null) {
    global $CFG;

    if ($context->contextlevel != CONTEXT_COURSE and $context->contextlevel != CONTEXT_COURSECAT) {
        throw new coding_exception('Only course or course category context expected');
    }

    if (has_capability($capability, $context, $user)) {
        // User already has the capability, it could be only removed if CAP_PROHIBIT
        // was involved here, but we ignore that.
        return true;
    }

    if (!has_capability('moodle/course:create', $context, $user)) {
        return false;
    }

    if (!enrol_is_enabled('manual')) {
        return false;
    }

    if (empty($CFG->creatornewroleid)) {
        return false;
    }

    if ($context->contextlevel == CONTEXT_COURSE) {
        if (is_viewing($context, $user, 'moodle/role:assign') or is_enrolled($context, $user, 'moodle/role:assign')) {
            return false;
        }
    } else {
        if (has_capability('moodle/course:view', $context, $user) and has_capability('moodle/role:assign', $context, $user)) {
            return false;
        }
    }

    // Most likely they will be enrolled after the course creation is finished,
    // does the new role have the required capability?
    list($neededroles, $forbiddenroles) = get_roles_with_cap_in_context($context, $capability);
    return isset($neededroles[$CFG->creatornewroleid]);
}

/**
 * Check if the user is an admin at the site level.
 *
 * Please note that use of proper capabilities is always encouraged,
 * this function is supposed to be used from core or for temporary hacks.
 *
 * @category access
 *
 * @param  int|stdClass  $user_or_id user id or user object
 * @return bool true if user is one of the administrators, false otherwise
 */
function is_siteadmin($user_or_id = null) {
    global $CFG, $USER;

    if ($user_or_id === null) {
        $user_or_id = $USER;
    }

    if (empty($user_or_id)) {
        return false;
    }
    if (!empty($user_or_id->id)) {
        $userid = $user_or_id->id;
    } else {
        $userid = $user_or_id;
    }

    // Because this script is called many times (150+ for course page) with
    // the same parameters, it is worth doing minor optimisations. This static
    // cache stores the value for a single userid, saving about 2ms from course
    // page load time without using significant memory. As the static cache
    // also includes the value it depends on, this cannot break unit tests.
    static $knownid, $knownresult, $knownsiteadmins;
    if ($knownid === $userid && $knownsiteadmins === $CFG->siteadmins) {
        return $knownresult;
    }
    $knownid = $userid;
    $knownsiteadmins = $CFG->siteadmins;

    $siteadmins = explode(',', $CFG->siteadmins);
    $knownresult = in_array($userid, $siteadmins);
    return $knownresult;
}

/**
 * Returns true if user has at least one role assign
 * of 'coursecontact' role (is potentially listed in some course descriptions).
 *
 * @param int $userid
 * @return bool
 */
function has_coursecontact_role($userid) {
    global $DB, $CFG;

    if (empty($CFG->coursecontact)) {
        return false;
    }
    $sql = "SELECT 1
              FROM {role_assignments}
             WHERE userid = :userid AND roleid IN ($CFG->coursecontact)";
    return $DB->record_exists_sql($sql, array('userid'=>$userid));
}

/**
 * Does the user have a capability to do something?
 *
 * Walk the accessdata array and return true/false.
 * Deals with prohibits, role switching, aggregating
 * capabilities, etc.
 *
 * The main feature of here is being FAST and with no
 * side effects.
 *
 * Notes:
 *
 * Switch Role merges with default role
 * ------------------------------------
 * If you are a teacher in course X, you have at least
 * teacher-in-X + defaultloggedinuser-sitewide. So in the
 * course you'll have techer+defaultloggedinuser.
 * We try to mimic that in switchrole.
 *
 * Permission evaluation
 * ---------------------
 * Originally there was an extremely complicated way
 * to determine the user access that dealt with
 * "locality" or role assignments and role overrides.
 * Now we simply evaluate access for each role separately
 * and then verify if user has at least one role with allow
 * and at the same time no role with prohibit.
 *
 * @access private
 * @param string $capability
 * @param context $context
 * @param array $accessdata
 * @return bool
 */
function has_capability_in_accessdata($capability, context $context, array &$accessdata) {
    global $CFG;

    // Build $paths as a list of current + all parent "paths" with order bottom-to-top
    $path = $context->path;
    $paths = array($path);
    while ($path = rtrim($path, '0123456789')) {
        $path = rtrim($path, '/');
        if ($path === '') {
            break;
        }
        $paths[] = $path;
    }

    $roles = array();
    $switchedrole = false;

    // Find out if role switched
    if (!empty($accessdata['rsw'])) {
        // From the bottom up...
        foreach ($paths as $path) {
            if (isset($accessdata['rsw'][$path])) {
                // Found a switchrole assignment - check for that role _plus_ the default user role
                $roles = array($accessdata['rsw'][$path]=>null, $CFG->defaultuserroleid=>null);
                $switchedrole = true;
                break;
            }
        }
    }

    if (!$switchedrole) {
        // get all users roles in this context and above
        foreach ($paths as $path) {
            if (isset($accessdata['ra'][$path])) {
                foreach ($accessdata['ra'][$path] as $roleid) {
                    $roles[$roleid] = null;
                }
            }
        }
    }

    // Now find out what access is given to each role, going bottom-->up direction
    $rdefs = get_role_definitions(array_keys($roles));
    $allowed = false;

    foreach ($roles as $roleid => $ignored) {
        foreach ($paths as $path) {
            if (isset($rdefs[$roleid][$path][$capability])) {
                $perm = (int)$rdefs[$roleid][$path][$capability];
                if ($perm === CAP_PROHIBIT) {
                    // any CAP_PROHIBIT found means no permission for the user
                    return false;
                }
                if (is_null($roles[$roleid])) {
                    $roles[$roleid] = $perm;
                }
            }
        }
        // CAP_ALLOW in any role means the user has a permission, we continue only to detect prohibits
        $allowed = ($allowed or $roles[$roleid] === CAP_ALLOW);
    }

    return $allowed;
}

/**
 * A convenience function that tests has_capability, and displays an error if
 * the user does not have that capability.
 *
 * NOTE before Moodle 2.0, this function attempted to make an appropriate
 * require_login call before checking the capability. This is no longer the case.
 * You must call require_login (or one of its variants) if you want to check the
 * user is logged in, before you call this function.
 *
 * @see has_capability()
 *
 * @param string $capability the name of the capability to check. For example mod/forum:view
 * @param context $context the context to check the capability in. You normally get this with context_xxxx::instance().
 * @param int $userid A user id. By default (null) checks the permissions of the current user.
 * @param bool $doanything If false, ignore effect of admin role assignment
 * @param string $errormessage The error string to to user. Defaults to 'nopermissions'.
 * @param string $stringfile The language file to load the error string from. Defaults to 'error'.
 * @return void terminates with an error if the user does not have the given capability.
 */
function require_capability($capability, context $context, $userid = null, $doanything = true,
                            $errormessage = 'nopermissions', $stringfile = '') {
    if (!has_capability($capability, $context, $userid, $doanything)) {
        throw new required_capability_exception($context, $capability, $errormessage, $stringfile);
    }
}

/**
 * Return a nested array showing all role assignments for the user.
 * [ra] => [contextpath][roleid] = roleid
 *
 * @access private
 * @param int $userid - the id of the user
 * @return array access info array
 */
function get_user_roles_sitewide_accessdata($userid) {
    global $CFG, $DB;

    $accessdata = get_empty_accessdata();

    // start with the default role
    if (!empty($CFG->defaultuserroleid)) {
        $syscontext = context_system::instance();
        $accessdata['ra'][$syscontext->path][(int)$CFG->defaultuserroleid] = (int)$CFG->defaultuserroleid;
    }

    // load the "default frontpage role"
    if (!empty($CFG->defaultfrontpageroleid)) {
        $frontpagecontext = context_course::instance(get_site()->id);
        if ($frontpagecontext->path) {
            $accessdata['ra'][$frontpagecontext->path][(int)$CFG->defaultfrontpageroleid] = (int)$CFG->defaultfrontpageroleid;
        }
    }

    // Preload every assigned role.
    $sql = "SELECT ctx.path, ra.roleid, ra.contextid
              FROM {role_assignments} ra
              JOIN {context} ctx ON ctx.id = ra.contextid
             WHERE ra.userid = :userid";

    $rs = $DB->get_recordset_sql($sql, array('userid' => $userid));

    foreach ($rs as $ra) {
        // RAs leafs are arrays to support multi-role assignments...
        $accessdata['ra'][$ra->path][(int)$ra->roleid] = (int)$ra->roleid;
    }

    $rs->close();

    return $accessdata;
}

/**
 * Returns empty accessdata structure.
 *
 * @access private
 * @return array empt accessdata
 */
function get_empty_accessdata() {
    $accessdata               = array(); // named list
    $accessdata['ra']         = array();
    $accessdata['time']       = time();
    $accessdata['rsw']        = array();

    return $accessdata;
}

/**
 * Get accessdata for a given user.
 *
 * @access private
 * @param int $userid
 * @param bool $preloadonly true means do not return access array
 * @return array accessdata
 */
function get_user_accessdata($userid, $preloadonly=false) {
    global $CFG, $ACCESSLIB_PRIVATE, $USER;

    if (isset($USER->access)) {
        $ACCESSLIB_PRIVATE->accessdatabyuser[$USER->id] = $USER->access;
    }

    if (!isset($ACCESSLIB_PRIVATE->accessdatabyuser[$userid])) {
        if (empty($userid)) {
            if (!empty($CFG->notloggedinroleid)) {
                $accessdata = get_role_access($CFG->notloggedinroleid);
            } else {
                // weird
                return get_empty_accessdata();
            }

        } else if (isguestuser($userid)) {
            if ($guestrole = get_guest_role()) {
                $accessdata = get_role_access($guestrole->id);
            } else {
                //weird
                return get_empty_accessdata();
            }

        } else {
            // Includes default role and frontpage role.
            $accessdata = get_user_roles_sitewide_accessdata($userid);
        }

        $ACCESSLIB_PRIVATE->accessdatabyuser[$userid] = $accessdata;
    }

    if ($preloadonly) {
        return;
    } else {
        return $ACCESSLIB_PRIVATE->accessdatabyuser[$userid];
    }
}

/**
 * A convenience function to completely load all the capabilities
 * for the current user. It is called from has_capability() and functions change permissions.
 *
 * Call it only _after_ you've setup $USER and called check_enrolment_plugins();
 * @see check_enrolment_plugins()
 *
 * @access private
 * @return void
 */
function load_all_capabilities() {
    global $USER;

    // roles not installed yet - we are in the middle of installation
    if (during_initial_install()) {
        return;
    }

    if (!isset($USER->id)) {
        // this should not happen
        $USER->id = 0;
    }

    unset($USER->access);
    $USER->access = get_user_accessdata($USER->id);

    // Clear to force a refresh
    unset($USER->mycourses);

    // init/reset internal enrol caches - active course enrolments and temp access
    $USER->enrol = array('enrolled'=>array(), 'tempguest'=>array());
}

/**
 * A convenience function to completely reload all the capabilities
 * for the current user when roles have been updated in a relevant
 * context -- but PRESERVING switchroles and loginas.
 * This function resets all accesslib and context caches.
 *
 * That is - completely transparent to the user.
 *
 * Note: reloads $USER->access completely.
 *
 * @access private
 * @return void
 */
function reload_all_capabilities() {
    global $USER, $DB, $ACCESSLIB_PRIVATE;

    // copy switchroles
    $sw = array();
    if (!empty($USER->access['rsw'])) {
        $sw = $USER->access['rsw'];
    }

    accesslib_clear_all_caches(true);
    unset($USER->access);

    // Prevent dirty flags refetching on this page.
    $ACCESSLIB_PRIVATE->dirtycontexts = array();
    $ACCESSLIB_PRIVATE->dirtyusers    = array($USER->id => false);

    load_all_capabilities();

    foreach ($sw as $path => $roleid) {
        if ($record = $DB->get_record('context', array('path'=>$path))) {
            $context = context::instance_by_id($record->id);
            if (has_capability('moodle/role:switchroles', $context)) {
                role_switch($roleid, $context);
            }
        }
    }
}

/**
 * Adds a temp role to current USER->access array.
 *
 * Useful for the "temporary guest" access we grant to logged-in users.
 * This is useful for enrol plugins only.
 *
 * @since Moodle 2.2
 * @param context_course $coursecontext
 * @param int $roleid
 * @return void
 */
function load_temp_course_role(context_course $coursecontext, $roleid) {
    global $USER, $SITE;

    if (empty($roleid)) {
        debugging('invalid role specified in load_temp_course_role()');
        return;
    }

    if ($coursecontext->instanceid == $SITE->id) {
        debugging('Can not use temp roles on the frontpage');
        return;
    }

    if (!isset($USER->access)) {
        load_all_capabilities();
    }

    $coursecontext->reload_if_dirty();

    if (isset($USER->access['ra'][$coursecontext->path][$roleid])) {
        return;
    }

    $USER->access['ra'][$coursecontext->path][(int)$roleid] = (int)$roleid;
}

/**
 * Removes any extra guest roles from current USER->access array.
 * This is useful for enrol plugins only.
 *
 * @since Moodle 2.2
 * @param context_course $coursecontext
 * @return void
 */
function remove_temp_course_roles(context_course $coursecontext) {
    global $DB, $USER, $SITE;

    if ($coursecontext->instanceid == $SITE->id) {
        debugging('Can not use temp roles on the frontpage');
        return;
    }

    if (empty($USER->access['ra'][$coursecontext->path])) {
        //no roles here, weird
        return;
    }

    $sql = "SELECT DISTINCT ra.roleid AS id
              FROM {role_assignments} ra
             WHERE ra.contextid = :contextid AND ra.userid = :userid";
    $ras = $DB->get_records_sql($sql, array('contextid'=>$coursecontext->id, 'userid'=>$USER->id));

    $USER->access['ra'][$coursecontext->path] = array();
    foreach ($ras as $r) {
        $USER->access['ra'][$coursecontext->path][(int)$r->id] = (int)$r->id;
    }
}

/**
 * Returns array of all role archetypes.
 *
 * @return array
 */
function get_role_archetypes() {
    return array(
        'manager'        => 'manager',
        'coursecreator'  => 'coursecreator',
        'editingteacher' => 'editingteacher',
        'teacher'        => 'teacher',
        'student'        => 'student',
        'guest'          => 'guest',
        'user'           => 'user',
        'frontpage'      => 'frontpage'
    );
}

/**
 * Assign the defaults found in this capability definition to roles that have
 * the corresponding legacy capabilities assigned to them.
 *
 * @param string $capability
 * @param array $legacyperms an array in the format (example):
 *                      'guest' => CAP_PREVENT,
 *                      'student' => CAP_ALLOW,
 *                      'teacher' => CAP_ALLOW,
 *                      'editingteacher' => CAP_ALLOW,
 *                      'coursecreator' => CAP_ALLOW,
 *                      'manager' => CAP_ALLOW
 * @return boolean success or failure.
 */
function assign_legacy_capabilities($capability, $legacyperms) {

    $archetypes = get_role_archetypes();

    foreach ($legacyperms as $type => $perm) {

        $systemcontext = context_system::instance();
        if ($type === 'admin') {
            debugging('Legacy type admin in access.php was renamed to manager, please update the code.');
            $type = 'manager';
        }

        if (!array_key_exists($type, $archetypes)) {
            print_error('invalidlegacy', '', '', $type);
        }

        if ($roles = get_archetype_roles($type)) {
            foreach ($roles as $role) {
                // Assign a site level capability.
                if (!assign_capability($capability, $perm, $role->id, $systemcontext->id)) {
                    return false;
                }
            }
        }
    }
    return true;
}

/**
 * Verify capability risks.
 *
 * @param stdClass $capability a capability - a row from the capabilities table.
 * @return boolean whether this capability is safe - that is, whether people with the
 *      safeoverrides capability should be allowed to change it.
 */
function is_safe_capability($capability) {
    return !((RISK_DATALOSS | RISK_MANAGETRUST | RISK_CONFIG | RISK_XSS | RISK_PERSONAL) & $capability->riskbitmask);
}

/**
 * Get the local override (if any) for a given capability in a role in a context
 *
 * @param int $roleid
 * @param int $contextid
 * @param string $capability
 * @return stdClass local capability override
 */
function get_local_override($roleid, $contextid, $capability) {
    global $DB;

    return $DB->get_record_sql("
        SELECT rc.*
          FROM {role_capabilities} rc
          JOIN {capability} cap ON rc.capability = cap.name
         WHERE rc.roleid = :roleid AND rc.capability = :capability AND rc.contextid = :contextid", [
            'roleid' => $roleid,
            'contextid' => $contextid,
            'capability' => $capability,

        ]);
}

/**
 * Returns context instance plus related course and cm instances
 *
 * @param int $contextid
 * @return array of ($context, $course, $cm)
 */
function get_context_info_array($contextid) {
    global $DB;

    $context = context::instance_by_id($contextid, MUST_EXIST);
    $course  = null;
    $cm      = null;

    if ($context->contextlevel == CONTEXT_COURSE) {
        $course = $DB->get_record('course', array('id'=>$context->instanceid), '*', MUST_EXIST);

    } else if ($context->contextlevel == CONTEXT_MODULE) {
        $cm = get_coursemodule_from_id('', $context->instanceid, 0, false, MUST_EXIST);
        $course = $DB->get_record('course', array('id'=>$cm->course), '*', MUST_EXIST);

    } else if ($context->contextlevel == CONTEXT_BLOCK) {
        $parent = $context->get_parent_context();

        if ($parent->contextlevel == CONTEXT_COURSE) {
            $course = $DB->get_record('course', array('id'=>$parent->instanceid), '*', MUST_EXIST);
        } else if ($parent->contextlevel == CONTEXT_MODULE) {
            $cm = get_coursemodule_from_id('', $parent->instanceid, 0, false, MUST_EXIST);
            $course = $DB->get_record('course', array('id'=>$cm->course), '*', MUST_EXIST);
        }
    }

    return array($context, $course, $cm);
}

/**
 * Function that creates a role
 *
 * @param string $name role name
 * @param string $shortname role short name
 * @param string $description role description
 * @param string $archetype
 * @return int id or dml_exception
 */
function create_role($name, $shortname, $description, $archetype = '') {
    global $DB;

    if (strpos($archetype, 'moodle/legacy:') !== false) {
        throw new coding_exception('Use new role archetype parameter in create_role() instead of old legacy capabilities.');
    }

    // verify role archetype actually exists
    $archetypes = get_role_archetypes();
    if (empty($archetypes[$archetype])) {
        $archetype = '';
    }

    // Insert the role record.
    $role = new stdClass();
    $role->name        = $name;
    $role->shortname   = $shortname;
    $role->description = $description;
    $role->archetype   = $archetype;

    //find free sortorder number
    $role->sortorder = $DB->get_field('role', 'MAX(sortorder) + 1', array());
    if (empty($role->sortorder)) {
        $role->sortorder = 1;
    }
    $id = $DB->insert_record('role', $role);

    return $id;
}

/**
 * Function that deletes a role and cleanups up after it
 *
 * @param int $roleid id of role to delete
 * @return bool always true
 */
function delete_role($roleid) {
    global $DB;

    // first unssign all users
    role_unassign_all(array('roleid'=>$roleid));

    // cleanup all references to this role, ignore errors
    $DB->delete_records('role_capabilities',   array('roleid'=>$roleid));
    $DB->delete_records('role_allow_assign',   array('roleid'=>$roleid));
    $DB->delete_records('role_allow_assign',   array('allowassign'=>$roleid));
    $DB->delete_records('role_allow_override', array('roleid'=>$roleid));
    $DB->delete_records('role_allow_override', array('allowoverride'=>$roleid));
    $DB->delete_records('role_names',          array('roleid'=>$roleid));
    $DB->delete_records('role_context_levels', array('roleid'=>$roleid));

    // Get role record before it's deleted.
    $role = $DB->get_record('role', array('id'=>$roleid));

    // Finally delete the role itself.
    $DB->delete_records('role', array('id'=>$roleid));

    // Trigger event.
    $event = \core\event\role_deleted::create(
        array(
            'context' => context_system::instance(),
            'objectid' => $roleid,
            'other' =>
                array(
                    'shortname' => $role->shortname,
                    'description' => $role->description,
                    'archetype' => $role->archetype
                )
            )
        );
    $event->add_record_snapshot('role', $role);
    $event->trigger();

    // Reset any cache of this role, including MUC.
    accesslib_clear_role_cache($roleid);

    return true;
}

/**
 * Function to write context specific overrides, or default capabilities.
 *
 * @param string $capability string name
 * @param int $permission CAP_ constants
 * @param int $roleid role id
 * @param int|context $contextid context id
 * @param bool $overwrite
 * @return bool always true or exception
 */
function assign_capability($capability, $permission, $roleid, $contextid, $overwrite = false) {
    global $USER, $DB;

    if ($contextid instanceof context) {
        $context = $contextid;
    } else {
        $context = context::instance_by_id($contextid);
    }

    // Capability must exist.
    if (!$capinfo = get_capability_info($capability)) {
        throw new coding_exception("Capability '{$capability}' was not found! This has to be fixed in code.");
    }

    if (empty($permission) || $permission == CAP_INHERIT) { // if permission is not set
        unassign_capability($capability, $roleid, $context->id);
        return true;
    }

    $existing = $DB->get_record('role_capabilities', array('contextid'=>$context->id, 'roleid'=>$roleid, 'capability'=>$capability));

    if ($existing and !$overwrite) {   // We want to keep whatever is there already
        return true;
    }

    $cap = new stdClass();
    $cap->contextid    = $context->id;
    $cap->roleid       = $roleid;
    $cap->capability   = $capability;
    $cap->permission   = $permission;
    $cap->timemodified = time();
    $cap->modifierid   = empty($USER->id) ? 0 : $USER->id;

    if ($existing) {
        $cap->id = $existing->id;
        $DB->update_record('role_capabilities', $cap);
    } else {
        if ($DB->record_exists('context', array('id'=>$context->id))) {
            $DB->insert_record('role_capabilities', $cap);
        }
    }

    // Trigger capability_assigned event.
    \core\event\capability_assigned::create([
        'userid' => $cap->modifierid,
        'context' => $context,
        'objectid' => $roleid,
        'other' => [
            'capability' => $capability,
            'oldpermission' => $existing->permission ?? CAP_INHERIT,
            'permission' => $permission
        ]
    ])->trigger();

    // Reset any cache of this role, including MUC.
    accesslib_clear_role_cache($roleid);

    return true;
}

/**
 * Unassign a capability from a role.
 *
 * @param string $capability the name of the capability
 * @param int $roleid the role id
 * @param int|context $contextid null means all contexts
 * @return boolean true or exception
 */
function unassign_capability($capability, $roleid, $contextid = null) {
    global $DB, $USER;

    // Capability must exist.
    if (!$capinfo = get_capability_info($capability)) {
        throw new coding_exception("Capability '{$capability}' was not found! This has to be fixed in code.");
    }

    if (!empty($contextid)) {
        if ($contextid instanceof context) {
            $context = $contextid;
        } else {
            $context = context::instance_by_id($contextid);
        }
        // delete from context rel, if this is the last override in this context
        $DB->delete_records('role_capabilities', array('capability'=>$capability, 'roleid'=>$roleid, 'contextid'=>$context->id));
    } else {
        $DB->delete_records('role_capabilities', array('capability'=>$capability, 'roleid'=>$roleid));
    }

    // Trigger capability_assigned event.
    \core\event\capability_unassigned::create([
        'userid' => $USER->id,
        'context' => $context ?? context_system::instance(),
        'objectid' => $roleid,
        'other' => [
            'capability' => $capability,
        ]
    ])->trigger();

    // Reset any cache of this role, including MUC.
    accesslib_clear_role_cache($roleid);

    return true;
}

/**
 * Get the roles that have a given capability assigned to it
 *
 * This function does not resolve the actual permission of the capability.
 * It just checks for permissions and overrides.
 * Use get_roles_with_cap_in_context() if resolution is required.
 *
 * @param string $capability capability name (string)
 * @param string $permission optional, the permission defined for this capability
 *                      either CAP_ALLOW, CAP_PREVENT or CAP_PROHIBIT. Defaults to null which means any.
 * @param stdClass $context null means any
 * @return array of role records
 */
function get_roles_with_capability($capability, $permission = null, $context = null) {
    global $DB;

    if ($context) {
        $contexts = $context->get_parent_context_ids(true);
        l…

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