[moodle.git] / lib / accesslib.php

<?php // $Id$

///////////////////////////////////////////////////////////////////////////
//                                                                       //
// NOTICE OF COPYRIGHT                                                   //
//                                                                       //
// Moodle - Modular Object-Oriented Dynamic Learning Environment         //
//          http://moodle.org                                            //
//                                                                       //
// Copyright (C) 1999 onwards Martin Dougiamas  http://dougiamas.com     //
//                                                                       //
// This program 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 2 of the License, or     //
// (at your option) any later version.                                   //
//                                                                       //
// This program 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:                          //
//                                                                       //
//          http://www.gnu.org/copyleft/gpl.html                         //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

/**
 * Public API vs internals
 * -----------------------
 *
 * General users probably only care about
 *
 * Context handling
 * - get_context_instance()
 * - get_context_instance_by_id()
 * - get_parent_contexts()
 * - get_child_contexts()
 *
 * Whether the user can do something...
 * - has_capability()
 * - has_any_capability()
 * - has_all_capabilities()
 * - require_capability()
 * - require_login() (from moodlelib)
 *
 * What courses has this user access to?
 * - get_user_courses_bycap()
 *
 * What users can do X in this context?
 * - get_users_by_capability()
 *
 * Enrol/unenrol
 * - enrol_into_course()
 * - role_assign()/role_unassign()
 *
 *
 * Advanced use
 * - load_all_capabilities()
 * - reload_all_capabilities()
 * - has_capability_in_accessdata()
 * - is_siteadmin()
 * - get_user_access_sitewide()
 * - load_subcontext()
 * - get_role_access_bycontext()
 *
 * Name conventions
 * ----------------
 *
 * - "ctx" means context
 *
 * accessdata
 * ----------
 *
 * 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.
 *
 * $accessdata[ra][$contextpath]= array($roleid)
 *                [$contextpath]= array($roleid)
 *                [$contextpath]= array($roleid)
 *
 * Role definitions are stored like this
 * (no cap merge is done - so it's compact)
 *
 * $accessdata[rdef][$contextpath:$roleid][mod/forum:viewpost] = 1
 *                                        [mod/forum:editallpost] = -1
 *                                        [mod/forum:startdiscussion] = -1000
 *
 * See how has_capability_in_accessdata() walks up/down the tree.
 *
 * Normally - specially for the logged-in user, 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
 *
 * $accessdata[loaded] = array($contextpath, $contextpath)
 *
 * Stale accessdata
 * ----------------
 *
 * 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 sytem level will force the reload for everyone.
 *
 * Default role caps
 * -----------------
 * 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.
 *
 * @license http://www.gnu.org/copyleft/gpl.html GNU Public License
 * @package roles
 */

// permission definitions
define('CAP_INHERIT', 0);
define('CAP_ALLOW', 1);
define('CAP_PREVENT', -1);
define('CAP_PROHIBIT', -1000);

// context definitions
define('CONTEXT_SYSTEM', 10);
define('CONTEXT_USER', 30);
define('CONTEXT_COURSECAT', 40);
define('CONTEXT_COURSE', 50);
define('CONTEXT_MODULE', 70);
define('CONTEXT_BLOCK', 80);

// capability risks - see http://docs.moodle.org/en/Development:Hardening_new_Roles_system
define('RISK_MANAGETRUST', 0x0001);
define('RISK_CONFIG',      0x0002);
define('RISK_XSS',         0x0004);
define('RISK_PERSONAL',    0x0008);
define('RISK_SPAM',        0x0010);
define('RISK_DATALOSS',    0x0020);

// rolename displays
define('ROLENAME_ORIGINAL', 0);// the name as defined in the role definition
define('ROLENAME_ALIAS', 1);   // the name as defined by a role alias
define('ROLENAME_BOTH', 2);    // Both, like this:  Role alias (Original)
define('ROLENAME_ORIGINALANDSHORT', 3); // the name as defined in the role definition and the shortname in brackets
define('ROLENAME_ALIAS_RAW', 4);   // the name as defined by a role alias, in raw form suitable for editing

// size limit for context cache
if (!defined('MAX_CONTEXT_CACHE_SIZE')) { 
    define('MAX_CONTEXT_CACHE_SIZE', 5000);
}

// 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 variale is the only way to impleemnt this, withough rewriting everything
// as methods of a class, instead of functions.
$ACCESSLIB_PRIVATE = new stdClass;
$ACCESSLIB_PRIVATE->contexts = array(); // Cache of context objects by level and instance
$ACCESSLIB_PRIVATE->contextsbyid = array(); // Cache of context objects by id
$ACCESSLIB_PRIVATE->systemcontext = null; // Used in get_system_context
$ACCESSLIB_PRIVATE->dirtycontexts = null; // Dirty contexts cache
$ACCESSLIB_PRIVATE->accessdatabyuser = array(); // Holds the $accessdata structure for users other than $USER
$ACCESSLIB_PRIVATE->roledefinitions = array(); // role definitions cache - helps a lot with mem usage in cron
$ACCESSLIB_PRIVATE->croncache = array(); // Used in get_role_access
$ACCESSLIB_PRIVATE->preloadedcourses = array(); // Used in preload_course_contexts.
$ACCESSLIB_PRIVATE->capabilitynames = null; // Used in is_valid_capability (only in developer debug mode)

/**
 * 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 fo the tests.
 */
function accesslib_clear_all_caches_for_unit_testing() {
    global $UNITTEST, $USER, $ACCESSLIB_PRIVATE;
    if (empty($UNITTEST->running)) {
        throw new coding_exception('You must not call clear_all_caches outside of unit tests.');
    }
    $ACCESSLIB_PRIVATE->contexts = array();
    $ACCESSLIB_PRIVATE->contextsbyid = array();
    $ACCESSLIB_PRIVATE->systemcontext = null;
    $ACCESSLIB_PRIVATE->dirtycontexts = null;
    $ACCESSLIB_PRIVATE->accessdatabyuser = array();
    $ACCESSLIB_PRIVATE->roledefinitions = array();
    $ACCESSLIB_PRIVATE->croncache = array();
    $ACCESSLIB_PRIVATE->preloadedcourses = array();
    $ACCESSLIB_PRIVATE->capabilitynames = null;

    unset($USER->access);
}

/**
 * Private function. Add a context object to accesslib's caches.
 */
function cache_context($context) {
    global $ACCESSLIB_PRIVATE;

    // If there are too many items in the cache already, remove items until
    // there is space
    while (count($ACCESSLIB_PRIVATE->contextsbyid) >= MAX_CONTEXT_CACHE_SIZE) {
        $first = array_shift($ACCESSLIB_PRIVATE->contextsbyid);
        unset($ACCESSLIB_PRIVATE->contexts[$first->contextlevel][$first->instanceid]);
    }

    $ACCESSLIB_PRIVATE->contexts[$context->contextlevel][$context->instanceid] = $context;
    $ACCESSLIB_PRIVATE->contextsbyid[$context->id] = $context;
}

function get_role_context_caps($roleid, $context) {
    global $DB;

    //this is really slow!!!! - do not use above course context level!
    $result = array();
    $result[$context->id] = array();

    // first emulate the parent context capabilities merging into context
    $searchcontexts = array_reverse(get_parent_contexts($context));
    array_push($searchcontexts, $context->id);
    foreach ($searchcontexts as $cid) {
        if ($capabilities = $DB->get_records('role_capabilities', array('roleid'=>$roleid, 'contextid'=>$cid))) {
            foreach ($capabilities as $cap) {
                if (!array_key_exists($cap->capability, $result[$context->id])) {
                    $result[$context->id][$cap->capability] = 0;
                }
                $result[$context->id][$cap->capability] += $cap->permission;
            }
        }
    }

    // now go through the contexts bellow given context
    $searchcontexts = array_keys(get_child_contexts($context));
    foreach ($searchcontexts as $cid) {
        if ($capabilities = $DB->get_records('role_capabilities', array('roleid'=>$roleid, 'contextid'=>$cid))) {
            foreach ($capabilities as $cap) {
                if (!array_key_exists($cap->contextid, $result)) {
                    $result[$cap->contextid] = array();
                }
                $result[$cap->contextid][$cap->capability] = $cap->permission;
            }
        }
    }

    return $result;
}

/**
 * Gets the accessdata for role "sitewide"
 * (system down to course)
 *
 * @return array
 */
function get_role_access($roleid, $accessdata=NULL) {

    global $CFG, $DB;

    /* Get it in 1 cheap DB query...
     * - relevant role caps at the root and down
     *   to the course level - but not below
     */
    if (is_null($accessdata)) {
        $accessdata           = array(); // named list
        $accessdata['ra']     = array();
        $accessdata['rdef']   = array();
        $accessdata['loaded'] = array();
    }

    //
    // 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
             WHERE rc.roleid = ?
                   AND ctx.contextlevel <= ".CONTEXT_COURSE."
          ORDER BY ctx.depth, ctx.path";
    $params = array($roleid);

    // we need extra caching in CLI scripts and cron
    if (CLI_SCRIPT) {
        global $ACCESSLIB_PRIVATE;

        if (!isset($ACCESSLIB_PRIVATE->croncache[$roleid])) {
            $ACCESSLIB_PRIVATE->croncache[$roleid] = array();
            if ($rs = $DB->get_recordset_sql($sql, $params)) {
                foreach ($rs as $rd) {
                    $ACCESSLIB_PRIVATE->croncache[$roleid][] = $rd;
                }
                $rs->close();
            }
        }

        foreach ($ACCESSLIB_PRIVATE->croncache[$roleid] as $rd) {
            $k = "{$rd->path}:{$roleid}";
            $accessdata['rdef'][$k][$rd->capability] = $rd->permission;
        }

    } else {
        if ($rs = $DB->get_recordset_sql($sql, $params)) {
            foreach ($rs as $rd) {
                $k = "{$rd->path}:{$roleid}";
                $accessdata['rdef'][$k][$rd->capability] = $rd->permission;
            }
            unset($rd);
            $rs->close();
        }
    }

    return $accessdata;
}

/**
 * Gets the accessdata for role "sitewide"
 * (system down to course)
 *
 * @return array
 */
function get_default_frontpage_role_access($roleid, $accessdata=NULL) {

    global $CFG, $DB;

    $frontpagecontext = get_context_instance(CONTEXT_COURSE, SITEID);
    $base = '/'. SYSCONTEXTID .'/'. $frontpagecontext->id;

    //
    // Overrides for the role in any contexts related to the course
    //
    $sql = "SELECT ctx.path,
                   rc.capability, rc.permission
              FROM {context} ctx
              JOIN {role_capabilities} rc
                   ON rc.contextid=ctx.id
             WHERE rc.roleid = ?
                   AND (ctx.id = ".SYSCONTEXTID." OR ctx.path LIKE ?)
                   AND ctx.contextlevel <= ".CONTEXT_COURSE."
          ORDER BY ctx.depth, ctx.path";
    $params = array($roleid, "$base/%");

    if ($rs = $DB->get_recordset_sql($sql, $params)) {
        foreach ($rs as $rd) {
            $k = "{$rd->path}:{$roleid}";
            $accessdata['rdef'][$k][$rd->capability] = $rd->permission;
        }
        unset($rd);
        $rs->close();
    }

    return $accessdata;
}


/**
 * Get the default guest role
 * @return object role
 */
function get_guest_role() {
    global $CFG, $DB;

    if (empty($CFG->guestroleid)) {
        if ($roles = get_roles_with_capability('moodle/legacy:guest', CAP_ALLOW)) {
            $guestrole = array_shift($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();
        }
    }
}

/**
 * This function returns whether the current user has the capability of performing a function
 * For example, we can do has_capability('mod/forum:replypost',$context) in forum
 * @param string $capability - name of the capability (or debugcache or clearcache)
 * @param object $context - a context object (record from context table)
 * @param integer $userid - a userid number, empty if current $USER
 * @param bool $doanything - if false, ignore do anything
 * @return bool
 */
function has_capability($capability, $context, $userid=NULL, $doanything=true) {
    global $USER, $CFG, $DB, $SCRIPT, $ACCESSLIB_PRIVATE;

    if (empty($CFG->rolesactive)) {
        if ($SCRIPT === "/$CFG->admin/index.php" or $SCRIPT === "/$CFG->admin/cliupgrade.php") {
            // we are in an installer - roles can not work yet
            return true;
        } else {
            return false;
        }
    }

    // the original $CONTEXT here was hiding serious errors
    // for security reasons do not reuse previous context
    if (empty($context)) {
        debugging('Incorrect context specified');
        return false;
    }

/// Some sanity checks
    if (debugging('',DEBUG_DEVELOPER)) {
        if (!is_valid_capability($capability)) {
            debugging('Capability "'.$capability.'" was not found! This should be fixed in code.');
        }
        if (!is_bool($doanything)) {
            debugging('Capability parameter "doanything" is wierd ("'.$doanything.'"). This should be fixed in code.');
        }
    }

    if (empty($userid)) { // we must accept null, 0, '0', '' etc. in $userid
        $userid = $USER->id;
    }

    if (is_null($context->path) or $context->depth == 0) {
        //this should not happen
        $contexts = array(SYSCONTEXTID, $context->id);
        $context->path = '/'.SYSCONTEXTID.'/'.$context->id;
        debugging('Context id '.$context->id.' does not have valid path, please use build_context_path()', DEBUG_DEVELOPER);

    } else {
        $contexts = explode('/', $context->path);
        array_shift($contexts);
    }

    if (CLI_SCRIPT && !isset($USER->access)) {
        // In cron, some modules setup a 'fake' $USER,
        // ensure we load the appropriate accessdata.
        if (isset($ACCESSLIB_PRIVATE->accessdatabyuser[$userid])) {
            $ACCESSLIB_PRIVATE->dirtycontexts = NULL; //load fresh dirty contexts
        } else {
            load_user_accessdata($userid);
            $ACCESSLIB_PRIVATE->dirtycontexts = array();
        }
        $USER->access = $ACCESSLIB_PRIVATE->accessdatabyuser[$userid];

    } else if ($USER->id == $userid && !isset($USER->access)) {
        // caps not loaded yet - better to load them to keep BC with 1.8
        // not-logged-in user or $USER object set up manually first time here
        load_all_capabilities();
        $ACCESSLIB_PRIVATE->accessdatabyuser = array(); // reset the cache for other users too, the dirty contexts are empty now
        $ACCESSLIB_PRIVATE->roledefinitions = array();
    }

    // Load dirty contexts list if needed
    if (!isset($ACCESSLIB_PRIVATE->dirtycontexts)) {
        if (isset($USER->access['time'])) {
            $ACCESSLIB_PRIVATE->dirtycontexts = get_dirty_contexts($USER->access['time']);
        }
        else {
            $ACCESSLIB_PRIVATE->dirtycontexts = array();
        }
    }

    // Careful check for staleness...
    if (count($ACCESSLIB_PRIVATE->dirtycontexts) !== 0 and is_contextpath_dirty($contexts, $ACCESSLIB_PRIVATE->dirtycontexts)) {
        // reload all capabilities - preserving loginas, roleswitches, etc
        // and then cleanup any marks of dirtyness... at least from our short
        // term memory! :-)
        $ACCESSLIB_PRIVATE->accessdatabyuser = array();
        $ACCESSLIB_PRIVATE->roledefinitions = array();

        if (CLI_SCRIPT) {
            load_user_accessdata($userid);
            $USER->access = $ACCESSLIB_PRIVATE->accessdatabyuser[$userid];
            $ACCESSLIB_PRIVATE->dirtycontexts = array();

        } else {
            reload_all_capabilities();
        }
    }

    // divulge how many times we are called
    //// error_log("has_capability: id:{$context->id} path:{$context->path} userid:$userid cap:$capability");

    if ($USER->id == $userid) { // we must accept strings and integers in $userid
        //
        // For the logged in user, we have $USER->access
        // which will have all RAs and caps preloaded for
        // course and above contexts.
        //
        // Contexts below courses && contexts that do not
        // hang from courses are loaded into $USER->access
        // on demand, and listed in $USER->access[loaded]
        //
        if ($context->contextlevel <= CONTEXT_COURSE) {
            // Course and above are always preloaded
            return has_capability_in_accessdata($capability, $context, $USER->access, $doanything);
        }
        // Load accessdata for below-the-course contexts
        if (!path_inaccessdata($context->path,$USER->access)) {
            // error_log("loading access for context {$context->path} for $capability at {$context->contextlevel} {$context->id}");
            // $bt = debug_backtrace();
            // error_log("bt {$bt[0]['file']} {$bt[0]['line']}");
            load_subcontext($USER->id, $context, $USER->access);
        }
        return has_capability_in_accessdata($capability, $context, $USER->access, $doanything);
    }

    if (!isset($ACCESSLIB_PRIVATE->accessdatabyuser[$userid])) {
        load_user_accessdata($userid);
    }
    if ($context->contextlevel <= CONTEXT_COURSE) {
        // Course and above are always preloaded
        return has_capability_in_accessdata($capability, $context, $ACCESSLIB_PRIVATE->accessdatabyuser[$userid], $doanything);
    }
    // Load accessdata for below-the-course contexts as needed
    if (!path_inaccessdata($context->path, $ACCESSLIB_PRIVATE->accessdatabyuser[$userid])) {
        // error_log("loading access for context {$context->path} for $capability at {$context->contextlevel} {$context->id}");
        // $bt = debug_backtrace();
        // error_log("bt {$bt[0]['file']} {$bt[0]['line']}");
        load_subcontext($userid, $context, $ACCESSLIB_PRIVATE->accessdatabyuser[$userid]);
    }
    return has_capability_in_accessdata($capability, $context, $ACCESSLIB_PRIVATE->accessdatabyuser[$userid], $doanything);
}

/**
 * This function returns whether the current user has any of the capabilities in the
 * $capabilities array. This is a simple wrapper around has_capability for convinience.
 *
 * There are probably tricks that could be done to improve the performance here, for example,
 * check the capabilities that are already cached first.
 *
 * @param array $capabilities - an array of capability names.
 * @param object $context - a context object (record from context table)
 * @param integer $userid - a userid number, empty if current $USER
 * @param bool $doanything - if false, ignore do anything
 * @return bool
 */
function has_any_capability($capabilities, $context, $userid=NULL, $doanything=true) {
    foreach ($capabilities as $capability) {
        if (has_capability($capability, $context, $userid, $doanything)) {
            return true;
        }
    }
    return false;
}

/**
 * This function returns whether the current user has all of the capabilities in the
 * $capabilities array. This is a simple wrapper around has_capability for convinience.
 *
 * There are probably tricks that could be done to improve the performance here, for example,
 * check the capabilities that are already cached first.
 *
 * @param array $capabilities - an array of capability names.
 * @param object $context - a context object (record from context table)
 * @param integer $userid - a userid number, empty if current $USER
 * @param bool $doanything - if false, ignore do anything
 * @return bool
 */
function has_all_capabilities($capabilities, $context, $userid=NULL, $doanything=true) {
    if (!is_array($capabilities)) {
        debugging('Incorrect $capabilities parameter in has_all_capabilities() call - must be an array');
        return false;
    }
    foreach ($capabilities as $capability) {
        if (!has_capability($capability, $context, $userid, $doanything)) {
            return false;
        }
    }
    return true;
}

/**
 * Uses 1 DB query to answer whether a user is an admin at the sitelevel.
 * It depends on DB schema >=1.7 but does not depend on the new datastructures
 * in v1.9 (context.path, or $USER->access)
 *
 * Will return true if the userid has any of
 *  - moodle/site:config
 *  - moodle/legacy:admin
 *  - moodle/site:doanything
 *
 * @param   int  $userid
 * @returns bool true is user can administer server settings
 */
function is_siteadmin($userid) {
    global $CFG, $DB;

    $sql = "SELECT SUM(rc.permission)
              FROM {role_capabilities} rc
              JOIN {context} ctx
                   ON ctx.id=rc.contextid
              JOIN {role_assignments} ra
                   ON ra.roleid=rc.roleid AND ra.contextid=ctx.id
             WHERE ctx.contextlevel=10
                   AND ra.userid=?
                   AND rc.capability IN (?, ?, ?)
          GROUP BY rc.capability
            HAVING SUM(rc.permission) > 0";
    $params = array($userid, 'moodle/site:config', 'moodle/legacy:admin', 'moodle/site:doanything');

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

/**
 * @param integer $roleid a role id.
 * @return boolean, whether this role is an admin role.
 */
function is_admin_role($roleid) {
    global $DB;

    $sql = "SELECT 1
              FROM {role_capabilities} rc
              JOIN {context} ctx ON ctx.id = rc.contextid
             WHERE ctx.contextlevel = 10
                   AND rc.roleid = ?
                   AND rc.capability IN (?, ?, ?)
          GROUP BY rc.capability
            HAVING SUM(rc.permission) > 0";
    $params = array($roleid, 'moodle/site:config', 'moodle/legacy:admin', 'moodle/site:doanything');

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

/**
 * @return all the roles for which is_admin_role($role->id) is true.
 */
function get_admin_roles() {
    global $DB;

    $sql = "SELECT *
              FROM {role} r
             WHERE EXISTS (
                    SELECT 1
                      FROM {role_capabilities} rc
                      JOIN {context} ctx ON ctx.id = rc.contextid
                     WHERE ctx.contextlevel = 10
                           AND rc.roleid = r.id
                           AND rc.capability IN (?, ?, ?)
                  GROUP BY rc.capability
                    HAVING SUM(rc.permission) > 0
             )
          ORDER BY r.sortorder";
    $params = array('moodle/site:config', 'moodle/legacy:admin', 'moodle/site:doanything');

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

function get_course_from_path ($path) {
    // assume that nothing is more than 1 course deep
    if (preg_match('!^(/.+)/\d+$!', $path, $matches)) {
        return $matches[1];
    }
    return false;
}

function path_inaccessdata($path, $accessdata) {

    // assume that contexts hang from sys or from a course
    // this will only work well with stuff that hangs from a course
    if (in_array($path, $accessdata['loaded'], true)) {
            // error_log("found it!");
        return true;
    }
    $base = '/' . SYSCONTEXTID;
    while (preg_match('!^(/.+)/\d+$!', $path, $matches)) {
        $path = $matches[1];
        if ($path === $base) {
            return false;
        }
        if (in_array($path, $accessdata['loaded'], true)) {
            return true;
        }
    }
    return false;
}

/**
 * Walk the accessdata array and return true/false.
 * Deals with prohibits, roleswitching, aggregating
 * capabilities, etc.
 *
 * The main feature of here is being FAST and with no
 * side effects.
 *
 * Notes:
 *
 * Switch Roles exits early
 * -----------------------
 * cap checks within a switchrole need to exit early
 * in our bottom up processing so they don't "see" that
 * there are real RAs that can do all sorts of things.
 *
 * 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.
 *
 * Local-most role definition and role-assignment wins
 * ---------------------------------------------------
 * So if the local context has said 'allow', it wins
 * over a high-level context that says 'deny'.
 * This is applied when walking rdefs, and RAs.
 * Only at the same context the values are SUM()med.
 *
 * The exception is CAP_PROHIBIT.
 *
 * "Guest default role" exception
 * ------------------------------
 *
 * See MDL-7513 and $ignoreguest below for details.
 *
 * The rule is that
 *
 *    IF we are being asked about moodle/legacy:guest
 *                             OR moodle/course:view
 *    FOR a real, logged-in user
 *    AND we reached the top of the path in ra and rdef
 *    AND that role has moodle/legacy:guest === 1...
 *    THEN we act as if we hadn't seen it.
 *
 * Note that this function must be kept in synch with has_capability_in_accessdata.
 *
 * To Do:
 *
 * - Document how it works
 * - Rewrite in ASM :-)
 *
 */
function has_capability_in_accessdata($capability, $context, $accessdata, $doanything) {

    global $CFG;

    $path = $context->path;

    // build $contexts as a list of "paths" of the current
    // contexts and parents with the order top-to-bottom
    $contexts = array($path);
    while (preg_match('!^(/.+)/\d+$!', $path, $matches)) {
        $path = $matches[1];
        array_unshift($contexts, $path);
    }

    $ignoreguest = false;
    if (isset($accessdata['dr'])
        && ($capability    == 'moodle/course:view'
            || $capability == 'moodle/legacy:guest')) {
        // At the base, ignore rdefs where moodle/legacy:guest
        // is set
        $ignoreguest = $accessdata['dr'];
    }

    // Coerce it to an int
    $CAP_PROHIBIT = (int)CAP_PROHIBIT;

    $cc = count($contexts);

    $can = 0;
    $capdepth = 0;

    //
    // role-switches loop
    //
    if (isset($accessdata['rsw'])) {
        // check for isset() is fast
        // empty() is slow...
        if (empty($accessdata['rsw'])) {
            unset($accessdata['rsw']); // keep things fast and unambiguous
            break;
        }
        // From the bottom up...
        for ($n=$cc-1;$n>=0;$n--) {
            $ctxp = $contexts[$n];
            if (isset($accessdata['rsw'][$ctxp])) {
                // Found a switchrole assignment
                // check for that role _plus_ the default user role
                $ras = array($accessdata['rsw'][$ctxp],$CFG->defaultuserroleid);
                for ($rn=0;$rn<2;$rn++) {
                    $roleid = (int)$ras[$rn];
                    // Walk the path for capabilities
                    // from the bottom up...
                    for ($m=$cc-1;$m>=0;$m--) {
                        $capctxp = $contexts[$m];
                        if (isset($accessdata['rdef']["{$capctxp}:$roleid"][$capability])) {
                            $perm = (int)$accessdata['rdef']["{$capctxp}:$roleid"][$capability];

                            // The most local permission (first to set) wins
                            // the only exception is CAP_PROHIBIT
                            if ($can === 0) {
                                $can = $perm;
                            } elseif ($perm === $CAP_PROHIBIT) {
                                $can = $perm;
                                break;
                            }
                        }
                    }
                }
                // As we are dealing with a switchrole,
                // we return _here_, do _not_ walk up
                // the hierarchy any further
                if ($can < 1) {
                    if ($doanything) {
                        // didn't find it as an explicit cap,
                        // but maybe the user can doanything in this context...
                        return has_capability_in_accessdata('moodle/site:doanything', $context, $accessdata, false);
                    } else {
                        return false;
                    }
                } else {
                    return true;
                }

            }
        }
    }

    //
    // Main loop for normal RAs
    // From the bottom up...
    //
    for ($n=$cc-1;$n>=0;$n--) {
        $ctxp = $contexts[$n];
        if (isset($accessdata['ra'][$ctxp])) {
            // Found role assignments on this leaf
            $ras = $accessdata['ra'][$ctxp];

            $rc          = count($ras);
            $ctxcan      = 0;
            $ctxcapdepth = 0;
            for ($rn=0;$rn<$rc;$rn++) {
                $roleid  = (int)$ras[$rn];
                $rolecan = 0;
                $rolecapdepth = 0;
                // Walk the path for capabilities
                // from the bottom up...
                for ($m=$cc-1;$m>=0;$m--) {
                    $capctxp = $contexts[$m];
                    // ignore some guest caps
                    // at base ra and rdef
                    if ($ignoreguest == $roleid
                        && $n === 0
                        && $m === 0
                        && isset($accessdata['rdef']["{$capctxp}:$roleid"]['moodle/legacy:guest'])
                        && $accessdata['rdef']["{$capctxp}:$roleid"]['moodle/legacy:guest'] > 0) {
                            continue;
                    }
                    if (isset($accessdata['rdef']["{$capctxp}:$roleid"][$capability])) {
                        $perm = (int)$accessdata['rdef']["{$capctxp}:$roleid"][$capability];
                        // The most local permission (first to set) wins
                        // the only exception is CAP_PROHIBIT
                        if ($rolecan === 0) {
                            $rolecan      = $perm;
                            $rolecapdepth = $m;
                        } elseif ($perm === $CAP_PROHIBIT) {
                            $rolecan      = $perm;
                            $rolecapdepth = $m;
                            break;
                        }
                    }
                }
                // Rules for RAs at the same context...
                // - prohibits always wins
                // - permissions at the same ctxlevel & capdepth are added together
                // - deeper capdepth wins
                if ($ctxcan === $CAP_PROHIBIT || $rolecan === $CAP_PROHIBIT) {
                    $ctxcan      = $CAP_PROHIBIT;
                    $ctxcapdepth = 0;
                } elseif ($ctxcapdepth === $rolecapdepth) {
                    $ctxcan += $rolecan;
                } elseif ($ctxcapdepth < $rolecapdepth) {
                    $ctxcan      = $rolecan;
                    $ctxcapdepth = $rolecapdepth;
                } else { // ctxcaptdepth is deeper
                    // rolecap ignored
                }
            }
            // The most local RAs with a defined
            // permission ($ctxcan) win, except
            // for CAP_PROHIBIT
            // NOTE: If we want the deepest RDEF to
            // win regardless of the depth of the RA,
            // change the elseif below to read
            // ($can === 0 || $capdepth < $ctxcapdepth) {
            if ($ctxcan === $CAP_PROHIBIT) {
                $can = $ctxcan;
                break;
            } elseif ($can === 0) { // see note above
                $can      = $ctxcan;
                $capdepth = $ctxcapdepth;
            }
        }
    }

    if ($can < 1) {
        if ($doanything) {
            // didn't find it as an explicit cap,
            // but maybe the user can doanything in this context...
            return has_capability_in_accessdata('moodle/site:doanything', $context, $accessdata, false);
        } else {
            return false;
        }
    } else {
        return true;
    }

}

function aggregate_roles_from_accessdata($context, $accessdata) {

    $path = $context->path;

    // build $contexts as a list of "paths" of the current
    // contexts and parents with the order top-to-bottom
    $contexts = array($path);
    while (preg_match('!^(/.+)/\d+$!', $path, $matches)) {
        $path = $matches[1];
        array_unshift($contexts, $path);
    }

    $cc = count($contexts);

    $roles = array();
    // From the bottom up...
    for ($n=$cc-1;$n>=0;$n--) {
        $ctxp = $contexts[$n];
        if (isset($accessdata['ra'][$ctxp]) && count($accessdata['ra'][$ctxp])) {
            // Found assignments on this leaf
            $addroles = $accessdata['ra'][$ctxp];
            $roles    = array_merge($roles, $addroles);
        }
    }

    return array_unique($roles);
}

/**
 * This is an easy to use function, combining has_capability() with require_course_login().
 * And will call those where needed.
 *
 * It checks for a capability assertion being true.  If it isn't
 * then the page is terminated neatly with a standard error message.
 *
 * If the user is not logged in, or is using 'guest' access or other special "users,
 * it provides a logon prompt.
 *
 * @param string $capability - name of the capability
 * @param object $context - a context object (record from context table)
 * @param integer $userid - a userid number
 * @param bool $doanything - if false, ignore do anything
 * @param string $errorstring - an errorstring
 * @param string $stringfile - which stringfile to get it from
 */
function require_capability($capability, $context, $userid=NULL, $doanything=true,
                            $errormessage='nopermissions', $stringfile='') {

    global $USER, $CFG, $DB;

    /* Empty $userid means current user, if the current user is not logged in,
     * then make sure they are (if needed).
     * Originally there was a check for loaded permissions - it is not needed here.
     * Context is now required parameter, the cached $CONTEXT was only hiding errors.
     */
    $errorlink = '';

    if (empty($userid)) {
        if ($context->contextlevel == CONTEXT_COURSE) {
            require_login($context->instanceid);

        } else if ($context->contextlevel == CONTEXT_MODULE) {
            if (!$cm = $DB->get_record('course_modules', array('id'=>$context->instanceid))) {
                print_error('invalidmodule');
            }
            if (!$course = $DB->get_record('course', array('id'=>$cm->course))) {
                print_error('invalidcourseid');
            }
            require_course_login($course, true, $cm);
            $errorlink = $CFG->wwwroot.'/course/view.php?id='.$cm->course;

        } else if ($context->contextlevel == CONTEXT_SYSTEM) {
            if (!empty($CFG->forcelogin)) {
                require_login();
            }

        } else {
            require_login();
        }
    }

/// OK, if they still don't have the capability then print a nice error message

    if (!has_capability($capability, $context, $userid, $doanything)) {
        $capabilityname = get_capability_string($capability);
        print_error('nopermissions', '', $errorlink, $capabilityname);
    }
}

/**
 * Get an array of courses (with magic extra bits)
 * where the accessdata and in DB enrolments show
 * that the cap requested is available.
 *
 * The main use is for get_my_courses().
 *
 * Notes
 *
 * - $fields is an array of fieldnames to ADD
 *   so name the fields you really need, which will
 *   be added and uniq'd
 *
 * - the course records have $c->context which is a fully
 *   valid context object. Saves you a query per course!
 *
 * - the course records have $c->categorypath to make
 *   category lookups cheap
 *
 * - current implementation is split in -
 *
 *   - if the user has the cap systemwide, stupidly
 *     grab *every* course for a capcheck. This eats
 *     a TON of bandwidth, specially on large sites
 *     with separate DBs...
 *
 *   - otherwise, fetch "likely" courses with a wide net
 *     that should get us _cheaply_ at least the courses we need, and some
 *     we won't - we get courses that...
 *      - are in a category where user has the cap
 *      - or where use has a role-assignment (any kind)
 *      - or where the course has an override on for this cap
 *
 *   - walk the courses recordset checking the caps oneach one
 *     the checks are all in memory and quite fast
 *     (though we could implement a specialised variant of the
 *     has_capability_in_accessdata() code to speed it up)
 *
 * @param string $capability - name of the capability
 * @param array  $accessdata - accessdata session array
 * @param bool   $doanything - if false, ignore do anything
 * @param string $sort - sorting fields - prefix each fieldname with "c."
 * @param array  $fields - additional fields you are interested in...
 * @param int    $limit  - set if you want to limit the number of courses
 * @return array $courses - ordered array of course objects - see notes above
 *
 */
function get_user_courses_bycap($userid, $cap, $accessdata, $doanything, $sort='c.sortorder ASC', $fields=NULL, $limit=0) {

    global $CFG, $DB;

    // Slim base fields, let callers ask for what they need...
    $basefields = array('id', 'sortorder', 'shortname', 'idnumber');

    if (!is_null($fields)) {
        $fields = array_merge($basefields, $fields);
        $fields = array_unique($fields);
    } else {
        $fields = $basefields;
    }
    // If any of the fields is '*', leave it alone, discarding the rest
    // to avoid ambiguous columns under some silly DBs. See MDL-18746 :-D
    if (in_array('*', $fields)) {
        $fields = array('*');
    }
    $coursefields = 'c.' .implode(',c.', $fields);

    $sort = trim($sort);
    if ($sort !== '') {
        $sort = "ORDER BY $sort";
    }

    $sysctx = get_context_instance(CONTEXT_SYSTEM);
    if (has_capability_in_accessdata($cap, $sysctx, $accessdata, $doanything)) {
        //
        // Apparently the user has the cap sitewide, so walk *every* course
        // (the cap checks are moderately fast, but this moves massive bandwidth w the db)
        // Yuck.
        //
        $sql = "SELECT $coursefields,
                       ctx.id AS ctxid, ctx.path AS ctxpath,
                       ctx.depth AS ctxdepth, ctx.contextlevel AS ctxlevel,
                       cc.path AS categorypath
                  FROM {course} c
                  JOIN {course_categories} cc
                       ON c.category=cc.id
                  JOIN {context} ctx
                       ON (c.id=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSE.")
                 $sort ";
        $rs = $DB->get_recordset_sql($sql);
    } else {
        //
        // narrow down where we have the caps to a few contexts
        // this will be a combination of
        // - courses    where user has an explicit enrolment
        // - courses    that have an override (any status) on that capability
        // - categories where user has the rights (granted status) on that capability
        //
        $sql = "SELECT ctx.*
                  FROM {context} ctx
                 WHERE ctx.contextlevel=".CONTEXT_COURSECAT."
              ORDER BY ctx.depth";
        $rs = $DB->get_recordset_sql($sql);
        $catpaths = array();
        foreach ($rs as $catctx) {
            if ($catctx->path != ''
                && has_capability_in_accessdata($cap, $catctx, $accessdata, $doanything)) {
                $catpaths[] = $catctx->path;
            }
        }
        $rs->close();
        $catclause = '';
        $params = array();
        if (count($catpaths)) {
            $cc = count($catpaths);
            for ($n=0;$n<$cc;$n++) {
                $catpaths[$n] = "ctx.path LIKE '{$catpaths[$n]}/%'";
            }
            $catclause = 'WHERE (' . implode(' OR ', $catpaths) .')';
        }
        unset($catpaths);

        $capany = '';
        if ($doanything) {
            $capany = " OR rc.capability=:doany";
            $params['doany'] = 'moodle/site:doanything';
        }

        /// UNION 3 queries:
        /// - user role assignments in courses
        /// - user capability (override - any status) in courses
        /// - user right (granted status) in categories (optionally executed)
        /// Enclosing the 3-UNION into an inline_view to avoid column names conflict and making the ORDER BY cross-db
        /// and to allow selection of TEXT columns in the query (MSSQL and Oracle limitation). MDL-16209
        $sql = "
            SELECT $coursefields, ctxid, ctxpath, ctxdepth, ctxlevel, categorypath
              FROM (
                    SELECT c.id,
                           ctx.id AS ctxid, ctx.path AS ctxpath,
                           ctx.depth AS ctxdepth, ctx.contextlevel AS ctxlevel,
                           cc.path AS categorypath
                    FROM {course} c
                    JOIN {course_categories} cc
                      ON c.category=cc.id
                    JOIN {context} ctx
                      ON (c.id=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSE.")
                    JOIN {role_assignments} ra
                      ON (ra.contextid=ctx.id AND ra.userid=:userid)
                    UNION
                    SELECT c.id,
                           ctx.id AS ctxid, ctx.path AS ctxpath,
                           ctx.depth AS ctxdepth, ctx.contextlevel AS ctxlevel,
                           cc.path AS categorypath
                    FROM {course} c
                    JOIN {course_categories} cc
                      ON c.category=cc.id
                    JOIN {context} ctx
                      ON (c.id=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSE.")
                    JOIN {role_capabilities} rc
                      ON (rc.contextid=ctx.id AND (rc.capability=:cap $capany)) ";

        if (!empty($catclause)) { /// If we have found the right in categories, add child courses here too
            $sql .= "
                    UNION
                    SELECT c.id,
                           ctx.id AS ctxid, ctx.path AS ctxpath,
                           ctx.depth AS ctxdepth, ctx.contextlevel AS ctxlevel,
                           cc.path AS categorypath
                    FROM {course} c
                    JOIN {course_categories} cc
                      ON c.category=cc.id
                    JOIN {context} ctx
                      ON (c.id=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSE.")
                    $catclause";
        }

    /// Close the inline_view and join with courses table to get requested $coursefields
        $sql .= "
                ) inline_view
                INNER JOIN {course} c
                    ON inline_view.id = c.id";

    /// To keep cross-db we need to strip any prefix in the ORDER BY clause for queries using UNION
        $sql .= "
                " . preg_replace('/[a-z]+\./i', '', $sort); /// Add ORDER BY clause

        $params['userid'] = $userid;
        $params['cap']    = $cap;
        $rs = $DB->get_recordset_sql($sql, $params);
    }

/// Confirm rights (granted capability) for each course returned
    $courses = array();
    $cc = 0; // keep count
    if ($rs) {
        foreach ($rs as $c) {
            // build the context obj
            $c = make_context_subobj($c);

            if (has_capability_in_accessdata($cap, $c->context, $accessdata, $doanything)) {
                $courses[] = $c;
                if ($limit > 0 && $cc++ > $limit) {
                    break;
                }
            }
        }
        $rs->close();
    }

    return $courses;
}


/**
 * It will return a nested array showing role assignments
 * all relevant role capabilities for the user at
 * site/metacourse/course_category/course levels
 *
 * We do _not_ delve deeper than courses because the number of
 * overrides at the module/block levels is HUGE.
 *
 * [ra]   => [/path/] = array(roleid, roleid)
 * [rdef] => [/path/:roleid][capability]=permission
 * [loaded] => array('/path', '/path')
 *
 * @param $userid integer - the id of the user
 *
 */
function get_user_access_sitewide($userid) {

    global $CFG, $DB;

    /* Get in 3 cheap DB queries...
     * - role assignments - with role_caps
     * - relevant role caps
     *   - above this user's RAs
     *   - below this user's RAs - limited to course level
     */

    $accessdata           = array(); // named list
    $accessdata['ra']     = array();
    $accessdata['rdef']   = array();
    $accessdata['loaded'] = array();

    $sitectx = get_system_context();
    $base = '/'.$sitectx->id;

    //
    // Role assignments - and any rolecaps directly linked
    // because it's cheap to read rolecaps here over many
    // RAs
    //
    $sql = "SELECT ctx.path, ra.roleid, rc.capability, rc.permission
              FROM {role_assignments} ra
              JOIN {context} ctx
                   ON ra.contextid=ctx.id
              LEFT OUTER JOIN {role_capabilities} rc
                   ON (rc.roleid=ra.roleid AND rc.contextid=ra.contextid)
             WHERE ra.userid = ? AND ctx.contextlevel <= ".CONTEXT_COURSE."
          ORDER BY ctx.depth, ctx.path, ra.roleid";
    $params = array($userid);
    $rs = $DB->get_recordset_sql($sql, $params);
    //
    // raparents collects paths & roles we need to walk up
    // the parenthood to build the rdef
    //
    // the array will bulk up a bit with dups
    // which we'll later clear up
    //
    $raparents = array();
    $lastseen  = '';
    if ($rs) {
        foreach ($rs as $ra) {
            // RAs leafs are arrays to support multi
            // role assignments...
            if (!isset($accessdata['ra'][$ra->path])) {
                $accessdata['ra'][$ra->path] = array();
            }
            // only add if is not a repeat caused
            // by capability join...
            // (this check is cheaper than in_array())
            if ($lastseen !== $ra->path.':'.$ra->roleid) {
                $lastseen = $ra->path.':'.$ra->roleid;
                array_push($accessdata['ra'][$ra->path], $ra->roleid);
                $parentids = explode('/', $ra->path);
                array_shift($parentids); // drop empty leading "context"
                array_pop($parentids);   // drop _this_ context

                if (isset($raparents[$ra->roleid])) {
                    $raparents[$ra->roleid] = array_merge($raparents[$ra->roleid],
                                                          $parentids);
                } else {
                    $raparents[$ra->roleid] = $parentids;
                }
            }
            // Always add the roleded
            if (!empty($ra->capability)) {
                $k = "{$ra->path}:{$ra->roleid}";
                $accessdata['rdef'][$k][$ra->capability] = $ra->permission;
            }
        }
        unset($ra);
        $rs->close();
    }

    // Walk up the tree to grab all the roledefs
    // of interest to our user...
    // NOTE: we use a series of IN clauses here - which
    // might explode on huge sites with very convoluted nesting of
    // categories... - extremely unlikely that the number of categories
    // and roletypes is so large that we hit the limits of IN()
    $clauses = array();
    $cparams = array();
    foreach ($raparents as $roleid=>$contexts) {
        $contexts = implode(',', array_unique($contexts));
        if ($contexts ==! '') {
            $clauses[] = "(roleid=? AND contextid IN ($contexts))";
            $cparams[] = $roleid;
        }
    }
    $clauses = implode(" OR ", $clauses);
    if ($clauses !== '') {
        $sql = "SELECT ctx.path, rc.roleid, rc.capability, rc.permission
                FROM {role_capabilities} rc
                JOIN {context} ctx
                  ON rc.contextid=ctx.id
                WHERE $clauses
                ORDER BY ctx.depth ASC, ctx.path DESC, rc.roleid ASC ";
        $rs = $DB->get_recordset_sql($sql, $cparams);
        unset($clauses);

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

    //
    // Overrides for the role assignments IN SUBCONTEXTS
    // (though we still do _not_ go below the course level.
    //
    // NOTE that the JOIN w sctx is with 3-way triangulation to
    // catch overrides to the applicable role in any subcontext, based
    // on the path field of the parent.
    //
    $sql = "SELECT sctx.path, ra.roleid,
                   ctx.path AS parentpath,
                   rco.capability, rco.permission
              FROM {role_assignments} ra
              JOIN {context} ctx
                   ON ra.contextid=ctx.id
              JOIN {context} sctx
                   ON (sctx.path LIKE " . $DB->sql_concat('ctx.path',"'/%'"). " )
              JOIN {role_capabilities} rco
                   ON (rco.roleid=ra.roleid AND rco.contextid=sctx.id)
             WHERE ra.userid = ?
               AND ctx.contextlevel <= ".CONTEXT_COURSECAT."
               AND sctx.contextlevel <= ".CONTEXT_COURSE."
          ORDER BY sctx.depth, sctx.path, ra.roleid";
    $params = array($userid);
    $rs = $DB->get_recordset_sql($sql, $params);
    if ($rs) {
        foreach ($rs as $rd) {
            $k = "{$rd->path}:{$rd->roleid}";
            $accessdata['rdef'][$k][$rd->capability] = $rd->permission;
        }
        unset($rd);
        $rs->close();
    }
    return $accessdata;
}

/**
 * It add to the access ctrl array the data
 * needed by a user for a given context
 *
 * @param $userid  integer - the id of the user
 * @param $context context obj - needs path!
 * @param $accessdata array  accessdata array
 */
function load_subcontext($userid, $context, &$accessdata) {

    global $CFG, $DB;

    /* Get the additional RAs and relevant rolecaps
     * - role assignments - with role_caps
     * - relevant role caps
     *   - above this user's RAs
     *   - below this user's RAs - limited to course level
     */

    $base = "/" . SYSCONTEXTID;

    //
    // Replace $context with the target context we will
    // load. Normally, this will be a course context, but
    // may be a different top-level context.
    //
    // We have 3 cases
    //
    // - Course
    // - BLOCK/PERSON/USER/COURSE(sitecourse) hanging from SYSTEM
    // - BLOCK/MODULE/GROUP hanging from a course
    //
    // For course contexts, we _already_ have the RAs
    // but the cost of re-fetching is minimal so we don't care.
    //
    if ($context->contextlevel !== CONTEXT_COURSE
        && $context->path !== "$base/{$context->id}") {
        // Case BLOCK/MODULE/GROUP hanging from a course
        // Assumption: the course _must_ be our parent
        // If we ever see stuff nested further this needs to
        // change to do 1 query over the exploded path to
        // find out which one is the course
        $courses = explode('/',get_course_from_path($context->path));
        $targetid = array_pop($courses);
        $context = get_context_instance_by_id($targetid);

    }

    //
    // Role assignments in the context and below
    //
    $sql = "SELECT ctx.path, ra.roleid
              FROM {role_assignments} ra
              JOIN {context} ctx
                   ON ra.contextid=ctx.id
             WHERE ra.userid = ?
                   AND (ctx.path = ? OR ctx.path LIKE ?)
          ORDER BY ctx.depth, ctx.path, ra.roleid";
    $params = array($userid, $context->path, $context->path."/%");
    $rs = $DB->get_recordset_sql($sql, $params);

    //
    // Read in the RAs, preventing duplicates
    //
    if ($rs) {
        $localroles = array();
        $lastseen  = '';
        foreach ($rs as $ra) {
            if (!isset($accessdata['ra'][$ra->path])) {
                $accessdata['ra'][$ra->path] = array();
            }
            // only add if is not a repeat caused
            // by capability join...
            // (this check is cheaper than in_array())
            if ($lastseen !== $ra->path.':'.$ra->roleid) {
                $lastseen = $ra->path.':'.$ra->roleid;
                array_push($accessdata['ra'][$ra->path], $ra->roleid);
                array_push($localroles,           $ra->roleid);
            }
        }
        $rs->close();
    }

    //
    // Walk up and down the tree to grab all the roledefs
    // of interest to our user...
    //
    // NOTES
    // - we use IN() but the number of roles is very limited.
    //
    $courseroles    = aggregate_roles_from_accessdata($context, $accessdata);

    // Do we have any interesting "local" roles?
    $localroles = array_diff($localroles,$courseroles); // only "new" local roles
    $wherelocalroles='';
    if (count($localroles)) {
        // Role defs for local roles in 'higher' contexts...
        $contexts = substr($context->path, 1); // kill leading slash
        $contexts = str_replace('/', ',', $contexts);
        $localroleids = implode(',',$localroles);
        $wherelocalroles="OR (rc.roleid IN ({$localroleids})
                              AND ctx.id IN ($contexts))" ;
    }

    // We will want overrides for all of them
    $whereroles = '';
    if ($roleids  = implode(',',array_merge($courseroles,$localroles))) {
        $whereroles = "rc.roleid IN ($roleids) AND";
    }
    $sql = "SELECT ctx.path, rc.roleid, rc.capability, rc.permission
              FROM {role_capabilities} rc
              JOIN {context} ctx
                   ON rc.contextid=ctx.id
             WHERE ($whereroles
                    (ctx.id=? OR ctx.path LIKE ?))
                   $wherelocalroles
          ORDER BY ctx.depth ASC, ctx.path DESC, rc.roleid ASC ";
    $params = array($context->id, $context->path."/%");

    $newrdefs = array();
    if ($rs = $DB->get_recordset_sql($sql, $params)) {
        foreach ($rs as $rd) {
            $k = "{$rd->path}:{$rd->roleid}";
            if (!array_key_exists($k, $newrdefs)) {
                $newrdefs[$k] = array();
            }
            $newrdefs[$k][$rd->capability] = $rd->permission;
        }
        $rs->close();
    } else {
        debugging('Bad SQL encountered!');
    }

    compact_rdefs($newrdefs);
    foreach ($newrdefs as $key=>$value) {
        $accessdata['rdef'][$key] =& $newrdefs[$key];
    }

    // error_log("loaded {$context->path}");
    $accessdata['loaded'][] = $context->path;
}

/**
 * It 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 to get an overview of what a role gets under a
 * given context and below...
 *
 * @param $roleid  integer - the id of the user
 * @param $context context obj - needs path!
 * @param $accessdata      accessdata array
 *
 */
function get_role_access_bycontext($roleid, $context, $accessdata=NULL) {

    global $CFG, $DB;

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

    if (is_null($accessdata)) {
        $accessdata           = array(); // named list
        $accessdata['ra']     = array();
        $accessdata['rdef']   = array();
        $accessdata['loaded'] = array();
    }

    $contexts = substr($context->path, 1); // kill leading slash
    $contexts = str_replace('/', ',', $contexts);

    //
    // Walk up and down the tree to grab all the roledefs
    // of interest to our role...
    //
    // NOTE: we use an IN clauses here - which
    // might explode on huge sites with very convoluted nesting of
    // categories... - extremely unlikely that the number of nested
    // categories is so large that we hit the limits of IN()
    //
    $sql = "SELECT ctx.path, rc.capability, rc.permission
              FROM {role_capabilities} rc
              JOIN {context} ctx
                   ON rc.contextid=ctx.id
             WHERE rc.roleid=? AND
                   ( ctx.id IN ($contexts) OR
                    ctx.path LIKE ? )
          ORDER BY ctx.depth ASC, ctx.path DESC, rc.roleid ASC ";
    $params = array($roleid, $context->path."/%");

    if ($rs = $DB->get_recordset_sql($sql, $params)) {
        foreach ($rs as $rd) {
            $k = "{$rd->path}:{$roleid}";
            $accessdata['rdef'][$k][$rd->capability] = $rd->permission;
        }
        $rs->close();
    }

    return $accessdata;
}

/**
 * Load accessdata for a user
 * into the $ACCESSLIB_PRIVATE->accessdatabyuser global
 *
 * Used by has_capability() - but feel free
 * to call it if you are about to run a BIG
 * cron run across a bazillion users.
 *
 */
function load_user_accessdata($userid) {
    global $CFG, $ACCESSLIB_PRIVATE;

    $base = '/'.SYSCONTEXTID;

    $accessdata = get_user_access_sitewide($userid);
    $frontpagecontext = get_context_instance(CONTEXT_COURSE, SITEID);
    //
    // provide "default role" & set 'dr'
    //
    if (!empty($CFG->defaultuserroleid)) {
        $accessdata = get_role_access($CFG->defaultuserroleid, $accessdata);
        if (!isset($accessdata['ra'][$base])) {
            $accessdata['ra'][$base] = array($CFG->defaultuserroleid);
        } else {
            array_push($accessdata['ra'][$base], $CFG->defaultuserroleid);
        }
        $accessdata['dr'] = $CFG->defaultuserroleid;
    }

    //
    // provide "default frontpage role"
    //
    if (!empty($CFG->defaultfrontpageroleid)) {
        $base = '/'. SYSCONTEXTID .'/'. $frontpagecontext->id;
        $accessdata = get_default_frontpage_role_access($CFG->defaultfrontpageroleid, $accessdata);
        if (!isset($accessdata['ra'][$base])) {
            $accessdata['ra'][$base] = array($CFG->defaultfrontpageroleid);
        } else {
            array_push($accessdata['ra'][$base], $CFG->defaultfrontpageroleid);
        }
    }
    // for dirty timestamps in cron
    $accessdata['time'] = time();

    $ACCESSLIB_PRIVATE->accessdatabyuser[$userid] = $accessdata;
    compact_rdefs($ACCESSLIB_PRIVATE->accessdatabyuser[$userid]['rdef']);

    return $ACCESSLIB_PRIVATE->accessdatabyuser[$userid];
}

/**
 * Use shared copy of role definistions stored in $ACCESSLIB_PRIVATE->roledefinitions;
 * @param array $rdefs array of role definitions in contexts
 */
function compact_rdefs(&$rdefs) {
    global $ACCESSLIB_PRIVATE;

    /*
     * This is a basic sharing only, we could also
     * use md5 sums of values. The main purpose is to
     * reduce mem in cron jobs - many users in $ACCESSLIB_PRIVATE->accessdatabyuser array.
     */

    foreach ($rdefs as $key => $value) {
        if (!array_key_exists($key, $ACCESSLIB_PRIVATE->roledefinitions)) {
            $ACCESSLIB_PRIVATE->roledefinitions[$key] = $rdefs[$key];
        }
        $rdefs[$key] =& $ACCESSLIB_PRIVATE->roledefinitions[$key];
    }
}

/**
 *  A convenience function to completely load all the capabilities
 *  for the current user.   This is what gets called from complete_user_login()
 *  for example. Call it only _after_ you've setup $USER and called
 *  check_enrolment_plugins();
 *
 */
function load_all_capabilities() {
    global $USER, $CFG, $ACCESSLIB_PRIVATE;

    // roles not installed yet - we are in the middle of installation
    if (empty($CFG->rolesactive)) {
        return;
    }

    $base = '/'.SYSCONTEXTID;

    if (isguestuser()) {
        $guest = get_guest_role();

        // Load the rdefs
        $USER->access = get_role_access($guest->id);
        // Put the ghost enrolment in place...
        $USER->access['ra'][$base] = array($guest->id);


    } else if (isloggedin()) {

        $accessdata = get_user_access_sitewide($USER->id);

        //
        // provide "default role" & set 'dr'
        //
        if (!empty($CFG->defaultuserroleid)) {
            $accessdata = get_role_access($CFG->defaultuserroleid, $accessdata);
            if (!isset($accessdata['ra'][$base])) {
                $accessdata['ra'][$base] = array($CFG->defaultuserroleid);
            } else {
                array_push($accessdata['ra'][$base], $CFG->defaultuserroleid);
            }
            $accessdata['dr'] = $CFG->defaultuserroleid;
        }

        $frontpagecontext = get_context_instance(CONTEXT_COURSE, SITEID);

        //
        // provide "default frontpage role"
        //
        if (!empty($CFG->defaultfrontpageroleid)) {
            $base = '/'. SYSCONTEXTID .'/'. $frontpagecontext->id;
            $accessdata = get_default_frontpage_role_access($CFG->defaultfrontpageroleid, $accessdata);
            if (!isset($accessdata['ra'][$base])) {
                $accessdata['ra'][$base] = array($CFG->defaultfrontpageroleid);
            } else {
                array_push($accessdata['ra'][$base], $CFG->defaultfrontpageroleid);
            }
        }
        $USER->access = $accessdata;

    } else if (!empty($CFG->notloggedinroleid)) {
        $USER->access = get_role_access($CFG->notloggedinroleid);
        $USER->access['ra'][$base] = array($CFG->notloggedinroleid);
    }

    // Timestamp to read dirty context timestamps later
    $USER->access['time'] = time();
    $ACCESSLIB_PRIVATE->dirtycontexts = array();

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

/**
 * 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.
 *
 * That is - completely transparent to the user.
 *
 * Note: rewrites $USER->access completely.
 *
 */
function reload_all_capabilities() {
    global $USER, $DB;

    // error_log("reloading");
    // copy switchroles
    $sw = array();
    if (isset($USER->access['rsw'])) {
        $sw = $USER->access['rsw'];
        // error_log(print_r($sw,1));
    }

    unset($USER->access);
    unset($USER->mycourses);

    load_all_capabilities();

    foreach ($sw as $path => $roleid) {
        $context = $DB->get_record('context', array('path'=>$path));
        role_switch($roleid, $context);
    }

}

/**
 * Adds a temp role to an accessdata array.
 *
 * Useful for the "temporary guest" access
 * we grant to logged-in users.
 *
 * Note - assumes a course context!
 *
 */
function load_temp_role($context, $roleid, $accessdata) {

    global $CFG, $DB;

    //
    // Load rdefs for the role in -
    // - this context
    // - all the parents
    // - and below - IOWs overrides...
    //

    // turn the path into a list of context ids
    $contexts = substr($context->path, 1); // kill leading slash
    $contexts = str_replace('/', ',', $contexts);

    $sql = "SELECT ctx.path, rc.capability, rc.permission
              FROM {context} ctx
              JOIN {role_capabilities} rc
                   ON rc.contextid=ctx.id
             WHERE (ctx.id IN ($contexts)
                    OR ctx.path LIKE ?)
                   AND rc.roleid = ?
          ORDER BY ctx.depth, ctx.path";
    $params = array($context->path."/%", $roleid);
    if ($rs = $DB->get_recordset_sql($sql, $params)) {
        foreach ($rs as $rd) {
            $k = "{$rd->path}:{$roleid}";
            $accessdata['rdef'][$k][$rd->capability] = $rd->permission;
        }
        $rs->close();
    }

    //
    // Say we loaded everything for the course context
    // - which we just did - if the user gets a proper
    // RA in this session, this data will need to be reloaded,
    // but that is handled by the complete accessdata reload
    //
    array_push($accessdata['loaded'], $context->path);

    //
    // Add the ghost RA
    //
    if (isset($accessdata['ra'][$context->path])) {
        array_push($accessdata['ra'][$context->path], $roleid);
    } else {
        $accessdata['ra'][$context->path] = array($roleid);
    }

    return $accessdata;
}


/**
 * Check all the login enrolment information for the given user object
 * by querying the enrolment plugins
 * @return void
 */
function check_enrolment_plugins(&$user) {
    global $CFG;

    if (empty($user->id) or isguestuser($user)) {
        // shortcut - there is no enrolment work for guests and not-logged-in users
        return;
    }

    static $inprogress = array();  // To prevent this function being called more than once in an invocation

    if (!empty($inprogress[$user->id])) {
        return;
    }

    $inprogress[$user->id] = true;  // Set the flag

    require_once($CFG->dirroot .'/enrol/enrol.class.php');

    if (!($plugins = explode(',', $CFG->enrol_plugins_enabled))) {
        $plugins = array($CFG->enrol);
    }

    foreach ($plugins as $plugin) {
        $enrol = enrolment_factory::factory($plugin);
        if (method_exists($enrol, 'setup_enrolments')) {  /// Plugin supports Roles (Moodle 1.7 and later)
            $enrol->setup_enrolments($user);
        } else {                                          /// Run legacy enrolment methods
            if (method_exists($enrol, 'get_student_courses')) {
                $enrol->get_student_courses($user);
            }
            if (method_exists($enrol, 'get_teacher_courses')) {
                $enrol->get_teacher_courses($user);
            }

        /// deal with $user->students and $user->teachers stuff
            unset($user->student);
            unset($user->teacher);
        }
        unset($enrol);
    }

    unset($inprogress[$user->id]);  // Unset the flag
}

/**
 * Returns array of all legacy roles.
 */
function get_legacy_roles() {
    return array(
        'admin'          => 'moodle/legacy:admin',
        'coursecreator'  => 'moodle/legacy:coursecreator',
        'editingteacher' => 'moodle/legacy:editingteacher',
        'teacher'        => 'moodle/legacy:teacher',
        'student'        => 'moodle/legacy:student',
        'guest'          => 'moodle/legacy:guest',
        'user'           => 'moodle/legacy:user'
    );
}

function get_legacy_type($roleid) {
    $sitecontext = get_context_instance(CONTEXT_SYSTEM);
    $legacyroles = get_legacy_roles();

    $result = '';
    foreach($legacyroles as $ltype=>$lcap) {
        $localoverride = get_local_override($roleid, $sitecontext->id, $lcap);
        if (!empty($localoverride->permission) and $localoverride->permission == CAP_ALLOW) {
            //choose first selected legacy capability - reset the rest
            if (empty($result)) {
                $result = $ltype;
            } else {
                unassign_capability($lcap, $roleid);
            }
        }
    }

    return $result;
}

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

    $legacyroles = get_legacy_roles();

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

        $systemcontext = get_context_instance(CONTEXT_SYSTEM);

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

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


/**
 * Checks to see if a capability is one of the special capabilities
 *      (either a legacy capability, or moodle/site:doanything).
 * @param string $capabilityname the capability name, e.g. mod/forum:view.
 * @return boolean whether this is one of the special capabilities.
 */
function is_legacy($capabilityname) {
    if ($capabilityname == 'moodle/site:doanything' || strpos($capabilityname, 'moodle/legacy') === 0) {
        return true;
    } else {
        return false;
    }
}

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

/**********************************
 * Context Manipulation functions *
 **********************************/

/**
 * Create a new context record for use by all roles-related stuff
 * assumes that the caller has done the homework.
 *
 * @param $level
 * @param $instanceid
 *
 * @return object newly created context
 */
function create_context($contextlevel, $instanceid) {

    global $CFG, $DB;

    if ($contextlevel == CONTEXT_SYSTEM) {
        return create_system_context();
    }

    $context = new object();
    $context->contextlevel = $contextlevel;
    $context->instanceid = $instanceid;

    // Define $context->path based on the parent
    // context. In other words... Who is your daddy?
    $basepath  = '/' . SYSCONTEXTID;
    $basedepth = 1;

    $result = true;
    $error_message = null;

    switch ($contextlevel) {
        case CONTEXT_COURSECAT:
            $sql = "SELECT ctx.path, ctx.depth
                      FROM {context}           ctx
                      JOIN {course_categories} cc
                           ON (cc.parent=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSECAT.")
                     WHERE cc.id=?";
            $params = array($instanceid);
            if ($p = $DB->get_record_sql($sql, $params)) {
                $basepath  = $p->path;
                $basedepth = $p->depth;
            } else if ($category = $DB->get_record('course_categories', array('id'=>$instanceid))) {
                if (empty($category->parent)) {
                    // ok - this is a top category
                } else if ($parent = get_context_instance(CONTEXT_COURSECAT, $category->parent)) {
                    $basepath  = $parent->path;
                    $basedepth = $parent->depth;
                } else {
                    // wrong parent category - no big deal, this can be fixed later
                    $basepath  = null;
                    $basedepth = 0;
                }
            } else {
                // incorrect category id
                $error_message = "incorrect course category id ($instanceid)";
                $result = false;
            }
            break;

        case CONTEXT_COURSE:
            $sql = "SELECT ctx.path, ctx.depth
                      FROM {context} ctx
                      JOIN {course}  c
                           ON (c.category=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSECAT.")
                     WHERE c.id=? AND c.id !=" . SITEID;
            $params = array($instanceid);
            if ($p = $DB->get_record_sql($sql, $params)) {
                $basepath  = $p->path;
                $basedepth = $p->depth;
            } else if ($course = $DB->get_record('course', array('id'=>$instanceid))) {
                if ($course->id == SITEID) {
                    //ok - no parent category
                } else if ($parent = get_context_instance(CONTEXT_COURSECAT, $course->category)) {
                    $basepath  = $parent->path;
                    $basedepth = $parent->depth;
                } else {
                    // wrong parent category of course - no big deal, this can be fixed later
                    $basepath  = null;
                    $basedepth = 0;
                }
            } else if ($instanceid == SITEID) {
                // no errors for missing site course during installation
                return false;
            } else {
                // incorrect course id
                $error_message = "incorrect course id ($instanceid)";
                $result = false;
            }
            break;

        case CONTEXT_MODULE:
            $sql = "SELECT ctx.path, ctx.depth
                      FROM {context}        ctx
                      JOIN {course_modules} cm
                           ON (cm.course=ctx.instanceid AND ctx.contextlevel=".CONTEXT_COURSE.")
                     WHERE cm.id=?";
            $params = array($instanceid);
            if ($p = $DB->get_record_sql($sql, $params)) {
                $basepath  = $p->path;
                $basedepth = $p->depth;
            } else if ($cm = $DB->get_record('course_modules', array('id'=>$instanceid))) {
                if ($parent = get_context_instance(CONTEXT_COURSE, $cm->course)) {
                    $basepath  = $parent->path;
                    $basedepth = $parent->depth;
                } else {
                    // course does not exist - modules can not exist without a course
                    $error_message = "course does not exist ($cm->course) - modules can not exist without a course";
                    $result = false;
                }
            } else {
                // cm does not exist
                $error_message = "cm with id $instanceid does not exist";
                $result = false;
            }
            break;

        case CONTEXT_BLOCK:
            // Only non-pinned & course-page based
            $sql = "SELECT ctx.path, ctx.depth
                      FROM {context} ctx
                      JOIN {block_instances} bi ON (bi.contextid=ctx.id)
                     WHERE bi.id=? AND ctx.contextlevel=?";
            $params = array($instanceid, CONTEXT_COURSE);
            if ($p = $DB->get_record_sql($sql, $params)) {
                $basepath  = $p->path;
                $basedepth = $p->depth;
            } else {
                // block does not exist
                $error_message = 'block or parent context does not exist';
                $result = false;
            }
            break;
        case CONTEXT_USER:
            // default to basepath
            break;
    }

    // if grandparents unknown, maybe rebuild_context_path() will solve it later
    if ($basedepth != 0) {
        $context->depth = $basedepth+1;
    }

    if ($result and $id = $DB->insert_record('context', $context)) {
        // can't set the full path till we know the id!
        if ($basedepth != 0 and !empty($basepath)) {
            $DB->set_field('context', 'path', $basepath.'/'. $id, array('id'=>$id));
        }
        return get_context_instance_by_id($id);

    } else {
        debugging('Error: could not insert new context level "'.
                  s($contextlevel).'", instance "'.
                  s($instanceid).'". ' . $error_message);

        return false;
    }
}

/**
 * Returns system context or null if can not be created yet.
 * @param bool $cache use caching
 * @return mixed system context or null
 */
function get_system_context($cache=true) {
    global $DB, $ACCESSLIB_PRIVATE;
    if ($cache and defined('SYSCONTEXTID')) {
        if (is_null($ACCESSLIB_PRIVATE->systemcontext)) {
            $ACCESSLIB_PRIVATE->systemcontext = new object();
            $ACCESSLIB_PRIVATE->systemcontext->id           = SYSCONTEXTID;
            $ACCESSLIB_PRIVATE->systemcontext->contextlevel = CONTEXT_SYSTEM;
            $ACCESSLIB_PRIVATE->systemcontext->instanceid   = 0;
            $ACCESSLIB_PRIVATE->systemcontext->path         = '/'.SYSCONTEXTID;
            $ACCESSLIB_PRIVATE->systemcontext->depth        = 1;
        }
        return $ACCESSLIB_PRIVATE->systemcontext;
    }
    try {
        // TODO: can not use get_record() because we do not know if query failed :-(
        //       switch to get_record() later
        $contextarr = $DB->get_records('context', array('contextlevel'=>CONTEXT_SYSTEM));
        if ($contextarr === false) {
            return null;
        }
        $context = $contextarr ? reset($contextarr) : null;
    } catch (dml_exception $e) {
        //table does not exist yet, sorry
        return null;
    }

    if (!$context) {
        $context = new object();
        $context->contextlevel = CONTEXT_SYSTEM;
        $context->instanceid   = 0;
        $context->depth        = 1;
        $context->path         = NULL; //not known before insert

        try {
            if (!$context->id = $DB->insert_record('context', $context)) {
            // can not create context yet, sorry
                return null;
            }
        } catch (dml_exception $e) {
            return null;
        }
    }

    if (!isset($context->depth) or $context->depth != 1 or $context->instanceid != 0 or $context->path != '/'.$context->id) {
        $context->instanceid   = 0;
        $context->path         = '/'.$context->id;
        $context->depth        = 1;
        $DB->update_record('context', $context);
    }

    if (!defined('SYSCONTEXTID')) {
        define('SYSCONTEXTID', $context->id);
    }

    $ACCESSLIB_PRIVATE->systemcontext = $context;
    return $ACCESSLIB_PRIVATE->systemcontext;
}

/**
 * Remove a context record and any dependent entries,
 * removes context from static context cache too
 * @param $level
 * @param $instanceid
 *
 * @return bool properly deleted
 */
function delete_context($contextlevel, $instanceid) {
    global $DB, $ACCESSLIB_PRIVATE;

    // do not use get_context_instance(), because the related object might not exist,
    // or the context does not exist yet and it would be created now
    if ($context = $DB->get_record('context', array('contextlevel'=>$contextlevel, 'instanceid'=>$instanceid))) {
        $result = $DB->delete_records('role_assignments', array('contextid'=>$context->id)) &&
                  $DB->delete_records('role_capabilities', array('contextid'=>$context->id)) &&
                  $DB->delete_records('role_names', array('contextid'=>$context->id)) &&
                  $DB->delete_records('context', array('id'=>$context->id));

        // do not mark dirty contexts if parents unknown
        if (!is_null($context->path) and $context->depth > 0) {
            mark_context_dirty($context->path);
        }

        // purge static context cache if entry present
        unset($ACCESSLIB_PRIVATE->contexts[$contextlevel][$instanceid]);
        unset($ACCESSLIB_PRIVATE->contextsbyid[$context->id]);

        blocks_delete_all_for_context($context->id);
        filter_delete_all_for_context($context->id);

        return $result;
    } else {

        return true;
    }
}

/**
 * Precreates all contexts including all parents
 * @param int $contextlevel, empty means all
 * @param bool $buildpaths update paths and depths
 * @return void
 */
function create_contexts($contextlevel=null, $buildpaths=true) {
    global $DB;

    //make sure system context exists
    $syscontext = get_system_context(false);

    if (empty($contextlevel) or $contextlevel == CONTEXT_COURSECAT
                             or $contextlevel == CONTEXT_COURSE
                             or $contextlevel == CONTEXT_MODULE
                             or $contextlevel == CONTEXT_BLOCK) {
        $sql = "INSERT INTO {context} (contextlevel, instanceid)
                SELECT ".CONTEXT_COURSECAT.", cc.id
                  FROM {course}_categories cc
                 WHERE NOT EXISTS (SELECT 'x'
                                     FROM {context} cx
                                    WHERE cc.id = cx.instanceid AND cx.contextlevel=".CONTEXT_COURSECAT.")";
        $DB->execute($sql);

    }

    if (empty($contextlevel) or $contextlevel == CONTEXT_COURSE
                             or $contextlevel == CONTEXT_MODULE
                             or $contextlevel == CONTEXT_BLOCK) {
        $sql = "INSERT INTO {context} (contextlevel, instanceid)
                SELECT ".CONTEXT_COURSE.", c.id
                  FROM {course} c
                 WHERE NOT EXISTS (SELECT 'x'
                                     FROM {context} cx
                                    WHERE c.id = cx.instanceid AND cx.contextlevel=".CONTEXT_COURSE.")";
        $DB->execute($sql);

    }

    if (empty($contextlevel) or $contextlevel == CONTEXT_MODULE) {
        $sql = "INSERT INTO {context} (contextlevel, instanceid)
                SELECT ".CONTEXT_MODULE.", cm.id
                  FROM {course}_modules cm
                 WHERE NOT EXISTS (SELECT 'x'
                                     FROM {context} cx
                                    WHERE cm.id = cx.instanceid AND cx.contextlevel=".CONTEXT_MODULE.")";
        $DB->execute($sql);
    }

    if (empty($contextlevel) or $contextlevel == CONTEXT_BLOCK) {
        $sql = "INSERT INTO {context} (contextlevel, instanceid)
                SELECT ".CONTEXT_BLOCK.", bi.id
                  FROM {block_instances} bi
                 WHERE NOT EXISTS (SELECT 'x'
                                     FROM {context} cx
                                    WHERE bi.id = cx.instanceid AND cx.contextlevel=".CONTEXT_BLOCK.")";
        $DB->execute($sql);
    }

    if (empty($contextlevel) or $contextlevel == CONTEXT_USER) {
        $sql = "INSERT INTO {context} (contextlevel, instanceid)
                SELECT ".CONTEXT_USER.", u.id
                  FROM {user} u
                 WHERE u.deleted=0
                   AND NOT EXISTS (SELECT 'x'
                                     FROM {context} cx
                                    WHERE u.id = cx.instanceid AND cx.contextlevel=".CONTEXT_USER.")";
        $DB->execute($sql);

    }

    if ($buildpaths) {
        build_context_path(false);
    }
}

/**
 * Remove stale context records
 *
 * @return bool
 */
function cleanup_contexts() {
    global $DB;

    $sql = "  SELECT c.contextlevel,
                     c.instanceid AS instanceid
                FROM {context} c
                LEFT OUTER JOIN {course}_categories t
                     ON c.instanceid = t.id
               WHERE t.id IS NULL AND c.contextlevel = ".CONTEXT_COURSECAT."
            UNION
              SELECT c.contextlevel,
                     c.instanceid
                FROM {context} c
                LEFT OUTER JOIN {course} t
                     ON c.instanceid = t.id
               WHERE t.id IS NULL AND c.contextlevel = ".CONTEXT_COURSE."
            UNION
              SELECT c.contextlevel,
                     c.instanceid
                FROM {context} c
                LEFT OUTER JOIN {course}_modules t
                     ON c.instanceid = t.id
               WHERE t.id IS NULL AND c.contextlevel = ".CONTEXT_MODULE."
            UNION
              SELECT c.contextlevel,
                     c.instanceid
                FROM {context} c
                LEFT OUTER JOIN {user} t
                     ON c.instanceid = t.id
               WHERE t.id IS NULL AND c.contextlevel = ".CONTEXT_USER."
            UNION
              SELECT c.contextlevel,
                     c.instanceid
                FROM {context} c
                LEFT OUTER JOIN {block_instances} t
                     ON c.instanceid = t.id
               WHERE t.id IS NULL AND c.contextlevel = ".CONTEXT_BLOCK."
           ";
    if ($rs = $DB->get_recordset_sql($sql)) {
        $DB->begin_sql();
        $ok = true;
        foreach ($rs as $ctx) {
            if (!delete_context($ctx->contextlevel, $ctx->instanceid)) {
                $ok = false;
                break;
            }
        }
        $rs->close();
        if ($ok) {
            $DB->commit_sql();
            return true;
        } else {
            $DB->rollback_sql();
            return false;
        }
    }
    return true;
}

/**
 * Preloads all contexts relating to a course: course, modules, and blocks.
 *
 * @param int $courseid Course ID
 * @return void
 */
function preload_course_contexts($courseid) {
    global $DB, $ACCESSLIB_PRIVATE;

    // Users can call this multiple times without doing any harm
    global $ACCESSLIB_PRIVATE;
    if (array_key_exists($courseid, $ACCESSLIB_PRIVATE->preloadedcourses)) {
        return;
    }

    $params = array($courseid, $courseid, $courseid);
    $sql = "SELECT x.instanceid, x.id, x.contextlevel, x.path, x.depth
              FROM {course_modules} cm
              JOIN {context} x ON x.instanceid=cm.id
             WHERE cm.course=? AND x.contextlevel=".CONTEXT_MODULE."

         UNION ALL

            SELECT x.instanceid, x.id, x.contextlevel, x.path, x.depth
              FROM {context} px
              JOIN {block_instances} bi ON bi.contextid = px.id
              JOIN {context} x ON x.instanceid=bi.id
              WHERE px.instanceid = ? AND px.contextlevel = ".CONTEXT_COURSE."
                   AND x.contextlevel=".CONTEXT_BLOCK."

         UNION ALL

            SELECT x.instanceid, x.id, x.contextlevel, x.path, x.depth
              FROM {context} x
             WHERE x.instanceid=? AND x.contextlevel=".CONTEXT_COURSE."";

    $rs = $DB->get_recordset_sql($sql, $params);
    foreach($rs as $context) {
        cache_context($context);
    }
    $rs->close();
    $ACCESSLIB_PRIVATE->preloadedcourses[$courseid] = true;
}

/**
 * Get the context instance as an object. This function will create the
 * context instance if it does not exist yet.
 * @param integer $level The context level, for example CONTEXT_COURSE, or CONTEXT_MODULE.
 * @param integer $instance The instance id. For $level = CONTEXT_COURSE, this would be $course->id,
 *      for $level = CONTEXT_MODULE, this would be $cm->id. And so on.
 * @return object The context object.
 */
function get_context_instance($contextlevel, $instance=0) {

    global $DB, $ACCESSLIB_PRIVATE;
    static $allowed_contexts = array(CONTEXT_SYSTEM, CONTEXT_USER, CONTEXT_COURSECAT, CONTEXT_COURSE, CONTEXT_MODULE, CONTEXT_BLOCK);

    if ($contextlevel === 'clearcache') {
        // TODO: Remove for v2.0
        // No longer needed, but we'll catch it to avoid erroring out on custom code.
        // This used to be a fix for MDL-9016
        // "Restoring into existing course, deleting first
        //  deletes context and doesn't recreate it"
        return false;
    }

/// System context has special cache
    if ($contextlevel == CONTEXT_SYSTEM) {
        return get_system_context();
    }

/// check allowed context levels
    if (!in_array($contextlevel, $allowed_contexts)) {
        // fatal error, code must be fixed - probably typo or switched parameters
        print_error('invalidcourselevel');
    }

    if (!is_array($instance)) {
    /// Check the cache
        if (isset($ACCESSLIB_PRIVATE->contexts[$contextlevel][$instance])) {  // Already cached
            return $ACCESSLIB_PRIVATE->contexts[$contextlevel][$instance];
        }

    /// Get it from the database, or create it
        if (!$context = $DB->get_record('context', array('contextlevel'=>$contextlevel, 'instanceid'=>$instance))) {
            $context = create_context($contextlevel, $instance);
        }

    /// Only add to cache if context isn't empty.
        if (!empty($context)) {
            cache_context($context);
        }

        return $context;
    }


/// ok, somebody wants to load several contexts to save some db queries ;-)
    $instances = $instance;
    $result = array();

    foreach ($instances as $key=>$instance) {
    /// Check the cache first
        if (isset($ACCESSLIB_PRIVATE->contexts[$contextlevel][$instance])) {  // Already cached
            $result[$instance] = $ACCESSLIB_PRIVATE->contexts[$contextlevel][$instance];
            unset($instances[$key]);
            continue;
        }
    }

    if ($instances) {
        list($instanceids, $params) = $DB->get_in_or_equal($instances, SQL_PARAMS_QM);
        array_unshift($params, $contextlevel);
        $sql = "SELECT instanceid, id, contextlevel, path, depth
                  FROM {context}
                 WHERE contextlevel=? AND instanceid $instanceids";

        if (!$contexts = $DB->get_records_sql($sql, $params)) {
            $contexts = array();
        }

        foreach ($instances as $instance) {
            if (isset($contexts[$instance])) {
                $context = $contexts[$instance];
            } else {
                $context = create_context($contextlevel, $instance);
            }

            if (!empty($context)) {
                cache_context($context);
            }

            $result[$instance] = $context;
        }
    }

    return $result;
}


/**
 * Get a context instance as an object, from a given context id.
 * @param mixed $id a context id or array of ids.
 * @return mixed object or array of the context object.
 */
function get_context_instance_by_id($id) {
    global $DB, $ACCESSLIB_PRIVATE;

    if ($id == SYSCONTEXTID) {
        return get_system_context();
    }

    if (isset($ACCESSLIB_PRIVATE->contextsbyid[$id])) {  // Already cached
        return $ACCESSLIB_PRIVATE->contextsbyid[$id];
    }

    if ($context = $DB->get_record('context', array('id'=>$id))) {
        cache_context($context);
        return $context;
    }

    return false;
}


/**
 * Get the local override (if any) for a given capability in a role in a context
 * @param $roleid
 * @param $contextid
 * @param $capability
 */
function get_local_override($roleid, $contextid, $capability) {
    global $DB;
    return $DB->get_record('role_capabilities', array('roleid'=>$roleid, 'capability'=>$capability, 'contextid'=>$contextid));
}


/************************************
 *    DB TABLE RELATED FUNCTIONS    *
 ************************************/

/**
 * function that creates a role
 * @param name - role name
 * @param shortname - role short name
 * @param description - role description
 * @param legacy - optional legacy capability
 * @return id or dml_exception
 */
function create_role($name, $shortname, $description, $legacy='') {
    global $DB;

    // Get the system context.
    $context = get_context_instance(CONTEXT_SYSTEM);

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

    //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);

    if ($legacy) {
        assign_capability($legacy, CAP_ALLOW, $id, $context->id);
    }

    return $id;
}

/**
 * function that deletes a role and cleanups up after it
 * @param roleid - id of role to delete
 * @return success
 */
function delete_role($roleid) {
    global $CFG, $DB;
    $success = true;

// mdl 10149, check if this is the last active admin role
// if we make the admin role not deletable then this part can go

    $systemcontext = get_context_instance(CONTEXT_SYSTEM);

    if ($role = $DB->get_record('role', array('id'=>$roleid))) {
        if ($DB->record_exists('role_capabilities', array('contextid'=>$systemcontext->id, 'roleid'=>$roleid, 'capability'=>'moodle/site:doanything'))) {
            // deleting an admin role
            $status = false;
            if ($adminroles = get_roles_with_capability('moodle/site:doanything', CAP_ALLOW, $systemcontext)) {
                foreach ($adminroles as $adminrole) {
                    if ($adminrole->id != $roleid) {
                        // some other admin role
                        if ($DB->record_exists('role_assignments', array('roleid'=>$adminrole->id, 'contextid'=>$systemcontext->id))) {
                            // found another admin role with at least 1 user assigned
                            $status = true;
                            break;
                        }
                    }
                }
            }
            if ($status !== true) {
                print_error('cannotdeleterolenoadmin', 'access');
            }
        }
    }

// first unssign all users
    if (!role_unassign($roleid)) {
        debugging("Error while unassigning all users from role with ID $roleid!");
        $success = false;
    }

// cleanup all references to this role, ignore errors
    if ($success) {
        $DB->delete_records('role_capabilities',   array('roleid'=>$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));

    if ($success and !$DB->delete_records('role', array('id'=>$roleid))) {
        debugging("Could not delete role record with ID $roleid!");
        $success = false;
    }

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

    return $success;
}

/**
 * Function to write context specific overrides, or default capabilities.
 * @param module - string name
 * @param capability - string name
 * @param contextid - context id
 * @param roleid - role id
 * @param permission - int 1,-1 or -1000
 * should not be writing if permission is 0
 */
function assign_capability($capability, $permission, $roleid, $contextid, $overwrite=false) {

    global $USER, $DB;

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

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

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

    $cap = new object;
    $cap->contextid = $contextid;
    $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;
        return $DB->update_record('role_capabilities', $cap);
    } else {
        $c = $DB->get_record('context', array('id'=>$contextid));
        return $DB->insert_record('role_capabilities', $cap);
    }
}

/**
 * Unassign a capability from a role.
 * @param $roleid - the role id
 * @param $capability - the name of the capability
 * @return boolean - success or failure
 */
function unassign_capability($capability, $roleid, $contextid=NULL) {
    global $DB;

    if (isset($contextid)) {
        // delete from context rel, if this is the last override in this context
        $status = $DB->delete_records('role_capabilities', array('capability'=>$capability,
                'roleid'=>$roleid, 'contextid'=>$contextid));
    } else {
        $status = $DB->delete_records('role_capabilities', array('capability'=>$capability,
                'roleid'=>$roleid));
    }
    return $status;
}


/**
 * 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 assignment only.
 * @param $capability - capability name (string)
 * @param $permission - optional, the permission defined for this capability
 *                      either CAP_ALLOW, CAP_PREVENT or CAP_PROHIBIT
 * @return array or role objects
 */
function get_roles_with_capability($capability, $permission=NULL, $context='') {

    global $CFG, $DB;

    $params = array();

    if ($context) {
        if ($contexts = get_parent_contexts($context)) {
            $listofcontexts = '('.implode(',', $contexts).')';
        } else {
            $sitecontext = get_context_instance(CONTEXT_SYSTEM);
            $listofcontexts = '('.$sitecontext->id.')'; // must be site
        }
        $contextstr = "AND (rc.contextid = ? OR  rc.contextid IN $listofcontexts)";
        $params[] = $context->id;
    } else {
        $contextstr = '';
    }

    $selectroles = "SELECT r.*
                      FROM {role} r,
                           {role_capabilities} rc
                     WHERE rc.capability = ?
                           AND rc.roleid = r.id $contextstr";

    array_unshift($params, $capability);

    if (isset($permission)) {
        $selectroles .= " AND rc.permission = ?";
        $params[] = $permission;
    }
    return $DB->get_records_sql($selectroles, $params);
}


/**
 * This function makes a role-assignment (a role for a user or group in a particular context)
 * @param $roleid - the role of the id
 * @param $userid - userid
 * @param $groupid - group id
 * @param $contextid - id of the context
 * @param $timestart - time this assignment becomes effective
 * @param $timeend - time this assignemnt ceases to be effective
 * @uses $USER
 * @return id - new id of the assigment
 */
function role_assign($roleid, $userid, $groupid, $contextid, $timestart=0, $timeend=0, $hidden=0, $enrol='manual',$timemodified='') {
    global $USER, $CFG, $DB;

/// Do some data validation

    if (empty($roleid)) {
        debugging('Role ID not provided');
        return false;
    }

    if (empty($userid) && empty($groupid)) {
        debugging('Either userid or groupid must be provided');
        return false;
    }

    if ($userid && !$DB->record_exists('user', array('id'=>$userid))) {
        debugging('User ID '.intval($userid).' does not exist!');
        return false;
    }

    if ($groupid && !groups_group_exists($groupid)) {
        debugging('Group ID '.intval($groupid).' does not exist!');
        return false;
    }

    if (!$context = get_context_instance_by_id($contextid)) {
        debugging('Context ID '.intval($contextid).' does not exist!');
        return false;
    }

    if (($timestart and $timeend) and ($timestart > $timeend)) {
        debugging('The end time can not be earlier than the start time');
        return false;
    }

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

/// Check for existing entry
    if ($userid) {
        $ra = $DB->get_record('role_assignments', array('roleid'=>$roleid, 'contextid'=>$context->id, 'userid'=>$userid));
    } else {
        $ra = $DB->get_record('role_assignments', array('roleid'=>$roleid, 'contextid'=>$context->id, 'groupid'=>$groupid));
    }

    if (empty($ra)) {             // Create a new entry
        $ra = new object();
        $ra->roleid = $roleid;
        $ra->contextid = $context->id;
        $ra->userid = $userid;
        $ra->hidden = $hidden;
        $ra->enrol = $enrol;
    /// Always round timestart downto 100 secs to help DBs to use their own caching algorithms
    /// by repeating queries with the same exact parameters in a 100 secs time window
        $ra->timestart = round($timestart, -2);
        $ra->timeend = $timeend;
        $ra->timemodified = $timemodified;
        $ra->modifierid = empty($USER->id) ? 0 : $USER->id;

        if (!$ra->id = $DB->insert_record('role_assignments', $ra)) {
            return false;
        }

    } else {                      // We already have one, just update it
        $ra->id = $ra->id;
        $ra->hidden = $hidden;
        $ra->enrol = $enrol;
    /// Always round timestart downto 100 secs to help DBs to use their own caching algorithms
    /// by repeating queries with the same exact parameters in a 100 secs time window
        $ra->timestart = round($timestart, -2);
        $ra->timeend = $timeend;
        $ra->timemodified = $timemodified;
        $ra->modifierid = empty($USER->id) ? 0 : $USER->id;

        if (!$DB->update_record('role_assignments', $ra)) {
            return false;
        }
    }

/// mark context as dirty - modules might use has_capability() in xxx_role_assing()
/// again expensive, but needed
    mark_context_dirty($context->path);

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

/// Ask all the modules if anything needs to be done for this user
    if ($mods = get_list_of_plugins('mod')) {
        foreach ($mods as $mod) {
            include_once($CFG->dirroot.'/mod/'.$mod.'/lib.php');
            $functionname = $mod.'_role_assign';
            if (function_exists($functionname)) {
                $functionname($userid, $context, $roleid);
            }
        }
    }

    /// now handle metacourse role assignments if in course context
    if ($context->contextlevel == CONTEXT_COURSE) {
        if ($parents = $DB->get_records('course_meta', array('child_course'=>$context->instanceid))) {
            foreach ($parents as $parent) {
                sync_metacourse($parent->parent_course);
            }
        }
    }

    events_trigger('role_assigned', $ra);

    return $ra->id;
}


/**
 * Deletes one or more role assignments.   You must specify at least one parameter.
 * @param $roleid
 * @param $userid
 * @param $groupid
 * @param $contextid
 * @param $enrol unassign only if enrolment type matches, NULL means anything
 * @return boolean - success or failure
 */
function role_unassign($roleid=0, $userid=0, $groupid=0, $contextid=0, $enrol=NULL) {

    global $USER, $CFG, $DB;
    require_once($CFG->dirroot.'/group/lib.php');

    $success = true;

    $args = array('roleid', 'userid', 'groupid', 'contextid');
    $select = array();
    $params = array();

    foreach ($args as $arg) {
        if ($$arg) {
            $select[] = "$arg = ?";
            $params[] = $$arg;
        }
    }
    if (!empty($enrol)) {
        $select[] = "enrol=?";
        $params[] = $enrol;
    }

    if ($select) {
        if ($ras = $DB->get_records_select('role_assignments', implode(' AND ', $select), $params)) {
            $mods = get_list_of_plugins('mod');
            foreach($ras as $ra) {
                $fireevent = false;
                /// infinite loop protection when deleting recursively
                if (!$ra = $DB->get_record('role_assignments', array('id'=>$ra->id))) {
                    continue;
                }
                if ($DB->delete_records('role_assignments', array('id'=>$ra->id))) {
                    $fireevent = true;
                } else {
                    $success = false;
                }

                if (!$context = get_context_instance_by_id($ra->contextid)) {
                    // strange error, not much to do
                    continue;
                }

                /* mark contexts as dirty here, because we need the refreshed
                 * caps bellow to delete group membership and user_lastaccess!
                 * and yes, this is very expensive for bulk operations :-(
                 */
                mark_context_dirty($context->path);

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

                /// Ask all the modules if anything needs to be done for this user
                foreach ($mods as $mod) {
                    include_once($CFG->dirroot.'/mod/'.$mod.'/lib.php');
                    $functionname = $mod.'_role_unassign';
                    if (function_exists($functionname)) {
                        $functionname($ra->userid, $context); // watch out, $context might be NULL if something goes wrong
                    }
                }

                /// now handle metacourse role unassigment and removing from goups if in course context
                if ($context->contextlevel == CONTEXT_COURSE) {

                    // cleanup leftover course groups/subscriptions etc when user has
                    // no capability to view course
                    // this may be slow, but this is the proper way of doing it
                    if (!has_capability('moodle/course:view', $context, $ra->userid)) {
                        // remove from groups
                        groups_delete_group_members($context->instanceid, $ra->userid);

                        // delete lastaccess records
                        $DB->delete_records('user_lastaccess', array('userid'=>$ra->userid, 'courseid'=>$context->instanceid));
                    }

                    //unassign roles in metacourses if needed
                    if ($parents = $DB->get_records('course_meta', array('child_course'=>$context->instanceid))) {
                        foreach ($parents as $parent) {
                            sync_metacourse($parent->parent_course);
                        }
                    }
                }

                if ($fireevent) {
                    events_trigger('role_unassigned', $ra);
                }
            }
        }
    }

    return $success;
}

/**
 * A convenience function to take care of the common case where you
 * just want to enrol someone using the default role into a course
 *
 * @param object $course
 * @param object $user
 * @param string $enrol - the plugin used to do this enrolment
 */
function enrol_into_course($course, $user, $enrol) {

    $timestart = time();
    // remove time part from the timestamp and keep only the date part
    $timestart = make_timestamp(date('Y', $timestart), date('m', $timestart), date('d', $timestart), 0, 0, 0);
    if ($course->enrolperiod) {
        $timeend = $timestart + $course->enrolperiod;
    } else {
        $timeend = 0;
    }

    if ($role = get_default_course_role($course)) {

        $context = get_context_instance(CONTEXT_COURSE, $course->id);

        if (!role_assign($role->id, $user->id, 0, $context->id, $timestart, $timeend, 0, $enrol)) {
            return false;
        }

        // force accessdata refresh for users visiting this context...
        mark_context_dirty($context->path);

        email_welcome_message_to_user($course, $user);

        add_to_log($course->id, 'course', 'enrol',
                'view.php?id='.$course->id, $course->id);

        return true;
    }

    return false;
}

/**
 * Loads the capability definitions for the component (from file). If no
 * capabilities are defined for the component, we simply return an empty array.
 * @param $component - examples: 'moodle', 'mod/forum', 'block/quiz_results'
 * @return array of capabilities
 */
function load_capability_def($component) {
    global $CFG;

    if ($component == 'moodle') {
        $defpath = $CFG->libdir.'/db/access.php';
        $varprefix = 'moodle';
    } else {
        $compparts = explode('/', $component);

        if ($compparts[0] == 'report') {
            $defpath = $CFG->dirroot.'/'.$CFG->admin.'/report/'.$compparts[1].'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else if ($compparts[0] == 'block') {
            // Blocks are an exception. Blocks directory is 'blocks', and not
            // 'block'. So we need to jump through hoops.
            $defpath = $CFG->dirroot.'/'.$compparts[0].
                                's/'.$compparts[1].'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else if ($compparts[0] == 'format') {
            // Similar to the above, course formats are 'format' while they
            // are stored in 'course/format'.
            $defpath = $CFG->dirroot.'/course/'.$component.'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else if ($compparts[0] == 'editor') {
            $defpath = $CFG->dirroot.'/lib/editor/'.$compparts[1].'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else if ($compparts[0] == 'gradeimport') {
            $defpath = $CFG->dirroot.'/grade/import/'.$compparts[1].'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else if ($compparts[0] == 'gradeexport') {
            $defpath = $CFG->dirroot.'/grade/export/'.$compparts[1].'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else if ($compparts[0] == 'gradereport') {
            $defpath = $CFG->dirroot.'/grade/report/'.$compparts[1].'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else if ($compparts[0] == 'quizreport') {
            $defpath = $CFG->dirroot.'/mod/quiz/report/'.$compparts[1].'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else if ($compparts[0] == 'coursereport') {
            $defpath = $CFG->dirroot.'/course/report/'.$compparts[1].'/db/access.php';
            $varprefix = $compparts[0].'_'.$compparts[1];

        } else {
            $defpath = $CFG->dirroot.'/'.$component.'/db/access.php';
            $varprefix = str_replace('/', '_', $component);
        }
    }
    $capabilities = array();

    if (file_exists($defpath)) {
        require($defpath);
        $capabilities = ${$varprefix.'_capabilities'};
    }
    return $capabilities;
}


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

    if ($component == 'moodle') {
        $storedcaps = $DB->get_records_select('capabilities', "name LIKE ?", array('moodle/%:%'));

    } else if ($component == 'local') {
        $storedcaps = $DB->get_records_select('capabilities', "name LIKE ?", array('moodle/local:%'));

    } else {
        $storedcaps = $DB->get_records_select('capabilities', "name LIKE ?", array("$component:%"));
    }

    return $storedcaps;
}

/**
 * Returns default capabilities for given legacy role type.
 *
 * @param string legacy role name
 * @return array
 */
function get_default_capabilities($legacyrole) {
    global $DB;
    $allcaps = $DB->get_records('capabilities');
    $alldefs = array();
    $defaults = array();
    $components = array();
    foreach ($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) {
        if (isset($def['legacy'][$legacyrole])) {
            $defaults[$name] = $def['legacy'][$legacyrole];
        }
    }

    //some exceptions
    $defaults['moodle/legacy:'.$legacyrole] = CAP_ALLOW;
    if ($legacyrole == 'admin') {
        $defaults['moodle/site:doanything'] = CAP_ALLOW;
    }
    return $defaults;
}

/**
 * Reset role capabilitites to default according to selected legacy capability.
 * If several legacy caps selected, use the first from get_default_capabilities.
 * If no legacy selected, removes all capabilities.
 *
 * @param int @roleid
 */
function reset_role_capabilities($roleid) {
    global $DB;

    $sitecontext = get_context_instance(CONTEXT_SYSTEM);
    $legacyroles = get_legacy_roles();

    $defaultcaps = array();
    foreach($legacyroles as $ltype=>$lcap) {
        $localoverride = get_local_override($roleid, $sitecontext->id, $lcap);
        if (!empty($localoverride->permission) and $localoverride->permission == CAP_ALLOW) {
            //choose first selected legacy capability
            $defaultcaps = get_default_capabilities($ltype);
            break;
        }
    }

    $DB->delete_records('role_capabilities', array('roleid'=>$roleid));
    if (!empty($defaultcaps)) {
        foreach($defaultcaps as $cap=>$permission) {
            assign_capability($cap, $permission, $roleid, $sitecontext->id);