[moodle.git] / lib / moodlelib.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                         //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

/**
 * moodlelib.php - Moodle main library
 *
 * Main library file of miscellaneous general-purpose Moodle functions.
 * Other main libraries:
 *  - weblib.php      - functions that produce web output
 *  - datalib.php     - functions that access the database
 * @author Martin Dougiamas
 * @version $Id$
 * @license http://www.gnu.org/copyleft/gpl.html GNU Public License
 * @package moodlecore
 */

/// CONSTANTS (Encased in phpdoc proper comments)/////////////////////////

/**
 * Used by some scripts to check they are being called by Moodle
 */
define('MOODLE_INTERNAL', true);

/// Date and time constants ///
/**
 * Time constant - the number of seconds in a year
 */

define('YEARSECS', 31536000);

/**
 * Time constant - the number of seconds in a week
 */
define('WEEKSECS', 604800);

/**
 * Time constant - the number of seconds in a day
 */
define('DAYSECS', 86400);

/**
 * Time constant - the number of seconds in an hour
 */
define('HOURSECS', 3600);

/**
 * Time constant - the number of seconds in a minute
 */
define('MINSECS', 60);

/**
 * Time constant - the number of minutes in a day
 */
define('DAYMINS', 1440);

/**
 * Time constant - the number of minutes in an hour
 */
define('HOURMINS', 60);

/// Parameter constants - every call to optional_param(), required_param()  ///
/// or clean_param() should have a specified type of parameter.  //////////////

/**
 * PARAM_RAW specifies a parameter that is not cleaned/processed in any way;
 * originally was 0, but changed because we need to detect unknown
 * parameter types and swiched order in clean_param().
 */
define('PARAM_RAW', 666);

/**
 * PARAM_CLEAN - obsoleted, please try to use more specific type of parameter.
 * It was one of the first types, that is why it is abused so much ;-)
 */
define('PARAM_CLEAN',    0x0001);

/**
 * PARAM_INT - integers only, use when expecting only numbers.
 */
define('PARAM_INT',      0x0002);

/**
 * PARAM_INTEGER - an alias for PARAM_INT
 */
define('PARAM_INTEGER',  0x0002);

/**
 * PARAM_NUMBER - a real/floating point number.
 */
define('PARAM_NUMBER',  0x000a);

/**
 * PARAM_ALPHA - contains only english letters.
 */
define('PARAM_ALPHA',    0x0004);

/**
 * PARAM_ACTION - an alias for PARAM_ALPHA, use for various actions in formas and urls
 * @TODO: should we alias it to PARAM_ALPHANUM ?
 */
define('PARAM_ACTION',   0x0004);

/**
 * PARAM_FORMAT - an alias for PARAM_ALPHA, use for names of plugins, formats, etc.
 * @TODO: should we alias it to PARAM_ALPHANUM ?
 */
define('PARAM_FORMAT',   0x0004);

/**
 * PARAM_NOTAGS - all html tags are stripped from the text. Do not abuse this type.
 */
define('PARAM_NOTAGS',   0x0008);

 /**
 * PARAM_MULTILANG - alias of PARAM_TEXT.
 */
define('PARAM_MULTILANG',  0x0009);

 /**
 * PARAM_TEXT - general plain text compatible with multilang filter, no other html tags.
 */
define('PARAM_TEXT',  0x0009);

/**
 * PARAM_FILE - safe file name, all dangerous chars are stripped, protects against XSS, SQL injections and directory traversals
 */
define('PARAM_FILE',     0x0010);

/**
 * PARAM_TAG - one tag (interests, blogs, etc.) - mostly international alphanumeric with spaces
 */
define('PARAM_TAG',   0x0011);

/**
 * PARAM_TAGLIST - list of tags separated by commas (interests, blogs, etc.)
 */
define('PARAM_TAGLIST',   0x0012);

/**
 * PARAM_PATH - safe relative path name, all dangerous chars are stripped, protects against XSS, SQL injections and directory traversals
 * note: the leading slash is not removed, window drive letter is not allowed
 */
define('PARAM_PATH',     0x0020);

/**
 * PARAM_HOST - expected fully qualified domain name (FQDN) or an IPv4 dotted quad (IP address)
 */
define('PARAM_HOST',     0x0040);

/**
 * PARAM_URL - expected properly formatted URL. Please note that domain part is required, http://localhost/ is not acceppted but http://localhost.localdomain/ is ok.
 */
define('PARAM_URL',      0x0080);

/**
 * PARAM_LOCALURL - expected properly formatted URL as well as one that refers to the local server itself. (NOT orthogonal to the others! Implies PARAM_URL!)
 */
define('PARAM_LOCALURL', 0x0180);

/**
 * PARAM_CLEANFILE - safe file name, all dangerous and regional chars are removed,
 * use when you want to store a new file submitted by students
 */
define('PARAM_CLEANFILE',0x0200);

/**
 * PARAM_ALPHANUM - expected numbers and letters only.
 */
define('PARAM_ALPHANUM', 0x0400);

/**
 * PARAM_BOOL - converts input into 0 or 1, use for switches in forms and urls.
 */
define('PARAM_BOOL',     0x0800);

/**
 * PARAM_CLEANHTML - cleans submitted HTML code and removes slashes
 * note: do not forget to addslashes() before storing into database!
 */
define('PARAM_CLEANHTML',0x1000);

/**
 * PARAM_ALPHAEXT the same contents as PARAM_ALPHA plus the chars in quotes: "/-_" allowed,
 * suitable for include() and require()
 * @TODO: should we rename this function to PARAM_SAFEDIRS??
 */
define('PARAM_ALPHAEXT', 0x2000);

/**
 * PARAM_SAFEDIR - safe directory name, suitable for include() and require()
 */
define('PARAM_SAFEDIR',  0x4000);

/**
 * PARAM_SEQUENCE - expects a sequence of numbers like 8 to 1,5,6,4,6,8,9.  Numbers and comma only.
 */
define('PARAM_SEQUENCE',  0x8000);

/**
 * PARAM_PEM - Privacy Enhanced Mail format
 */
define('PARAM_PEM',      0x10000);

/**
 * PARAM_BASE64 - Base 64 encoded format
 */
define('PARAM_BASE64',   0x20000);


/// Page types ///
/**
 * PAGE_COURSE_VIEW is a definition of a page type. For more information on the page class see moodle/lib/pagelib.php.
 */
define('PAGE_COURSE_VIEW', 'course-view');

/// Debug levels ///
/** no warnings at all */
define ('DEBUG_NONE', 0);
/** E_ERROR | E_PARSE */
define ('DEBUG_MINIMAL', 5);
/** E_ERROR | E_PARSE | E_WARNING | E_NOTICE */
define ('DEBUG_NORMAL', 15);
/** E_ALL without E_STRICT for now, do show recoverable fatal errors */
define ('DEBUG_ALL', 6143);
/** DEBUG_ALL with extra Moodle debug messages - (DEBUG_ALL | 32768) */
define ('DEBUG_DEVELOPER', 38911);

/**
 * Blog access level constant declaration
 */
define ('BLOG_USER_LEVEL', 1);
define ('BLOG_GROUP_LEVEL', 2);
define ('BLOG_COURSE_LEVEL', 3);
define ('BLOG_SITE_LEVEL', 4);
define ('BLOG_GLOBAL_LEVEL', 5);

/**
 * Tag constanst
 */
define('TAG_MAX_LENGTH', 50);

if (!defined('SORT_LOCALE_STRING')) { // PHP < 4.4.0 - TODO: remove in 2.0
    define('SORT_LOCALE_STRING', SORT_STRING);
}


/// PARAMETER HANDLING ////////////////////////////////////////////////////

/**
 * Returns a particular value for the named variable, taken from
 * POST or GET.  If the parameter doesn't exist then an error is
 * thrown because we require this variable.
 *
 * This function should be used to initialise all required values
 * in a script that are based on parameters.  Usually it will be
 * used like this:
 *    $id = required_param('id');
 *
 * @param string $parname the name of the page parameter we want
 * @param int $type expected type of parameter
 * @return mixed
 */
function required_param($parname, $type=PARAM_CLEAN) {

    // detect_unchecked_vars addition
    global $CFG;
    if (!empty($CFG->detect_unchecked_vars)) {
        global $UNCHECKED_VARS;
        unset ($UNCHECKED_VARS->vars[$parname]);
    }

    if (isset($_POST[$parname])) {       // POST has precedence
        $param = $_POST[$parname];
    } else if (isset($_GET[$parname])) {
        $param = $_GET[$parname];
    } else {
        error('A required parameter ('.$parname.') was missing');
    }

    return clean_param($param, $type);
}

/**
 * Returns a particular value for the named variable, taken from
 * POST or GET, otherwise returning a given default.
 *
 * This function should be used to initialise all optional values
 * in a script that are based on parameters.  Usually it will be
 * used like this:
 *    $name = optional_param('name', 'Fred');
 *
 * @param string $parname the name of the page parameter we want
 * @param mixed  $default the default value to return if nothing is found
 * @param int $type expected type of parameter
 * @return mixed
 */
function optional_param($parname, $default=NULL, $type=PARAM_CLEAN) {

    // detect_unchecked_vars addition
    global $CFG;
    if (!empty($CFG->detect_unchecked_vars)) {
        global $UNCHECKED_VARS;
        unset ($UNCHECKED_VARS->vars[$parname]);
    }

    if (isset($_POST[$parname])) {       // POST has precedence
        $param = $_POST[$parname];
    } else if (isset($_GET[$parname])) {
        $param = $_GET[$parname];
    } else {
        return $default;
    }

    return clean_param($param, $type);
}

/**
 * Used by {@link optional_param()} and {@link required_param()} to
 * clean the variables and/or cast to specific types, based on
 * an options field.
 * <code>
 * $course->format = clean_param($course->format, PARAM_ALPHA);
 * $selectedgrade_item = clean_param($selectedgrade_item, PARAM_CLEAN);
 * </code>
 *
 * @uses $CFG
 * @uses PARAM_RAW
 * @uses PARAM_CLEAN
 * @uses PARAM_CLEANHTML
 * @uses PARAM_INT
 * @uses PARAM_NUMBER
 * @uses PARAM_ALPHA
 * @uses PARAM_ALPHANUM
 * @uses PARAM_ALPHAEXT
 * @uses PARAM_SEQUENCE
 * @uses PARAM_BOOL
 * @uses PARAM_NOTAGS
 * @uses PARAM_TEXT
 * @uses PARAM_SAFEDIR
 * @uses PARAM_CLEANFILE
 * @uses PARAM_FILE
 * @uses PARAM_PATH
 * @uses PARAM_HOST
 * @uses PARAM_URL
 * @uses PARAM_LOCALURL
 * @uses PARAM_PEM
 * @uses PARAM_BASE64
 * @uses PARAM_TAG
 * @uses PARAM_TAGLIST
 * @uses PARAM_SEQUENCE
 * @param mixed $param the variable we are cleaning
 * @param int $type expected format of param after cleaning.
 * @return mixed
 */
function clean_param($param, $type) {

    global $CFG;

    if (is_array($param)) {              // Let's loop
        $newparam = array();
        foreach ($param as $key => $value) {
            $newparam[$key] = clean_param($value, $type);
        }
        return $newparam;
    }

    switch ($type) {
        case PARAM_RAW:          // no cleaning at all
            return $param;

        case PARAM_CLEAN:        // General HTML cleaning, try to use more specific type if possible
            if (is_numeric($param)) {
                return $param;
            }
            $param = stripslashes($param);   // Needed for kses to work fine
            $param = clean_text($param);     // Sweep for scripts, etc
            return addslashes($param);       // Restore original request parameter slashes

        case PARAM_CLEANHTML:    // prepare html fragment for display, do not store it into db!!
            $param = stripslashes($param);   // Remove any slashes
            $param = clean_text($param);     // Sweep for scripts, etc
            return trim($param);

        case PARAM_INT:
            return (int)$param;  // Convert to integer

        case PARAM_NUMBER:
            return (float)$param;  // Convert to integer

        case PARAM_ALPHA:        // Remove everything not a-z
            return eregi_replace('[^a-zA-Z]', '', $param);

        case PARAM_ALPHANUM:     // Remove everything not a-zA-Z0-9
            return eregi_replace('[^A-Za-z0-9]', '', $param);

        case PARAM_ALPHAEXT:     // Remove everything not a-zA-Z/_-
            return eregi_replace('[^a-zA-Z/_-]', '', $param);

        case PARAM_SEQUENCE:     // Remove everything not 0-9,
            return eregi_replace('[^0-9,]', '', $param);

        case PARAM_BOOL:         // Convert to 1 or 0
            $tempstr = strtolower($param);
            if ($tempstr == 'on' or $tempstr == 'yes' ) {
                $param = 1;
            } else if ($tempstr == 'off' or $tempstr == 'no') {
                $param = 0;
            } else {
                $param = empty($param) ? 0 : 1;
            }
            return $param;

        case PARAM_NOTAGS:       // Strip all tags
            return strip_tags($param);

        case PARAM_TEXT:    // leave only tags needed for multilang
            return clean_param(strip_tags($param, '<lang><span>'), PARAM_CLEAN);

        case PARAM_SAFEDIR:      // Remove everything not a-zA-Z0-9_-
            return eregi_replace('[^a-zA-Z0-9_-]', '', $param);

        case PARAM_CLEANFILE:    // allow only safe characters
            return clean_filename($param);

        case PARAM_FILE:         // Strip all suspicious characters from filename
            $param = ereg_replace('[[:cntrl:]]|[<>"`\|\':\\/]', '', $param);
            $param = ereg_replace('\.\.+', '', $param);
            if($param == '.') {
                $param = '';
            }
            return $param;

        case PARAM_PATH:         // Strip all suspicious characters from file path
            $param = str_replace('\\\'', '\'', $param);
            $param = str_replace('\\"', '"', $param);
            $param = str_replace('\\', '/', $param);
            $param = ereg_replace('[[:cntrl:]]|[<>"`\|\':]', '', $param);
            $param = ereg_replace('\.\.+', '', $param);
            $param = ereg_replace('//+', '/', $param);
            return ereg_replace('/(\./)+', '/', $param);

        case PARAM_HOST:         // allow FQDN or IPv4 dotted quad
            $param = preg_replace('/[^\.\d\w-]/','', $param ); // only allowed chars
            // match ipv4 dotted quad
            if (preg_match('/(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})/',$param, $match)){
                // confirm values are ok
                if ( $match[0] > 255
                     || $match[1] > 255
                     || $match[3] > 255
                     || $match[4] > 255 ) {
                    // hmmm, what kind of dotted quad is this?
                    $param = '';
                }
            } elseif ( preg_match('/^[\w\d\.-]+$/', $param) // dots, hyphens, numbers
                       && !preg_match('/^[\.-]/',  $param) // no leading dots/hyphens
                       && !preg_match('/[\.-]$/',  $param) // no trailing dots/hyphens
                       ) {
                // all is ok - $param is respected
            } else {
                // all is not ok...
                $param='';
            }
            return $param;

        case PARAM_URL:          // allow safe ftp, http, mailto urls
            include_once($CFG->dirroot . '/lib/validateurlsyntax.php');
            if (!empty($param) && validateUrlSyntax($param, 's?H?S?F?E?u-P-a?I?p?f?q?r?')) {
                // all is ok, param is respected
            } else {
                $param =''; // not really ok
            }
            return $param;

        case PARAM_LOCALURL:     // allow http absolute, root relative and relative URLs within wwwroot
            $param = clean_param($param, PARAM_URL);
            if (!empty($param)) {
                if (preg_match(':^/:', $param)) {
                    // root-relative, ok!
                } elseif (preg_match('/^'.preg_quote($CFG->wwwroot, '/').'/i',$param)) {
                    // absolute, and matches our wwwroot
                } else {
                    // relative - let's make sure there are no tricks
                    if (validateUrlSyntax($param, 's-u-P-a-p-f+q?r?')) {
                        // looks ok.
                    } else {
                        $param = '';
                    }
                }
            }
            return $param;

        case PARAM_PEM:
            $param = trim($param);
            // PEM formatted strings may contain letters/numbers and the symbols
            // forward slash: /
            // plus sign:     +
            // equal sign:    =
            // , surrounded by BEGIN and END CERTIFICATE prefix and suffixes
            if (preg_match('/^-----BEGIN CERTIFICATE-----([\s\w\/\+=]+)-----END CERTIFICATE-----$/', trim($param), $matches)) {
                list($wholething, $body) = $matches;
                unset($wholething, $matches);
                $b64 = clean_param($body, PARAM_BASE64);
                if (!empty($b64)) {
                    return "-----BEGIN CERTIFICATE-----\n$b64\n-----END CERTIFICATE-----\n";
                } else {
                    return '';
                }
            }
            return '';

        case PARAM_BASE64:
            if (!empty($param)) {
                // PEM formatted strings may contain letters/numbers and the symbols
                // forward slash: /
                // plus sign:     +
                // equal sign:    =
                if (0 >= preg_match('/^([\s\w\/\+=]+)$/', trim($param))) {
                    return '';
                }
                $lines = preg_split('/[\s]+/', $param, -1, PREG_SPLIT_NO_EMPTY);
                // Each line of base64 encoded data must be 64 characters in
                // length, except for the last line which may be less than (or
                // equal to) 64 characters long.
                for ($i=0, $j=count($lines); $i < $j; $i++) {
                    if ($i + 1 == $j) {
                        if (64 < strlen($lines[$i])) {
                            return '';
                        }
                        continue;
                    }

                    if (64 != strlen($lines[$i])) {
                        return '';
                    }
                }
                return implode("\n",$lines);
            } else {
                return '';
            }

        case PARAM_TAG:
            //first fix whitespace
            $param = preg_replace('/\s+/', ' ', $param);
            //remove blacklisted ASCII ranges of chars - security FIRST - keep only ascii letters, numbers and spaces
            //the result should be safe to be used directly in html and SQL
            $param = preg_replace("/[\\000-\\x1f\\x21-\\x2f\\x3a-\\x40\\x5b-\\x60\\x7b-\\x7f]/", '', $param);
            //now remove some unicode ranges we do not want
            $param = preg_replace("/[\\x{80}-\\x{bf}\\x{d7}\\x{f7}]/u", '', $param);
            //cleanup the spaces
            $param = preg_replace('/ +/', ' ', $param);
            $param = trim($param);
            $textlib = textlib_get_instance();
            $param = $textlib->substr($param, 0, TAG_MAX_LENGTH);
            //numeric tags not allowed
            return is_numeric($param) ? '' : $param;

        case PARAM_TAGLIST:
            $tags = explode(',', $param);
            $result = array();
            foreach ($tags as $tag) {
                $res = clean_param($tag, PARAM_TAG);
                if ($res != '') {
                    $result[] = $res;
                }
            }
            if ($result) {
                return implode(',', $result);
            } else {
                return '';
            }

        default:                 // throw error, switched parameters in optional_param or another serious problem
            error("Unknown parameter type: $type");
    }
}


/**
 * Set a key in global configuration
 *
 * Set a key/value pair in both this session's {@link $CFG} global variable
 * and in the 'config' database table for future sessions.
 *
 * Can also be used to update keys for plugin-scoped configs in config_plugin table.
 * In that case it doesn't affect $CFG.
 *
 * A NULL value will delete the entry.
 *
 * @param string $name the key to set
 * @param string $value the value to set (without magic quotes)
 * @param string $plugin (optional) the plugin scope
 * @uses $CFG
 * @return bool
 */
function set_config($name, $value, $plugin=NULL) {
/// No need for get_config because they are usually always available in $CFG

    global $CFG;

    if (empty($plugin)) {
        if (!array_key_exists($name, $CFG->config_php_settings)) {
            // So it's defined for this invocation at least
            if (is_null($value)) {
                unset($CFG->$name);
            } else {
                $CFG->$name = (string)$value; // settings from db are always strings
            }
        }

        if (get_field('config', 'name', 'name', $name)) {
            if ($value===null) {
                return delete_records('config', 'name', $name);
            } else {
                return set_field('config', 'value', addslashes($value), 'name', $name);
            }
        } else {
            if ($value===null) {
                return true;
            }
            $config = new object();
            $config->name = $name;
            $config->value = addslashes($value);
            return insert_record('config', $config);
        }
    } else { // plugin scope
        if ($id = get_field('config_plugins', 'id', 'name', $name, 'plugin', $plugin)) {
            if ($value===null) {
                return delete_records('config_plugins', 'name', $name, 'plugin', $plugin);
            } else {
                return set_field('config_plugins', 'value', addslashes($value), 'id', $id);
            }
        } else {
            if ($value===null) {
                return true;
            }
            $config = new object();
            $config->plugin = addslashes($plugin);
            $config->name   = $name;
            $config->value  = addslashes($value);
            return insert_record('config_plugins', $config);
        }
    }
}

/**
 * Get configuration values from the global config table
 * or the config_plugins table.
 *
 * If called with no parameters it will do the right thing
 * generating $CFG safely from the database without overwriting
 * existing values.
 *
 * If called with 2 parameters it will return a $string single
 * value or false of the value is not found.
 *
 * @param string $plugin
 * @param string $name
 * @uses $CFG
 * @return hash-like object or single value
 *
 */
function get_config($plugin=NULL, $name=NULL) {

    global $CFG;

    if (!empty($name)) { // the user is asking for a specific value
        if (!empty($plugin)) {
            return get_field('config_plugins', 'value', 'plugin' , $plugin, 'name', $name);
        } else {
            return get_field('config', 'value', 'name', $name);
        }
    }

    // the user is after a recordset
    if (!empty($plugin)) {
        if ($configs=get_records('config_plugins', 'plugin', $plugin, '', 'name,value')) {
            $configs = (array)$configs;
            $localcfg = array();
            foreach ($configs as $config) {
                $localcfg[$config->name] = $config->value;
            }
            return (object)$localcfg;
        } else {
            return false;
        }
    } else {
        // this was originally in setup.php
        if ($configs = get_records('config')) {
            $localcfg = (array)$CFG;
            foreach ($configs as $config) {
                if (!isset($localcfg[$config->name])) {
                    $localcfg[$config->name] = $config->value;
                }
                // do not complain anymore if config.php overrides settings from db
            }

            $localcfg = (object)$localcfg;
            return $localcfg;
        } else {
            // preserve $CFG if DB returns nothing or error
            return $CFG;
        }

    }
}

/**
 * Removes a key from global configuration
 *
 * @param string $name the key to set
 * @param string $plugin (optional) the plugin scope
 * @uses $CFG
 * @return bool
 */
function unset_config($name, $plugin=NULL) {

    global $CFG;

    unset($CFG->$name);

    if (empty($plugin)) {
        return delete_records('config', 'name', $name);
    } else {
        return delete_records('config_plugins', 'name', $name, 'plugin', $plugin);
    }
}

/**
 * Get volatile flags
 *
 * @param string $type
 * @param int    $changedsince
 * @return records array
 *
 */
function get_cache_flags($type, $changedsince=NULL) {

    $type = addslashes($type);

    $sqlwhere = 'flagtype=\'' . $type . '\' AND expiry >= ' . time();
    if ($changedsince !== NULL) {
        $changedsince = (int)$changedsince;
        $sqlwhere .= ' AND timemodified > ' . $changedsince;
    }
    $cf = array();
    if ($flags=get_records_select('cache_flags', $sqlwhere, '', 'name,value')) {
        foreach ($flags as $flag) {
            $cf[$flag->name] = $flag->value;
        }
    }
    return $cf;
}


/**
 * Set a volatile flag
 *
 * @param string $type the "type" namespace for the key
 * @param string $name the key to set
 * @param string $value the value to set (without magic quotes) - NULL will remove the flag
 * @param int $expiry (optional) epoch indicating expiry - defaults to now()+ 24hs
 * @return bool
 */
function set_cache_flag($type, $name, $value, $expiry=NULL) {


    $timemodified = time();
    if ($expiry===NULL || $expiry < $timemodified) {
        $expiry = $timemodified + 24 * 60 * 60;
    } else {
        $expiry = (int)$expiry;
    }

    if ($value === NULL) {
        return unset_cache_flag($type,$name);
    }

    $type = addslashes($type);
    $name = addslashes($name);
    if ($f = get_record('cache_flags', 'name', $name, 'flagtype', $type)) { // this is a potentail problem in DEBUG_DEVELOPER
        if ($f->value == $value and $f->expiry == $expiry and $f->timemodified == $timemodified) {
            return true; //no need to update; helps rcache too
        }
        $f->value        = addslashes($value);
        $f->expiry       = $expiry;
        $f->timemodified = $timemodified;
        return update_record('cache_flags', $f);
    } else {
        $f = new object();
        $f->flagtype     = $type;
        $f->name         = $name;
        $f->value        = addslashes($value);
        $f->expiry       = $expiry;
        $f->timemodified = $timemodified;
        return (bool)insert_record('cache_flags', $f);
    }
}

/**
 * Removes a single volatile flag
 *
 * @param string $type the "type" namespace for the key
 * @param string $name the key to set
 * @uses $CFG
 * @return bool
 */
function unset_cache_flag($type, $name) {

    return delete_records('cache_flags',
                          'name', addslashes($name),
                          'flagtype', addslashes($type));
}

/**
 * Garbage-collect volatile flags
 *
 */
function gc_cache_flags() {
    return delete_records_select('cache_flags', 'expiry < ' . time());
}

/**
 * Refresh current $USER session global variable with all their current preferences.
 * @uses $USER
 */
function reload_user_preferences() {

    global $USER;

    //reset preference
    $USER->preference = array();

    if (!isloggedin() or isguestuser()) {
        // no pernament storage for not-logged-in user and guest

    } else if ($preferences = get_records('user_preferences', 'userid', $USER->id)) {
        foreach ($preferences as $preference) {
            $USER->preference[$preference->name] = $preference->value;
        }
    }

    return true;
}

/**
 * Sets a preference for the current user
 * Optionally, can set a preference for a different user object
 * @uses $USER
 * @todo Add a better description and include usage examples. Add inline links to $USER and user functions in above line.

 * @param string $name The key to set as preference for the specified user
 * @param string $value The value to set forthe $name key in the specified user's record
 * @param int $otheruserid A moodle user ID
 * @return bool
 */
function set_user_preference($name, $value, $otheruserid=NULL) {

    global $USER;

    if (!isset($USER->preference)) {
        reload_user_preferences();
    }

    if (empty($name)) {
        return false;
    }

    $nostore = false;

    if (empty($otheruserid)){
        if (!isloggedin() or isguestuser()) {
            $nostore = true;
        }
        $userid = $USER->id;
    } else {
        if (isguestuser($otheruserid)) {
            $nostore = true;
        }
        $userid = $otheruserid;
    }

    $return = true;
    if ($nostore) {
        // no pernament storage for not-logged-in user and guest

    } else if ($preference = get_record('user_preferences', 'userid', $userid, 'name', addslashes($name))) {
        if ($preference->value === $value) {
            return true;
        }
        if (!set_field('user_preferences', 'value', addslashes((string)$value), 'id', $preference->id)) {
            $return = false;
        }

    } else {
        $preference = new object();
        $preference->userid = $userid;
        $preference->name   = addslashes($name);
        $preference->value  = addslashes((string)$value);
        if (!insert_record('user_preferences', $preference)) {
            $return = false;
        }
    }

    // update value in USER session if needed
    if ($userid == $USER->id) {
        $USER->preference[$name] = (string)$value;
    }

    return $return;
}

/**
 * Unsets a preference completely by deleting it from the database
 * Optionally, can set a preference for a different user id
 * @uses $USER
 * @param string  $name The key to unset as preference for the specified user
 * @param int $otheruserid A moodle user ID
 */
function unset_user_preference($name, $otheruserid=NULL) {

    global $USER;

    if (!isset($USER->preference)) {
        reload_user_preferences();
    }

    if (empty($otheruserid)){
        $userid = $USER->id;
    } else {
        $userid = $otheruserid;
    }

    //Delete the preference from $USER if needed
    if ($userid == $USER->id) {
        unset($USER->preference[$name]);
    }

    //Then from DB
    return delete_records('user_preferences', 'userid', $userid, 'name', addslashes($name));
}


/**
 * Sets a whole array of preferences for the current user
 * @param array $prefarray An array of key/value pairs to be set
 * @param int $otheruserid A moodle user ID
 * @return bool
 */
function set_user_preferences($prefarray, $otheruserid=NULL) {

    if (!is_array($prefarray) or empty($prefarray)) {
        return false;
    }

    $return = true;
    foreach ($prefarray as $name => $value) {
        // The order is important; test for return is done first
        $return = (set_user_preference($name, $value, $otheruserid) && $return);
    }
    return $return;
}

/**
 * If no arguments are supplied this function will return
 * all of the current user preferences as an array.
 * If a name is specified then this function
 * attempts to return that particular preference value.  If
 * none is found, then the optional value $default is returned,
 * otherwise NULL.
 * @param string $name Name of the key to use in finding a preference value
 * @param string $default Value to be returned if the $name key is not set in the user preferences
 * @param int $otheruserid A moodle user ID
 * @uses $USER
 * @return string
 */
function get_user_preferences($name=NULL, $default=NULL, $otheruserid=NULL) {
    global $USER;

    if (!isset($USER->preference)) {
        reload_user_preferences();
    }

    if (empty($otheruserid)){
        $userid = $USER->id;
    } else {
        $userid = $otheruserid;
    }

    if ($userid == $USER->id) {
        $preference = $USER->preference;

    } else {
        $preference = array();
        if ($prefdata = get_records('user_preferences', 'userid', $userid)) {
            foreach ($prefdata as $pref) {
                $preference[$pref->name] = $pref->value;
            }
        }
    }

    if (empty($name)) {
        return $preference;            // All values

    } else if (array_key_exists($name, $preference)) {
        return $preference[$name];    // The single value

    } else {
        return $default;              // Default value (or NULL)
    }
}


/// FUNCTIONS FOR HANDLING TIME ////////////////////////////////////////////

/**
 * Given date parts in user time produce a GMT timestamp.
 *
 * @param int $year The year part to create timestamp of
 * @param int $month The month part to create timestamp of
 * @param int $day The day part to create timestamp of
 * @param int $hour The hour part to create timestamp of
 * @param int $minute The minute part to create timestamp of
 * @param int $second The second part to create timestamp of
 * @param float $timezone ?
 * @param bool $applydst ?
 * @return int timestamp
 * @todo Finish documenting this function
 */
function make_timestamp($year, $month=1, $day=1, $hour=0, $minute=0, $second=0, $timezone=99, $applydst=true) {

    $timezone = get_user_timezone_offset($timezone);

    if (abs($timezone) > 13) {
        $time = mktime((int)$hour, (int)$minute, (int)$second, (int)$month, (int)$day, (int)$year);
    } else {
        $time = gmmktime((int)$hour, (int)$minute, (int)$second, (int)$month, (int)$day, (int)$year);
        $time = usertime($time, $timezone);
        if($applydst) {
            $time -= dst_offset_on($time);
        }
    }

    return $time;

}

/**
 * Given an amount of time in seconds, returns string
 * formatted nicely as weeks, days, hours etc as needed
 *
 * @uses MINSECS
 * @uses HOURSECS
 * @uses DAYSECS
 * @uses YEARSECS
 * @param int $totalsecs ?
 * @param array $str ?
 * @return string
 */
 function format_time($totalsecs, $str=NULL) {

    $totalsecs = abs($totalsecs);

    if (!$str) {  // Create the str structure the slow way
        $str->day   = get_string('day');
        $str->days  = get_string('days');
        $str->hour  = get_string('hour');
        $str->hours = get_string('hours');
        $str->min   = get_string('min');
        $str->mins  = get_string('mins');
        $str->sec   = get_string('sec');
        $str->secs  = get_string('secs');
        $str->year  = get_string('year');
        $str->years = get_string('years');
    }


    $years     = floor($totalsecs/YEARSECS);
    $remainder = $totalsecs - ($years*YEARSECS);
    $days      = floor($remainder/DAYSECS);
    $remainder = $totalsecs - ($days*DAYSECS);
    $hours     = floor($remainder/HOURSECS);
    $remainder = $remainder - ($hours*HOURSECS);
    $mins      = floor($remainder/MINSECS);
    $secs      = $remainder - ($mins*MINSECS);

    $ss = ($secs == 1)  ? $str->sec  : $str->secs;
    $sm = ($mins == 1)  ? $str->min  : $str->mins;
    $sh = ($hours == 1) ? $str->hour : $str->hours;
    $sd = ($days == 1)  ? $str->day  : $str->days;
    $sy = ($years == 1)  ? $str->year  : $str->years;

    $oyears = '';
    $odays = '';
    $ohours = '';
    $omins = '';
    $osecs = '';

    if ($years)  $oyears  = $years .' '. $sy;
    if ($days)  $odays  = $days .' '. $sd;
    if ($hours) $ohours = $hours .' '. $sh;
    if ($mins)  $omins  = $mins .' '. $sm;
    if ($secs)  $osecs  = $secs .' '. $ss;

    if ($years) return trim($oyears .' '. $odays);
    if ($days)  return trim($odays .' '. $ohours);
    if ($hours) return trim($ohours .' '. $omins);
    if ($mins)  return trim($omins .' '. $osecs);
    if ($secs)  return $osecs;
    return get_string('now');
}

/**
 * Returns a formatted string that represents a date in user time
 * <b>WARNING: note that the format is for strftime(), not date().</b>
 * Because of a bug in most Windows time libraries, we can't use
 * the nicer %e, so we have to use %d which has leading zeroes.
 * A lot of the fuss in the function is just getting rid of these leading
 * zeroes as efficiently as possible.
 *
 * If parameter fixday = true (default), then take off leading
 * zero from %d, else mantain it.
 *
 * @uses HOURSECS
 * @param  int $date timestamp in GMT
 * @param string $format strftime format
 * @param float $timezone
 * @param bool $fixday If true (default) then the leading
 * zero from %d is removed. If false then the leading zero is mantained.
 * @return string
 */
function userdate($date, $format='', $timezone=99, $fixday = true) {

    global $CFG;

    if (empty($format)) {
        $format = get_string('strftimedaydatetime');
    }

    if (!empty($CFG->nofixday)) {  // Config.php can force %d not to be fixed.
        $fixday = false;
    } else if ($fixday) {
        $formatnoday = str_replace('%d', 'DD', $format);
        $fixday = ($formatnoday != $format);
    }

    $date += dst_offset_on($date);

    $timezone = get_user_timezone_offset($timezone);

    if (abs($timezone) > 13) {   /// Server time
        if ($fixday) {
            $datestring = strftime($formatnoday, $date);
            $daystring  = str_replace(' 0', '', strftime(' %d', $date));
            $datestring = str_replace('DD', $daystring, $datestring);
        } else {
            $datestring = strftime($format, $date);
        }
    } else {
        $date += (int)($timezone * 3600);
        if ($fixday) {
            $datestring = gmstrftime($formatnoday, $date);
            $daystring  = str_replace(' 0', '', gmstrftime(' %d', $date));
            $datestring = str_replace('DD', $daystring, $datestring);
        } else {
            $datestring = gmstrftime($format, $date);
        }
    }

/// If we are running under Windows convert from windows encoding to UTF-8
/// (because it's impossible to specify UTF-8 to fetch locale info in Win32)

   if ($CFG->ostype == 'WINDOWS') {
       if ($localewincharset = get_string('localewincharset')) {
           $textlib = textlib_get_instance();
           $datestring = $textlib->convert($datestring, $localewincharset, 'utf-8');
       }
   }

    return $datestring;
}

/**
 * Given a $time timestamp in GMT (seconds since epoch),
 * returns an array that represents the date in user time
 *
 * @uses HOURSECS
 * @param int $time Timestamp in GMT
 * @param float $timezone ?
 * @return array An array that represents the date in user time
 * @todo Finish documenting this function
 */
function usergetdate($time, $timezone=99) {

    $timezone = get_user_timezone_offset($timezone);

    if (abs($timezone) > 13) {    // Server time
        return getdate($time);
    }

    // There is no gmgetdate so we use gmdate instead
    $time += dst_offset_on($time);
    $time += intval((float)$timezone * HOURSECS);

    $datestring = gmstrftime('%S_%M_%H_%d_%m_%Y_%w_%j_%A_%B', $time);

    list(
        $getdate['seconds'],
        $getdate['minutes'],
        $getdate['hours'],
        $getdate['mday'],
        $getdate['mon'],
        $getdate['year'],
        $getdate['wday'],
        $getdate['yday'],
        $getdate['weekday'],
        $getdate['month']
    ) = explode('_', $datestring);

    return $getdate;
}

/**
 * Given a GMT timestamp (seconds since epoch), offsets it by
 * the timezone.  eg 3pm in India is 3pm GMT - 7 * 3600 seconds
 *
 * @uses HOURSECS
 * @param  int $date Timestamp in GMT
 * @param float $timezone
 * @return int
 */
function usertime($date, $timezone=99) {

    $timezone = get_user_timezone_offset($timezone);

    if (abs($timezone) > 13) {
        return $date;
    }
    return $date - (int)($timezone * HOURSECS);
}

/**
 * Given a time, return the GMT timestamp of the most recent midnight
 * for the current user.
 *
 * @param int $date Timestamp in GMT
 * @param float $timezone ?
 * @return ?
 */
function usergetmidnight($date, $timezone=99) {

    $timezone = get_user_timezone_offset($timezone);
    $userdate = usergetdate($date, $timezone);

    // Time of midnight of this user's day, in GMT
    return make_timestamp($userdate['year'], $userdate['mon'], $userdate['mday'], 0, 0, 0, $timezone);

}

/**
 * Returns a string that prints the user's timezone
 *
 * @param float $timezone The user's timezone
 * @return string
 */
function usertimezone($timezone=99) {

    $tz = get_user_timezone($timezone);

    if (!is_float($tz)) {
        return $tz;
    }

    if(abs($tz) > 13) { // Server time
        return get_string('serverlocaltime');
    }

    if($tz == intval($tz)) {
        // Don't show .0 for whole hours
        $tz = intval($tz);
    }

    if($tz == 0) {
        return 'UTC';
    }
    else if($tz > 0) {
        return 'UTC+'.$tz;
    }
    else {
        return 'UTC'.$tz;
    }

}

/**
 * Returns a float which represents the user's timezone difference from GMT in hours
 * Checks various settings and picks the most dominant of those which have a value
 *
 * @uses $CFG
 * @uses $USER
 * @param float $tz If this value is provided and not equal to 99, it will be returned as is and no other settings will be checked
 * @return int
 */
function get_user_timezone_offset($tz = 99) {

    global $USER, $CFG;

    $tz = get_user_timezone($tz);

    if (is_float($tz)) {
        return $tz;
    } else {
        $tzrecord = get_timezone_record($tz);
        if (empty($tzrecord)) {
            return 99.0;
        }
        return (float)$tzrecord->gmtoff / HOURMINS;
    }
}

/**
 * Returns a float or a string which denotes the user's timezone
 * A float value means that a simple offset from GMT is used, while a string (it will be the name of a timezone in the database)
 * means that for this timezone there are also DST rules to be taken into account
 * Checks various settings and picks the most dominant of those which have a value
 *
 * @uses $USER
 * @uses $CFG
 * @param float $tz If this value is provided and not equal to 99, it will be returned as is and no other settings will be checked
 * @return mixed
 */
function get_user_timezone($tz = 99) {
    global $USER, $CFG;

    $timezones = array(
        $tz,
        isset($CFG->forcetimezone) ? $CFG->forcetimezone : 99,
        isset($USER->timezone) ? $USER->timezone : 99,
        isset($CFG->timezone) ? $CFG->timezone : 99,
        );

    $tz = 99;

    while(($tz == '' || $tz == 99) && $next = each($timezones)) {
        $tz = $next['value'];
    }

    return is_numeric($tz) ? (float) $tz : $tz;
}

/**
 * ?
 *
 * @uses $CFG
 * @uses $db
 * @param string $timezonename ?
 * @return object
 */
function get_timezone_record($timezonename) {
    global $CFG, $db;
    static $cache = NULL;

    if ($cache === NULL) {
        $cache = array();
    }

    if (isset($cache[$timezonename])) {
        return $cache[$timezonename];
    }

    return $cache[$timezonename] = get_record_sql('SELECT * FROM '.$CFG->prefix.'timezone
                                      WHERE name = '.$db->qstr($timezonename).' ORDER BY year DESC', true);
}

/**
 * ?
 *
 * @uses $CFG
 * @uses $USER
 * @param ? $fromyear ?
 * @param ? $to_year ?
 * @return bool
 */
function calculate_user_dst_table($from_year = NULL, $to_year = NULL) {
    global $CFG, $SESSION;

    $usertz = get_user_timezone();

    if (is_float($usertz)) {
        // Trivial timezone, no DST
        return false;
    }

    if (!empty($SESSION->dst_offsettz) && $SESSION->dst_offsettz != $usertz) {
        // We have precalculated values, but the user's effective TZ has changed in the meantime, so reset
        unset($SESSION->dst_offsets);
        unset($SESSION->dst_range);
    }

    if (!empty($SESSION->dst_offsets) && empty($from_year) && empty($to_year)) {
        // Repeat calls which do not request specific year ranges stop here, we have already calculated the table
        // This will be the return path most of the time, pretty light computationally
        return true;
    }

    // Reaching here means we either need to extend our table or create it from scratch

    // Remember which TZ we calculated these changes for
    $SESSION->dst_offsettz = $usertz;

    if(empty($SESSION->dst_offsets)) {
        // If we 're creating from scratch, put the two guard elements in there
        $SESSION->dst_offsets = array(1 => NULL, 0 => NULL);
    }
    if(empty($SESSION->dst_range)) {
        // If creating from scratch
        $from = max((empty($from_year) ? intval(date('Y')) - 3 : $from_year), 1971);
        $to   = min((empty($to_year)   ? intval(date('Y')) + 3 : $to_year),   2035);

        // Fill in the array with the extra years we need to process
        $yearstoprocess = array();
        for($i = $from; $i <= $to; ++$i) {
            $yearstoprocess[] = $i;
        }

        // Take note of which years we have processed for future calls
        $SESSION->dst_range = array($from, $to);
    }
    else {
        // If needing to extend the table, do the same
        $yearstoprocess = array();

        $from = max((empty($from_year) ? $SESSION->dst_range[0] : $from_year), 1971);
        $to   = min((empty($to_year)   ? $SESSION->dst_range[1] : $to_year),   2035);

        if($from < $SESSION->dst_range[0]) {
            // Take note of which years we need to process and then note that we have processed them for future calls
            for($i = $from; $i < $SESSION->dst_range[0]; ++$i) {
                $yearstoprocess[] = $i;
            }
            $SESSION->dst_range[0] = $from;
        }
        if($to > $SESSION->dst_range[1]) {
            // Take note of which years we need to process and then note that we have processed them for future calls
            for($i = $SESSION->dst_range[1] + 1; $i <= $to; ++$i) {
                $yearstoprocess[] = $i;
            }
            $SESSION->dst_range[1] = $to;
        }
    }

    if(empty($yearstoprocess)) {
        // This means that there was a call requesting a SMALLER range than we have already calculated
        return true;
    }

    // From now on, we know that the array has at least the two guard elements, and $yearstoprocess has the years we need
    // Also, the array is sorted in descending timestamp order!

    // Get DB data

    static $presets_cache = array();
    if (!isset($presets_cache[$usertz])) {
        $presets_cache[$usertz] = get_records('timezone', 'name', $usertz, 'year DESC', 'year, gmtoff, dstoff, dst_month, dst_startday, dst_weekday, dst_skipweeks, dst_time, std_month, std_startday, std_weekday, std_skipweeks, std_time');
    }
    if(empty($presets_cache[$usertz])) {
        return false;
    }

    // Remove ending guard (first element of the array)
    reset($SESSION->dst_offsets);
    unset($SESSION->dst_offsets[key($SESSION->dst_offsets)]);

    // Add all required change timestamps
    foreach($yearstoprocess as $y) {
        // Find the record which is in effect for the year $y
        foreach($presets_cache[$usertz] as $year => $preset) {
            if($year <= $y) {
                break;
            }
        }

        $changes = dst_changes_for_year($y, $preset);

        if($changes === NULL) {
            continue;
        }
        if($changes['dst'] != 0) {
            $SESSION->dst_offsets[$changes['dst']] = $preset->dstoff * MINSECS;
        }
        if($changes['std'] != 0) {
            $SESSION->dst_offsets[$changes['std']] = 0;
        }
    }

    // Put in a guard element at the top
    $maxtimestamp = max(array_keys($SESSION->dst_offsets));
    $SESSION->dst_offsets[($maxtimestamp + DAYSECS)] = NULL; // DAYSECS is arbitrary, any "small" number will do

    // Sort again
    krsort($SESSION->dst_offsets);

    return true;
}

function dst_changes_for_year($year, $timezone) {

    if($timezone->dst_startday == 0 && $timezone->dst_weekday == 0 && $timezone->std_startday == 0 && $timezone->std_weekday == 0) {
        return NULL;
    }

    $monthdaydst = find_day_in_month($timezone->dst_startday, $timezone->dst_weekday, $timezone->dst_month, $year);
    $monthdaystd = find_day_in_month($timezone->std_startday, $timezone->std_weekday, $timezone->std_month, $year);

    list($dst_hour, $dst_min) = explode(':', $timezone->dst_time);
    list($std_hour, $std_min) = explode(':', $timezone->std_time);

    $timedst = make_timestamp($year, $timezone->dst_month, $monthdaydst, 0, 0, 0, 99, false);
    $timestd = make_timestamp($year, $timezone->std_month, $monthdaystd, 0, 0, 0, 99, false);

    // Instead of putting hour and minute in make_timestamp(), we add them afterwards.
    // This has the advantage of being able to have negative values for hour, i.e. for timezones
    // where GMT time would be in the PREVIOUS day than the local one on which DST changes.

    $timedst += $dst_hour * HOURSECS + $dst_min * MINSECS;
    $timestd += $std_hour * HOURSECS + $std_min * MINSECS;

    return array('dst' => $timedst, 0 => $timedst, 'std' => $timestd, 1 => $timestd);
}

// $time must NOT be compensated at all, it has to be a pure timestamp
function dst_offset_on($time) {
    global $SESSION;

    if(!calculate_user_dst_table() || empty($SESSION->dst_offsets)) {
        return 0;
    }

    reset($SESSION->dst_offsets);
    while(list($from, $offset) = each($SESSION->dst_offsets)) {
        if($from <= $time) {
            break;
        }
    }

    // This is the normal return path
    if($offset !== NULL) {
        return $offset;
    }

    // Reaching this point means we haven't calculated far enough, do it now:
    // Calculate extra DST changes if needed and recurse. The recursion always
    // moves toward the stopping condition, so will always end.

    if($from == 0) {
        // We need a year smaller than $SESSION->dst_range[0]
        if($SESSION->dst_range[0] == 1971) {
            return 0;
        }
        calculate_user_dst_table($SESSION->dst_range[0] - 5, NULL);
        return dst_offset_on($time);
    }
    else {
        // We need a year larger than $SESSION->dst_range[1]
        if($SESSION->dst_range[1] == 2035) {
            return 0;
        }
        calculate_user_dst_table(NULL, $SESSION->dst_range[1] + 5);
        return dst_offset_on($time);
    }
}

function find_day_in_month($startday, $weekday, $month, $year) {

    $daysinmonth = days_in_month($month, $year);

    if($weekday == -1) {
        // Don't care about weekday, so return:
        //    abs($startday) if $startday != -1
        //    $daysinmonth otherwise
        return ($startday == -1) ? $daysinmonth : abs($startday);
    }

    // From now on we 're looking for a specific weekday

    // Give "end of month" its actual value, since we know it
    if($startday == -1) {
        $startday = -1 * $daysinmonth;
    }

    // Starting from day $startday, the sign is the direction

    if($startday < 1) {

        $startday = abs($startday);
        $lastmonthweekday  = strftime('%w', mktime(12, 0, 0, $month, $daysinmonth, $year, 0));

        // This is the last such weekday of the month
        $lastinmonth = $daysinmonth + $weekday - $lastmonthweekday;
        if($lastinmonth > $daysinmonth) {
            $lastinmonth -= 7;
        }

        // Find the first such weekday <= $startday
        while($lastinmonth > $startday) {
            $lastinmonth -= 7;
        }

        return $lastinmonth;

    }
    else {

        $indexweekday = strftime('%w', mktime(12, 0, 0, $month, $startday, $year, 0));

        $diff = $weekday - $indexweekday;
        if($diff < 0) {
            $diff += 7;
        }

        // This is the first such weekday of the month equal to or after $startday
        $firstfromindex = $startday + $diff;

        return $firstfromindex;

    }
}

/**
 * Calculate the number of days in a given month
 *
 * @param int $month The month whose day count is sought
 * @param int $year The year of the month whose day count is sought
 * @return int
 */
function days_in_month($month, $year) {
   return intval(date('t', mktime(12, 0, 0, $month, 1, $year, 0)));
}

/**
 * Calculate the position in the week of a specific calendar day
 *
 * @param int $day The day of the date whose position in the week is sought
 * @param int $month The month of the date whose position in the week is sought
 * @param int $year The year of the date whose position in the week is sought
 * @return int
 */
function dayofweek($day, $month, $year) {
    // I wonder if this is any different from
    // strftime('%w', mktime(12, 0, 0, $month, $daysinmonth, $year, 0));
    return intval(date('w', mktime(12, 0, 0, $month, $day, $year, 0)));
}

/// USER AUTHENTICATION AND LOGIN ////////////////////////////////////////

/**
 * Makes sure that $USER->sesskey exists, if $USER itself exists. It sets a new sesskey
 * if one does not already exist, but does not overwrite existing sesskeys. Returns the
 * sesskey string if $USER exists, or boolean false if not.
 *
 * @uses $USER
 * @return string
 */
function sesskey() {
    global $USER;

    if(!isset($USER)) {
        return false;
    }

    if (empty($USER->sesskey)) {
        $USER->sesskey = random_string(10);
    }

    return $USER->sesskey;
}


/**
 * For security purposes, this function will check that the currently
 * given sesskey (passed as a parameter to the script or this function)
 * matches that of the current user.
 *
 * @param string $sesskey optionally provided sesskey
 * @return bool
 */
function confirm_sesskey($sesskey=NULL) {
    global $USER;

    if (!empty($USER->ignoresesskey) || !empty($CFG->ignoresesskey)) {
        return true;
    }

    if (empty($sesskey)) {
        $sesskey = required_param('sesskey', PARAM_RAW);  // Check script parameters
    }

    if (!isset($USER->sesskey)) {
        return false;
    }

    return ($USER->sesskey === $sesskey);
}

/**
 * Setup all global $CFG course variables, set locale and also themes
 * This function can be used on pages that do not require login instead of require_login()
 *
 * @param mixed $courseorid id of the course or course object
 */
function course_setup($courseorid=0) {
    global $COURSE, $CFG, $SITE;

/// Redefine global $COURSE if needed
    if (empty($courseorid)) {
        // no change in global $COURSE - for backwards compatibiltiy
        // if require_rogin() used after require_login($courseid);
    } else if (is_object($courseorid)) {
        $COURSE = clone($courseorid);
    } else {
        global $course; // used here only to prevent repeated fetching from DB - may be removed later
        if (!empty($course->id) and $course->id == SITEID) {
            $COURSE = clone($SITE);
        } else if (!empty($course->id) and $course->id == $courseorid) {
            $COURSE = clone($course);
        } else {
            if (!$COURSE = get_record('course', 'id', $courseorid)) {
                error('Invalid course ID');
            }
        }
    }

/// set locale and themes
    moodle_setlocale();
    theme_setup();

}

/**
 * This function checks that the current user is logged in and has the
 * required privileges
 *
 * This function checks that the current user is logged in, and optionally
 * whether they are allowed to be in a particular course and view a particular
 * course module.
 * If they are not logged in, then it redirects them to the site login unless
 * $autologinguest is set and {@link $CFG}->autologinguests is set to 1 in which
 * case they are automatically logged in as guests.
 * If $courseid is given and the user is not enrolled in that course then the
 * user is redirected to the course enrolment page.
 * If $cm is given and the coursemodule is hidden and the user is not a teacher
 * in the course then the user is redirected to the course home page.
 *
 * @uses $CFG
 * @uses $SESSION
 * @uses $USER
 * @uses $FULLME
 * @uses SITEID
 * @uses $COURSE
 * @param mixed $courseorid id of the course or course object
 * @param bool $autologinguest
 * @param object $cm course module object
 */
function require_login($courseorid=0, $autologinguest=true, $cm=null) {

    global $CFG, $SESSION, $USER, $COURSE, $FULLME;

/// setup global $COURSE, themes, language and locale
    course_setup($courseorid);

/// If the user is not even logged in yet then make sure they are
    if (!isloggedin()) {
        //NOTE: $USER->site check was obsoleted by session test cookie,
        //      $USER->confirmed test is in login/index.php
        $SESSION->wantsurl = $FULLME;
        if (!empty($_SERVER['HTTP_REFERER'])) {
            $SESSION->fromurl  = $_SERVER['HTTP_REFERER'];
        }
        if ($autologinguest and !empty($CFG->guestloginbutton) and !empty($CFG->autologinguests) and ($COURSE->id == SITEID or $COURSE->guest) ) {
            $loginguest = '?loginguest=true';
        } else {
            $loginguest = '';
        }
        if (empty($CFG->loginhttps) or $loginguest) { //do not require https for guest logins
            redirect($CFG->wwwroot .'/login/index.php'. $loginguest);
        } else {
            $wwwroot = str_replace('http:','https:', $CFG->wwwroot);
            redirect($wwwroot .'/login/index.php');
        }
        exit;
    }

/// loginas as redirection if needed
    if ($COURSE->id != SITEID and !empty($USER->realuser)) {
        if ($USER->loginascontext->contextlevel == CONTEXT_COURSE) {
            if ($USER->loginascontext->instanceid != $COURSE->id) {
                print_error('loginasonecourse', '', $CFG->wwwroot.'/course/view.php?id='.$USER->loginascontext->instanceid);
            }
        }
    }


/// check whether the user should be changing password (but only if it is REALLY them)
    if (get_user_preferences('auth_forcepasswordchange') && empty($USER->realuser)) {
        $userauth = get_auth_plugin($USER->auth);
        if ($userauth->can_change_password()) {
            $SESSION->wantsurl = $FULLME;
            if ($changeurl = $userauth->change_password_url()) {
                //use plugin custom url
                redirect($changeurl);
            } else {
                //use moodle internal method
                if (empty($CFG->loginhttps)) {
                    redirect($CFG->wwwroot .'/login/change_password.php');
                } else {
                    $wwwroot = str_replace('http:','https:', $CFG->wwwroot);
                    redirect($wwwroot .'/login/change_password.php');
                }
            }
        } else {
            error(get_string('nopasswordchangeforced', 'auth'));
        }
    }

/// Check that the user account is properly set up
    if (user_not_fully_set_up($USER)) {
        $SESSION->wantsurl = $FULLME;
        redirect($CFG->wwwroot .'/user/edit.php?id='. $USER->id .'&amp;course='. SITEID);
    }

/// Make sure current IP matches the one for this session (if required)
    if (!empty($CFG->tracksessionip)) {
        if ($USER->sessionIP != md5(getremoteaddr())) {
            error(get_string('sessionipnomatch', 'error'));
        }
    }

/// Make sure the USER has a sesskey set up.  Used for checking script parameters.
    sesskey();

    // Check that the user has agreed to a site policy if there is one
    if (!empty($CFG->sitepolicy)) {
        if (!$USER->policyagreed) {
            $SESSION->wantsurl = $FULLME;
            redirect($CFG->wwwroot .'/user/policy.php');
        }
    }

    // Fetch the system context, we are going to use it a lot.
    $sysctx = get_context_instance(CONTEXT_SYSTEM);

/// If the site is currently under maintenance, then print a message
    if (!has_capability('moodle/site:config', $sysctx)) {
        if (file_exists($CFG->dataroot.'/'.SITEID.'/maintenance.html')) {
            print_maintenance_message();
            exit;
        }
    }

/// groupmembersonly access control
    if (!empty($CFG->enablegroupings) and $cm and $cm->groupmembersonly and !has_capability('moodle/site:accessallgroups', get_context_instance(CONTEXT_MODULE, $cm->id))) {
        if (isguestuser() or !groups_has_membership($cm)) {
            error(get_string('groupmembersonlyerror', 'group'), $CFG->wwwroot.'/course/view.php?id='.$cm->course);
        }
    }

    // Fetch the course context, and prefetch its child contexts
    if (!isset($COURSE->context)) {
        if ( ! $COURSE->context = get_context_instance(CONTEXT_COURSE, $COURSE->id) ) {
            print_error('nocontext');        
        }
    }
    if ($COURSE->id == SITEID) {
        /// Eliminate hidden site activities straight away
        if (!empty($cm) && !$cm->visible 
            && !has_capability('moodle/course:viewhiddenactivities', $COURSE->context)) {
            redirect($CFG->wwwroot, get_string('activityiscurrentlyhidden'));
        }
        return;

    } else {

        /// Check if the user can be in a particular course
        if (empty($USER->access['rsw'][$COURSE->context->path])) {
            //
            // Spaghetti logic construct
            // 
            // - able to view course?
            // - able to view category?
            // => if either is missing, course is hidden from this user
            //
            // It's carefully ordered so we run the cheap checks first, and the
            // more costly checks last...
            //
            if (! (($COURSE->visible || has_capability('moodle/course:viewhiddencourses', $COURSE->context))
                   && (course_parent_visible($COURSE)) || has_capability('moodle/course:viewhiddencourses', 
                                                                        get_context_instance(CONTEXT_COURSECAT,
                                                                                             $COURSE->category)))) {
                print_header_simple();
                notice(get_string('coursehidden'), $CFG->wwwroot .'/');
            }
        }    
        
    /// Non-guests who don't currently have access, check if they can be allowed in as a guest

        if ($USER->username != 'guest' and !has_capability('moodle/course:view', $COURSE->context)) {
            if ($COURSE->guest == 1) {
                 // Temporarily assign them guest role for this context, if it fails later user is asked to enrol
                 $USER->access = load_temp_role($COURSE->context, $CFG->guestroleid, $USER->access);
            }
        }

    /// If the user is a guest then treat them according to the course policy about guests

        if (has_capability('moodle/legacy:guest', $COURSE->context, NULL, false)) {
            switch ($COURSE->guest) {    /// Check course policy about guest access

                case 1:    /// Guests always allowed 
                    if (!has_capability('moodle/course:view', $COURSE->context)) {    // Prohibited by capability
                        print_header_simple();
                        notice(get_string('guestsnotallowed', '', format_string($COURSE->fullname)), "$CFG->wwwroot/login/index.php");
                    }
                    if (!empty($cm) and !$cm->visible) { // Not allowed to see module, send to course page
                        redirect($CFG->wwwroot.'/course/view.php?id='.$cm->course,
                                 get_string('activityiscurrentlyhidden'));
                    }

                    return;   // User is allowed to see this course

                    break;

                case 2:    /// Guests allowed with key
                    if (!empty($USER->enrolkey[$COURSE->id])) {   // Set by enrol/manual/enrol.php
                        return true;
                    }
                    //  otherwise drop through to logic below (--> enrol.php)
                    break;

                default:    /// Guests not allowed
                    $strloggedinasguest = get_string('loggedinasguest');
                    print_header_simple('', '',
                            build_navigation(array(array('name' => $strloggedinasguest, 'link' => null, 'type' => 'misc'))));
                    if (empty($USER->access['rsw'][$COURSE->context->path])) {  // Normal guest
                        notice(get_string('guestsnotallowed', '', format_string($COURSE->fullname)), "$CFG->wwwroot/login/index.php");
                    } else {
                        notify(get_string('guestsnotallowed', '', format_string($COURSE->fullname)));
                        echo '<div class="notifyproblem">'.switchroles_form($COURSE->id).'</div>';
                        print_footer($COURSE);
                        exit;
                    }
                    break;
            }

    /// For non-guests, check if they have course view access

        } else if (has_capability('moodle/course:view', $COURSE->context)) {
            if (!empty($USER->realuser)) {   // Make sure the REAL person can also access this course
                if (!has_capability('moodle/course:view', $COURSE->context, $USER->realuser)) {
                    print_header_simple();
                    notice(get_string('studentnotallowed', '', fullname($USER, true)), $CFG->wwwroot .'/');
                }
            }

        /// Make sure they can read this activity too, if specified

            if (!empty($cm) and !$cm->visible and !has_capability('moodle/course:viewhiddenactivities', $COURSE->context)) { 
                redirect($CFG->wwwroot.'/course/view.php?id='.$cm->course, get_string('activityiscurrentlyhidden'));
            }
            return;   // User is allowed to see this course

        }


    /// Currently not enrolled in the course, so see if they want to enrol
        $SESSION->wantsurl = $FULLME;
        redirect($CFG->wwwroot .'/course/enrol.php?id='. $COURSE->id);
        die;
    }
}


/**
 * This function just makes sure a user is logged out.
 *
 * @uses $CFG
 * @uses $USER
 */
function require_logout() {

    global $USER, $CFG, $SESSION;

    if (isloggedin()) {
        add_to_log(SITEID, "user", "logout", "view.php?id=$USER->id&course=".SITEID, $USER->id, 0, $USER->id);

        $authsequence = get_enabled_auth_plugins(); // auths, in sequence
        foreach($authsequence as $authname) {
            $authplugin = get_auth_plugin($authname);
            $authplugin->prelogout_hook();
        }
    }

    if (ini_get_bool("register_globals") and check_php_version("4.3.0")) {
        // This method is just to try to avoid silly warnings from PHP 4.3.0
        session_unregister("USER");
        session_unregister("SESSION");
    }

    // Initialize variable to pass-by-reference to headers_sent(&$file, &$line)
    $file = $line = null;
    if (headers_sent($file, $line)) {
        error_log('MoodleSessionTest cookie could not be set in moodlelib.php:'.__LINE__);
        error_log('Headers were already sent in file: '.$file.' on line '.$line);
    } else {
        setcookie('MoodleSessionTest'.$CFG->sessioncookie, '', time() - 3600, $CFG->sessioncookiepath);
    }

    unset($_SESSION['USER']);
    unset($_SESSION['SESSION']);

    unset($SESSION);
    unset($USER);

}

/**
 * This is a weaker version of {@link require_login()} which only requires login
 * when called from within a course rather than the site page, unless
 * the forcelogin option is turned on.
 *
 * @uses $CFG
 * @param mixed $courseorid The course object or id in question
 * @param bool $autologinguest Allow autologin guests if that is wanted
 * @param object $cm Course activity module if known
 */
function require_course_login($courseorid, $autologinguest=true, $cm=null) {
    global $CFG;
    if (!empty($CFG->forcelogin)) {
        // login required for both SITE and courses
        require_login($courseorid, $autologinguest, $cm);

    } else if (!empty($cm) and !$cm->visible) {
        // always login for hidden activities
        require_login($courseorid, $autologinguest, $cm);

    } else if ((is_object($courseorid) and $courseorid->id == SITEID)
          or (!is_object($courseorid) and $courseorid == SITEID)) {
        //login for SITE not required
        return;

    } else {
        // course login always required
        require_login($courseorid, $autologinguest, $cm);
    }
}

/**
 * Require key login. Function terminates with error if key not found or incorrect.
 * @param string $script unique script identifier
 * @param int $instance optional instance id
 */
function require_user_key_login($script, $instance=null) {
    global $nomoodlecookie, $USER, $SESSION, $CFG;

    if (empty($nomoodlecookie)) {
        error('Incorrect use of require_key_login() - session cookies must be disabled!');
    }

/// extra safety
    @session_write_close();

    $keyvalue = required_param('key', PARAM_ALPHANUM);

    if (!$key = get_record('user_private_key', 'script', $script, 'value', $keyvalue, 'instance', $instance)) {
        error('Incorrect key');
    }

    if (!empty($key->validuntil) and $key->validuntil < time()) {
        error('Expired key');
    }

    if ($key->iprestriction) {
        $remoteaddr = getremoteaddr();
        if ($remoteaddr == '' or !address_in_subnet($remoteaddr, $key->iprestriction)) {
            error('Client IP address mismatch');
        }
    }

    if (!$user = get_record('user', 'id', $key->userid)) {
        error('Incorrect user record');
    }

/// emulate normal session
    $SESSION = new object();
    $USER    = $user;

/// note we are not using normal login
    if (!defined('USER_KEY_LOGIN')) {
        define('USER_KEY_LOGIN', true);
    }

    load_all_capabilities();

/// return isntance id - it might be empty
    return $key->instance;
}

/**
 * Creates a new private user access key.
 * @param string $script unique target identifier
 * @param int $userid
 * @param instance $int optional instance id
 * @param string $iprestriction optional ip restricted access
 * @param timestamp $validuntil key valid only until given data
 * @return string access key value
 */
function create_user_key($script, $userid, $instance=null, $iprestriction=null, $validuntil=null) {
    $key = new object();
    $key->script        = $script;
    $key->userid        = $userid;
    $key->instance      = $instance;
    $key->iprestriction = $iprestriction;
    $key->validuntil    = $validuntil;
    $key->timecreated   = time();

    $key->value         = md5($userid.'_'.time().random_string(40)); // something long and unique
    while (record_exists('user_private_key', 'value', $key->value)) {
        // must be unique
        $key->value     = md5($userid.'_'.time().random_string(40));
    }

    if (!insert_record('user_private_key', $key)) {
        error('Can not insert new key');
    }

    return $key->value;
}

/**
 * Modify the user table by setting the currently logged in user's
 * last login to now.
 *
 * @uses $USER
 * @return bool
 */
function update_user_login_times() {
    global $USER;

    $user = new object();
    $USER->lastlogin = $user->lastlogin = $USER->currentlogin;
    $USER->currentlogin = $user->lastaccess = $user->currentlogin = time();

    $user->id = $USER->id;

    return update_record('user', $user);
}

/**
 * Determines if a user has completed setting up their account.
 *
 * @param user $user A {@link $USER} object to test for the existance of a valid name and email
 * @return bool
 */
function user_not_fully_set_up($user) {
    return ($user->username != 'guest' and (empty($user->firstname) or empty($user->lastname) or empty($user->email) or over_bounce_threshold($user)));
}

function over_bounce_threshold($user) {

    global $CFG;

    if (empty($CFG->handlebounces)) {
        return false;
    }
    // set sensible defaults
    if (empty($CFG->minbounces)) {
        $CFG->minbounces = 10;
    }
    if (empty($CFG->bounceratio)) {
        $CFG->bounceratio = .20;
    }
    $bouncecount = 0;
    $sendcount = 0;
    if ($bounce = get_record('user_preferences','userid',$user->id,'name','email_bounce_count')) {
        $bouncecount = $bounce->value;
    }
    if ($send = get_record('user_preferences','userid',$user->id,'name','email_send_count')) {
        $sendcount = $send->value;
    }
    return ($bouncecount >= $CFG->minbounces && $bouncecount/$sendcount >= $CFG->bounceratio);
}

/**
 * @param $user - object containing an id
 * @param $reset - will reset the count to 0
 */
function set_send_count($user,$reset=false) {
    if ($pref = get_record('user_preferences','userid',$user->id,'name','email_send_count')) {
        $pref->value = (!empty($reset)) ? 0 : $pref->value+1;
        update_record('user_preferences',$pref);
    }
    else if (!empty($reset)) { // if it's not there and we're resetting, don't bother.
        // make a new one
        $pref->name = 'email_send_count';
        $pref->value = 1;
        $pref->userid = $user->id;
        insert_record('user_preferences',$pref, false);
    }
}

/**
* @param $user - object containing an id
 * @param $reset - will reset the count to 0
 */
function set_bounce_count($user,$reset=false) {
    if ($pref = get_record('user_preferences','userid',$user->id,'name','email_bounce_count')) {
        $pref->value = (!empty($reset)) ? 0 : $pref->value+1;
        update_record('user_preferences',$pref);
    }
    else if (!empty($reset)) { // if it's not there and we're resetting, don't bother.
        // make a new one
        $pref->name = 'email_bounce_count';
        $pref->value = 1;
        $pref->userid = $user->id;
        insert_record('user_preferences',$pref, false);
    }
}

/**
 * Keeps track of login attempts
 *
 * @uses $SESSION
 */
function update_login_count() {

    global $SESSION;

    $max_logins = 10;

    if (empty($SESSION->logincount)) {
        $SESSION->logincount = 1;
    } else {
        $SESSION->logincount++;
    }

    if ($SESSION->logincount > $max_logins) {
        unset($SESSION->wantsurl);
        error(get_string('errortoomanylogins'));
    }
}

/**
 * Resets login attempts
 *
 * @uses $SESSION
 */
function reset_login_count() {
    global $SESSION;

    $SESSION->logincount = 0;
}

function sync_metacourses() {

    global $CFG;

    if (!$courses = get_records('course', 'metacourse', 1)) {
        return;
    }

    foreach ($courses as $course) {
        sync_metacourse($course);
    }
}

/**
 * Goes through all enrolment records for the courses inside the metacourse and sync with them.
 *
 * @param mixed $course the metacourse to synch. Either the course object itself, or the courseid.
 */
function sync_metacourse($course) {
    global $CFG;

    // Check the course is valid.
    if (!is_object($course)) {
        if (!$course = get_record('course', 'id', $course)) {
            return false; // invalid course id
        }
    }

    // Check that we actually have a metacourse.
    if (empty($course->metacourse)) {
        return false;
    }

    // Get a list of roles that should not be synced.
    if (!empty($CFG->nonmetacoursesyncroleids)) {
        $roleexclusions = 'ra.roleid NOT IN (' . $CFG->nonmetacoursesyncroleids . ') AND';
    } else {
        $roleexclusions = '';
    }

    // Get the context of the metacourse.
    $context = get_context_instance(CONTEXT_COURSE, $course->id); // SITEID can not be a metacourse

    // We do not ever want to unassign the list of metacourse manager, so get a list of them.
    if ($users = get_users_by_capability($context, 'moodle/course:managemetacourse')) {
        $managers = array_keys($users);
    } else {
        $managers = array();
    }

    // Get assignments of a user to a role that exist in a child course, but
    // not in the meta coure. That is, get a list of the assignments that need to be made.
    if (!$assignments = get_records_sql("
            SELECT
                ra.id, ra.roleid, ra.userid
            FROM
                {$CFG->prefix}role_assignments ra,
                {$CFG->prefix}context con,
                {$CFG->prefix}course_meta cm
            WHERE
                ra.contextid = con.id AND
                con.contextlevel = " . CONTEXT_COURSE . " AND
                con.instanceid = cm.child_course AND
                cm.parent_course = {$course->id} AND
                $roleexclusions
                NOT EXISTS (
                    SELECT 1 FROM
                        {$CFG->prefix}role_assignments ra2
                    WHERE
                        ra2.userid = ra.userid AND
                        ra2.roleid = ra.roleid AND
                        ra2.contextid = {$context->id}
                )
    ")) {
        $assignments = array();
    }

    // Get assignments of a user to a role that exist in the meta course, but
    // not in any child courses. That is, get a list of the unassignments that need to be made.
    if (!$unassignments = get_records_sql("
            SELECT
                ra.id, ra.roleid, ra.userid
            FROM
                {$CFG->prefix}role_assignments ra
            WHERE
                ra.contextid = {$context->id} AND
                $roleexclusions
                NOT EXISTS (
                    SELECT 1 FROM
                        {$CFG->prefix}role_assignments ra2,
                        {$CFG->prefix}context con2,
                        {$CFG->prefix}course_meta cm
                    WHERE
                        ra2.userid = ra.userid AND
                        ra2.roleid = ra.roleid AND
                        ra2.contextid = con2.id AND
                        con2.contextlevel = " . CONTEXT_COURSE . " AND
                        con2.instanceid = cm.child_course AND
                        cm.parent_course = {$course->id}
                )
    ")) {
        $unassignments = array();
    }

    $success = true;

    // Make the unassignments, if they are not managers.
    foreach ($unassignments as $unassignment) {
        if (!in_array($unassignment->userid, $managers)) {
            $success = role_unassign($unassignment->roleid, $unassignment->userid, 0, $context->id) && $success;
        }
    }

    // Make the assignments.
    foreach ($assignments as $assignment) {
        $success = role_assign($assignment->roleid, $assignment->userid, 0, $context->id) && $success;
    }

    return $success;

// TODO: finish timeend and timestart
// maybe we could rely on cron job to do the cleaning from time to time
}

/**
 * Adds a record to the metacourse table and calls sync_metacoures
 */
function add_to_metacourse ($metacourseid, $courseid) {

    if (!$metacourse = get_record("course","id",$metacourseid)) {
        return false;
    }

    if (!$course = get_record("course","id",$courseid)) {
        return false;
    }

    if (!$record = get_record("course_meta","parent_course",$metacourseid,"child_course",$courseid)) {
        $rec = new object();
        $rec->parent_course = $metacourseid;
        $rec->child_course = $courseid;
        if (!insert_record('course_meta',$rec)) {
            return false;
        }
        return sync_metacourse($metacourseid);
    }
    return true;

}

/**
 * Removes the record from the metacourse table and calls sync_metacourse
 */
function remove_from_metacourse($metacourseid, $courseid) {

    if (delete_records('course_meta','parent_course',$metacourseid,'child_course',$courseid)) {
        return sync_metacourse($metacourseid);
    }
    return false;
}


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

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

/**
 * Determines if a user is logged in as real guest user with username 'guest'.
 * This function is similar to original isguest() in 1.6 and earlier.
 * Current isguest() is deprecated - do not use it anymore.
 *
 * @param $user mixed user object or id, $USER if not specified
 * @return bool true if user is the real guest user, false if not logged in or other user
 */
function isguestuser($user=NULL) {
    global $USER;
    if ($user === NULL) {
        $user = $USER;
    } else if (is_numeric($user)) {
        $user = get_record('user', 'id', $user, '', '', '', '', 'id, username');
    }

    if (empty($user->id)) {
        return false; // not logged in, can not be guest
    }

    return ($user->username == 'guest');
}

/**
 * Determines if the currently logged in user is in editing mode.
 * Note: originally this function had $userid parameter - it was not usable anyway
 *
 * @uses $USER, $PAGE
 * @return bool
 */
function isediting() {
    global $USER, $PAGE;

    if (empty($USER->editing)) {
        return false;
    } elseif (is_object($PAGE) && method_exists($PAGE,'user_allowed_editing')) {
        return $PAGE->user_allowed_editing();
    }
    return true;//false;
}

/**
 * Determines if the logged in user is currently moving an activity
 *
 * @uses $USER
 * @param int $courseid The id of the course being tested
 * @return bool
 */
function ismoving($courseid) {
    global $USER;

    if (!empty($USER->activitycopy)) {
        return ($USER->activitycopycourse == $courseid);
    }
    return false;
}

/**
 * Given an object containing firstname and lastname
 * values, this function returns a string with the
 * full name of the person.
 * The result may depend on system settings
 * or language.  'override' will force both names
 * to be used even if system settings specify one.
 *
 * @uses $CFG
 * @uses $SESSION
 * @param object $user A {@link $USER} object to get full name of
 * @param bool $override If true then the name will be first name followed by last name rather than adhering to fullnamedisplay setting.
 */
function fullname($user, $override=false) {

    global $CFG, $SESSION;

    if (!isset($user->firstname) and !isset($user->lastname)) {
        return '';
    }

    if (!$override) {
        if (!empty($CFG->forcefirstname)) {
            $user->firstname = $CFG->forcefirstname;
        }
        if (!empty($CFG->forcelastname)) {
            $user->lastname = $CFG->forcelastname;
        }
    }

    if (!empty($SESSION->fullnamedisplay)) {
        $CFG->fullnamedisplay = $SESSION->fullnamedisplay;
    }

    if ($CFG->fullnamedisplay == 'firstname lastname') {
        return $user->firstname .' '. $user->lastname;

    } else if ($CFG->fullnamedisplay == 'lastname firstname') {
        return $user->lastname .' '. $user->firstname;

    } else if ($CFG->fullnamedisplay == 'firstname') {
        if ($override) {
            return get_string('fullnamedisplay', '', $user);
        } else {
            return $user->firstname;
        }
    }

    return get_string('fullnamedisplay', '', $user);
}

/**
 * Sets a moodle cookie with an encrypted string
 *
 * @uses $CFG
 * @uses DAYSECS
 * @uses HOURSECS
 * @param string $thing The string to encrypt and place in a cookie
 */
function set_moodle_cookie($thing) {
    global $CFG;

    if ($thing == 'guest') {  // Ignore guest account
        return;
    }

    $cookiename = 'MOODLEID_'.$CFG->sessioncookie;

    $days = 60;
    $seconds = DAYSECS*$days;

    setCookie($cookiename, '', time() - HOURSECS, $CFG->sessioncookiepath);
    setCookie($cookiename, rc4encrypt($thing), time()+$seconds, $CFG->sessioncookiepath);
}

/**
 * Gets a moodle cookie with an encrypted string
 *
 * @uses $CFG
 * @return string
 */
function get_moodle_cookie() {
    global $CFG;

    $cookiename = 'MOODLEID_'.$CFG->sessioncookie;

    if (empty($_COOKIE[$cookiename])) {
        return '';
    } else {
        $thing = rc4decrypt($_COOKIE[$cookiename]);
        return ($thing == 'guest') ? '': $thing;  // Ignore guest account
    }
}

/**
 * Returns whether a given authentication plugin exists.
 *
 * @uses $CFG
 * @param string $auth Form of authentication to check for. Defaults to the
 *        global setting in {@link $CFG}.
 * @return boolean Whether the plugin is available.
 */
function exists_auth_plugin($auth) {
    global $CFG;

    if (file_exists("{$CFG->dirroot}/auth/$auth/auth.php")) {
        return is_readable("{$CFG->dirroot}/auth/$auth/auth.php");
    }
    return false;
}

/**
 * Checks if a given plugin is in the list of enabled authentication plugins.
 *
 * @param string $auth Authentication plugin.
 * @return boolean Whether the plugin is enabled.
 */
function is_enabled_auth($auth) {
    if (empty($auth)) {
        return false;
    }

    $enabled = get_enabled_auth_plugins();

    return in_array($auth, $enabled);
}

/**
 * Returns an authentication plugin instance.
 *
 * @uses $CFG
 * @param string $auth name of authentication plugin
 * @return object An instance of the required authentication plugin.
 */
function get_auth_plugin($auth) {
    global $CFG;

    // check the plugin exists first
    if (! exists_auth_plugin($auth)) {
        error("Authentication plugin '$auth' not found.");
    }

    // return auth plugin instance
    require_once "{$CFG->dirroot}/auth/$auth/auth.php";
    $class = "auth_plugin_$auth";
    return new $class;
}

/**
 * Returns array of active auth plugins.
 *
 * @param bool $fix fix $CFG->auth if needed
 * @return array
 */
function get_enabled_auth_plugins($fix=false) {
    global $CFG;

    $default = array('manual', 'nologin');

    if (empty($CFG->auth)) {
        $auths = array();
    } else {
        $auths = explode(',', $CFG->auth);
    }

    if ($fix) {
        $auths = array_unique($auths);
        foreach($auths as $k=>$authname) {
            if (!exists_auth_plugin($authname) or in_array($authname, $default)) {
                unset($auths[$k]);
            }
        }
        $newconfig = implode(',', $auths);
        if (!isset($CFG->auth) or $newconfig != $CFG->auth) {
            set_config('auth', $newconfig);
        }
    }

    return (array_merge($default, $auths));
}

/**
 * Returns true if an internal authentication method is being used.
 * if method not specified then, global default is assumed
 *
 * @uses $CFG
 * @param string $auth Form of authentication required
 * @return bool
 */
function is_internal_auth($auth) {
    $authplugin = get_auth_plugin($auth); // throws error if bad $auth
    return $authplugin->is_internal();
}

/**
 * Returns an array of user fields
 *
 * @uses $CFG
 * @uses $db
 * @return array User field/column names
 */
function get_user_fieldnames() {

    global $CFG, $db;

    $fieldarray = $db->MetaColumnNames($CFG->prefix.'user');
    unset($fieldarray['ID']);

    return $fieldarray;
}

/**
 * Creates the default "guest" user. Used both from
 * admin/index.php and login/index.php
 * @return mixed user object created or boolean false if the creation has failed
 */
function create_guest_record() {

    global $CFG;

    $guest = new stdClass();
    $guest->auth        = 'manual';
    $guest->username    = 'guest';
    $guest->password    = hash_internal_user_password('guest');
    $guest->firstname   = addslashes(get_string('guestuser'));
    $guest->lastname    = ' ';
    $guest->email       = 'root@localhost';
    $guest->description = addslashes(get_string('guestuserinfo'));
    $guest->mnethostid  = $CFG->mnet_localhost_id;
    $guest->confirmed   = 1;
    $guest->lang        = $CFG->lang;
    $guest->timemodified= time();

    if (! $guest->id = insert_record("user", $guest)) {
        return false;
    }

    return $guest;
}

/**
 * Creates a bare-bones user record
 *
 * @uses $CFG
 * @param string $username New user's username to add to record
 * @param string $password New user's password to add to record
 * @param string $auth Form of authentication required
 * @return object A {@link $USER} object
 * @todo Outline auth types and provide code example
 */
function create_user_record($username, $password, $auth='manual') {
    global $CFG;

    //just in case check text case
    $username = trim(moodle_strtolower($username));

    $authplugin = get_auth_plugin($auth);

    if ($newinfo = $authplugin->get_userinfo($username)) {
        $newinfo = truncate_userinfo($newinfo);
        foreach ($newinfo as $key => $value){
            $newuser->$key = addslashes($value);
        }
    }

    if (!empty($newuser->email)) {
        if (email_is_not_allowed($newuser->email)) {
            unset($newuser->email);
        }
    }

    $newuser->auth = $auth;
    $newuser->username = $username;

    // fix for MDL-8480
    // user CFG lang for user if $newuser->lang is empty
    // or $user->lang is not an installed language
    $sitelangs = array_keys(get_list_of_languages());
    if (empty($newuser->lang) || !in_array($newuser->lang, $sitelangs)) {
        $newuser -> lang = $CFG->lang;
    }
    $newuser->confirmed = 1;
    $newuser->lastip = getremoteaddr();
    $newuser->timemodified = time();
    $newuser->mnethostid = $CFG->mnet_localhost_id;

    if (insert_record('user', $newuser)) {
        $user = get_complete_user_data('username', $newuser->username);
        if(!empty($CFG->{'auth_'.$newuser->auth.'_forcechangepassword'})){
            set_user_preference('auth_forcepasswordchange', 1, $user->id);
        }
        update_internal_user_password($user, $password);
        return $user;
    }
    return false;
}

/**
 * Will update a local user record from an external source
 *
 * @uses $CFG
 * @param string $username New user's username to add to record
 * @return user A {@link $USER} object
 */
function update_user_record($username, $authplugin) {
    $username = trim(moodle_strtolower($username)); /// just in case check text case

    $oldinfo = get_record('user', 'username', $username, '','','','', 'username, auth');
    $userauth = get_auth_plugin($oldinfo->auth);

    if ($newinfo = $userauth->get_userinfo($username)) {
        $newinfo = truncate_userinfo($newinfo);
        foreach ($newinfo as $key => $value){
            $confkey = 'field_updatelocal_' . $key;
            if (!empty($userauth->config->$confkey) and $userauth->config->$confkey === 'onlogin') {
                $value = addslashes(stripslashes($value));   // Just in case
                set_field('user', $key, $value, 'username', $username)
                    or error_log("Error updating $key for $username");
            }
        }
    }

    return get_complete_user_data('username', $username);
}

function truncate_userinfo($info) {
/// will truncate userinfo as it comes from auth_get_userinfo (from external auth)
/// which may have large fields

    // define the limits
    $limit = array(
                    'username'    => 100,
                    'idnumber'    =>  64,
                    'firstname'   => 100,
                    'lastname'    => 100,
                    'email'       => 100,
                    'icq'         =>  15,
                    'phone1'      =>  20,
                    'phone2'      =>  20,
                    'institution' =>  40,
                    'department'  =>  30,
                    'address'     =>  70,
                    'city'        =>  20,
                    'country'     =>   2,
                    'url'         => 255,
                    );

    // apply where needed
    foreach (array_keys($info) as $key) {
        if (!empty($limit[$key])) {
            $info[$key] = trim(substr($info[$key],0, $limit[$key]));
        }
    }

    return $info;
}

/**
 * Marks user deleted in internal user database and notifies the auth plugin.
 * Also unenrols user from all roles and does other cleanup.
 * @param object $user       Userobject before delete    (without system magic quotes)
 * @return boolean success
 */
function delete_user($user) {
    global $CFG;
    require_once($CFG->libdir.'/grouplib.php');
    require_once($CFG->libdir.'/gradelib.php');

    begin_sql();

    // delete all grades - backup is kept in grade_grades_history table
    if ($grades = grade_grade::fetch_all(array('userid'=>$user->id))) {
        foreach ($grades as $grade) {
            $grade->delete('userdelete');
        }
    }

    // remove from all groups
    delete_records('groups_members', 'userid', $user->id);

    // unenrol from all roles in all contexts
    role_unassign(0, $user->id); // this might be slow but it is really needed - modules might do some extra cleanup!

    // now do a final accesslib cleanup - removes all role assingments in user context and context itself
    delete_context(CONTEXT_USER, $user->id);

    // workaround for bulk deletes of users with the same email address
    $delname = addslashes("$user->email.".time());
    while (record_exists('user', 'username', $delname)) { // no need to use mnethostid here
        $delname++;
    }

    // mark internal user record as "deleted"
    $updateuser = new object();
    $updateuser->id           = $user->id;
    $updateuser->deleted      = 1;
    $updateuser->username     = $delname;         // Remember it just in case
    $updateuser->email        = '';               // Clear this field to free it up
    $updateuser->idnumber     = '';               // Clear this field to free it up
    $updateuser->timemodified = time();

    if (update_record('user', $updateuser)) {
        commit_sql();
        // notify auth plugin - do not block the delete even when plugin fails
        $authplugin = get_auth_plugin($user->auth);
        $authplugin->user_delete($user);
        return true;

    } else {
        rollback_sql();
        return false;
    }
}

/**
 * Retrieve the guest user object
 *
 * @uses $CFG
 * @return user A {@link $USER} object
 */
function guest_user() {
    global $CFG;

    if ($newuser = get_record('user', 'username', 'guest', 'mnethostid',  $CFG->mnet_localhost_id)) {
        $newuser->confirmed = 1;
        $newuser->lang = $CFG->lang;
        $newuser->lastip = getremoteaddr();
    }

    return $newuser;
}

/**
 * Given a username and password, this function looks them
 * up using the currently selected authentication mechanism,
 * and if the authentication is successful, it returns a
 * valid $user object from the 'user' table.
 *
 * Uses auth_ functions from the currently active auth module
 *
 * After authenticate_user_login() returns success, you will need to
 * log that the user has logged in, and call complete_user_login() to set
 * the session up.
 *
 * @uses $CFG
 * @param string $username  User's username (with system magic quotes)
 * @param string $password  User's password (with system magic quotes)
 * @return user|flase A {@link $USER} object or false if error
 */
function authenticate_user_login($username, $password) {

    global $CFG;

    $authsenabled = get_enabled_auth_plugins();

    if ($user = get_complete_user_data('username', $username)) {
        $auth = empty($user->auth) ? 'manual' : $user->auth;  // use manual if auth not set
        if ($auth=='nologin' or !is_enabled_auth($auth)) {
            add_to_log(0, 'login', 'error', 'index.php', $username);
            error_log('[client '.$_SERVER['REMOTE_ADDR']."]  $CFG->wwwroot  Disabled Login:  $username  ".$_SERVER['HTTP_USER_AGENT']);
            return false;
        }
        if (!empty($user->deleted)) {
            add_to_log(0, 'login', 'error', 'index.php', $username);
            error_log('[client '.$_SERVER['REMOTE_ADDR']."]  $CFG->wwwroot  Deleted Login:  $username  ".$_SERVER['HTTP_USER_AGENT']);
            return false;
        }
        $auths = array($auth);

    } else {
        $auths = $authsenabled;
        $user = new object();
        $user->id = 0;     // User does not exist
    }

    foreach ($auths as $auth) {
        $authplugin = get_auth_plugin($auth);

        // on auth fail fall through to the next plugin
        if (!$authplugin->user_login($username, $password)) {
            continue;
        }

        // successful authentication
        if ($user->id) {                          // User already exists in database
            if (empty($user->auth)) {             // For some reason auth isn't set yet
                set_field('user', 'auth', $auth, 'username', $username);
                $user->auth = $auth;
            }

            update_internal_user_password($user, $password); // just in case salt or encoding were changed (magic quotes too one day)

            if (!$authplugin->is_internal()) {            // update user record from external DB
                $user = update_user_record($username, get_auth_plugin($user->auth));
            }
        } else {
            // if user not found, create him
            $user = create_user_record($username, $password, $auth);
        }

        $authplugin->sync_roles($user);

        foreach ($authsenabled as $hau) {
            $hauth = get_auth_plugin($hau);
            $hauth->user_authenticated_hook($user, $username, $password);
        }

    /// Log in to a second system if necessary
    /// NOTICE: /sso/ will be moved to auth and deprecated soon; use user_authenticated_hook() instead
        if (!empty($CFG->sso)) {
            include_once($CFG->dirroot .'/sso/'. $CFG->sso .'/lib.php');
            if (function_exists('sso_user_login')) {
                if (!sso_user_login($username, $password)) {   // Perform the signon process
                    notify('Second sign-on failed');
                }
            }
        }

        return $user;

    }

    // failed if all the plugins have failed
    add_to_log(0, 'login', 'error', 'index.php', $username);
    error_log('[client '.$_SERVER['REMOTE_ADDR']."]  $CFG->wwwroot  Failed Login:  $username  ".$_SERVER['HTTP_USER_AGENT']);
    return false;
}

/**
 * Call to complete the user login process after authenticate_user_login()
 * has succeeded. It will setup the $USER variable and other required bits
 * and pieces.
 * 
 * NOTE:
 * - It will NOT log anything -- up to the caller to decide what to log.
 *
 *
 *
 * @uses $CFG, $USER
 * @param string $user obj
 * @return user|flase A {@link $USER} object or false if error
 */
function complete_user_login($user) {
    global $CFG, $USER;
    
    $USER = $user; // this is required because we need to access preferences here!

    reload_user_preferences();

    update_user_login_times();
    if (empty($CFG->nolastloggedin)) {
        set_moodle_cookie($USER->username);
    } else {
        // do not store last logged in user in cookie
        // auth plugins can temporarily override this from loginpage_hook()
        // do not save $CFG->nolastloggedin in database!
        set_moodle_cookie('nobody');
    }
    set_login_session_preferences();

    // Call enrolment plugins
    check_enrolment_plugins($user);

    /// This is what lets the user do anything on the site :-)
    load_all_capabilities();

    /// Select password change url
    $userauth = get_auth_plugin($USER->auth);

    /// check whether the user should be changing password
    if (get_user_preferences('auth_forcepasswordchange', false)){
        if ($userauth->can_change_password()) {
            if ($changeurl = $userauth->change_password_url()) {
                redirect($changeurl);
            } else {
                redirect($CFG->httpswwwroot.'/login/change_password.php');
            }
        } else {
            error(get_string('nopasswordchangeforced', 'auth'));
        }
    }
    return $USER;
}

/**
 * Compare password against hash stored in internal user table.
 * If necessary it also updates the stored hash to new format.
 *
 * @param object user
 * @param string plain text password
 * @return bool is password valid?
 */
function validate_internal_user_password(&$user, $password) {
    global $CFG;

    if (!isset($CFG->passwordsaltmain)) {
        $CFG->passwordsaltmain = '';
    }

    $validated = false;

    // get password original encoding in case it was not updated to unicode yet
    $textlib = textlib_get_instance();
    $convpassword = $textlib->convert($password, 'utf-8', get_string('oldcharset'));

    if ($user->password == md5($password.$CFG->passwordsaltmain) or $user->password == md5($password)
        or $user->password == md5($convpassword.$CFG->passwordsaltmain) or $user->password == md5($convpassword)) {
        $validated = true;
    } else {
        for ($i=1; $i<=20; $i++) { //20 alternative salts should be enough, right?
            $alt = 'passwordsaltalt'.$i;
            if (!empty($CFG->$alt)) {
                if ($user->password == md5($password.$CFG->$alt) or $user->password == md5($convpassword.$CFG->$alt)) {
                    $validated = true;
                    break;
                }
            }
        }
    }

    if ($validated) {
        // force update of password hash using latest main password salt and encoding if needed
        update_internal_user_password($user, $password);
    }

    return $validated;
}

/**
 * Calculate hashed value from password using current hash mechanism.
 *
 * @param string password
 * @return string password hash
 */
function hash_internal_user_password($password) {
    global $CFG;

    if (isset($CFG->passwordsaltmain)) {
        return md5($password.$CFG->passwordsaltmain);
    } else {
        return md5($password);
    }
}

/**
 * Update pssword hash in user object.
 *
 * @param object user
 * @param string plain text password
 * @param bool store changes also in db, default true
 * @return true if hash changed
 */
function update_internal_user_password(&$user, $password) {
    global $CFG;

    $authplugin = get_auth_plugin($user->auth);
    if (!empty($authplugin->config->preventpassindb)) {
        $hashedpassword = 'not cached';
    } else {
        $hashedpassword = hash_internal_user_password($password);
    }

    return set_field('user', 'password',  $hashedpassword, 'id', $user->id);
}

/**
 * Get a complete user record, which includes all the info
 * in the user record
 * Intended for setting as $USER session variable
 *
 * @uses $CFG
 * @uses SITEID
 * @param string $field The user field to be checked for a given value.
 * @param string $value The value to match for $field.
 * @return user A {@link $USER} object.
 */
function get_complete_user_data($field, $value, $mnethostid=null) {

    global $CFG;

    if (!$field || !$value) {
        return false;
    }

/// Build the WHERE clause for an SQL query

    $constraints = $field .' = \''. $value .'\' AND deleted <> \'1\'';

    if (is_null($mnethostid)) {
        // if null, we restrict to local users
        // ** testing for local user can be done with
        //    mnethostid = $CFG->mnet_localhost_id
        //    or with
        //    auth != 'mnet'
        //    but the first one is FAST with our indexes
        $mnethostid = $CFG->mnet_localhost_id;
    }
    $mnethostid = (int)$mnethostid;
    $constraints .= ' AND mnethostid = \''.$mnethostid.'\'';

/// Get all the basic user data

    if (! $user = get_record_select('user', $constraints)) {
        return false;
    }

/// Get various settings and preferences

    if ($displays = get_records('course_display', 'userid', $user->id)) {
        foreach ($displays as $display) {
            $user->display[$display->course] = $display->display;
        }
    }

    $user->preference = get_user_preferences(null, null, $user->id);

    if ($lastaccesses = get_records('user_lastaccess', 'userid', $user->id)) {
        foreach ($lastaccesses as $lastaccess) {
            $user->lastcourseaccess[$lastaccess->courseid] = $lastaccess->timeaccess;
        }
    }

    $sql = "SELECT g.id, g.courseid
              FROM {$CFG->prefix}groups g, {$CFG->prefix}groups_members gm
             WHERE gm.groupid=g.id AND gm.userid={$user->id}";

    // this is a special hack to speedup calendar display
    $user->groupmember = array();
    if ($groups = get_records_sql($sql)) {
        foreach ($groups as $group) {
            if (!array_key_exists($group->courseid, $user->groupmember)) {
                $user->groupmember[$group->courseid] = array();
            }
            $user->groupmember[$group->courseid][$group->id] = $group->id;
        }
    }

/// Add the custom profile fields to the user record
    include_once($CFG->dirroot.'/user/profile/lib.php');
    $customfields = (array)profile_user_record($user->id);
    foreach ($customfields as $cname=>$cvalue) {
        if (!isset($user->$cname)) { // Don't overwrite any standard fields
            $user->$cname = $cvalue;
        }
    }

/// Rewrite some variables if necessary
    if (!empty($user->description)) {
        $user->description = true;   // No need to cart all of it around
    }
    if ($user->username == 'guest') {
        $user->lang       = $CFG->lang;               // Guest language always same as site
        $user->firstname  = get_string('guestuser');  // Name always in current language
        $user->lastname   = ' ';
    }

    $user->sesskey  = random_string(10);
    $user->sessionIP = md5(getremoteaddr());   // Store the current IP in the session

    return $user;
}

/**
 * @uses $CFG
 * @param string $password the password to be checked agains the password policy
 * @param string $errmsg the error message to display when the password doesn't comply with the policy.
 * @return bool true if the password is valid according to the policy. false otherwise.
 */
function check_password_policy($password, &$errmsg) {
    global $CFG;

    if (empty($CFG->passwordpolicy)) {
        return true;
    }

    $textlib = textlib_get_instance();
    $errmsg = '';
    if ($textlib->strlen($password) < $CFG->m