[moodle.git] / lib / accesslib.php

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

/**
 * 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_siteadmin()
 *
 * What courses has this user access to?
 * - get_enrolled_users()
 *
 * What users can do X in this context?
 * - get_users_by_capability()
 *
 * 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_access_sitewide()
 * - load_course_context()
 * - load_role_access_by_context()
 * - etc.
 *
 * <b>Name conventions</b>
 *
 * "ctx" means context
 *
 * <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-capabilities-perm sets
 * (role defs) and a list of courses we have loaded
 * data for.
 *
 * 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>
 *
 * Role definitions are stored like this
 * (no cap merge is done - so it's compact)
 *
 * <code>
 * $accessdata['rdef']["$contextpath:$roleid"]['mod/forum:viewpost'] = 1
 *                                            ['mod/forum:editallpost'] = -1
 *                                            ['mod/forum:startdiscussion'] = -1000
 * </code>
 *
 * See how has_capability_in_accessdata() walks up the tree.
 *
 * First we only load rdef and ra down to the course level, but not below.
 * This keeps accessdata small and compact. Below-the-course ra/rdef
 * are loaded as needed. We keep track of which courses we have loaded ra/rdef in
 * <code>
 * $accessdata['loaded'] = array($courseid1=>1, $courseid2=>1)
 * </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
 * @subpackage role
 * @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 scritped 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 otehrs 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 */
define('ROLENAME_ORIGINAL', 0);
/** rolename displays - the name as defined by a role alias */
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);

/** maximum size of context cache - it is possible to tweak this config.php or in any script before inclusion of context.php */
if (!defined('CONTEXT_CACHE_MAX_SIZE')) {
    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.
 *
 * @private
 * @global stdClass $ACCESSLIB_PRIVATE
 * @name $ACCESSLIB_PRIVATE
 */
global $ACCESSLIB_PRIVATE;
$ACCESSLIB_PRIVATE = new stdClass();
$ACCESSLIB_PRIVATE->dirtycontexts    = null;    // Dirty contexts cache, loaded from DB once per page
$ACCESSLIB_PRIVATE->accessdatabyuser = array(); // Holds the cache of $accessdata structure for users (including $USER)
$ACCESSLIB_PRIVATE->rolepermissions  = array(); // role permissions cache - helps a lot with mem usage
$ACCESSLIB_PRIVATE->capabilities     = null;    // detailed information about the capabilities

/**
 * 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.
 *
 * @return void
 */
function accesslib_clear_all_caches_for_unit_testing() {
    global $UNITTEST, $USER;
    if (empty($UNITTEST->running)) {
        throw new coding_exception('You must not call clear_all_caches outside of unit tests.');
    }

    accesslib_clear_all_caches(true);

    unset($USER->access);
}

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

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

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

/**
 * Gets the accessdata for role "sitewide" (system down to course)
 *
 * @private
 * @param int $roleid
 * @return array
 */
function get_role_access($roleid) {
    global $DB, $ACCESSLIB_PRIVATE;

    /* Get it in 1 DB query...
     * - relevant role caps at the root and down
     *   to the course level - but not below
     */

    //TODO: MUC - this could be cached in shared memory to speed up first page loading, web crawlers, etc.

    $accessdata = get_empty_accessdata();

    $accessdata['ra']['/'.SYSCONTEXTID] = array((int)$roleid => (int)$roleid);

    //
    // Overrides for the role IN ANY CONTEXTS
    // down to COURSE - not below -
    //
    $sql = "SELECT ctx.path,
                   rc.capability, rc.permission
              FROM {context} ctx
              JOIN {role_capabilities} rc ON rc.contextid = ctx.id
         LEFT JOIN {context} cctx
                   ON (cctx.contextlevel = ".CONTEXT_COURSE." AND ctx.path LIKE ".$DB->sql_concat('cctx.path',"'/%'").")
             WHERE rc.roleid = ? AND cctx.id IS NULL";
    $params = array($roleid);

    // we need extra caching in CLI scripts and cron
    $rs = $DB->get_recordset_sql($sql, $params);
    foreach ($rs as $rd) {
        $k = "{$rd->path}:{$roleid}";
        $accessdata['rdef'][$k][$rd->capability] = (int)$rd->permission;
    }
    $rs->close();

    // share the role definitions
    foreach ($accessdata['rdef'] as $k=>$unused) {
        if (!isset($ACCESSLIB_PRIVATE->rolepermissions[$k])) {
            $ACCESSLIB_PRIVATE->rolepermissions[$k] = $accessdata['rdef'][$k];
        }
        $accessdata['rdef_count']++;
        $accessdata['rdef'][$k] =& $ACCESSLIB_PRIVATE->rolepermissions[$k];
    }

    return $accessdata;
}

/**
 * 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 = get_context_instance(CONTEXT_MODULE, $cm->id);
 *      has_capability('mod/forum:replypost',$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.
 *
 * @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 {@link get_context_instance}.
 * @param integer|object $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") {
            // 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;
    }

    // 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;
        }
    }

    // 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 build_context_path()');
        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];
    }


    // Load accessdata for below-the-course context if necessary,
    // all contexts at and above all courses are already loaded
    if ($context->contextlevel != CONTEXT_COURSE and $coursecontext = $context->get_course_context(false)) {
        load_course_context($userid, $coursecontext, $access);
    }

    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.
 *
 * @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 {@link get_context_instance}.
 * @param integer $userid A user id. 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, $userid = null, $doanything = true) {
    foreach ($capabilities as $capability) {
        if (has_capability($capability, $context, $userid, $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.
 *
 * @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 {@link get_context_instance}.
 * @param integer $userid A user id. 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, $userid = null, $doanything = true) {
    foreach ($capabilities as $capability) {
        if (!has_capability($capability, $context, $userid, $doanything)) {
            return false;
        }
    }
    return true;
}

/**
 * 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.
 *
 * @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;
    }

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

/**
 * 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.
 *
 * @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
    $allowed = false;
    foreach ($roles as $roleid => $ignored) {
        foreach ($paths as $path) {
            if (isset($accessdata['rdef']["{$path}:$roleid"][$capability])) {
                $perm = (int)$accessdata['rdef']["{$path}:$roleid"][$capability];
                if ($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 {@link get_context_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 role assignments
 * all relevant role capabilities for the user at
 * site/course_category/course levels
 *
 * We do _not_ delve deeper than courses because the number of
 * overrides at the module/block levels can be HUGE.
 *
 * [ra]   => [/path][roleid]=roleid
 * [rdef] => [/path:roleid][capability]=permission
 *
 * @private
 * @param int $userid - the id of the user
 * @return array access info array
 */
function get_user_access_sitewide($userid) {
    global $CFG, $DB, $ACCESSLIB_PRIVATE;

    /* Get in a few cheap DB queries...
     * - role assignments
     * - relevant role caps
     *   - above and within this user's RAs
     *   - below this user's RAs - limited to course level
     */

    // raparents collects paths & roles we need to walk up the parenthood to build the minimal rdef
    $raparents = array();
    $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;
        $raparents[$CFG->defaultuserroleid][$syscontext->id] = $syscontext->id;
    }

    // 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;
            $raparents[$CFG->defaultfrontpageroleid][$frontpagecontext->id] = $frontpagecontext->id;
        }
    }

    // preload every assigned role at and above course context
    $sql = "SELECT ctx.path, ra.roleid, ra.contextid
              FROM {role_assignments} ra
              JOIN {context} ctx
                   ON ctx.id = ra.contextid
         LEFT JOIN {block_instances} bi
                   ON (ctx.contextlevel = ".CONTEXT_BLOCK." AND bi.id = ctx.instanceid)
         LEFT JOIN {context} bpctx
                   ON (bpctx.id = bi.parentcontextid)
             WHERE ra.userid = :userid
                   AND (ctx.contextlevel <= ".CONTEXT_COURSE." OR bpctx.contextlevel < ".CONTEXT_COURSE.")";
    $params = array('userid'=>$userid);
    $rs = $DB->get_recordset_sql($sql, $params);
    foreach ($rs as $ra) {
        // RAs leafs are arrays to support multi-role assignments...
        $accessdata['ra'][$ra->path][(int)$ra->roleid] = (int)$ra->roleid;
        $raparents[$ra->roleid][$ra->contextid] = $ra->contextid;
    }
    $rs->close();

    if (empty($raparents)) {
        return $accessdata;
    }

    // now get overrides of interesting roles in all interesting child contexts
    // hopefully we will not run out of SQL limits here,
    // users would have to have very many roles at/above course context...
    $sqls = array();
    $params = array();

    static $cp = 0;
    foreach ($raparents as $roleid=>$ras) {
        $cp++;
        list($sqlcids, $cids) = $DB->get_in_or_equal($ras, SQL_PARAMS_NAMED, 'c'.$cp.'_');
        $params = array_merge($params, $cids);
        $params['r'.$cp] = $roleid;
        $sqls[] = "(SELECT ctx.path, rc.roleid, rc.capability, rc.permission
                     FROM {role_capabilities} rc
                     JOIN {context} ctx
                          ON (ctx.id = rc.contextid)
                     JOIN {context} pctx
                          ON (pctx.id $sqlcids
                              AND (ctx.id = pctx.id
                                   OR ctx.path LIKE ".$DB->sql_concat('pctx.path',"'/%'")."
                                   OR pctx.path LIKE ".$DB->sql_concat('ctx.path',"'/%'")."))
                LEFT JOIN {block_instances} bi
                          ON (ctx.contextlevel = ".CONTEXT_BLOCK." AND bi.id = ctx.instanceid)
                LEFT JOIN {context} bpctx
                          ON (bpctx.id = bi.parentcontextid)
                    WHERE rc.roleid = :r{$cp}
                          AND (ctx.contextlevel <= ".CONTEXT_COURSE." OR bpctx.contextlevel < ".CONTEXT_COURSE.")
                   )";
    }

    // fixed capability order is necessary for rdef dedupe
    $rs = $DB->get_recordset_sql(implode("\nUNION\n", $sqls). "ORDER BY capability", $params);

    foreach ($rs as $rd) {
        $k = $rd->path.':'.$rd->roleid;
        $accessdata['rdef'][$k][$rd->capability] = (int)$rd->permission;
    }
    $rs->close();

    // share the role definitions
    foreach ($accessdata['rdef'] as $k=>$unused) {
        if (!isset($ACCESSLIB_PRIVATE->rolepermissions[$k])) {
            $ACCESSLIB_PRIVATE->rolepermissions[$k] = $accessdata['rdef'][$k];
        }
        $accessdata['rdef_count']++;
        $accessdata['rdef'][$k] =& $ACCESSLIB_PRIVATE->rolepermissions[$k];
    }

    return $accessdata;
}

/**
 * Add to the access ctrl array the data needed by a user for a given course.
 *
 * This function injects all course related access info into the accessdata array.
 *
 * @private
 * @param int $userid the id of the user
 * @param context_course $coursecontext course context
 * @param array $accessdata accessdata array (modified)
 * @return void modifies $accessdata parameter
 */
function load_course_context($userid, context_course $coursecontext, &$accessdata) {
    global $DB, $CFG, $ACCESSLIB_PRIVATE;

    if (empty($coursecontext->path)) {
        // weird, this should not happen
        return;
    }

    if (isset($accessdata['loaded'][$coursecontext->instanceid])) {
        // already loaded, great!
        return;
    }

    $roles = array();

    if (empty($userid)) {
        if (!empty($CFG->notloggedinroleid)) {
            $roles[$CFG->notloggedinroleid] = $CFG->notloggedinroleid;
        }

    } else if (isguestuser($userid)) {
        if ($guestrole = get_guest_role()) {
            $roles[$guestrole->id] = $guestrole->id;
        }

    } else {
        // Interesting role assignments at, above and below the course context
        list($parentsaself, $params) = $DB->get_in_or_equal($coursecontext->get_parent_context_ids(true), SQL_PARAMS_NAMED, 'pc_');
        $params['userid'] = $userid;
        $params['children'] = $coursecontext->path."/%";
        $sql = "SELECT ra.*, ctx.path
                  FROM {role_assignments} ra
                  JOIN {context} ctx ON ra.contextid = ctx.id
                 WHERE ra.userid = :userid AND (ctx.id $parentsaself OR ctx.path LIKE :children)";
        $rs = $DB->get_recordset_sql($sql, $params);

        // add missing role definitions
        foreach ($rs as $ra) {
            $accessdata['ra'][$ra->path][(int)$ra->roleid] = (int)$ra->roleid;
            $roles[$ra->roleid] = $ra->roleid;
        }
        $rs->close();

        // add the "default frontpage role" when on the frontpage
        if (!empty($CFG->defaultfrontpageroleid)) {
            $frontpagecontext = context_course::instance(get_site()->id);
            if ($frontpagecontext->id == $coursecontext->id) {
                $roles[$CFG->defaultfrontpageroleid] = $CFG->defaultfrontpageroleid;
            }
        }

        // do not forget the default role
        if (!empty($CFG->defaultuserroleid)) {
            $roles[$CFG->defaultuserroleid] = $CFG->defaultuserroleid;
        }
    }

    if (!$roles) {
        // weird, default roles must be missing...
        $accessdata['loaded'][$coursecontext->instanceid] = 1;
        return;
    }

    // now get overrides of interesting roles in all interesting contexts (this course + children + parents)
    $params = array('c'=>$coursecontext->id);
    list($parentsaself, $rparams) = $DB->get_in_or_equal($coursecontext->get_parent_context_ids(true), SQL_PARAMS_NAMED, 'pc_');
    $params = array_merge($params, $rparams);
    list($roleids, $rparams) = $DB->get_in_or_equal($roles, SQL_PARAMS_NAMED, 'r_');
    $params = array_merge($params, $rparams);

    $sql = "SELECT ctx.path, rc.roleid, rc.capability, rc.permission
                 FROM {role_capabilities} rc
                 JOIN {context} ctx
                      ON (ctx.id = rc.contextid)
                 JOIN {context} cctx
                      ON (cctx.id = :c
                          AND (ctx.id $parentsaself OR ctx.path LIKE ".$DB->sql_concat('cctx.path',"'/%'")."))
                WHERE rc.roleid $roleids
             ORDER BY rc.capability"; // fixed capability order is necessary for rdef dedupe
    $rs = $DB->get_recordset_sql($sql, $params);

    $newrdefs = array();
    foreach ($rs as $rd) {
        $k = $rd->path.':'.$rd->roleid;
        if (isset($accessdata['rdef'][$k])) {
            continue;
        }
        $newrdefs[$k][$rd->capability] = (int)$rd->permission;
    }
    $rs->close();

    // share new role definitions
    foreach ($newrdefs as $k=>$unused) {
        if (!isset($ACCESSLIB_PRIVATE->rolepermissions[$k])) {
            $ACCESSLIB_PRIVATE->rolepermissions[$k] = $newrdefs[$k];
        }
        $accessdata['rdef_count']++;
        $accessdata['rdef'][$k] =& $ACCESSLIB_PRIVATE->rolepermissions[$k];
    }

    $accessdata['loaded'][$coursecontext->instanceid] = 1;

    // we want to deduplicate the USER->access from time to time, this looks like a good place,
    // because we have to do it before the end of session
    dedupe_user_access();
}

/**
 * Add to the access ctrl array the data needed by a role for a given context.
 *
 * The data is added in the rdef key.
 * This role-centric function is useful for role_switching
 * and temporary course roles.
 *
 * @private
 * @param int $roleid the id of the user
 * @param context $context needs path!
 * @param array $accessdata accessdata array (is modified)
 * @return array
 */
function load_role_access_by_context($roleid, context $context, &$accessdata) {
    global $DB, $ACCESSLIB_PRIVATE;

    /* Get the relevant rolecaps into rdef
     * - relevant role caps
     *   - at ctx and above
     *   - below this ctx
     */

    if (empty($context->path)) {
        // weird, this should not happen
        return;
    }

    list($parentsaself, $params) = $DB->get_in_or_equal($context->get_parent_context_ids(true), SQL_PARAMS_NAMED, 'pc_');
    $params['roleid'] = $roleid;
    $params['childpath'] = $context->path.'/%';

    $sql = "SELECT ctx.path, rc.capability, rc.permission
              FROM {role_capabilities} rc
              JOIN {context} ctx ON (rc.contextid = ctx.id)
             WHERE rc.roleid = :roleid AND (ctx.id $parentsaself OR ctx.path LIKE :childpath)
          ORDER BY rc.capability"; // fixed capability order is necessary for rdef dedupe
    $rs = $DB->get_recordset_sql($sql, $params);

    $newrdefs = array();
    foreach ($rs as $rd) {
        $k = $rd->path.':'.$roleid;
        if (isset($accessdata['rdef'][$k])) {
            continue;
        }
        $newrdefs[$k][$rd->capability] = (int)$rd->permission;
    }
    $rs->close();

    // share new role definitions
    foreach ($newrdefs as $k=>$unused) {
        if (!isset($ACCESSLIB_PRIVATE->rolepermissions[$k])) {
            $ACCESSLIB_PRIVATE->rolepermissions[$k] = $newrdefs[$k];
        }
        $accessdata['rdef_count']++;
        $accessdata['rdef'][$k] =& $ACCESSLIB_PRIVATE->rolepermissions[$k];
    }
}

/**
 * Returns empty accessdata structure.
 *
 * @private
 * @return array empt accessdata
 */
function get_empty_accessdata() {
    $accessdata               = array(); // named list
    $accessdata['ra']         = array();
    $accessdata['rdef']       = array();
    $accessdata['rdef_count'] = 0;       // this bloody hack is necessary because count($array) is slooooowwww in PHP
    $accessdata['rdef_lcc']   = 0;       // rdef_count during the last compression
    $accessdata['loaded']     = array(); // loaded course contexts
    $accessdata['time']       = time();

    return $accessdata;
}

/**
 * Get accessdata for a given user.
 *
 * @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 (!empty($USER->acces['rdef']) and empty($ACCESSLIB_PRIVATE->rolepermissions)) {
        // share rdef from USER session with rolepermissions cache in order to conserve memory
        foreach($USER->acces['rdef'] as $k=>$v) {
            $ACCESSLIB_PRIVATE->rolepermissions[$k] =& $USER->acces['rdef'][$k];
        }
        $ACCESSLIB_PRIVATE->accessdatabyuser[$USER->id] = $USER->acces;
    }

    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 {
            $accessdata = get_user_access_sitewide($userid); // includes default role and frontpage role
        }

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

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

/**
 * Try to minimise the size of $USER->access by eliminating duplicate override storage,
 * this function looks for contexts with the same overrides and shares them.
 *
 * @private
 * @return void
 */
function dedupe_user_access() {
    global $USER;

    if (CLI_SCRIPT) {
        // no session in CLI --> no compression necessary
        return;
    }

    if (empty($USER->access['rdef_count'])) {
        // weird, this should not happen
        return;
    }

    // the rdef is growing only, we never remove stuff from it, the rdef_lcc helps us to detect new stuff in rdef
    if ($USER->access['rdef_count'] - $USER->access['rdef_lcc'] > 10) {
        // do not compress after each change, wait till there is more stuff to be done
        return;
    }

    $hashmap = array();
    foreach ($USER->access['rdef'] as $k=>$def) {
        $hash = sha1(serialize($def));
        if (isset($hashmap[$hash])) {
            $USER->access['rdef'][$k] =& $hashmap[$hash];
        } else {
            $hashmap[$hash] =& $USER->access['rdef'][$k];
        }
    }

    $USER->access['rdef_lcc'] = $USER->access['rdef_count'];
}

/**
 * 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()
 *
 * @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);

    // deduplicate the overrides to minimize session size
    dedupe_user_access();

    // 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.
 *
 * @private
 * @return void
 */
function reload_all_capabilities() {
    global $USER, $DB, $ACCESSLIB_PRIVATE;

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

    accesslib_clear_all_caches(true);
    unset($USER->access);
    $ACCESSLIB_PRIVATE->dirtycontexts = array(); // prevent dirty flags refetching on this page

    load_all_capabilities();

    foreach ($sw as $path => $roleid) {
        if ($record = $DB->get_record('context', array('path'=>$path))) {
            $context = context::instance_by_id($record->id);
            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.
 * @since 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;
    }

    // load course stuff first
    load_course_context($USER->id, $coursecontext, $USER->access);

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

    load_role_access_by_context($roleid, $coursecontext, $USER->access);
}

/**
 * Removes any extra guest roles from current USER->access array.
 * @since 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 object $capability a capability - a row from the capabilities table.
 * @return boolean whether this capability is safe - that is, whether people with the
 *      safeoverrides capability should be allowed to change it.
 */
function is_safe_capability($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 $DB->get_record('role_capabilities', array('roleid'=>$roleid, 'capability'=>$capability, 'contextid'=>$contextid));
}

/**
 * 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));

    // finally delete the role itself
    // get this before the name is gone for logging
    $rolename = $DB->get_field('role', 'name', array('id'=>$roleid));

    $DB->delete_records('role', array('id'=>$roleid));

    add_to_log(SITEID, 'role', 'delete', 'admin/roles/action=delete&roleid='.$roleid, $rolename, '');

    return true;
}

/**
 * Function to write context specific overrides, or default capabilities.
 *
 * NOTE: use $context->mark_dirty() after this
 *
 * @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);
    }

    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);
        }
    }
    return true;
}

/**
 * Unassign a capability from a role.
 *
 * NOTE: use $context->mark_dirty() after this
 *
 * @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;

    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));
    }
    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 = $context->get_parent_context_ids(true);
        list($insql, $params) = $DB->get_in_or_equal($contexts, SQL_PARAMS_NAMED, 'ctx');
        $contextsql = "AND rc.contextid $insql";
    } else {
        $params = array();
        $contextsql = '';
    }

    if ($permission) {
        $permissionsql = " AND rc.permission = :permission";
        $params['permission'] = $permission;
    } else {
        $permissionsql = '';
    }

    $sql = "SELECT r.*
              FROM {role} r
             WHERE r.id IN (SELECT rc.roleid
                              FROM {role_capabilities} rc
                             WHERE rc.capability = :capname
                                   $contextsql
                                   $permissionsql)";
    $params['capname'] = $capability;


    return $DB->get_records_sql($sql, $params);
}

/**
 * This function makes a role-assignment (a role for a user in a particular context)
 *
 * @param int $roleid the role of the id
 * @param int $userid userid
 * @param int|context $contextid id of the context
 * @param string $component example 'enrol_ldap', defaults to '' which means manual assignment,
 * @param int $itemid id of enrolment/auth plugin
 * @param string $timemodified defaults to current time
 * @return int new/existing id of the assignment
 */
function role_assign($roleid, $userid, $contextid, $component = '', $itemid = 0, $timemodified = '') {
    global $USER, $DB;

    // first of all detect if somebody is using old style parameters
    if ($contextid === 0 or is_numeric($component)) {
        throw new coding_exception('Invalid call to role_assign(), code needs to be updated to use new order of parameters');
    }

    // now validate all parameters
    if (empty($roleid)) {
        throw new coding_exception('Invalid call to role_assign(), roleid can not be empty');
    }

    if (empty($userid)) {
        throw new coding_exception('Invalid call to role_assign(), userid can not be empty');
    }

    if ($itemid) {
        if (strpos($component, '_') === false) {
            throw new coding_exception('Invalid call to role_assign(), component must start with plugin type such as"enrol_" when itemid specified', 'component:'.$component);
        }
    } else {
        $itemid = 0;
        if ($component !== '' and strpos($component, '_') === false) {
            throw new coding_exception('Invalid call to role_assign(), invalid component string', 'component:'.$component);
        }
    }

    if (!$DB->record_exists('user', array('id'=>$userid, 'deleted'=>0))) {
        throw new coding_exception('User ID does not exist or is deleted!', 'userid:'.$userid);
    }

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

    if (!$timemodified) {
        $timemodified = time();
    }

/// Check for existing entry
    $ras = $DB->get_records('role_assignments', array('roleid'=>$roleid, 'contextid'=>$context->id, 'userid'=>$userid, 'component'=>$component, 'itemid'=>$itemid), 'id');

    if ($ras) {
        // role already assigned - this should not happen
        if (count($ras) > 1) {
            // very weird - remove all duplicates!
            $ra = array_shift($ras);
            foreach ($ras as $r) {
                $DB->delete_records('role_assignments', array('id'=>$r->id));
            }
        } else {
            $ra = reset($ras);
        }

        // actually there is no need to update, reset anything or trigger any event, so just return
        return $ra->id;
    }

    // Create a new entry
    $ra = new stdClass();
    $ra->roleid       = $roleid;
    $ra->contextid    = $context->id;
    $ra->userid       = $userid;
    $ra->component    = $component;
    $ra->itemid       = $itemid;
    $ra->timemodified = $timemodified;
    $ra->modifierid   = empty($USER->id) ? 0 : $USER->id;

    $ra->id = $DB->insert_record('role_assignments', $ra);

    // mark context as dirty - again expensive, but needed
    $context->mark_dirty();

    if (!empty($USER->id) && $USER->id == $userid) {
        // If the user is the current user, then do full reload of capabilities too.
        reload_all_capabilities();
    }

    events_trigger('role_assigned', $ra);

    return $ra->id;
}

/**
 * Removes one role assignment
 *
 * @param int $roleid
 * @param int  $userid
 * @param int|context  $contextid
 * @param string $component
 * @param int  $itemid
 * @return void
 */
function role_unassign($roleid, $userid, $contextid, $component = '', $itemid = 0) {
    // first make sure the params make sense
    if ($roleid == 0 or $userid == 0 or $contextid == 0) {
        throw new coding_exception('Invalid call to role_unassign(), please use role_unassign_all() when removing multiple role assignments');
    }

    if ($itemid) {
        if (strpos($component, '_') === false) {
            throw new coding_exception('Invalid call to role_assign(), component must start with plugin type such as "enrol_" when itemid specified', 'component:'.$component);
        }
    } else {
        $itemid = 0;
        if ($component !== '' and strpos($component, '_') === false) {
            throw new coding_exception('Invalid call to role_assign(), invalid component string', 'component:'.$component);
        }
    }

    role_unassign_all(array('roleid'=>$roleid, 'userid'=>$userid, 'contextid'=>$contextid, 'component'=>$component, 'itemid'=>$itemid), false, false);
}

/**
 * Removes multiple role assignments, parameters may contain:
 *   'roleid', 'userid', 'contextid', 'component', 'enrolid'.
 *
 * @param array $params role assignment parameters
 * @param bool $subcontexts unassign in subcontexts too
 * @param bool $includemanual include manual role assignments too
 * @return void
 */
function role_unassign_all(array $params, $subcontexts = false, $includemanual = false) {
    global $USER, $CFG, $DB;

    if (!$params) {
        throw new coding_exception('Missing parameters in role_unsassign_all() call');
    }

    $allowed = array('roleid', 'userid', 'contextid', 'component', 'itemid');
    foreach ($params as $key=>$value) {
        if (!in_array($key, $allowed)) {
            throw new coding_exception('Unknown role_unsassign_all() parameter key', 'key:'.$key);
        }
    }

    if (isset($params['component']) and $params['component'] !== '' and strpos($params['component'], '_') === false) {
        throw new coding_exception('Invalid component paramter in role_unsassign_all() call', 'component:'.$params['component']);
    }

    if ($includemanual) {
        if (!isset($params['component']) or $params['component'] === '') {
            throw new coding_exception('include manual parameter requires component parameter in role_unsassign_all() call');
        }
    }

    if ($subcontexts) {
        if (empty($params['contextid'])) {
            throw new coding_exception('subcontexts paramtere requires component parameter in role_unsassign_all() call');
        }
    }

    $ras = $DB->get_records('role_assignments', $params);
    foreach($ras as $ra) {
        $DB->delete_records('role_assignments', array('id'=>$ra->id));
        if ($context = context::instance_by_id($ra->contextid, IGNORE_MISSING)) {
            // this is a bit expensive but necessary
            $context->mark_dirty();
            /// If the user is the current user, then do full reload of capabilities too.
            if (!empty($USER->id) && $USER->id == $ra->userid) {
                reload_all_capabilities();
            }
        }
        events_trigger('role_unassigned', $ra);
    }
    unset($ras);

    // process subcontexts
    if ($subcontexts and $context = context::instance_by_id($params['contextid'], IGNORE_MISSING)) {
        if ($params['contextid'] instanceof context) {
            $context = $params['contextid'];
        } else {
            $context = context::instance_by_id($params['contextid'], IGNORE_MISSING);
        }

        if ($context) {
            $contexts = $context->get_child_contexts();
            $mparams = $params;
            foreach($contexts as $context) {
                $mparams['contextid'] = $context->id;
                $ras = $DB->get_records('role_assignments', $mparams);
                foreach($ras as $ra) {
                    $DB->delete_records('role_assignments', array('id'=>$ra->id));
                    // this is a bit expensive but necessary
                    $context->mark_dirty();
                    /// If the user is the current user, then do full reload of capabilities too.
                    if (!empty($USER->id) && $USER->id == $ra->userid) {
                        reload_all_capabilities();
                    }
                    events_trigger('role_unassigned', $ra);
                }
            }
        }
    }

    // do this once more for all manual role assignments
    if ($includemanual) {
        $params['component'] = '';
        role_unassign_all($params, $subcontexts, false);
    }
}

/**
 * Determines if a user is currently logged in
 *
 * @return bool
 */
function isloggedin() {
    global $USER;

    return (!empty($USER->id));
}

/**
 * Determines if a user is logged in as real guest user with username 'guest'.
 *
 * @param int|object $user mixed user object or id, $USER if not specified
 * @return bool true if user is the real guest user, false if not logged in or other user
 */
function isguestuser($user = null) {
    global $USER, $DB, $CFG;

    // make sure we have the user id cached in config table, because we are going to use it a lot
    if (empty($CFG->siteguest)) {
        if (!$guestid = $DB->get_field('user', 'id', array('username'=>'guest', 'mnethostid'=>$CFG->mnet_localhost_id))) {
            // guest does not exist yet, weird
            return false;
        }
        set_config('siteguest', $guestid);
    }
    if ($user === null) {
        $user = $USER;
    }

    if ($user === null) {
        // happens when setting the $USER
        return false;

    } else if (is_numeric($user)) {
        return ($CFG->siteguest == $user);

    } else if (is_object($user)) {
        if (empty($user->id)) {
            return false; // not logged in means is not be guest
        } else {
            return ($CFG->siteguest == $user->id);
        }

    } else {
        throw new coding_exception('Invalid user parameter supplied for isguestuser() function!');
    }
}

/**
 * Does user have a (temporary or real) guest access to course?
 *
 * @param context $context
 * @param stdClass|int $user
 * @return bool
 */
function is_guest(context $context, $user = null) {
    global $USER;

    // first find the course context
    $coursecontext = $context->get_course_context();

    // make sure there is a real user specified
    if ($user === null) {
        $userid = isset($USER->id) ? $USER->id : 0;
    } else {
        $userid = is_object($user) ? $user->id : $user;
    }

    if (isguestuser($userid)) {
        // can not inspect or be enrolled
        return true;
    }

    if (has_capability('moodle/course:view', $coursecontext, $user)) {
        // viewing users appear out of nowhere, they are neither guests nor participants
        return false;
    }

    // consider only real active enrolments here
    if (is_enrolled($coursecontext, $user, '', true)) {
        return false;
    }

    return true;
}

/**
 * Returns true if the user has moodle/course:view capability in the course,
 * this is intended for admins, managers (aka small admins), inspectors, etc.
 *
 * @param context $context
 * @param int|stdClass $user, if null $USER is used
 * @param string $withcapability extra capability name
 * @return bool
 */
function is_viewing(context $context, $user = null, $withcapability = '') {
    // first find the course context
    $coursecontext = $context->get_course_context();

    if (isguestuser($user)) {
        // can not inspect
        return false;
    }

    if (!has_capability('moodle/course:view', $coursecontext, $user)) {
        // admins are allowed to inspect courses
        return false;
    }

    if ($withcapability and !has_capability($withcapability, $context, $user)) {
        // site admins always have the capability, but the enrolment above blocks
        return false;
    }

    return true;
}

/**
 * Returns true if user is enrolled (is participating) in course
 * this is intended for students and teachers.
 *
 * Since 2.2 the result for active enrolments and current user are cached.
 *
 * @param context $context
 * @param int|stdClass $user, if null $USER is used, otherwise user object or id expected
 * @param string $withcapability extra capability name
 * @param bool $onlyactive consider only active enrolments in enabled plugins and time restrictions
 * @return bool
 */
function is_enrolled(context $context, $user = null, $withcapability = '', $onlyactive = false) {
    global $USER, $DB;

    // first find the course context
    $coursecontext = $context->get_course_context();

    // make sure there is a real user specified
    if ($user === null) {
        $userid = isset($USER->id) ? $USER->id : 0;
    } else {
        $userid = is_object($user) ? $user->id : $user;
    }

    if (empty($userid)) {
        // not-logged-in!
        return false;
    } else if (isguestuser($userid)) {
        // guest account can not be enrolled anywhere
        return false;
    }

    if ($coursecontext->instanceid == SITEID) {
        // everybody participates on frontpage
    } else {
        // try cached info first - the enrolled flag is set only when active enrolment present
        if ($USER->id == $userid) {
            $coursecontext->reload_if_dirty();
            if (isset($USER->enrol['enrolled'][$coursecontext->instanceid])) {
                if ($USER->enrol['enrolled'][$coursecontext->instanceid] > time()) {
                    return true;
                }
            }
        }

        if ($onlyactive) {
            // look for active enrolments only
            $until = enrol_get_enrolment_end($coursecontext->instanceid, $userid);

            if ($until === false) {
                return false;
            }

            if ($USER->id == $userid) {
                if ($until == 0) {
                    $until = ENROL_MAX_TIMESTAMP;
                }
                $USER->enrol['enrolled'][$coursecontext->instanceid] = $until;
                if (isset($USER->enrol['tempguest'][$coursecontext->instanceid])) {
                    unset($USER->enrol['tempguest'][$coursecontext->instanceid]);
                    remove_temp_course_roles($coursecontext);
                }
            }

        } else {
            // any enrolment is good for us here, even outdated, disabled or inactive
            $sql = "SELECT 'x'
                      FROM {user_enrolments} ue
                      JOIN {enrol} e ON (e.id = ue.enrolid AND e.courseid = :courseid)
                      JOIN {user} u ON u.id = ue.userid
                     WHERE ue.userid = :userid AND u.deleted = 0";
            $params = array('userid'=>$userid, 'courseid'=>$coursecontext->instanceid);
            if (!$DB->record_exists_sql($sql, $params)) {
                return false;
            }
        }
    }

    if ($withcapability and !has_capability($withcapability, $context, $userid)) {
        return false;
    }

    return true;
}

/**
 * Returns true if the user is able to access the course.
 *
 * This function is in no way, shape, or form a substitute for require_login.
 * It should only be used in circumstances where it is not possible to call require_login
 * such as the navigation.
 *
 * This function checks many of the methods of access to a course such as the view
 * capability, enrollments, and guest access. It also makes use of the cache
 * generated by require_login for guest access.
 *
 * The flags within the $USER object that are used here should NEVER be used outside
 * of this function can_access_course and require_login. Doing so WILL break future
 * versions.
 *
 * @param stdClass $course record
 * @param stdClass|int|null $user user record or id, current user if null
 * @param string $withcapability Check for this capability as well.
 * @param bool $onlyactive consider only active enrolments in enabled plugins and time restrictions
 * @return boolean Returns true if the user is able to access the course
 */
function can_access_course(stdClass $course, $user = null, $withcapability = '', $onlyactive = false) {
    global $DB, $USER;

    // this function originally accepted $coursecontext parameter
    if ($course instanceof context) {
        if ($course instanceof context_course) {
            debugging('deprecated context parameter, please use $course record');
            $coursecontext = $course;
            $course = $DB->get_record('course', array('id'=>$coursecontext->instanceid));
        } else {
            debugging('Invalid context parameter, please use $course record');
            return false;
        }
    } else {
        $coursecontext = context_course::instance($course->id);
    }

    if (!isset($USER->id)) {
        // should never happen
        $USER->id = 0;
    }

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

    if ($withcapability and !has_capability($withcapability, $coursecontext, $userid)) {
        return false;
    }

    if ($userid == $USER->id) {
        if (!empty($USER->access['rsw'][$coursecontext->path])) {
            // the fact that somebody switched role means they can access the course no matter to what role they switched
            return true;
        }
    }

    if (!$course->visible and !has_capability('moodle/course:viewhiddencourses', $coursecontext, $userid)) {
        return false;
    }

    if (is_viewing($coursecontext, $userid)) {
        return true;
    }

    if ($userid != $USER->id) {
        // for performance reasons we do not verify temporary guest access for other users, sorry...
        return is_enrolled($coursecontext, $userid, '', $onlyactive);
    }

    // === from here we deal only with $USER ===

    $coursecontext->reload_if_dirty();

    if (isset($USER->enrol['enrolled'][$course->id])) {
        if ($USER->enrol['enrolled'][$course->id] > time()) {
            return true;
        }
    }
    if (isset($USER->enrol['tempguest'][$course->id])) {
        if ($USER->enrol['tempguest'][$course->id] > time()) {
            return true;
        }
    }

    if (is_enrolled($coursecontext, $USER, '', $onlyactive)) {
        return true;
    }

    // if not enrolled try to gain temporary guest access
    $instances = $DB->get_records('enrol', array('courseid'=>$course->id, 'status'=>ENROL_INSTANCE_ENABLED), 'sortorder, id ASC');
    $enrols = enrol_get_plugins(true);
    foreach($instances as $instance) {
        if (!isset($enrols[$instance->enrol])) {
            continue;
        }
        // Get a duration for the guest access, a timestamp in the future, 0 (always) or false.
        $until = $enrols[$instance->enrol]->try_guestaccess($instance);
        if ($until !== false and $until > time()) {
            $USER->enrol['tempguest'][$course->id] = $until;
            return true;
        }
    }
    if (isset($USER->enrol['tempguest'][$course->id])) {
        unset($USER->enrol['tempguest'][$course->id]);
        remove_temp_course_roles($coursecontext);
    }

    return false;
}

/**
 * Returns array with sql code and parameters returning all ids
 * of users enrolled into course.
 *
 * This function is using 'eu[0-9]+_' prefix for table names and parameters.
 *
 * @param context $context
 * @param string $withcapability
 * @param int $groupid 0 means ignore groups, any other value limits the result by group id
 * @param bool $onlyactive consider only active enrolments in enabled plugins and time restrictions
 * @return array list($sql, $params)
 */
function get_enrolled_sql(context $context, $withcapability = '', $groupid = 0, $onlyactive = false) {
    global $DB, $CFG;

    // use unique prefix just in case somebody makes some SQL magic with the result
    static $i = 0;
    $i++;
    $prefix = 'eu'.$i.'_';

    // first find the course context
    $coursecontext = $context->get_course_context();

    $isfrontpage = ($coursecontext->instanceid == SITEID);

    $joins  = array();
    $wheres = array();
    $params = array();

    list($contextids, $contextpaths) = get_context_info_list($context);

    // get all relevant capability info for all roles
    if ($withcapability) {
        list($incontexts, $cparams) = $DB->get_in_or_equal($contextids, SQL_PARAMS_NAMED, 'ctx');
        $cparams['cap'] = $withcapability;

        $defs = array();
        $sql = "SELECT rc.id, rc.roleid, rc.permission, ctx.path
                  FROM {role_capabilities} rc
                  JOIN {context} ctx on rc.contextid = ctx.id
                 WHERE rc.contextid $incontexts AND rc.capability = :cap";
        $rcs = $DB->get_records_sql($sql, $cparams);
        foreach ($rcs as $rc) {
            $defs[$rc->path][$rc->roleid] = $rc->permission;
        }

        $access = array();
        if (!empty($defs)) {
            foreach ($contextpaths as $path) {
                if (empty($defs[$path])) {
                    continue;
                }
                foreach($defs[$path] as $roleid => $perm) {
                    if ($perm == CAP_PROHIBIT) {
                        $access[$roleid] = CAP_PROHIBIT;
                        continue;
                    }
                    if (!isset($access[$roleid])) {
                        $access[$roleid] = (int)$perm;
                    }
                }
            }
        }

        unset($defs);

        // make lists of roles that are needed and prohibited
        $needed     = array(); // one of these is enough
        $prohibited = array(); // must not have any of these
        foreach ($access as $roleid => $perm) {
            if ($perm == CAP_PROHIBIT) {
                unset($needed[$roleid]);
                $prohibited[$roleid] = true;
            } else if ($perm == CAP_ALLOW and empty($prohibited[$roleid])) {
                $needed[$roleid] = true;
            }
        }

        $defaultuserroleid      = isset($CFG->defaultuserroleid) ? $CFG->defaultuserroleid : 0;
        $defaultfrontpageroleid = isset($CFG->defaultfrontpageroleid) ? $CFG->defaultfrontpageroleid : 0;

        $nobody = false;

        if ($isfrontpage) {
            if (!empty($prohibited[$defaultuserroleid]) or !empty($prohibited[$defaultfrontpageroleid])) {
                $nobody = true;
            } else if (!empty($needed[$defaultuserroleid]) or !empty($needed[$defaultfrontpageroleid])) {
                // everybody not having prohibit has the capability
                $needed = array();
            } else if (empty($needed)) {
                $nobody = true;
            }
        } else {
            if (!empty($prohibited[$defaultuserroleid])) {
                $nobody = true;
            } else if (!empty($needed[$defaultuserroleid])) {
                // everybody not having prohibit has the capability
                $needed = array();
            } else if (empty($needed)) {
                $nobody = true;
            }
        }

        if ($nobody) {
            // nobody can match so return some SQL that does not return any results
            $wheres[] = "1 = 2";

        } else {

            if ($needed) {
                $ctxids = implode(',', $contextids);
                $roleids = implode(',', array_keys($needed));
                $joins[] = "JOIN {role_assignments} {$prefix}ra3 ON ({$prefix}ra3.userid = {$prefix}u.id AND {$prefix}ra3.roleid IN ($roleids) AND {$prefix}ra3.contextid IN ($ctxids))";
            }

            if ($prohibited) {
                $ctxids = implode(',', $contextids);
                $roleids = implode(',', array_keys($prohibited));
                $joins[] = "LEFT JOIN {role_assignments} {$prefix}ra4 ON ({$prefix}ra4.userid = {$prefix}u.id AND {$prefix}ra4.roleid IN ($roleids) AND {$prefix}ra4.contextid IN ($ctxids))";
                $wheres[] = "{$prefix}ra4.id IS NULL";
            }

            if ($groupid) {
                $joins[] = "JOIN {groups_members} {$prefix}gm ON ({$prefix}gm.userid = {$prefix}u.id AND {$prefix}gm.groupid = :{$prefix}gmid)";
                $params["{$prefix}gmid"] = $groupid;
            }
        }

    } else {
        if ($groupid) {
            $joins[] = "JOIN {groups_members} {$prefix}gm ON ({$prefix}gm.userid = {$prefix}u.id AND {$prefix}gm.groupid = :{$prefix}gmid)";
            $params["{$prefix}gmid"] = $groupid;
        }
    }

    $wheres[] = "{$prefix}u.deleted = 0 AND {$prefix}u.id <> :{$prefix}guestid";
    $params["{$prefix}guestid"] = $CFG->siteguest;

    if ($isfrontpage) {
        // all users are "enrolled" on the frontpage
    } else {
        $joins[] = "JOIN {user_enrolments} {$prefix}ue ON {$prefix}ue.userid = {$prefix}u.id";
        $joins[] = "JOIN {enrol} {$prefix}e ON ({$prefix}e.id = {$prefix}ue.enrolid AND {$prefix}e.courseid = :{$prefix}courseid)";
        $params[$prefix.'courseid'] = $coursecontext->instanceid;

        if ($onlyactive) {
            $wheres[] = "{$prefix}ue.status = :{$prefix}active AND {$prefix}e.status = :{$prefix}enabled";
            $wheres[] = "{$prefix}ue.timestart < :{$prefix}now1 AND ({$prefix}ue.timeend = 0 OR {$prefix}ue.timeend > :{$prefix}now2)";
            $now = round(time(), -2); // rounding helps caching in DB
            $params = array_merge($params, array($prefix.'enabled'=>ENROL_INSTANCE_ENABLED,
                                                 $prefix.'active'=>ENROL_USER_ACTIVE,
                                                 $prefix.'now1'=>$now, $prefix.'now2'=>$now));
        }
    }

    $joins = implode("\n", $joins);
    $wheres = "WHERE ".implode(" AND ", $wheres);

    $sql = "SELECT DISTINCT {$prefix}u.id
              FROM {user} {$prefix}u
            $joins
           $wheres";

    return array($sql, $params);
}

/**
 * Returns list of users enrolled into course.
 *
 * @param context $context
 * @param string $withcapability
 * @param int $groupid 0 means ignore groups, any other value limits the result by group id
 * @param string $userfields requested user record fields
 * @param string $orderby
 * @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).
 * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
 * @return array of user records
 */
function get_enrolled_users(context $context, $withcapability = '', $groupid = 0, $userfields = 'u.*', $orderby = '', $limitfrom = 0, $limitnum = 0) {
    global $DB;

    list($esql, $params) = get_enrolled_sql($context, $withcapability, $groupid);
    $sql = "SELECT $userfields
              FROM {user} u
              JOIN ($esql) je ON je.id = u.id
             WHERE u.deleted = 0";

    if ($orderby) {
        $sql = "$sql ORDER BY $orderby";
    } else {
        $sql = "$sql ORDER BY u.lastname ASC, u.firstname ASC";
    }

    return $DB->get_records_sql($sql, $params, $limitfrom, $limitnum);
}

/**
 * Counts list of users enrolled into course (as per above function)
 *
 * @param context $context
 * @param string $withcapability
 * @param int $groupid 0 means ignore groups, any other value limits the result by group id
 * @return array of user records
 */
function count_enrolled_users(context $context, $withcapability = '', $groupid = 0) {
    global $DB;

    list($esql, $params) = get_enrolled_sql($context, $withcapability, $groupid);
    $sql = "SELECT count(u.id)
              FROM {user} u
              JOIN ($esql) je ON je.id = u.id
             WHERE u.deleted = 0";

    return $DB->count_records_sql($sql, $params);
}

/**
 * Loads the capability definitions for the component (from file).
 *
 * Loads the capability definitions for the component (from file). If no
 * capabilities are defined for the component, we simply return an empty array.
 *
 * @param string $component full plugin name, examples: 'moodle', 'mod_forum'
 * @return array array of capabilities
 */
function load_capability_def($component) {
    $defpath = get_component_directory($component).'/db/access.php';

    $capabilities = array();
    if (file_exists($defpath)) {
        require($defpath);
        if (!empty(${$component.'_capabilities'})) {
            // BC capability array name
            // since 2.0 we prefer $capabilities instead - it is easier to use and matches db/* files
            debugging('componentname_capabilities array is deprecated, please use $capabilities array only in access.php files');
            $capabilities = ${$component.'_capabilities'};
        }
    }

    return $capabilities;
}

/**
 * Gets the capabilities that have been cached in the database for this component.
 *
 * @param string $component - examples: 'moodle', 'mod_forum'
 * @return array array of capabilities
 */
function get_cached_capabilities($component = 'moodle') {
    global $DB;
    return $DB->get_records('capabilities', array('component'=>$component));
}

/**
 * Returns default capabilities for given role archetype.
 *
 * @param string $archetype role archetype
 * @return array
 */
function get_default_capabilities($archetype) {
    global $DB;

    if (!$archetype) {
        return array();
    }

    $alldefs = array();
    $defaults = array();
    $components = array();
    $allcaps = $DB->get_records('capabilities');

    foreach ($allcaps as $cap) {
        if (!in_array($cap->component, $components)) {
            $components[] = $cap->component;
            $alldefs = array_merge($alldefs, load_capability_def($cap->component));
        }
    }
    foreach($alldefs as $name=>$def) {
        // Use array 'archetypes if available. Only if not specified, use 'legacy'.
        if (isset($def['archetypes'])) {
            if (isset($def['archetypes'][$archetype])) {
                $defaults[$name] = $def['archetypes'][$archetype];
            }
        // 'legacy' is for backward compatibility with 1.9 access.php
        } else {
            if (isset($def['legacy'][$archetype])) {
                $defaults[$name] = $def['legacy'][$archetype];
            }
        }
    }

    return $defaults;
}

/**
 * Reset role capabilities to default according to selected role archetype.
 * If no archetype selected, removes all capabilities.
 *
 * @param int $roleid
 * @return void
 */
function reset_role_capabilities($roleid) {
    global $DB;

    $role = $DB->get_record('role', array('id'=>$roleid), '*', MUST_EXIST);
    $defaultcaps = get_default_capabilities($role->archetype);

    $systemcontext = context_system::instance();

    $DB->delete_records('role_capabilities', array('roleid'=>$roleid));

    foreach($defaultcaps as $cap=>$permission) {
        assign_capability($cap, $permission, $roleid, $systemcontext->id);
    }
}

/**
 * Updates the capabilities table with the component capability definitions.
 * If no parameters are given, the function updates the core moodle
 * capabilities.
 *
 * Note that the absence of the db/access.php capabilities definition file
 * will cause any stored capabilities for the component to be removed from
 * the database.
 *
 * @param string $component examples: 'moodle', 'mod/forum', 'block/quiz_results'
 * @return boolean true if success, exception in case of any problems
 */
function update_capabilities($component = 'moodle') {
    global $DB, $OUTPUT;

    $storedcaps = array();

    $filecaps = load_capability_def($component);
    foreach($filecaps as $capname=>$unused) {
        if (!preg_match('|^[a-z]+/[a-z_0-9]+:[a-z_0-9]+$|', $capname)) {
            debugging("Coding problem: Invalid capability name '$capname', use 'clonepermissionsfrom' field for migration.");
        }
    }

    $cachedcaps = get_cached_capabilities($component);
    if ($cachedcaps) {
        foreach ($cachedcaps as $cachedcap) {
            array_push($storedcaps, $cachedcap->name);
            // update risk bitmasks and context levels in existing capabilities if needed
            if (array_key_exists($cachedcap->name, $filecaps)) {
                if (!array_key_exists('riskbitmask', $filecaps[$cachedcap->name])) {
                    $filecaps[$cachedcap->name]['riskbitmask'] = 0; // no risk if not specified
                }
                if ($cachedcap->captype != $filecaps[$cachedcap->name]['captype']) {
                    $updatecap = new stdClass();
                    $updatecap->id = $cachedcap->id;
                    $updatecap->captype = $filecaps[$cachedcap->name]['captype'];
                    $DB->update_record('capabilities', $updatecap);
                }
                if ($cachedcap->riskbitmask != $filecaps[$cachedcap->name]['riskbitmask']) {
                    $updatecap = new stdClass();
                    $updatecap->id = $cachedcap->id;
                    $updatecap->riskbitmask = $filecaps[$cachedcap->name]['riskbitmask'];
                    $DB->update_record('capabilities', $updatecap);
                }

                if (!array_key_exists('contextlevel', $filecaps[$cachedcap->name])) {
                    $filecaps[$cachedcap->name]['contextlevel'] = 0; // no context level defined
                }
                if ($cachedcap->contextlevel != $filecaps[$cachedcap->name]['contextlevel']) {
                    $updatecap = new stdClass();
                    $updatecap->id = $cachedcap->id;
                    $updatecap->contextlevel = $filecaps[$cachedcap->name]['contextlevel'];
                    $DB->update_record('capabilities', $updatecap);
                }
            }
        }
    }

    // Are there new capabilities in the file definition?
    $newcaps = array();

    foreach ($filecaps as $filecap => $def) {
        if (!$storedcaps ||
                ($storedcaps && in_array($filecap, $storedcaps) === false)) {
            if (!array_key_exists('riskbitmask', $def)) {
                $def['riskbitmask'] = 0; // no risk if not specified
            }
            $newcaps[$filecap] = $def;
        }
    }
    // Add new capabilities to the stored definition.
    foreach ($newcaps as $capname => $capdef) {
        $capability = new stdClass();
        $capability->name         = $capname;
        $capability->captype      = $capdef['captype'];
        $capability->contextlevel = $capdef['contextlevel'];
        $capability->component    = $component;
        $capability->riskbitmask  = $capdef['riskbitmask'];

        $DB->insert_record('capabilities', $capability, false);

        if (isset($capdef['clonepermissionsfrom']) && in_array($capdef['clonepermissionsfrom'], $storedcaps)){
            if ($rolecapabilities = $DB->get_records('role_capabilities', array('capability'=>$capdef['clonepermissionsfrom']))){
                foreach ($rolecapabilities as $rolecapability){
                    //assign_capability will update rather than insert if capability exists
                    if (!assign_capability($capname, $rolecapability->permission,
                                            $rolecapability->roleid, $rolecapability->contextid, true)){
                         echo $OUTPUT->notification('Could not clone capabilities for '.$capname);
                    }
                }
            }
        // we ignore archetype key if we have cloned permissions
        } else if (isset($capdef['archetypes']) && is_array($capdef['archetypes'])) {
            assign_legacy_capabilities($capname, $capdef['archetypes']);
        // 'legacy' is for backward compatibility with 1.9 access.php
        } else if (isset($capdef['legacy']) && is_array($capdef['legacy'])) {
            assign_legacy_capabilities($capname, $capdef['legacy']);
        }
    }
    // Are there any capabilities that have been removed from the file
    // definition that we need to delete from the stored capabilities and
    // role assignments?
    capabilities_cleanup($component, $filecaps);

    // reset static caches
    accesslib_clear_all_caches(false);

    return true;
}

/**
 * Deletes cached capabilities that are no longer needed by the component.
 * Also unassigns these capabilities from any roles that have them.
 *
 * @param string $component examples: 'moodle', 'mod_forum', 'block_quiz_results'
 * @param array $newcapdef array of the new capability definitions that will be
 *                     compared with the cached capabilities
 * @return int number of deprecated capabilities that have been removed
 */
function capabilities_cleanup($component, $newcapdef = null) {
    global $DB;

    $removedcount = 0;

    if ($cachedcaps = get_cached_capabilities($component)) {
        foreach ($cachedcaps as $cachedcap) {
            if (empty($newcapdef) ||
                        array_key_exists($cachedcap->name, $newcapdef) === false) {

                // Remove from capabilities cache.
                $DB->delete_records('capabilities', array('name'=>$cachedcap->name));
                $removedcount++;
                // Delete from roles.
                if ($roles = get_roles_with_capability($cachedcap->name)) {
                    foreach($roles as $role) {
                        if (!unassign_capability($cachedcap->name, $role->id)) {
                            print_error('cannotunassigncap', 'error', '', (object)array('cap'=>$cachedcap->name, 'role'=>$role->name));
                        }
                    }
                }
            } // End if.
        }
    }
    return $removedcount;
}

/**
 * Returns an array of all the known types of risk
 * The array keys can be used, for example as CSS class names, or in calls to
 * print_risk_icon. The values are the corresponding RISK_ constants.
 *
 * @return array all the known types of risk.
 */
function get_all_risks() {
    return array(
        'riskmanagetrust' => RISK_MANAGETRUST,
        'riskconfig'      => RISK_CONFIG,
        'riskxss'         => RISK_XSS,
        'riskpersonal'    => RISK_PERSONAL,
        'riskspam'        => RISK_SPAM,
        'riskdataloss'    => RISK_DATALOSS,
    );
}

/**
 * Return a link to moodle docs for a given capability name
 *
 * @param object $capability a capability - a row from the mdl_capabilities table.
 * @return string the human-readable capability name as a link to Moodle Docs.
 */
function get_capability_docs_link($capability) {
    $url = get_docs_url('Capabilities/' . $capability->name);
    return '<a onclick="this.target=\'docspopup\'" href="' . $url . '">' . get_capability_string($capability->name) . '</a>';
}

/**
 * This function pulls out all the resolved capabilities (overrides and
 * defaults) of a role used in capability overrides in contexts at a given
 * context.
 *
 * @param context $context
 * @param int $roleid
 * @param string $cap capability, optional, defaults to ''
 * @return array of capabilities
 */
function role_context_capabilities($roleid, context $context, $cap = '') {
    global $DB;

    $contexts = $context->get_parent_context_ids(true);
    $contexts = '('.implode(',', $contexts).')';

    $params = array($roleid);

    if ($cap) {
        $search = " AND rc.capability = ? ";
        $params[] = $cap;
    } else {
        $search = '';
    }

    $sql = "SELECT rc.*
              FROM {role_capabilities} rc, {context} c
             WHERE rc.contextid in $contexts
                   AND rc.roleid = ?
                   AND rc.contextid = c.id $search
          ORDER BY c.contextlevel DESC, rc.capability DESC";

    $capabilities = array();

    if ($records = $DB->get_records_sql($sql, $params)) {
        // We are traversing via reverse order.
        foreach ($records as $record) {
            // If not set yet (i.e. inherit or not set at all), or currently we have a prohibit
            if (!isset($capabilities[$record->capability]) || $record->permission<-500) {
                $capabilities[$record->capability] = $record->permission;
            }
        }
    }
    return $capabilities;
}

/**
 * Constructs array with contextids as first parameter and context paths,
 * in both cases bottom top including self.
 *
 * @private
 * @param context $context
 * @return array
 */
function get_context_info_list(context $context) {
    $contextids = explode('/', ltrim($context->path, '/'));
    $contextpaths = array();
    $contextids2 = $contextids;
    while ($contextids2) {
        $contextpaths[] = '/' . implode('/', $contextids2);
        array_pop($contextids2);
    }
    return array($contextids, $contextpaths);
}

/**
 * Check if context is the front page context or a context inside it
 *
 * Returns true if this context is the front page context, or a context inside it,
 * otherwise false.
 *
 * @param context $context a context object.
 * @return bool
 */
function is_inside_frontpage(context $context) {
    $frontpagecontext = context_course::instance(SITEID);
    return strpos($context->path . '/', $frontpagecontext->path . '/') === 0;
}

/**
 * Returns capability information (cached)
 *
 * @param string $capabilityname
 * @return object or null if capability not found
 */
function get_capability_info($capabilityname) {
    global $ACCESSLIB_PRIVATE, $DB; // one request per page only

    //TODO: MUC - this could be cached in shared memory, it would eliminate 1 query per page

    if (empty($ACCESSLIB_PRIVATE->capabilities)) {
        $ACCESSLIB_PRIVATE->capabilities = array();
        $caps = $DB->get_records('capabilities', array(), 'id, name, captype, riskbitmask');
        foreach ($caps as $cap) {
            $capname = $cap->name;
            unset($cap->id);
            unset($cap->name);
            $cap->riskbitmask = (int)$cap->riskbitmask;
            $ACCESSLIB_PRIVATE->capabilities[$capname] = $cap;
        }
    }

    return isset($ACCESSLIB_PRIVATE->capabilities[$capabilityname]) ? $ACCESSLIB_PRIVATE->capabilities[$capabilityname] : null;
}

/**
 * Returns the human-readable, translated version of the capability.
 * Basically a big switch statement.
 *
 * @param string $capabilityname e.g. mod/choice:readresponses
 * @return string
 */
function get_capability_string($capabilityname) {

    // Typical capability name is 'plugintype/pluginname:capabilityname'
    list($type, $name, $capname) = preg_split('|[/:]|', $capabilityname);

    if ($type === 'moodle') {
        $component = 'core_role';
    } else if ($type === 'quizreport') {
        //ugly hack!!
        $component = 'quiz_'.$name;
    } else {
        $component = $type.'_'.$name;
    }

    $stringname = $name.':'.$capname;

    if ($component === 'core_role' or get_string_manager()->string_exists($stringname, $component)) {
        return get_string($stringname, $component);
    }

    $dir = get_component_directory($component);
    if (!file_exists($dir)) {
        // plugin broken or does not exist, do not bother with printing of debug message
        return $capabilityname.' ???';
    }

    // something is wrong in plugin, better print debug
    return get_string($stringname, $component);
}

/**
 * This gets the mod/block/course/core etc strings.
 *
 * @param string $component
 * @param int $contextlevel
 * @return string|bool String is success, false if failed
 */
function get_component_string($component, $contextlevel) {

    if ($component === 'moodle' or $component === 'core') {
        switch ($contextlevel) {
            // TODO: this should probably use context level names instead
            case CONTEXT_SYSTEM:    return get_string('coresystem');
            case CONTEXT_USER:      return get_string('users');
            case CONTEXT_COURSECAT: return get_string('categories');
            case CONTEXT_COURSE:    return get_string('course');
            case CONTEXT_MODULE:    return get_string('activities');
            case CONTEXT_BLOCK:     return get_string('block');
            default:                print_error('unknowncontext');
        }
    }

    list($type, $name) = normalize_component($component);
    $dir = get_plugin_directory($type, $name);
    if (!file_exists($dir)) {
        // plugin not installed, bad luck, there is no way to find the name
        return $component.' ???';
    }

    switch ($type) {
        // TODO: this is really hacky, anyway it should be probably moved to lib/pluginlib.php
        case 'quiz':         return get_string($name.':componentname', $component);// insane hack!!!
        case 'repository':   return get_string('repository', 'repository').': '.get_string('pluginname', $component);
        case 'gradeimport':  return get_string('gradeimport', 'grades').': '.get_string('pluginname', $component);
        case 'gradeexport':  return get_string('gradeexport', 'grades').': '.get_string('pluginname', $component);
        case 'gradereport':  return get_string('gradereport', 'grades').': '.get_string('pluginname', $component);
        case 'webservice':   return get_string('webservice', 'webservice').': '.get_string('pluginname', $component);
        case 'block':        return get_string('block').': '.get_string('pluginname', basename($component));
        case 'mod':
            if (get_string_manager()->string_exists('pluginname', $component)) {
                return get_string('activity').': '.get_string('pluginname', $component);
            } else {
                return get_string('activity').': '.get_string('modulename', $component);
            }
        default: return get_string('pluginname', $component);
    }
}

/**
 * Gets the list of roles assigned to this context and up (parents)
 * from the list of roles that are visible on user profile page
 * and participants page.
 *
 * @param context $context
 * @return array
 */
function get_profile_roles(context $context) {
    global $CFG, $DB;

    if (empty($CFG->profileroles)) {
        return array();
    }

    list($rallowed, $params) = $DB->get_in_or_equal(explode(',', $CFG->profileroles), SQL_PARAMS_NAMED, 'a');
    list($contextlist, $cparams) = $DB->get_in_or_equal($context->get_parent_context_ids(true), SQL_PARAMS_NAMED, 'p');
    $params = array_merge($params, $cparams);

    $sql = "SELECT DISTINCT r.id, r.name, r.shortname, r.sortorder
              FROM {role_assignments} ra, {role} r
             WHERE r.id = ra.roleid
                   AND ra.contextid $contextlist
                   AND r.id $rallowed
          ORDER BY r.sortorder ASC";

    return $DB->get_records_sql($sql, $params);
}

/**
 * Gets the list of roles assigned to this context and up (parents)
 *
 * @param context $context
 * @return array
 */
function get_roles_used_in_context(context $context) {
    global $DB;

    list($contextlist, $params) = $DB->get_in_or_equal($context->get_parent_context_ids(true));

    $sql = "SELECT DISTINCT r.id, r.name, r.shortname, r.sortorder
              FROM {role_assignments} ra, {role} r
             WHERE r.id = ra.roleid
                   AND ra.contextid $contextlist
          ORDER BY r.sortorder ASC";

    return $DB->get_records_sql($sql, $params);
}

/**
 * This function is used to print roles column in user profile page.
 * It is using the CFG->profileroles to limit the list to only interesting roles.
 * (The permission tab has full details of user role assignments.)
 *
 * @param int $userid
 * @param int $courseid
 * @return string
 */
function get_user_roles_in_course($userid, $courseid) {
    global $CFG, $DB;

    if (empty($CFG->profileroles)) {
        return '';
    }

    if ($courseid == SITEID) {
        $context = context_system::instance();
    } else {
        $context = context_course::instance($courseid);
    }

    if (empty($CFG->profileroles)) {
        return array();
    }

    list($rallowed, $params) = $DB->get_in_or_equal(explode(',', $CFG->profileroles), SQL_PARAMS_NAMED, 'a');
    list($contextlist, $cparams) = $DB->get_in_or_equal($context->get_parent_context_ids(true), SQL_PARAMS_NAMED, 'p');
    $params = array_merge($params, $cparams);

    $sql = "SELECT DISTINCT r.id, r.name, r.shortname, r.sortorder
              FROM {role_assignments} ra, {role} r
             WHERE r.id = ra.roleid
                   AND ra.contextid $contextlist
                   AND r.id $rallowed
                   AND ra.userid = :userid
          ORDER BY r.sortorder ASC";
    $params['userid'] = $userid;

    $rolestring = '';

    if ($roles = $DB->get_records_sql($sql, $params)) {
        foreach ($roles as $userrole) {
            $rolenames[$userrole->id] = $userrole->name;
        }

        $rolenames = role_fix_names($rolenames, $context);   // Substitute aliases

        foreach ($rolenames as $roleid => $rolename) {
            $rolenames[$roleid] = '<a href="'.$CFG->wwwroot.'/user/index.php?contextid='.$context->id.'&amp;roleid='.$roleid.'">'.$rolename.'</a>';
        }
        $rolestring = implode(',', $rolenames);
    }

    return $rolestring;
}

/**
 * Checks if a user can assign users to a particular role in this context
 *
 * @param context $context
 * @param int $targetroleid - the id of the role you want to assign users to
 * @return boolean
 */
function user_can_assign(context $context, $targetroleid) {
    global $DB;

    // first check if user has override capability
    // if not return false;
    if (!has_capability('moodle/role:assign', $context)) {
        return false;
    }
    // pull out all active roles of this user from this context(or above)
    if ($userroles = get_user_roles($context)) {
        foreach ($userroles as $userrole) {
            // if any in the role_allow_override table, then it's ok
            if ($DB->get_record('role_allow_assign', array('roleid'=>$userrole->roleid, 'allowassign'=>$targetroleid))) {
                return true;
            }
        }
    }

    return false;
}

/**
 * Returns all site roles in correct sort order.
 *
 * @return array
 */
function get_all_roles() {
    global $DB;
    return $DB->get_records('role', null, 'sortorder ASC');
}

/**
 * Returns roles of a specified archetype
 *
 * @param string $archetype
 * @return array of full role records
 */
function get_archetype_roles($archetype) {
    global $DB;
    return $DB->get_records('role', array('archetype'=>$archetype), 'sortorder ASC');
}

/**
 * Gets all the user roles assigned in this context, or higher contexts
 * this is mainly used when checking if a user can assign a role, or overriding a role
 * i.e. we need to know what this user holds, in order to verify against allow_assign and
 * allow_override tables
 *
 * @param context $context
 * @param int $userid
 * @param bool $checkparentcontexts defaults to true
 * @param string $order defaults to 'c.contextlevel DESC, r.sortorder ASC'
 * @return array
 */
function get_user_roles(context $context, $userid = 0, $checkparentcontexts = true, $order = 'c.contextlevel DESC, r.sortorder ASC') {
    global $USER, $DB;

    if (empty($userid)) {
        if (empty($USER->id)) {
            return array();
        }
        $userid = $USER->id;
    }

    if ($checkparentcontexts) {
        $contextids = $context->get_parent_context_ids();
    } else {
        $contextids = array();
    }
    $contextids[] = $context->id;

    list($contextids, $params) = $DB->get_in_or_equal($contextids, SQL_PARAMS_QM);

    array_unshift($params, $userid);

    $sql = "SELECT ra.*, r.name, r.shortname
              FROM {role_assignments} ra, {role} r, {context} c
             WHERE ra.userid = ?
                   AND ra.roleid = r.id
                   AND ra.contextid = c.id
                   AND ra.contextid $contextids
          ORDER BY $order";

    return $DB->get_records_sql($sql ,$params);
}

/**
 * Creates a record in the role_allow_override table
 *
 * @param int $sroleid source roleid
 * @param int $troleid target roleid
 * @return void
 */
function allow_override($sroleid, $troleid) {
    global $DB;

    $record = new stdClass();
    $record->roleid        = $sroleid;
    $record->allowoverride = $troleid;
    $DB->insert_record('role_allow_override', $record);
}

/**
 * Creates a record in the role_allow_assign table
 *
 * @param int $fromroleid source roleid
 * @param int $targetroleid target roleid
 * @return void
 */
function allow_assign($fromroleid, $targetroleid) {
    global $DB;

    $record = new stdClass();
    $record->roleid      = $fromroleid;
    $record->allowassign = $targetroleid;
    $DB->insert_record('role_allow_assign', $record);
}

/**
 * Creates a record in the role_allow_switch table
 *
 * @param int $fromroleid source roleid
 * @param int $targetroleid target roleid
 * @return void
 */
function allow_switch($fromroleid, $targetroleid) {
    global $DB;

    $record = new stdClass();
    $record->roleid      = $fromroleid;
    $record->allowswitch = $targetroleid;
    $DB->insert_record('role_allow_switch', $record);
}

/**
 * Gets a list of roles that this user can assign in this context
 *
 * @param context $context the context.
 * @param int $rolenamedisplay the type of role name to display. One of the
 *      ROLENAME_X constants. Default ROLENAME_ALIAS.
 * @param bool $withusercounts if true, count the number of users with each role.
 * @param integer|object $user A user id or object. By default (null) checks the permissions of the current user.
 * @return array if $withusercounts is false, then an array $roleid => $rolename.
 *      if $withusercounts is true, returns a list of three arrays,
 *      $rolenames, $rolecounts, and $nameswithcounts.
 */
function get_assignable_roles(context $context, $rolenamedisplay = ROLENAME_ALIAS, $withusercounts = false, $user = null) {
    global $USER, $DB;

    // make sure there is a real user specified
    if ($user === null) {
        $userid = isset($USER->id) ? $USER->id : 0;
    } else {
        $userid = is_object($user) ? $user->id : $user;
    }

    if (!has_capability('moodle/role:assign', $context, $userid)) {
        if ($withusercounts) {
            return array(array(), array(), array());
        } else {
            return array();
        }
    }

    $parents = $context->get_parent_context_ids(true);
    $contexts = implode(',' , $parents);

    $params = array();
    $extrafields = '';
    if ($rolenamedisplay == ROLENAME_ORIGINALANDSHORT or $rolenamedisplay == ROLENAME_SHORT) {
        $extrafields .= ', r.shortname';
    }

    if ($withusercounts) {
        $extrafields = ', (SELECT count(u.id)
                             FROM {role_assignments} cra JOIN {user} u ON cra.userid = u.id
                            WHERE cra.roleid = r.id AND cra.contextid = :conid AND u.deleted = 0
                          ) AS usercount';
        $params['conid'] = $context->id;
    }

    if (is_siteadmin($userid)) {
        // show all roles allowed in this context to admins
        $assignrestriction = "";
    } else {
        $assignrestriction = "JOIN (SELECT DISTINCT raa.allowassign AS id
                                      FROM {role_allow_assign} raa
                                      JOIN {role_assignments} ra ON ra.roleid = raa.roleid
                                     WHERE ra.userid = :userid AND ra.contextid IN ($contexts)
                                   ) ar ON ar.id = r.id";
        $params['userid'] = $userid;
    }
    $params['contextlevel'] = $context->contextlevel;
    $sql = "SELECT r.id, r.name $extrafields
              FROM {role} r
              $assignrestriction
              JOIN {role_context_levels} rcl ON r.id = rcl.roleid
             WHERE rcl.contextlevel = :contextlevel
          ORDER BY r.sortorder ASC";
    $roles = $DB->get_records_sql($sql, $params);

    $rolenames = array();
    foreach ($roles as $role) {
        if ($rolenamedisplay == ROLENAME_SHORT) {
            $rolenames[$role->id] = $role->shortname;
            continue;
        }
        $rolenames[$role->id] = $role->name;
        if ($rolenamedisplay == ROLENAME_ORIGINALANDSHORT) {
            $rolenames[$role->id] .= ' (' . $role->shortname . ')';
        }
    }
    if ($rolenamedisplay != ROLENAME_ORIGINALANDSHORT and $rolenamedisplay != ROLENAME_SHORT) {
        $rolenames = role_fix_names($rolenames, $context, $rolenamedisplay);
    }

    if (!$withusercounts) {
        return $rolenames;
    }

    $rolecounts = array();
    $nameswithcounts = array();
    foreach ($roles as $role) {
        $nameswithcounts[$role->id] = $rolenames[$role->id] . ' (' . $roles[$role->id]->usercount . ')';
        $rolecounts[$role->id] = $roles[$role->id]->usercount;
    }
    return array($rolenames, $rolecounts, $nameswithcounts);
}

/**
 * Gets a list of roles that this user can switch to in a context
 *
 * Gets a list of roles that this user can switch to in a context, for the switchrole menu.
 * This function just process the contents of the role_allow_switch table. You also need to
 * test the moodle/role:switchroles to see if the user is allowed to switch in the first place.
 *
 * @param context $context a context.
 * @return array an array $roleid => $rolename.
 */
function get_switchable_roles(context $context) {
    global $USER, $DB;

    $params = array();
    $extrajoins = '';
    $extrawhere = '';
    if (!is_siteadmin()) {
        // Admins are allowed to switch to any role with.
        // Others are subject to the additional constraint that the switch-to role must be allowed by
        // 'role_allow_switch' for some role they have assigned in this context or any parent.
        $parents = $context->get_parent_context_ids(true);
        $contexts = implode(',' , $parents);

        $extrajoins = "JOIN {role_allow_switch} ras ON ras.allowswitch = rc.roleid
        JOIN {role_assignments} ra ON ra.roleid = ras.roleid";
        $extrawhere = "WHERE ra.userid = :userid AND ra.contextid IN ($contexts)";
        $params['userid'] = $USER->id;
    }

    $query = "
        SELECT r.id, r.name
          FROM (SELECT DISTINCT rc.roleid
                  FROM {role_capabilities} rc
                  $extrajoins
                  $extrawhere) idlist
          JOIN {role} r ON r.id = idlist.roleid
      ORDER BY r.sortorder";

    $rolenames = $DB->get_records_sql_menu($query, $params);
    return role_fix_names($rolenames, $context, ROLENAME_ALIAS);
}

/**
 * Gets a list of roles that this user can override in this context.
 *
 * @param context $context the context.
 * @param int $rolenamedisplay the type of role name to display. One of the
 *      ROLENAME_X constants. Default ROLENAME_ALIAS.
 * @param bool $withcounts if true, count the number of overrides that are set for each role.
 * @return array if $withcounts is false, then an array $roleid => $rolename.
 *      if $withusercounts is true, returns a list of three arrays,
 *      $rolenames, $rolecounts, and $nameswithcounts.
 */
function get_overridable_roles(context $context, $rolenamedisplay = ROLENAME_ALIAS, $withcounts = false) {
    global $USER, $DB;

    if (!has_any_capability(array('moodle/role:safeoverride', 'moodle/role:override'), $context)) {
        if ($withcounts) {
            return array(array(), array(), array());
        } else {
            return array();
        }
    }

    $parents = $context->get_parent_context_ids(true);
    $contexts = implode(',' , $parents);

    $params = array();
    $extrafields = '';
    if ($rolenamedisplay == ROLENAME_ORIGINALANDSHORT) {
        $extrafields .= ', ro.shortname';
    }

    $params['userid'] = $USER->id;
    if ($withcounts) {
        $extrafields = ', (SELECT COUNT(rc.id) FROM {role_capabilities} rc
                WHERE rc.roleid = ro.id AND rc.contextid = :conid) AS overridecount';
        $params['conid'] = $context->id;
    }

    if (is_siteadmin()) {
        // show all roles to admins
        $roles = $DB->get_records_sql("
            SELECT ro.id, ro.name$extrafields
              FROM {role} ro
          ORDER BY ro.sortorder ASC", $params);

    } else {
        $roles = $DB->get_records_sql("
            SELECT ro.id, ro.name$extrafields
              FROM {role} ro
              JOIN (SELECT DISTINCT r.id
                      FROM {role} r
                      JOIN {role_allow_override} rao ON r.id = rao.allowoverride
                      JOIN {role_assignments} ra ON rao.roleid = ra.roleid
                     WHERE ra.userid = :userid AND ra.contextid IN ($contexts)
                   ) inline_view ON ro.id = inline_view.id
          ORDER BY ro.sortorder ASC", $params);
    }

    $rolenames = array();
    foreach ($roles as $role) {
        $rolenames[$role->id] = $role->name;
        if ($rolenamedisplay == ROLENAME_ORIGINALANDSHORT) {
            $rolenames[$role->id] .= ' (' . $role->shortname . ')';
        }
    }
    if ($rolenamedisplay != ROLENAME_ORIGINALANDSHORT) {
        $rolenames = role_fix_names($rolenames, $context, $rolenamedisplay);
    }

    if (!$withcounts) {
        return $rolenames;
}

    $rolecounts = array();
    $nameswithcounts = array();
    foreach ($roles as $role) {
        $nameswithcounts[$role->id] = $rolenames[$role->id] . ' (' . $roles[$role->id]->overridecount . ')';
        $rolecounts[$role->id] = $roles[$role->id]->overridecount;
    }
    return array($rolenames, $rolecounts, $nameswithcounts);
}

/**
 * Create a role menu suitable for default role selection in enrol plugins.
 * @param context $context
 * @param int $addroleid current or default role - always added to list
 * @return array roleid=>localised role name
 */
function get_default_enrol_roles(context $context, $addroleid = null) {
    global $DB;

    $params = array('contextlevel'=>CONTEXT_COURSE);
    if ($addroleid) {
        $addrole = "OR r.id = :addroleid";
        $params['addroleid'] = $addroleid;
    } else {
        $addrole = "";
    }
    $sql = "SELECT r.id, r.name
              FROM {role} r
         LEFT JOIN {role_context_levels} rcl ON (rcl.roleid = r.id AND rcl.contextlevel = :contextlevel)
             WHERE rcl.id IS NOT NULL $addrole
          ORDER BY sortorder DESC";

    $roles = $DB->get_records_sql_menu($sql, $params);
    $roles = role_fix_names($roles, $context, ROLENAME_BOTH);

    return $roles;
}

/**
 * Return context levels where this role is assignable.
 * @param integer $roleid the id of a role.
 * @return array list of the context levels at which this role may be assigned.
 */
function get_role_contextlevels($roleid) {
    global $DB;
    return $DB->get_records_menu('role_context_levels', array('roleid' => $roleid),
            'contextlevel', 'id,contextlevel');
}

/**
 * Return roles suitable for assignment at the specified context level.
 *
 * NOTE: this function name looks like a typo, should be probably get_roles_for_contextlevel()
 *
 * @param integer $contextlevel a contextlevel.
 * @return array list of role ids that are assignable at this context level.
 */
function get_roles_for_contextlevels($contextlevel) {
    global $DB;
    return $DB->get_records_menu('role_context_levels', array('contextlevel' => $contextlevel),
            '', 'id,roleid');
}

/**
 * Returns default context levels where roles can be assigned.
 *
 * @param string $rolearchetype one of the role archetypes - that is, one of the keys
 *      from the array returned by get_role_archetypes();
 * @return array list of the context levels at which this type of role may be assigned by default.
 */
function get_default_contextlevels($rolearchetype) {
    static $defaults = array(
        'manager'        => array(CONTEXT_SYSTEM, CONTEXT_COURSECAT, CONTEXT_COURSE),
        'coursecreator'  => array(CONTEXT_SYSTEM, CONTEXT_COURSECAT),
        'editingteacher' => array(CONTEXT_COURSE, CONTEXT_MODULE),
        'teacher'        => array(CONTEXT_COURSE, CONTEXT_MODULE),
        'student'        => array(CONTEXT_COURSE, CONTEXT_MODULE),
        'guest'          => array(),
        'user'           => array(),
        'frontpage'      => array());

    if (isset($defaults[$rolearchetype])) {
        return $defaults[$rolearchetype];
    } else {
        return array();
    }
}

/**
 * Set the context levels at which a particular role can be assigned.
 * Throws exceptions in case of error.
 *
 * @param integer $roleid the id of a role.
 * @param array $contextlevels the context levels at which this role should be assignable,
 *      duplicate levels are removed.
 * @return void
 */
function set_role_contextlevels($roleid, array $contextlevels) {
    global $DB;
    $DB->delete_records('role_context_levels', array('roleid' => $roleid));
    $rcl = new stdClass();
    $rcl->roleid = $roleid;
    $contextlevels = array_unique($contextlevels);
    foreach ($contextlevels as $level) {
        $rcl->contextlevel = $level;
        $DB->insert_record('role_context_levels', $rcl, false, true);
    }
}

/**
 * Who has this capability in this context?
 *
 * This can be a very expensive call - use sparingly and keep
 * the results if you are going to need them again soon.
 *
 * Note if $fields is empty this function attempts to get u.*
 * which can get rather large - and has a serious perf impact
 * on some DBs.
 *
 * @param context $context
 * @param string|array $capability - capability name(s)
 * @param string $fields - fields to be pulled. The user table is aliased to 'u'. u.id MUST be included.
 * @param string $sort - the sort order. Default is lastaccess time.
 * @param mixed $limitfrom - number of records to skip (offset)
 * @param mixed $limitnum - number of records to fetch