/moodle/lib/moodlelib.php

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<?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
 * @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
 */
//To prevent problems with multibytes strings, this should not exceed the
//length of "varchar(255) / 3 (bytes / utf-8 character) = 85".
define('TAG_MAX_LENGTH', 50);

/**
 * Password policy constants
 */
define ('PASSWORD_LOWER', 'abcdefghijklmnopqrstuvwxyz');
define ('PASSWORD_UPPER', 'ABCDEFGHIJKLMNOPQRSTUVWXYZ');
define ('PASSWORD_DIGITS', '0123456789');
define ('PASSWORD_NONALPHANUM', '.,;:!?_-+/*@#&$');

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_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:
            //as long as magic_quotes_gpc is used, a backslash will be a
            //problem, so remove *all* backslash.
            $param = str_replace('\\', '', $param);
            //convert many whitespace chars into one
            $param = preg_replace('/\s+/', ' ', $param);
            $textlib = textlib_get_instance();
            $param = $textlib->substr(trim($param), 0, TAG_MAX_LENGTH);
            return $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");
    }
}

/**
 * Return true if given value is integer or string with integer value
 *
 * @param mixed $value String or Int
 * @return bool true if number, false if not
 */
function is_number($value) {
    if (is_int($value)) {
        return true;
    } else if (is_string($value)) {
        return ((string)(int)$value) === $value;
    } else {
        return false;
    }
}

/**
 * This function is useful for testing whether something you got back from
 * the HTML editor actually contains anything. Sometimes the HTML editor
 * appear to be empty, but actually you get back a <br> tag or something.
 *
 * @param string $string a string containing HTML.
 * @return boolean does the string contain any actual content - that is text,
 * images, objcts, etc.
 */
function html_is_blank($string) {
    return trim(strip_tags($string, '<img><object><applet><input><select><textarea><hr>')) == '';
}

/**
 * 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;
}

/**
 * Use this funciton to get a list of users from a config setting of type admin_setting_users_with_capability.
 * @param string $value the value of the config setting.
 * @param string $capability the capability - must match the one passed to the admin_setting_users_with_capability constructor.
 * @return array of user objects.
 */
function get_users_from_config($value, $capability) {
    global $CFG;
    if ($value == '$@ALL@$') {
        $users = get_users_by_capability(get_context_instance(CONTEXT_SYSTEM), $capability);
    } else if ($value) {
        $usernames = explode(',', $value);
        $users = get_records_select('user', "username IN ('" . implode("','", $usernames) . "') AND mnethostid = " . $CFG->mnet_localhost_id);
    } else {
        $users = array();
    }
    return $users;
}

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

    $type = addslashes($type);
    $name = addslashes($name);

    $sqlwhere = 'flagtype=\'' . $type . '\' AND name=\'' . $name . '\' AND expiry >= ' . time();
    if ($changedsince !== NULL) {
        $changedsince = (int)$changedsince;
        $sqlwhere .= ' AND timemodified > ' . $changedsince;
    }
    return get_field_select('cache_flags', 'value', $sqlwhere);
}

/**
 * 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 permanent 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 permanent 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) {

    $strtimezone = NULL;
    if (!is_numeric($timezone)) {
        $strtimezone = $timezone;
    }

    $timezone = get_user_timezone_offset($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, $strtimezone);
        }
    }

    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;

    $strtimezone = NULL;
    if (!is_numeric($timezone)) {
        $strtimezone = $timezone;
    }

    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, $strtimezone);

    $timezone = get_user_timezone_offset($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) {

    $strtimezone = NULL;
    if (!is_numeric($timezone)) {
        $strtimezone = $timezone;
    }

    $timezone = get_user_timezone_offset($timezone);

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

    // There is no gmgetdate so we use gmdate instead
    $time += dst_offset_on($time, $strtimezone);
    $time += intval((float)$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) {

    $userdate = usergetdate($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 an int which represents the systems's timezone difference from GMT in seconds
 * @param mixed $tz timezone
 * @return int if found, false is timezone 99 or error
 */
function get_timezone_offset($tz) {
    global $CFG;

    if ($tz == 99) {
        return false;
    }

    if (is_numeric($tz)) {
        return intval($tz * 60*60);
    }

    if (!$tzrecord = get_timezone_record($tz)) {
        return false;
    }
    return intval($tzrecord->gmtoff * 60);
}

/**
 * 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 || $tz == NULL) && $next = each($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, $strtimezone = NULL) {
    global $CFG, $SESSION;

    $usertz = get_user_timezone($strtimezone);

    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 elemen…