MDL-23167 adding cache reset after setting changed

[moodle.git] / lib / moodlelib.php

<?php

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

/**
 * 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
 *
 * @package   moodlecore
 * @copyright 1999 onwards Martin Dougiamas  http://dougiamas.com
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

/// 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_ALPHA - contains only english ascii letters a-zA-Z.
 */
define('PARAM_ALPHA',    'alpha');

/**
 * PARAM_ALPHAEXT the same contents as PARAM_ALPHA plus the chars in quotes: "_-" allowed
 * NOTE: originally this allowed "/" too, please use PARAM_SAFEPATH if "/" needed
 */
define('PARAM_ALPHAEXT', 'alphaext');

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

/**
 * PARAM_ALPHANUMEXT - expected numbers, letters only and _-.
 */
define('PARAM_ALPHANUMEXT', 'alphanumext');

/**
 * PARAM_AUTH - actually checks to make sure the string is a valid auth plugin
 */
define('PARAM_AUTH',  'auth');

/**
 * PARAM_BASE64 - Base 64 encoded format
 */
define('PARAM_BASE64',   'base64');

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

/**
 * PARAM_CAPABILITY - A capability name, like 'moodle/role:manage'. Actually
 * checked against the list of capabilities in the database.
 */
define('PARAM_CAPABILITY',   'capability');

/**
 * PARAM_CLEANHTML - cleans submitted HTML code and removes slashes. It stays as HTML.
 */
define('PARAM_CLEANHTML', 'cleanhtml');

/**
 * PARAM_EMAIL - an email address following the RFC
 */
define('PARAM_EMAIL',   'email');

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

/**
 * PARAM_FLOAT - a real/floating point number.
 */
define('PARAM_FLOAT',  'float');

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

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

/**
 * PARAM_LANG - checks to see if the string is a valid installed language in the current site.
 */
define('PARAM_LANG',  'lang');

/**
 * 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', 'localurl');

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

/**
 * 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',     'path');

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

/**
 * PARAM_PERMISSION - A permission, one of CAP_INHERIT, CAP_ALLOW, CAP_PREVENT or CAP_PROHIBIT.
 */
define('PARAM_PERMISSION',   'permission');

/**
 * PARAM_RAW specifies a parameter that is not cleaned/processed in any way
 */
define('PARAM_RAW', 'raw');

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

/**
 * PARAM_SAFEPATH - several PARAM_SAFEDIR joined by "/", suitable for include() and require(), plugin paths, etc.
 */
define('PARAM_SAFEPATH',  'safepath');

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

/**
 * PARAM_TAG - one tag (interests, blogs, etc.) - mostly international characters and space, <> not supported
 */
define('PARAM_TAG',   'tag');

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

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

/**
 * PARAM_THEME - Checks to see if the string is a valid theme name in the current site
 */
define('PARAM_THEME',  'theme');

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

/**
 * PARAM_USERNAME - Clean username to only contains allowed characters. This is to be used ONLY when manually creating user accounts, do NOT use when syncing with external systems!!
 */
define('PARAM_USERNAME',    'username');

/**
 * PARAM_STRINGID - used to check if the given string is valid string identifier for get_string()
 */
define('PARAM_STRINGID',    'stringid');

///// DEPRECATED PARAM TYPES OR ALIASES - DO NOT USE FOR NEW CODE  /////
/**
 * PARAM_CLEAN - obsoleted, please use a more specific type of parameter.
 * It was one of the first types, that is why it is abused so much ;-)
 */
define('PARAM_CLEAN',    'clean');

/**
 * PARAM_INTEGER - deprecated alias for PARAM_INT
 */
define('PARAM_INTEGER',  'int');

/**
 * PARAM_NUMBER - deprecated alias of PARAM_FLOAT
 */
define('PARAM_NUMBER',  'float');

/**
 * PARAM_ACTION - deprecated alias for PARAM_ALPHANUMEXT, use for various actions in forms and urls
 * NOTE: originally alias for PARAM_APLHA
 */
define('PARAM_ACTION',   'alphanumext');

/**
 * PARAM_FORMAT - deprecated alias for PARAM_ALPHANUMEXT, use for names of plugins, formats, etc.
 * NOTE: originally alias for PARAM_APLHA
 */
define('PARAM_FORMAT',   'alphanumext');

/**
 * PARAM_MULTILANG - deprecated alias of PARAM_TEXT.
 */
define('PARAM_MULTILANG',  'text');

/**
 * PARAM_CLEANFILE - deprecated alias of PARAM_FILE; originally was removing regional chars too
 */
define('PARAM_CLEANFILE', 'file');

/// Web Services ///

/**
 * VALUE_REQUIRED - if the parameter is not supplied, there is an error
 */
define('VALUE_REQUIRED', 1);

/**
 * VALUE_OPTIONAL - if the parameter is not supplied, then the param has no value
 */
define('VALUE_OPTIONAL', 2);

/**
 * VALUE_DEFAULT - if the parameter is not supplied, then the default value is used
 */
define('VALUE_DEFAULT', 0);

/**
 * NULL_NOT_ALLOWED - the parameter can not be set to null in the database
 */
define('NULL_NOT_ALLOWED', false);

/**
 * NULL_ALLOWED - the parameter can be set to null in the database
 */
define('NULL_ALLOWED', true);

/// 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');

/** Get remote addr constant */
define('GETREMOTEADDR_SKIP_HTTP_CLIENT_IP', '1');
/** Get remote addr constant */
define('GETREMOTEADDR_SKIP_HTTP_X_FORWARDED_FOR', '2');

/// 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 constants///
/**
 * To prevent problems with multibytes strings,Flag updating in nav not working on the review page. this should not exceed the
 * length of "varchar(255) / 3 (bytes / utf-8 character) = 85".
 * TODO: this is not correct, varchar(255) are 255 unicode chars ;-)
 *
 * @todo define(TAG_MAX_LENGTH) this is not correct, varchar(255) are 255 unicode chars ;-)
 */
define('TAG_MAX_LENGTH', 50);

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

/// Feature constants ///
// Used for plugin_supports() to report features that are, or are not, supported by a module.

/** True if module can provide a grade */
define('FEATURE_GRADE_HAS_GRADE', 'grade_has_grade');
/** True if module supports outcomes */
define('FEATURE_GRADE_OUTCOMES', 'outcomes');

/** True if module has code to track whether somebody viewed it */
define('FEATURE_COMPLETION_TRACKS_VIEWS', 'completion_tracks_views');
/** True if module has custom completion rules */
define('FEATURE_COMPLETION_HAS_RULES', 'completion_has_rules');

/** True if module supports outcomes */
define('FEATURE_IDNUMBER', 'idnumber');
/** True if module supports groups */
define('FEATURE_GROUPS', 'groups');
/** True if module supports groupings */
define('FEATURE_GROUPINGS', 'groupings');
/** True if module supports groupmembersonly */
define('FEATURE_GROUPMEMBERSONLY', 'groupmembersonly');

/** Type of module */
define('FEATURE_MOD_ARCHETYPE', 'mod_archetype');
/** True if module supports intro editor */
define('FEATURE_MOD_INTRO', 'mod_intro');
/** True if module has default completion */
define('FEATURE_MODEDIT_DEFAULT_COMPLETION', 'modedit_default_completion');

define('FEATURE_COMMENT', 'comment');

define('FEATURE_RATE', 'rate');
/** True if module supports backup/restore of moodle2 format */
define('FEATURE_BACKUP_MOODLE2', 'backup_moodle2');

/** Unspecified module archetype */
define('MOD_ARCHETYPE_OTHER', 0);
/** Resource-like type module */
define('MOD_ARCHETYPE_RESOURCE', 1);
/** Assignment module archetype */
define('MOD_ARCHETYPE_ASSIGNMENT', 2);

/**
 * Security token used for allowing access
 * from external application such as web services.
 * Scripts do not use any session, performance is relatively
 * low because we need to load access info in each request.
 * Scripts are executed in parallel.
 */
define('EXTERNAL_TOKEN_PERMANENT', 0);

/**
 * Security token used for allowing access
 * of embedded applications, the code is executed in the
 * active user session. Token is invalidated after user logs out.
 * Scripts are executed serially - normal session locking is used.
 */
define('EXTERNAL_TOKEN_EMBEDDED', 1);

/**
 * The home page should be the site home
 */
define('HOMEPAGE_SITE', 0);
/**
 * The home page should be the users my page
 */
define('HOMEPAGE_MY', 1);
/**
 * The home page can be chosen by the user
 */
define('HOMEPAGE_USER', 2);

/**
 * Hub directory url (should be moodle.org)
 */
define('HUB_HUBDIRECTORYURL', "http://hubdirectory.moodle.org");


/**
 * Moodle.org url (should be moodle.org)
 */
define('HUB_MOODLEORGHUBURL', "http://hub.moodle.org");


/// 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_INT);
 *
 * @param string $parname the name of the page parameter we want,
 *                        default PARAM_CLEAN
 * @param int $type expected type of parameter
 * @return mixed
 */
function required_param($parname, $type=PARAM_CLEAN) {
    if (isset($_POST[$parname])) {       // POST has precedence
        $param = $_POST[$parname];
    } else if (isset($_GET[$parname])) {
        $param = $_GET[$parname];
    } else {
        print_error('missingparam', '', '', $parname);
    }

    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_TEXT);
 *
 * @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 $type expected type of parameter, default PARAM_CLEAN
 * @return mixed
 */
function optional_param($parname, $default=NULL, $type=PARAM_CLEAN) {
    if (isset($_POST[$parname])) {       // POST has precedence
        $param = $_POST[$parname];
    } else if (isset($_GET[$parname])) {
        $param = $_GET[$parname];
    } else {
        return $default;
    }

    return clean_param($param, $type);
}

/**
 * Strict validation of parameter values, the values are only converted
 * to requested PHP type. Internally it is using clean_param, the values
 * before and after cleaning must be equal - otherwise
 * an invalid_parameter_exception is thrown.
 * Objects and classes are not accepted.
 *
 * @param mixed $param
 * @param int $type PARAM_ constant
 * @param bool $allownull are nulls valid value?
 * @param string $debuginfo optional debug information
 * @return mixed the $param value converted to PHP type or invalid_parameter_exception
 */
function validate_param($param, $type, $allownull=NULL_NOT_ALLOWED, $debuginfo='') {
    if (is_null($param)) {
        if ($allownull == NULL_ALLOWED) {
            return null;
        } else {
            throw new invalid_parameter_exception($debuginfo);
        }
    }
    if (is_array($param) or is_object($param)) {
        throw new invalid_parameter_exception($debuginfo);
    }

    $cleaned = clean_param($param, $type);
    if ((string)$param !== (string)$cleaned) {
        // conversion to string is usually lossless
        throw new invalid_parameter_exception($debuginfo);
    }

    return $cleaned;
}

/**
 * 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>
 *
 * @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 $param;
            }
            return clean_text($param);     // Sweep for scripts, etc

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

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

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

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

        case PARAM_ALPHAEXT:     // Remove everything not a-zA-Z_- (originally allowed "/" too)
            return preg_replace('/[^a-zA-Z_-]/i', '', $param);

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

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

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

        case PARAM_BOOL:         // Convert to 1 or 0
            $tempstr = strtolower($param);
            if ($tempstr === 'on' or $tempstr === 'yes' or $tempstr === 'true') {
                $param = 1;
            } else if ($tempstr === 'off' or $tempstr === 'no'  or $tempstr === 'false') {
                $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 preg_replace('/[^a-zA-Z0-9_-]/i', '', $param);

        case PARAM_SAFEPATH:     // Remove everything not a-zA-Z0-9/_-
            return preg_replace('/[^a-zA-Z0-9\/_-]/i', '', $param);

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

        case PARAM_PATH:         // Strip all suspicious characters from file path
            $param = str_replace('\\', '/', $param);
            $param = preg_replace('~[[:cntrl:]]|[&<>"`\|\':]~u', '', $param);
            $param = preg_replace('~\.\.+~', '', $param);
            $param = preg_replace('~//+~', '/', $param);
            return preg_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);
            //remove some nasties
            $param = preg_replace('~[[:cntrl:]]|[<>`]~', '', $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 '';
            }

        case PARAM_CAPABILITY:
            if (get_capability_info($param)) {
                return $param;
            } else {
                return '';
            }

        case PARAM_PERMISSION:
            $param = (int)$param;
            if (in_array($param, array(CAP_INHERIT, CAP_ALLOW, CAP_PREVENT, CAP_PROHIBIT))) {
                return $param;
            } else {
                return CAP_INHERIT;
            }

        case PARAM_AUTH:
            $param = clean_param($param, PARAM_SAFEDIR);
            if (exists_auth_plugin($param)) {
                return $param;
            } else {
                return '';
            }

        case PARAM_LANG:
            $param = clean_param($param, PARAM_SAFEDIR);
            if (get_string_manager()->translation_exists($param)) {
                return $param;
            } else {
                return ''; // Specified language is not installed or param malformed
            }

        case PARAM_THEME:
            $param = clean_param($param, PARAM_SAFEDIR);
            if (file_exists("$CFG->dirroot/theme/$param/config.php")) {
                return $param;
            } else if (!empty($CFG->themedir) and file_exists("$CFG->themedir/$param/config.php")) {
                return $param;
            } else {
                return '';  // Specified theme is not installed
            }

        case PARAM_USERNAME:
            $param = str_replace(" " , "", $param);
            $param = moodle_strtolower($param);  // Convert uppercase to lowercase MDL-16919
            if (empty($CFG->extendedusernamechars)) {
                // regular expression, eliminate all chars EXCEPT:
                // alphanum, dash (-), underscore (_), at sign (@) and period (.) characters.
                $param = preg_replace('/[^-\.@_a-z0-9]/', '', $param);
            }
            return $param;

        case PARAM_EMAIL:
            if (validate_email($param)) {
                return $param;
            } else {
                return '';
            }

        case PARAM_STRINGID:
            if (preg_match('|^[a-zA-Z][a-zA-Z0-9\.:/_-]*$|', $param)) {
                return $param;
            } else {
                return '';
            }

        default:                 // throw error, switched parameters in optional_param or another serious problem
            print_error("unknownparamtype", '', '', $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;
    }
}

/**
 * Returns host part from url
 * @param string $url full url
 * @return string host, null if not found
 */
function get_host_from_url($url) {
    preg_match('|^[a-z]+://([a-zA-Z0-9-.]+)|i', $url, $matches);
    if ($matches) {
        return $matches[1];
    }
    return null;
}

/**
 * Tests whether anything was returned by text editor
 *
 * 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 $string a string containing HTML.
 * @return boolean does the string contain any actual content - that is text,
 * images, objects, etc.
 */
function html_is_blank($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.
 *
 * @global object
 * @global object
 * @param string $name the key to set
 * @param string $value the value to set (without magic quotes)
 * @param string $plugin (optional) the plugin scope, default NULL
 * @return bool true or exception
 */
function set_config($name, $value, $plugin=NULL) {
    global $CFG, $DB;

    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 ($DB->get_field('config', 'name', array('name'=>$name))) {
            if ($value === null) {
                $DB->delete_records('config', array('name'=>$name));
            } else {
                $DB->set_field('config', 'value', $value, array('name'=>$name));
            }
        } else {
            if ($value !== null) {
                $config = new object();
                $config->name  = $name;
                $config->value = $value;
                $DB->insert_record('config', $config, false);
            }
        }

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

    return true;
}

/**
 * Get configuration values from the global config table
 * or the config_plugins table.
 *
 * If called with one parameter, it will load all the config
 * variables for one plugin, and return them as an object.
 *
 * If called with 2 parameters it will return a string single
 * value or false if the value is not found.
 *
 * @param string $plugin full component name
 * @param string $name default NULL
 * @return mixed hash-like object or single value, return false no config found
 */
function get_config($plugin, $name = NULL) {
    global $CFG, $DB;

    // normalise component name
    if ($plugin === 'moodle' or $plugin === 'core') {
        $plugin = NULL;
    }

    if (!empty($name)) { // the user is asking for a specific value
        if (!empty($plugin)) {
            if (isset($CFG->forced_plugin_settings[$plugin]) and array_key_exists($name, $CFG->forced_plugin_settings[$plugin])) {
                // setting forced in config file
                return $CFG->forced_plugin_settings[$plugin][$name];
            } else {
                return $DB->get_field('config_plugins', 'value', array('plugin'=>$plugin, 'name'=>$name));
            }
        } else {
            if (array_key_exists($name, $CFG->config_php_settings)) {
                // setting force in config file
                return $CFG->config_php_settings[$name];
            } else {
                return $DB->get_field('config', 'value', array('name'=>$name));
            }
        }
    }

    // the user is after a recordset
    if ($plugin) {
        $localcfg = $DB->get_records_menu('config_plugins', array('plugin'=>$plugin), '', 'name,value');
        if (isset($CFG->forced_plugin_settings[$plugin])) {
            foreach($CFG->forced_plugin_settings[$plugin] as $n=>$v) {
                if (is_null($v) or is_array($v) or is_object($v)) {
                    // we do not want any extra mess here, just real settings that could be saved in db
                    unset($localcfg[$n]);
                } else {
                    //convert to string as if it went through the DB
                    $localcfg[$n] = (string)$v;
                }
            }
        }
        return (object)$localcfg;

    } else {
        // this part is not really used any more, but anyway...
        $localcfg = $DB->get_records_menu('config', array(), '', 'name,value');
        foreach($CFG->config_php_settings as $n=>$v) {
            if (is_null($v) or is_array($v) or is_object($v)) {
                // we do not want any extra mess here, just real settings that could be saved in db
                unset($localcfg[$n]);
            } else {
                //convert to string as if it went through the DB
                $localcfg[$n] = (string)$v;
            }
        }
        return (object)$localcfg;
    }
}

/**
 * Removes a key from global configuration
 *
 * @param string $name the key to set
 * @param string $plugin (optional) the plugin scope
 * @global object
 * @return boolean whether the operation succeeded.
 */
function unset_config($name, $plugin=NULL) {
    global $CFG, $DB;

    if (empty($plugin)) {
        unset($CFG->$name);
        $DB->delete_records('config', array('name'=>$name));
    } else {
        $DB->delete_records('config_plugins', array('name'=>$name, 'plugin'=>$plugin));
    }

    return true;
}

/**
 * Remove all the config variables for a given plugin.
 *
 * @param string $plugin a plugin, for example 'quiz' or 'qtype_multichoice';
 * @return boolean whether the operation succeeded.
 */
function unset_all_config_for_plugin($plugin) {
    global $DB;
    $DB->delete_records('config_plugins', array('plugin' => $plugin));
    $DB->delete_records_select('config', 'name LIKE ?', array($plugin . '_%'));
    return true;
}

/**
 * Use this function to get a list of users from a config setting of type admin_setting_users_with_capability.
 *
 * All users are verified if they still have the necessary 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.
 * @param bool $include admins, include administrators
 * @return array of user objects.
 */
function get_users_from_config($value, $capability, $includeadmins = true) {
    global $CFG, $DB;

    if (empty($value) or $value === '$@NONE@$') {
        return array();
    }

    // we have to make sure that users still have the necessary capability,
    // it should be faster to fetch them all first and then test if they are present
    // instead of validating them one-by-one
    $users = get_users_by_capability(get_context_instance(CONTEXT_SYSTEM), $capability);
    if ($includeadmins) {
        $admins = get_admins();
        foreach ($admins as $admin) {
            $users[$admin->id] = $admin;
        }
    }

    if ($value === '$@ALL@$') {
        return $users;
    }

    $result = array(); // result in correct order
    $allowed = explode(',', $value);
    foreach ($allowed as $uid) {
        if (isset($users[$uid])) {
            $user = $users[$uid];
            $result[$user->id] = $user;
        }
    }

    return $result;
}

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

    $params = array('type'=>$type, 'expiry'=>time());
    $sqlwhere = "flagtype = :type AND expiry >= :expiry";
    if ($changedsince !== NULL) {
        $params['changedsince'] = $changedsince;
        $sqlwhere .= " AND timemodified > :changedsince";
    }
    $cf = array();

    if ($flags = $DB->get_records_select('cache_flags', $sqlwhere, $params, '', 'name,value')) {
        foreach ($flags as $flag) {
            $cf[$flag->name] = $flag->value;
        }
    }
    return $cf;
}

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

    $params = array('type'=>$type, 'name'=>$name, 'expiry'=>time());

    $sqlwhere = "flagtype = :type AND name = :name AND expiry >= :expiry";
    if ($changedsince !== NULL) {
        $params['changedsince'] = $changedsince;
        $sqlwhere .= " AND timemodified > :changedsince";
    }

    return $DB->get_field_select('cache_flags', 'value', $sqlwhere, $params);
}

/**
 * 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 $expiry (optional) epoch indicating expiry - defaults to now()+ 24hs
 * @return bool Always returns true
 */
function set_cache_flag($type, $name, $value, $expiry=NULL) {
    global $DB;

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

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

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

/**
 * Removes a single volatile flag
 *
 * @global object
 * @param string $type the "type" namespace for the key
 * @param string $name the key to set
 * @return bool
 */
function unset_cache_flag($type, $name) {
    global $DB;
    $DB->delete_records('cache_flags', array('name'=>$name, 'flagtype'=>$type));
    return true;
}

/**
 * Garbage-collect volatile flags
 *
 * @return bool Always returns true
 */
function gc_cache_flags() {
    global $DB;
    $DB->delete_records_select('cache_flags', 'expiry < ?', array(time()));
    return true;
}

/// FUNCTIONS FOR HANDLING USER PREFERENCES ////////////////////////////////////

/**
 * Refresh current $USER session global variable with all their current preferences.
 *
 * @global object
 * @param mixed $time default null
 * @return void
 */
function check_user_preferences_loaded($time = null) {
    global $USER, $DB;
    static $timenow = null; // Static cache, so we only check up-to-dateness once per request.

    if (!empty($USER->preference) && isset($USER->preference['_lastloaded'])) {
        // Already loaded. Are we up to date?

        if (is_null($timenow) || (!is_null($time) && $time != $timenow)) {
            $timenow = time();
            if (!get_cache_flag('userpreferenceschanged', $USER->id, $USER->preference['_lastloaded'])) {
                // We are up-to-date.
                return;
            }
        } else {
            // Already checked for up-to-date-ness.
            return;
        }
    }

    // OK, so we have to reload. Reset preference
    $USER->preference = array();

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

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

    $USER->preference['_lastloaded'] = $timenow;
}

/**
 * Called from set/delete_user_preferences, so that the prefs can be correctly reloaded.
 *
 * @global object
 * @global object
 * @param integer $userid the user whose prefs were changed.
 */
function mark_user_preferences_changed($userid) {
    global $CFG, $USER;
    if ($userid == $USER->id) {
        check_user_preferences_loaded(time());
    }
    set_cache_flag('userpreferenceschanged', $userid, 1, time() + $CFG->sessiontimeout);
}

/**
 * Sets a preference for the current user
 *
 * Optionally, can set a preference for a different user object
 *
 * @todo Add a better description and include usage examples. Add inline links to $USER and user functions in above line.
 *
 * @global object
 * @global object
 * @param string $name The key to set as preference for the specified user
 * @param string $value The value to set for the $name key in the specified user's record
 * @param int $otheruserid A moodle user ID, default null
 * @return bool
 */
function set_user_preference($name, $value, $otheruserid=NULL) {
    global $USER, $DB;

    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;
    }

    if ($nostore) {
        // no permanent storage for not-logged-in user and guest

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

    } else {
        $preference = new object();
        $preference->userid = $userid;
        $preference->name   = $name;
        $preference->value  = (string)$value;
        $DB->insert_record('user_preferences', $preference);
    }

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

    return true;
}

/**
 * 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;
    }

    foreach ($prefarray as $name => $value) {
        set_user_preference($name, $value, $otheruserid);
    }
    return true;
}

/**
 * Unsets a preference completely by deleting it from the database
 *
 * Optionally, can set a preference for a different user id
 *
 * @global object
 * @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, $DB;

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

    //Then from DB
    $DB->delete_records('user_preferences', array('userid'=>$userid, 'name'=>$name));

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

    return true;
}

/**
 * Used to fetch user preference(s)
 *
 * 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.
 *
 * @global object
 * @global object
 * @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 $otheruserid A moodle user ID
 * @return string
 */
function get_user_preferences($name=NULL, $default=NULL, $otheruserid=NULL) {
    global $USER, $DB;

    if (empty($otheruserid) || (isloggedin() && ($USER->id == $otheruserid))){
        check_user_preferences_loaded();

        if (empty($name)) {
            return $USER->preference; // All values
        } else if (array_key_exists($name, $USER->preference)) {
            return $USER->preference[$name]; // The single value
        } else {
            return $default; // Default value (or NULL)
        }

    } else {
        if (empty($name)) {
            return $DB->get_records_menu('user_preferences', array('userid'=>$otheruserid), '', 'name,value'); // All values
        } else if ($value = $DB->get_field('user_preferences', 'value', array('userid'=>$otheruserid, 'name'=>$name))) {
            return $value; // The single value
        } else {
            return $default; // Default value (or NULL)
        }
    }
}

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

/**
 * Given date parts in user time produce a GMT timestamp.
 *
 * @todo Finish documenting this function
 * @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 Timezone modifier
 * @param bool $applydst Toggle Daylight Saving Time, default true
 * @return int timestamp
 */
function make_timestamp($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;

}

/**
 * Format a date/time (seconds) as weeks, days, hours etc as needed
 *
 * 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 Time in seconds
 * @param object $str Should be a time object
 * @return string A nicely formatted date/time string
 */
 function format_time($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
 *
 * 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 maintain it.
 *
 * @param int $date the timestamp in UTC, as obtained from the database.
 * @param string $format strftime format. You should probably get this using
 *      get_string('strftime...', 'langconfig');
 * @param float $timezone by default, uses the user's time zone.
 * @param bool $fixday If true (default) then the leading zero from %d is removed.
 *      If false then the leading zero is maintained.
 * @return string the formatted date/time.
 */
function userdate($date, $format = '', $timezone = 99, $fixday = true) {

    global $CFG;

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

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

    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  = ltrim(str_replace(array(' 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  = ltrim(str_replace(array(' 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', 'langconfig')) {
           $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
 *
 * @todo Finish documenting this function
 * @uses HOURSECS
 * @param int $time Timestamp in GMT
 * @param float $timezone ?
 * @return array An array that represents the date in user time
 */
function usergetdate($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('%B_%A_%j_%Y_%m_%w_%d_%H_%M_%S', $time);

    //be careful to ensure the returned array matches that produced by getdate() above
    list(
        $getdate['month'],
        $getdate['weekday'],
        $getdate['yday'],
        $getdate['year'],
        $getdate['mon'],
        $getdate['wday'],
        $getdate['mday'],
        $getdate['hours'],
        $getdate['minutes'],
        $getdate['seconds']
    ) = 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 $timezone Defaults to user's timezone
 * @return int Returns a GMT timestamp
 */
function usergetmidnight($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
 *
 * @global object
 * @global object
 * @param float $tz If this value is provided and not equal to 99, it will be returned as is and no other settings will be checked
 * @return float
 */
function get_user_timezone_offset($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
 *
 * @global object
 * @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
 *
 * @global object
 * @global object
 * @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;
}

/**
 * Returns cached timezone record for given $timezonename
 *
 * @global object
 * @global object
 * @param string $timezonename
 * @return mixed timezonerecord object or false
 */
function get_timezone_record($timezonename) {
    global $CFG, $DB;
    static $cache = NULL;

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

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

    return $cache[$timezonename] = $DB->get_record_sql('SELECT * FROM {timezone}
                                                        WHERE name = ? ORDER BY year DESC', array($timezonename), true);
}

/**
 * Build and store the users Daylight Saving Time (DST) table
 *
 * @global object
 * @global object
 * @global object
 * @param mixed $from_year Start year for the table, defaults to 1971
 * @param mixed $to_year End year for the table, defaults to 2035
 * @param mixed $strtimezone
 * @return bool
 */
function calculate_user_dst_table($from_year = NULL, $to_year = NULL, $strtimezone = NULL) {
    global $CFG, $SESSION, $DB;

    $usertz = get_user_timezone($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] = $DB->get_records('timezone', array('name'=>$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;
}

/**
 * Calculates the required DST change and returns a Timestamp Array
 *
 * @uses HOURSECS
 * @uses MINSECS
 * @param mixed $year Int or String Year to focus on
 * @param object $timezone Instatiated Timezone object
 * @return mixed Null, or Array dst=>xx, 0=>xx, std=>yy, 1=>yy
 */
function dst_changes_for_year($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);
}

/**
 * Calculates the Daylight Saving Offset for a given date/time (timestamp)
 *
 * @global object
 * @param int $time must NOT be compensated at all, it has to be a pure timestamp
 * @return int
 */
function dst_offset_on($time, $strtimezone = NULL) {
    global $SESSION;

    if(!calculate_user_dst_table(NULL, NULL, $strtimezone) || empty($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, $strtimezone);
        return dst_offset_on($time, $strtimezone);
    }
    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, $strtimezone);
        return dst_offset_on($time, $strtimezone);
    }
}

/**
 * ?
 *
 * @todo Document what this function does
 * @param int $startday
 * @param int $weekday
 * @param int $month
 * @param int $year
 * @return int
 */
function find_day_in_month($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 ////////////////////////////////////////

/**
 * Returns full login url.
 *
 * @global object
 * @param bool $loginguest add login guest param, return false
 * @return string login url
 */
function get_login_url($loginguest=false) {
    global $CFG;

    if (empty($CFG->loginhttps) or $loginguest) { //do not require https for guest logins
        $loginguest = $loginguest ? '?loginguest=true' : '';
        $url = "$CFG->wwwroot/login/index.php$loginguest";

    } else {
        $wwwroot = str_replace('http:','https:', $CFG->wwwroot);
        $url = "$wwwroot/login/index.php";
    }

    return $url;
}

/**
 * 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 course module is hidden and the user is not a teacher
 * in the course then the user is redirected to the course home page.
 *
 * When $cm parameter specified, this function sets page layout to 'module'.
 * You need to change it manually later if some other layout needed.
 *
 * @param mixed $courseorid id of the course or course object
 * @param bool $autologinguest default true
 * @param object $cm course module object
 * @param bool $setwantsurltome Define if we want to set $SESSION->wantsurl, defaults to
 *             true. Used to avoid (=false) some scripts (file.php...) to set that variable,
 *             in order to keep redirects working properly. MDL-14495
 * @param bool $preventredirect set to true in scripts that can not redirect (CLI, rss feeds, etc.), throws exceptions
 * @return mixed Void, exit, and die depending on path
 */
function require_login($courseorid = NULL, $autologinguest = true, $cm = NULL, $setwantsurltome = true, $preventredirect = false) {
    global $CFG, $SESSION, $USER, $FULLME, $PAGE, $SITE, $DB, $OUTPUT;

    // setup global $COURSE, themes, language and locale
    if (!empty($courseorid)) {
        if (is_object($courseorid)) {
            $course = $courseorid;
        } else if ($courseorid == SITEID) {
            $course = clone($SITE);
        } else {
            $course = $DB->get_record('course', array('id' => $courseorid), '*', MUST_EXIST);
        }
        if ($cm) {
            if ($cm->course != $course->id) {
                throw new coding_exception('course and cm parameters in require_login() call do not match!!');
            }
            $PAGE->set_cm($cm, $course); // set's up global $COURSE
            $PAGE->set_pagelayout('incourse');
        } else {
            $PAGE->set_course($course); // set's up global $COURSE
        }
    } else {
        // do not touch global $COURSE via $PAGE->set_course(),
        // the reasons is we need to be able to call require_login() at any time!!
        $course = $SITE;
        if ($cm) {
            throw new coding_exception('cm parameter in require_login() requires valid course parameter!');
        }
    }

    // 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,
        //      $USER->confirmed test is in login/index.php
        if ($preventredirect) {
            throw new require_login_exception('You are not logged in');
        }

        if ($setwantsurltome) {
            $SESSION->wantsurl = $FULLME;
        }
        if (!empty($_SERVER['HTTP_REFERER'])) {
            $SESSION->fromurl  = $_SERVER['HTTP_REFERER'];
        }
        if ($autologinguest and !empty($CFG->guestloginbutton) and !empty($CFG->autologinguests)) {
            if ($course->id == SITEID) {
                $loginguest = true;
            } else {
                $loginguest = false;
            }
        } else {
            $loginguest = false;
        }
        redirect(get_login_url($loginguest));
        exit; // never reached
    }

    // loginas as redirection if needed
    if ($course->id != SITEID and session_is_loggedinas()) {
        if ($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') && !session_is_loggedinas()) {
        $userauth = get_auth_plugin($USER->auth);
        if ($userauth->can_change_password() and !$preventredirect) {
            $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 {
            print_error('nopasswordchangeforced', 'auth');
        }
    }

    // Check that the user account is properly set up
    if (user_not_fully_set_up($USER)) {
        if ($preventredirect) {
            throw new require_login_exception('User not fully set-up');
        }
        $SESSION->wantsurl = $FULLME;
        redirect($CFG->wwwroot .'/user/edit.php?id='. $USER->id .'&amp;course='. SITEID);
    }

    // Make sure the USER has a sesskey set up. Used for CSRF protection.
    sesskey();

    // Do not bother admins with any formalities
    if (is_siteadmin()) {
        //set accesstime or the user will appear offline which messes up messaging
        user_accesstime_log($course->id);
        return;
    }

    // Check that the user has agreed to a site policy if there is one
    if (!empty($CFG->sitepolicy)) {
        if ($preventredirect) {
            throw new require_login_exception('Policy not agreed');
        }
        if (!$USER->policyagreed) {
            $SESSION->wantsurl = $FULLME;
            redirect($CFG->wwwroot .'/user/policy.php');
        }
    }

    // Fetch the system context, the course context, and prefetch its child contexts
    $sysctx = get_context_instance(CONTEXT_SYSTEM);
    $coursecontext = get_context_instance(CONTEXT_COURSE, $course->id, MUST_EXIST);
    if ($cm) {
        $cmcontext = get_context_instance(CONTEXT_MODULE, $cm->id, MUST_EXIST);
    } else {
        $cmcontext = null;
    }

    // If the site is currently under maintenance, then print a message
    if (!empty($CFG->maintenance_enabled) and !has_capability('moodle/site:config', $sysctx)) {
        if ($preventredirect) {
            throw new require_login_exception('Maintenance in progress');
        }

        print_maintenance_message();
    }

    // make sure the course itself is not hidden
    if ($course->id == SITEID) {
        // frontpage can not be hidden
    } else {
        if (!empty($USER->access['rsw'][$coursecontext->path])) {
            // when switching roles ignore the hidden flag - user had to be in course to do the switch
        } else {
            if (!$course->visible and !has_capability('moodle/course:viewhiddencourses', $coursecontext)) {
                // originally there was also test of parent category visibility,
                // BUT is was very slow in complex queries involving "my courses"
                // now it is also possible to simply hide all courses user is not enrolled in :-)
                if ($preventredirect) {
                    throw new require_login_exception('Course is hidden');
                }
                notice(get_string('coursehidden'), $CFG->wwwroot .'/');
            }
        }
    }

    // is the user enrolled?
    if ($course->id == SITEID) {
        // everybody is enrolled on the frontpage

    } else {
        if (session_is_loggedinas()) {
            // Make sure the REAL person can access this course first
            $realuser = session_get_realuser();
            if (!is_enrolled($coursecontext, $realuser->id, '', true) and !is_viewing($coursecontext, $realuser->id) and !is_siteadmin($realuser->id)) {
                if ($preventredirect) {
                    throw new require_login_exception('Invalid course login-as access');
                }
                echo $OUTPUT->header();
                notice(get_string('studentnotallowed', '', fullname($USER, true)), $CFG->wwwroot .'/');
            }
        }

        // very simple enrolment caching - changes in course setting are not reflected immediately
        if (!isset($USER->enrol)) {
            $USER->enrol = array();
            $USER->enrol['enrolled'] = array();
            $USER->enrol['tempguest'] = array();
        }

        $access = false;

        if (is_viewing($coursecontext, $USER)) {
            // ok, no need to mess with enrol
            $access = true;

        } else {
            if (isset($USER->enrol['enrolled'][$course->id])) {
                if ($USER->enrol['enrolled'][$course->id] == 0) {
                    $access = true;
                } else if ($USER->enrol['enrolled'][$course->id] > time()) {
                    $access = true;
                } else {
                    //expired
                    unset($USER->enrol['enrolled'][$course->id]);
                }
            }
            if (isset($USER->enrol['tempguest'][$course->id])) {
                if ($USER->enrol['tempguest'][$course->id] == 0) {
                    $access = true;
                } else if ($USER->enrol['tempguest'][$course->id] > time()) {
                    $access = true;
                } else {
                    //expired
                    unset($USER->enrol['tempguest'][$course->id]);
                    $USER->access = remove_temp_roles($coursecontext, $USER->access);
                }
            }

            if ($access) {
                // cache ok
            } else if (is_enrolled($coursecontext, $USER, '', true)) {
                // active participants may always access
                // TODO: refactor this into some new function
                $now = time();
                $sql = "SELECT MAX(ue.timeend)
                          FROM {user_enrolments} ue
                          JOIN {enrol} e ON (e.id = ue.enrolid AND e.courseid = :courseid)
                          JOIN {user} u ON u.id = ue.userid
                         WHERE ue.userid = :userid AND ue.status = :active AND e.status = :enabled AND u.deleted = 0
                               AND ue.timestart < :now1 AND (ue.timeend = 0 OR ue.timeend > :now2)";
                $params = array('enabled'=>ENROL_INSTANCE_ENABLED, 'active'=>ENROL_USER_ACTIVE,
                                'userid'=>$USER->id, 'courseid'=>$coursecontext->instanceid, 'now1'=>$now, 'now2'=>$now);
                $until = $DB->get_field_sql($sql, $params);
                if (!$until or $until > time() + ENROL_REQUIRE_LOGIN_CACHE_PERIOD) {
                    $until = time() + ENROL_REQUIRE_LOGIN_CACHE_PERIOD;
                }

                $USER->enrol['enrolled'][$course->id] = $until;
                $access = true;

                // remove traces of previous temp guest access
                $USER->access = remove_temp_roles($coursecontext, $USER->access);

            } else {
                $instances = $DB->get_records('enrol', array('courseid'=>$course->id, 'status'=>ENROL_INSTANCE_ENABLED), 'sortorder, id ASC');
                $enrols = enrol_get_plugins(true);
                // first ask all enabled enrol instances in course if they want to auto enrol user
                foreach($instances as $instance) {
                    if (!isset($enrols[$instance->enrol])) {
                        continue;
                    }
                    $until = $enrols[$instance->enrol]->try_autoenrol($instance);
                    if ($until !== false) {
                        $USER->enrol['enrolled'][$course->id] = $until;
                        $USER->access = remove_temp_roles($coursecontext, $USER->access);
                        $access = true;
                        break;
                    }
                }
                // if not enrolled yet try to gain temporary guest access
                if (!$access) {
                    foreach($instances as $instance) {
                        if (!isset($enrols[$instance->enrol])) {
                            continue;
                        }
                        $until = $enrols[$instance->enrol]->try_guestaccess($instance);
                        if ($until !== false) {
                            $USER->enrol['tempguest'][$course->id] = $until;
                            $access = true;
                            break;
                        }
                    }
                }
            }
        }

        if (!$access) {
            if ($preventredirect) {
                throw new require_login_exception('Not enrolled');
            }
            $SESSION->wantsurl = $FULLME;
            redirect($CFG->wwwroot .'/enrol/index.php?id='. $course->id);
        }
    }

    // test visibility
    if ($cm && !$cm->visible && !has_capability('moodle/course:viewhiddenactivities', $cmcontext)) {
        if ($preventredirect) {
            throw new require_login_exception('Activity is hidden');
        }
        redirect($CFG->wwwroot, get_string('activityiscurrentlyhidden'));
    }

    // groupmembersonly access control
    if (!empty($CFG->enablegroupmembersonly) 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)) {
            if ($preventredirect) {
                throw new require_login_exception('Not member of a group');
            }
            print_error('groupmembersonlyerror', 'group', $CFG->wwwroot.'/course/view.php?id='.$cm->course);
        }
    }

    // Conditional activity access control
    if (!empty($CFG->enableavailability) and $cm) {
        // TODO: this is going to work with login-as-user, sorry!
        // We cache conditional access in session
        if (!isset($SESSION->conditionaccessok)) {
            $SESSION->conditionaccessok = array();
        }
        // If you have been allowed into the module once then you are allowed
        // in for rest of session, no need to do conditional checks
        if (!array_key_exists($cm->id, $SESSION->conditionaccessok)) {
            // Get condition info (does a query for the availability table)
            require_once($CFG->libdir.'/conditionlib.php');
            $ci = new condition_info($cm, CONDITION_MISSING_EXTRATABLE);
            // Check condition for user (this will do a query if the availability
            // information depends on grade or completion information)
            if ($ci->is_available($junk) || has_capability('moodle/course:viewhiddenactivities', $cmcontext)) {
                $SESSION->conditionaccessok[$cm->id] = true;
            } else {
                print_error('activityiscurrentlyhidden');
            }
        }
    }

    // Finally access granted, update lastaccess times
    user_accesstime_log($course->id);
}


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

    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();
        }
    }

    session_get_instance()->terminate_current();
}

/**
 * Weaker version of require_login()
 *
 * 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.
 * @see require_login()
 *
 * @global object
 * @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
 * @param bool $setwantsurltome Define if we want to set $SESSION->wantsurl, defaults to
 *             true. Used to avoid (=false) some scripts (file.php...) to set that variable,
 *             in order to keep redirects working properly. MDL-14495
 * @param bool $preventredirect set to true in scripts that can not redirect (CLI, rss feeds, etc.), throws exceptions
 * @return void
 */
function require_course_login($courseorid, $autologinguest = true, $cm = NULL, $setwantsurltome = true, $preventredirect = false) {
    global $CFG, $PAGE, $SITE;
    if (!empty($CFG->forcelogin)) {
        // login required for both SITE and courses
        require_login($courseorid, $autologinguest, $cm, $setwantsurltome, $preventredirect);

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

    } else if ((is_object($courseorid) and $courseorid->id == SITEID)
          or (!is_object($courseorid) and $courseorid == SITEID)) {
              //login for SITE not required
        if ($cm and empty($cm->visible)) {
            // hidden activities are not accessible without login
            require_login($courseorid, $autologinguest, $cm, $setwantsurltome, $preventredirect);
        } else if ($cm and !empty($CFG->enablegroupmembersonly) and $cm->groupmembersonly) {
            // not-logged-in users do not have any group membership
            require_login($courseorid, $autologinguest, $cm, $setwantsurltome, $preventredirect);
        } else {
            // We still need to instatiate PAGE vars properly so that things
            // that rely on it like navigation function correctly.
            if (!empty($courseorid)) {
                if (is_object($courseorid)) {
                    $course = $courseorid;
                } else {
                    $course = clone($SITE);
                }
                if ($cm) {
                    if ($cm->course != $course->id) {
                        throw new coding_exception('course and cm parameters in require_course_login() call do not match!!');
                    }
                    $PAGE->set_cm($cm, $course);
                    $PAGE->set_pagelayout('incourse');
                } else {
                    $PAGE->set_course($course);
                }
            } else {
                // If $PAGE->course, and hence $PAGE->context, have not already been set
                // up properly, set them up now.
                $PAGE->set_course($PAGE->course);
            }
            //TODO: verify conditional activities here
            user_accesstime_log(SITEID);
            return;
        }

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

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

    if (!NO_MOODLE_COOKIES) {
        print_error('sessioncookiesdisable');
    }

/// extra safety
    @session_write_close();

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

    if (!$key = $DB->get_record('user_private_key', array('script'=>$script, 'value'=>$keyvalue, 'instance'=>$instance))) {
        print_error('invalidkey');
    }

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

    if ($key->iprestriction) {
        $remoteaddr = getremoteaddr(null);
        if (empty($remoteaddr) or !address_in_subnet($remoteaddr, $key->iprestriction)) {
            print_error('ipmismatch');
        }
    }

    if (!$user = $DB->get_record('user', array('id'=>$key->userid))) {
        print_error('invaliduserid');
    }

/// emulate normal session
    session_set_user($user);

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

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

/**
 * Creates a new private user access key.
 *
 * @global object
 * @param string $script unique target identifier
 * @param int $userid
 * @param int $instance 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) {
    global $DB;

    $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 ($DB->record_exists('user_private_key', array('value'=>$key->value))) {
        // must be unique
        $key->value     = md5($userid.'_'.time().random_string(40));
    }
    $DB->insert_record('user_private_key', $key);
    return $key->value;
}

/**
 * Delete the user's new private user access keys for a particular script.
 *
 * @global object
 * @param string $script unique target identifier
 * @param int $userid
 * @return void
 */
function delete_user_key($script,$userid) {
    global $DB;
    $DB->delete_records('user_private_key', array('script'=>$script, 'userid'=>$userid));
}

/**
 * Gets a private user access key (and creates one if one doesn't exist).
 *
 * @global object
 * @param string $script unique target identifier
 * @param int $userid
 * @param int $instance optional instance id
 * @param string $iprestriction optional ip restricted access
 * @param timestamp $validuntil key valid only until given data
 * @return string access key value
 */
function get_user_key($script, $userid, $instance=null, $iprestriction=null, $validuntil=null) {
    global $DB;

    if ($key = $DB->get_record('user_private_key', array('script'=>$script, 'userid'=>$userid,
                                                         'instance'=>$instance, 'iprestriction'=>$iprestriction,
                                                         'validuntil'=>$validuntil))) {
        return $key->value;
    } else {
        return create_user_key($script, $userid, $instance, $iprestriction, $validuntil);
    }
}


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

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

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

    $DB->update_record('user', $user);
    return true;
}

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

/**
 * Check whether the user has exceeded the bounce threshold
 *
 * @global object
 * @global object
 * @param user $user A {@link $USER} object
 * @return bool true=>User has exceeded bounce threshold
 */
function over_bounce_threshold($user) {
    global $CFG, $DB;

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

    if (empty($user->id)) { /// No real (DB) user, nothing to do here.
        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 = $DB->get_record('user_preferences', array ('userid'=>$user->id, 'name'=>'email_bounce_count'))) {
        $bouncecount = $bounce->value;
    }
    if ($send = $DB->get_record('user_preferences', array('userid'=>$user->id, 'name'=>'email_send_count'))) {
        $sendcount = $send->value;
    }
    return ($bouncecount >= $CFG->minbounces && $bouncecount/$sendcount >= $CFG->bounceratio);
}

/**
 * Used to increment or reset email sent count
 *
 * @global object
 * @param user $user object containing an id
 * @param bool $reset will reset the count to 0
 * @return void
 */
function set_send_count($user,$reset=false) {
    global $DB;

    if (empty($user->id)) { /// No real (DB) user, nothing to do here.
        return;
    }

    if ($pref = $DB->get_record('user_preferences', array('userid'=>$user->id, 'name'=>'email_send_count'))) {
        $pref->value = (!empty($reset)) ? 0 : $pref->value+1;
        $DB->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 = new object();
        $pref->name   = 'email_send_count';
        $pref->value  = 1;
        $pref->userid = $user->id;
        $DB->insert_record('user_preferences', $pref, false);
    }
}

/**
 * Increment or reset user's email bounce count
 *
 * @global object
 * @param user $user object containing an id
 * @param bool $reset will reset the count to 0
 */
function set_bounce_count($user,$reset=false) {
    global $DB;

    if ($pref = $DB->get_record('user_preferences', array('userid'=>$user->id, 'name'=>'email_bounce_count'))) {
        $pref->value = (!empty($reset)) ? 0 : $pref->value+1;
        $DB->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 = new object();
        $pref->name   = 'email_bounce_count';
        $pref->value  = 1;
        $pref->userid = $user->id;
        $DB->insert_record('user_preferences', $pref, false);
    }
}

/**
 * Keeps track of login attempts
 *
 * @global object
 */
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);
        print_error('errortoomanylogins');
    }
}

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

    $SESSION->logincount = 0;
}

/**
 * Returns reference to full info about modules in course (including visibility).
 * Cached and as fast as possible (0 or 1 db query).
 *
 * @global object
 * @global object
 * @global object
 * @uses CONTEXT_MODULE
 * @uses MAX_MODINFO_CACHE_SIZE
 * @param mixed $course object or 'reset' string to reset caches, modinfo may be updated in db
 * @param int $userid Defaults to current user id
 * @return mixed courseinfo object or nothing if resetting
 */
function &get_fast_modinfo(&$course, $userid=0) {
    global $CFG, $USER, $DB;
    require_once($CFG->dirroot.'/course/lib.php');

    if (!empty($CFG->enableavailability)) {
        require_once($CFG->libdir.'/conditionlib.php');
    }

    static $cache = array();

    if ($course === 'reset') {
        $cache = array();
        $nothing = null;
        return $nothing; // we must return some reference
    }

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

    if (array_key_exists($course->id, $cache) and $cache[$course->id]->userid == $userid) {
        return $cache[$course->id];
    }

    if (empty($course->modinfo)) {
        // no modinfo yet - load it
        rebuild_course_cache($course->id);
        $course->modinfo = $DB->get_field('course', 'modinfo', array('id'=>$course->id));
    }

    $modinfo = new object();
    $modinfo->courseid  = $course->id;
    $modinfo->userid    = $userid;
    $modinfo->sections  = array();
    $modinfo->cms       = array();
    $modinfo->instances = array();
    $modinfo->groups    = null; // loaded only when really needed - the only one db query

    $info = unserialize($course->modinfo);
    if (!is_array($info)) {
        // hmm, something is wrong - lets try to fix it
        rebuild_course_cache($course->id);
        $course->modinfo = $DB->get_field('course', 'modinfo', array('id'=>$course->id));
        $info = unserialize($course->modinfo);
        if (!is_array($info)) {
            return $modinfo;
        }
    }

    if ($info) {
        // detect if upgrade required
        $first = reset($info);
        if (!isset($first->id)) {
            rebuild_course_cache($course->id);
            $course->modinfo = $DB->get_field('course', 'modinfo', array('id'=>$course->id));
            $info = unserialize($course->modinfo);
            if (!is_array($info)) {
                return $modinfo;
            }
        }
    }

    $modlurals = array();

    // If we haven't already preloaded contexts for the course, do it now
    preload_course_contexts($course->id);

    foreach ($info as $mod) {
        if (empty($mod->name)) {
            // something is wrong here
            continue;
        }
        // reconstruct minimalistic $cm
        $cm = new object();
        $cm->id               = $mod->cm;
        $cm->instance         = $mod->id;
        $cm->course           = $course->id;
        $cm->modname          = $mod->mod;
        $cm->idnumber         = $mod->idnumber;
        $cm->name             = $mod->name;
        $cm->visible          = $mod->visible;
        $cm->sectionnum       = $mod->section;
        $cm->groupmode        = $mod->groupmode;
        $cm->groupingid       = $mod->groupingid;
        $cm->groupmembersonly = $mod->groupmembersonly;
        $cm->indent           = $mod->indent;
        $cm->completion       = $mod->completion;
        $cm->extra            = isset($mod->extra) ? $mod->extra : '';
        $cm->icon             = isset($mod->icon) ? $mod->icon : '';
        $cm->iconcomponent    = isset($mod->iconcomponent) ? $mod->iconcomponent : '';
        $cm->uservisible      = true;
        if(!empty($CFG->enableavailability)) {
            // We must have completion information from modinfo. If it's not
            // there, cache needs rebuilding
            if(!isset($mod->availablefrom)) {
                debugging('enableavailability option was changed; rebuilding '.
                    'cache for course '.$course->id);
                rebuild_course_cache($course->id,true);
                // Re-enter this routine to do it all properly
                return get_fast_modinfo($course,$userid);
            }
            $cm->availablefrom    = $mod->availablefrom;
            $cm->availableuntil   = $mod->availableuntil;
            $cm->showavailability = $mod->showavailability;
            $cm->conditionscompletion = $mod->conditionscompletion;
            $cm->conditionsgrade  = $mod->conditionsgrade;
        }

        // preload long names plurals and also check module is installed properly
        if (!isset($modlurals[$cm->modname])) {
            if (!file_exists("$CFG->dirroot/mod/$cm->modname/lib.php")) {
                continue;
            }
            $modlurals[$cm->modname] = get_string('modulenameplural', $cm->modname);
        }
        $cm->modplural = $modlurals[$cm->modname];
        $modcontext = get_context_instance(CONTEXT_MODULE,$cm->id);

        if(!empty($CFG->enableavailability)) {
            // Unfortunately the next call really wants to call
            // get_fast_modinfo, but that would be recursive, so we fake up a
            // modinfo for it already
            if(empty($minimalmodinfo)) {
                $minimalmodinfo=new stdClass();
                $minimalmodinfo->cms=array();
                foreach($info as $mod) {
                    if (empty($mod->name)) {
                        // something is wrong here
                        continue;
                    }
                    $minimalcm = new stdClass();
                    $minimalcm->id = $mod->cm;
                    $minimalcm->name = $mod->name;
                    $minimalmodinfo->cms[$minimalcm->id]=$minimalcm;
                }
            }

            // Get availability information
            $ci = new condition_info($cm);
            $cm->available=$ci->is_available($cm->availableinfo, true, $userid, $minimalmodinfo);
        } else {
            $cm->available=true;
        }
        if ((!$cm->visible or !$cm->available) and !has_capability('moodle/course:viewhiddenactivities', $modcontext, $userid)) {
            $cm->uservisible = false;

        } else if (!empty($CFG->enablegroupmembersonly) and !empty($cm->groupmembersonly)
                and !has_capability('moodle/site:accessallgroups', $modcontext, $userid)) {
            if (is_null($modinfo->groups)) {
                $modinfo->groups = groups_get_user_groups($course->id, $userid);
            }
            if (empty($modinfo->groups[$cm->groupingid])) {
                $cm->uservisible = false;
            }
        }

        if (!isset($modinfo->instances[$cm->modname])) {
            $modinfo->instances[$cm->modname] = array();
        }
        $modinfo->instances[$cm->modname][$cm->instance] =& $cm;
        $modinfo->cms[$cm->id] =& $cm;

        // reconstruct sections
        if (!isset($modinfo->sections[$cm->sectionnum])) {
            $modinfo->sections[$cm->sectionnum] = array();
        }
        $modinfo->sections[$cm->sectionnum][] = $cm->id;

        unset($cm);
    }

    unset($cache[$course->id]); // prevent potential reference problems when switching users
    $cache[$course->id] = $modinfo;

    // Ensure cache does not use too much RAM
    if (count($cache) > MAX_MODINFO_CACHE_SIZE) {
        reset($cache);
        $key = key($cache);
        unset($cache[$key]);
    }

    return $cache[$course->id];
}

/**
 * Determines if the currently logged in user is in editing mode.
 * Note: originally this function had $userid parameter - it was not usable anyway
 *
 * @deprecated since Moodle 2.0 - use $PAGE->user_is_editing() instead.
 * @todo Deprecated function remove when ready
 *
 * @global object
 * @uses DEBUG_DEVELOPER
 * @return bool
 */
function isediting() {
    global $PAGE;
    debugging('call to deprecated function isediting(). Please use $PAGE->user_is_editing() instead', DEBUG_DEVELOPER);
    return $PAGE->user_is_editing();
}

/**
 * Determines if the logged in user is currently moving an activity
 *
 * @global object
 * @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;
}

/**
 * Returns a persons full name
 *
 * 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.
 *
 * @global object
 * @global object
 * @param object $user A {@link $USER} object to get full name of
 * @param bool $override If true then the name will be first name followed by last name rather than adhering to fullnamedisplay setting.
 * @return string
 */
function fullname($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 (!isset($CFG->fullnamedisplay) or $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);
}

/**
 * Returns whether a given authentication plugin exists.
 *
 * @global object
 * @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.
 *
 * @global object
 * @param string $auth name of authentication plugin
 * @return auth_plugin_base An instance of the required authentication plugin.
 */
function get_auth_plugin($auth) {
    global $CFG;

    // check the plugin exists first
    if (! exists_auth_plugin($auth)) {
        print_error('authpluginnotfound', 'debug', '', $auth);
    }

    // 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