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

defined('MOODLE_INTERNAL') || die();

// CONSTANTS (Encased in phpdoc proper comments).

// 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. Note that you almost never want
 * to use this. The normal mode of operation is to use PARAM_RAW when recieving
 * the input (required/optional_param or formslib) and then sanitse the HTML
 * using format_text on output. This is for the rare cases when you want to
 * sanitise the HTML on input. This cleaning may also fix xhtml strictness.
 */
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.
 *
 * Note that you should not use PARAM_FLOAT for numbers typed in by the user.
 * It does not work for languages that use , as a decimal separator.
 * Instead, do something like
 *     $rawvalue = required_param('name', PARAM_RAW);
 *     // ... other code including require_login, which sets current lang ...
 *     $realvalue = unformat_float($rawvalue);
 *     // ... then use $realvalue
 */
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 except the discarding of the invalid utf-8 characters
 */
define('PARAM_RAW', 'raw');

/**
 * PARAM_RAW_TRIMMED like PARAM_RAW but leading and trailing whitespace is stripped.
 */
define('PARAM_RAW_TRIMMED', 'raw_trimmed');

/**
 * 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. Please note '<', or '>' are allowed here.
 */
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 ;-)
 * @deprecated since 2.0
 */
define('PARAM_CLEAN',    'clean');

/**
 * PARAM_INTEGER - deprecated alias for PARAM_INT
 * @deprecated since 2.0
 */
define('PARAM_INTEGER',  'int');

/**
 * PARAM_NUMBER - deprecated alias of PARAM_FLOAT
 * @deprecated since 2.0
 */
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
 * @deprecated since 2.0
 */
define('PARAM_ACTION',   'alphanumext');

/**
 * PARAM_FORMAT - deprecated alias for PARAM_ALPHANUMEXT, use for names of plugins, formats, etc.
 * NOTE: originally alias for PARAM_APLHA
 * @deprecated since 2.0
 */
define('PARAM_FORMAT',   'alphanumext');

/**
 * PARAM_MULTILANG - deprecated alias of PARAM_TEXT.
 * @deprecated since 2.0
 */
define('PARAM_MULTILANG',  'text');

/**
 * PARAM_TIMEZONE - expected timezone. Timezone can be int +-(0-13) or float +-(0.5-12.5) or
 * string separated by '/' and can have '-' &/ '_' (eg. America/North_Dakota/New_Salem
 * America/Port-au-Prince)
 */
define('PARAM_TIMEZONE', 'timezone');

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

/**
 * PARAM_COMPONENT is used for full component names (aka frankenstyle) such as 'mod_forum', 'core_rating', 'auth_ldap'.
 * Short legacy subsystem names and module names are accepted too ex: 'forum', 'rating', 'user'.
 * Only lowercase ascii letters, numbers and underscores are allowed, it has to start with a letter.
 * NOTE: numbers and underscores are strongly discouraged in plugin names!
 */
define('PARAM_COMPONENT', 'component');

/**
 * PARAM_AREA is a name of area used when addressing files, comments, ratings, etc.
 * It is usually used together with context id and component.
 * Only lowercase ascii letters, numbers and underscores are allowed, it has to start with a letter.
 */
define('PARAM_AREA', 'area');

/**
 * PARAM_PLUGIN is used for plugin names such as 'forum', 'glossary', 'ldap', 'radius', 'paypal', 'completionstatus'.
 * Only lowercase ascii letters, numbers and underscores are allowed, it has to start with a letter.
 * NOTE: numbers and underscores are strongly discouraged in plugin names! Underscores are forbidden in module names.
 */
define('PARAM_PLUGIN', 'plugin');


// 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 supports advanced grading methods */
define('FEATURE_ADVANCED_GRADING', 'grade_advanced_grading');
/** True if module controls the grade visibility over the gradebook */
define('FEATURE_CONTROLS_GRADE_VISIBILITY', 'controlsgradevisbility');
/** True if module supports plagiarism plugins */
define('FEATURE_PLAGIARISM', 'plagiarism');

/** 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 has no 'view' page (like label) */
define('FEATURE_NO_VIEW_LINK', 'viewlink');
/** True (which is default) if the module wants support for setting the ID number for grade calculation purposes. */
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 (which no longer exists)
 * @deprecated Since Moodle 2.8
 */
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');

/** True if module can show description on course main page */
define('FEATURE_SHOW_DESCRIPTION', 'showdescription');

/** True if module uses the question bank */
define('FEATURE_USES_QUESTIONS', 'usesquestions');

/** 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);
/** System (not user-addable) module archetype */
define('MOD_ARCHETYPE_SYSTEM', 3);

/** Return this from modname_get_types callback to use default display in activity chooser */
define('MOD_SUBTYPE_NO_CHILDREN', 'modsubtypenochildren');

/**
 * 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");

/**
 * Moodle mobile app service name
 */
define('MOODLE_OFFICIAL_MOBILE_SERVICE', 'moodle_mobile_app');

/**
 * Indicates the user has the capabilities required to ignore activity and course file size restrictions
 */
define('USER_CAN_IGNORE_FILE_SIZE_LIMITS', -1);

/**
 * Course display settings: display all sections on one page.
 */
define('COURSE_DISPLAY_SINGLEPAGE', 0);
/**
 * Course display settings: split pages into a page per section.
 */
define('COURSE_DISPLAY_MULTIPAGE', 1);

/**
 * Authentication constant: String used in password field when password is not stored.
 */
define('AUTH_PASSWORD_NOT_CACHED', 'not cached');

// 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);
 *
 * Please note the $type parameter is now required and the value can not be array.
 *
 * @param string $parname the name of the page parameter we want
 * @param string $type expected type of parameter
 * @return mixed
 * @throws coding_exception
 */
function required_param($parname, $type) {
    if (func_num_args() != 2 or empty($parname) or empty($type)) {
        throw new coding_exception('required_param() requires $parname and $type to be specified (parameter: '.$parname.')');
    }
    // POST has precedence.
    if (isset($_POST[$parname])) {
        $param = $_POST[$parname];
    } else if (isset($_GET[$parname])) {
        $param = $_GET[$parname];
    } else {
        print_error('missingparam', '', '', $parname);
    }

    if (is_array($param)) {
        debugging('Invalid array parameter detected in required_param(): '.$parname);
        // TODO: switch to fatal error in Moodle 2.3.
        return required_param_array($parname, $type);
    }

    return clean_param($param, $type);
}

/**
 * Returns a particular array 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:
 *    $ids = required_param_array('ids', PARAM_INT);
 *
 *  Note: arrays of arrays are not supported, only alphanumeric keys with _ and - are supported
 *
 * @param string $parname the name of the page parameter we want
 * @param string $type expected type of parameter
 * @return array
 * @throws coding_exception
 */
function required_param_array($parname, $type) {
    if (func_num_args() != 2 or empty($parname) or empty($type)) {
        throw new coding_exception('required_param_array() requires $parname and $type to be specified (parameter: '.$parname.')');
    }
    // POST has precedence.
    if (isset($_POST[$parname])) {
        $param = $_POST[$parname];
    } else if (isset($_GET[$parname])) {
        $param = $_GET[$parname];
    } else {
        print_error('missingparam', '', '', $parname);
    }
    if (!is_array($param)) {
        print_error('missingparam', '', '', $parname);
    }

    $result = array();
    foreach ($param as $key => $value) {
        if (!preg_match('/^[a-z0-9_-]+$/i', $key)) {
            debugging('Invalid key name in required_param_array() detected: '.$key.', parameter: '.$parname);
            continue;
        }
        $result[$key] = clean_param($value, $type);
    }

    return $result;
}

/**
 * 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);
 *
 * Please note the $type parameter is now required and the value can not be array.
 *
 * @param string $parname the name of the page parameter we want
 * @param mixed  $default the default value to return if nothing is found
 * @param string $type expected type of parameter
 * @return mixed
 * @throws coding_exception
 */
function optional_param($parname, $default, $type) {
    if (func_num_args() != 3 or empty($parname) or empty($type)) {
        throw new coding_exception('optional_param requires $parname, $default + $type to be specified (parameter: '.$parname.')');
    }

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

    if (is_array($param)) {
        debugging('Invalid array parameter detected in required_param(): '.$parname);
        // TODO: switch to $default in Moodle 2.3.
        return optional_param_array($parname, $default, $type);
    }

    return clean_param($param, $type);
}

/**
 * Returns a particular array 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:
 *    $ids = optional_param('id', array(), PARAM_INT);
 *
 * Note: arrays of arrays are not supported, only alphanumeric keys with _ and - are supported
 *
 * @param string $parname the name of the page parameter we want
 * @param mixed $default the default value to return if nothing is found
 * @param string $type expected type of parameter
 * @return array
 * @throws coding_exception
 */
function optional_param_array($parname, $default, $type) {
    if (func_num_args() != 3 or empty($parname) or empty($type)) {
        throw new coding_exception('optional_param_array requires $parname, $default + $type to be specified (parameter: '.$parname.')');
    }

    // POST has precedence.
    if (isset($_POST[$parname])) {
        $param = $_POST[$parname];
    } else if (isset($_GET[$parname])) {
        $param = $_GET[$parname];
    } else {
        return $default;
    }
    if (!is_array($param)) {
        debugging('optional_param_array() expects array parameters only: '.$parname);
        return $default;
    }

    $result = array();
    foreach ($param as $key => $value) {
        if (!preg_match('/^[a-z0-9_-]+$/i', $key)) {
            debugging('Invalid key name in optional_param_array() detected: '.$key.', parameter: '.$parname);
            continue;
        }
        $result[$key] = clean_param($value, $type);
    }

    return $result;
}

/**
 * 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 string $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
 * @throws invalid_parameter_exception if $param is not of given type
 */
function validate_param($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 ($type == PARAM_FLOAT) {
        // Do not detect precision loss here.
        if (is_float($param) or is_int($param)) {
            // These always fit.
        } else if (!is_numeric($param) or !preg_match('/^[\+-]?[0-9]*\.?[0-9]*(e[-+]?[0-9]+)?$/i', (string)$param)) {
            throw new invalid_parameter_exception($debuginfo);
        }
    } else if ((string)$param !== (string)$cleaned) {
        // Conversion to string is usually lossless.
        throw new invalid_parameter_exception($debuginfo);
    }

    return $cleaned;
}

/**
 * Makes sure array contains only the allowed types, this function does not validate array key names!
 *
 * <code>
 * $options = clean_param($options, PARAM_INT);
 * </code>
 *
 * @param array $param the variable array we are cleaning
 * @param string $type expected format of param after cleaning.
 * @param bool $recursive clean recursive arrays
 * @return array
 * @throws coding_exception
 */
function clean_param_array(array $param = null, $type, $recursive = false) {
    // Convert null to empty array.
    $param = (array)$param;
    foreach ($param as $key => $value) {
        if (is_array($value)) {
            if ($recursive) {
                $param[$key] = clean_param_array($value, $type, true);
            } else {
                throw new coding_exception('clean_param_array can not process multidimensional arrays when $recursive is false.');
            }
        } else {
            $param[$key] = clean_param($value, $type);
        }
    }
    return $param;
}

/**
 * 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);
 * $selectedgradeitem = clean_param($selectedgradeitem, PARAM_INT);
 * </code>
 *
 * @param mixed $param the variable we are cleaning
 * @param string $type expected format of param after cleaning.
 * @return mixed
 * @throws coding_exception
 */
function clean_param($param, $type) {
    global $CFG;

    if (is_array($param)) {
        throw new coding_exception('clean_param() can not process arrays, please use clean_param_array() instead.');
    } else if (is_object($param)) {
        if (method_exists($param, '__toString')) {
            $param = $param->__toString();
        } else {
            throw new coding_exception('clean_param() can not process objects, please use clean_param_array() instead.');
        }
    }

    switch ($type) {
        case PARAM_RAW:
            // No cleaning at all.
            $param = fix_utf8($param);
            return $param;

        case PARAM_RAW_TRIMMED:
            // No cleaning, but strip leading and trailing whitespace.
            $param = fix_utf8($param);
            return trim($param);

        case PARAM_CLEAN:
            // General HTML cleaning, try to use more specific type if possible this is deprecated!
            // Please use more specific type instead.
            if (is_numeric($param)) {
                return $param;
            }
            $param = fix_utf8($param);
            // Sweep for scripts, etc.
            return clean_text($param);

        case PARAM_CLEANHTML:
            // Clean html fragment.
            $param = fix_utf8($param);
            // Sweep for scripts, etc.
            $param = clean_text($param, FORMAT_HTML);
            return trim($param);

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

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

        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.
            $param = fix_utf8($param);
            return strip_tags($param);

        case PARAM_TEXT:
            // Leave only tags needed for multilang.
            $param = fix_utf8($param);
            // If the multilang syntax is not correct we strip all tags because it would break xhtml strict which is required
            // for accessibility standards please note this cleaning does not strip unbalanced '>' for BC compatibility reasons.
            do {
                if (strpos($param, '</lang>') !== false) {
                    // Old and future mutilang syntax.
                    $param = strip_tags($param, '<lang>');
                    if (!preg_match_all('/<.*>/suU', $param, $matches)) {
                        break;
                    }
                    $open = false;
                    foreach ($matches[0] as $match) {
                        if ($match === '</lang>') {
                            if ($open) {
                                $open = false;
                                continue;
                            } else {
                                break 2;
                            }
                        }
                        if (!preg_match('/^<lang lang="[a-zA-Z0-9_-]+"\s*>$/u', $match)) {
                            break 2;
                        } else {
                            $open = true;
                        }
                    }
                    if ($open) {
                        break;
                    }
                    return $param;

                } else if (strpos($param, '</span>') !== false) {
                    // Current problematic multilang syntax.
                    $param = strip_tags($param, '<span>');
                    if (!preg_match_all('/<.*>/suU', $param, $matches)) {
                        break;
                    }
                    $open = false;
                    foreach ($matches[0] as $match) {
                        if ($match === '</span>') {
                            if ($open) {
                                $open = false;
                                continue;
                            } else {
                                break 2;
                            }
                        }
                        if (!preg_match('/^<span(\s+lang="[a-zA-Z0-9_-]+"|\s+class="multilang"){2}\s*>$/u', $match)) {
                            break 2;
                        } else {
                            $open = true;
                        }
                    }
                    if ($open) {
                        break;
                    }
                    return $param;
                }
            } while (false);
            // Easy, just strip all tags, if we ever want to fix orphaned '&' we have to do that in format_string().
            return strip_tags($param);

        case PARAM_COMPONENT:
            // We do not want any guessing here, either the name is correct or not
            // please note only normalised component names are accepted.
            if (!preg_match('/^[a-z]+(_[a-z][a-z0-9_]*)?[a-z0-9]+$/', $param)) {
                return '';
            }
            if (strpos($param, '__') !== false) {
                return '';
            }
            if (strpos($param, 'mod_') === 0) {
                // Module names must not contain underscores because we need to differentiate them from invalid plugin types.
                if (substr_count($param, '_') != 1) {
                    return '';
                }
            }
            return $param;

        case PARAM_PLUGIN:
        case PARAM_AREA:
            // We do not want any guessing here, either the name is correct or not.
            if (!is_valid_plugin_name($param)) {
                return '';
            }
            return $param;

        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.
            $param = fix_utf8($param);
            $param = preg_replace('~[[:cntrl:]]|[&<>"`\|\':\\\\/]~u', '', $param);
            if ($param === '.' || $param === '..') {
                $param = '';
            }
            return $param;

        case PARAM_PATH:
            // Strip all suspicious characters from file path.
            $param = fix_utf8($param);
            $param = str_replace('\\', '/', $param);

            // Explode the path and clean each element using the PARAM_FILE rules.
            $breadcrumb = explode('/', $param);
            foreach ($breadcrumb as $key => $crumb) {
                if ($crumb === '.' && $key === 0) {
                    // Special condition to allow for relative current path such as ./currentdirfile.txt.
                } else {
                    $crumb = clean_param($crumb, PARAM_FILE);
                }
                $breadcrumb[$key] = $crumb;
            }
            $param = implode('/', $breadcrumb);

            // Remove multiple current path (./././) and multiple slashes (///).
            $param = preg_replace('~//+~', '/', $param);
            $param = preg_replace('~/(\./)+~', '/', $param);
            return $param;

        case PARAM_HOST:
            // Allow FQDN or IPv4 dotted quad.
            $param = preg_replace('/[^\.\d\w-]/', '', $param );
            // 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?
                    $param = '';
                }
            } else if ( preg_match('/^[\w\d\.-]+$/', $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.
            $param = fix_utf8($param);
            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 {
                // Not really ok.
                $param ='';
            }
            return $param;

        case PARAM_LOCALURL:
            // Allow http absolute, root relative and relative URLs within wwwroot.
            $param = clean_param($param, PARAM_URL);
            if (!empty($param)) {

                // Simulate the HTTPS version of the site.
                $httpswwwroot = str_replace('http://', 'https://', $CFG->wwwroot);

                if ($param === $CFG->wwwroot) {
                    // Exact match;
                } else if (!empty($CFG->loginhttps) && $param === $httpswwwroot) {
                    // Exact match;
                } else if (preg_match(':^/:', $param)) {
                    // Root-relative, ok!
                } else if (preg_match('/^' . preg_quote($CFG->wwwroot . '/', '/') . '/i', $param)) {
                    // Absolute, and matches our wwwroot.
                } else if (!empty($CFG->loginhttps) && preg_match('/^' . preg_quote($httpswwwroot . '/', '/') . '/i', $param)) {
                    // Absolute, and matches our httpswwwroot.
                } 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:
            $param = fix_utf8($param);
            // Please note it is not safe to use the tag name directly anywhere,
            // it must be processed with s(), urlencode() before embedding anywhere.
            // Remove some nasties.
            $param = preg_replace('~[[:cntrl:]]|[<>`]~u', '', $param);
            // Convert many whitespace chars into one.
            $param = preg_replace('/\s+/u', ' ', $param);
            $param = core_text::substr(trim($param), 0, TAG_MAX_LENGTH);
            return $param;

        case PARAM_TAGLIST:
            $param = fix_utf8($param);
            $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_PLUGIN);
            if (empty($param)) {
                return '';
            } else if (exists_auth_plugin($param)) {
                return $param;
            } else {
                return '';
            }

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

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

        case PARAM_USERNAME:
            $param = fix_utf8($param);
            $param = trim($param);
            // Convert uppercase to lowercase MDL-16919.
            $param = core_text::strtolower($param);
            if (empty($CFG->extendedusernamechars)) {
                $param = str_replace(" " , "", $param);
                // 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:
            $param = fix_utf8($param);
            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 '';
            }

        case PARAM_TIMEZONE:
            // Can be int, float(with .5 or .0) or string seperated by '/' and can have '-_'.
            $param = fix_utf8($param);
            $timezonepattern = '/^(([+-]?(0?[0-9](\.[5|0])?|1[0-3](\.0)?|1[0-2]\.5))|(99)|[[:alnum:]]+(\/?[[:alpha:]_-])+)$/';
            if (preg_match($timezonepattern, $param)) {
                return $param;
            } else {
                return '';
            }

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

/**
 * Makes sure the data is using valid utf8, invalid characters are discarded.
 *
 * Note: this function is not intended for full objects with methods and private properties.
 *
 * @param mixed $value
 * @return mixed with proper utf-8 encoding
 */
function fix_utf8($value) {
    if (is_null($value) or $value === '') {
        return $value;

    } else if (is_string($value)) {
        if ((string)(int)$value === $value) {
            // Shortcut.
            return $value;
        }
        // No null bytes expected in our data, so let's remove it.
        $value = str_replace("\0", '', $value);

        // Note: this duplicates min_fix_utf8() intentionally.
        static $buggyiconv = null;
        if ($buggyiconv === null) {
            $buggyiconv = (!function_exists('iconv') or @iconv('UTF-8', 'UTF-8//IGNORE', '100'.chr(130).'€') !== '100€');
        }

        if ($buggyiconv) {
            if (function_exists('mb_convert_encoding')) {
                $subst = mb_substitute_character();
                mb_substitute_character('');
                $result = mb_convert_encoding($value, 'utf-8', 'utf-8');
                mb_substitute_character($subst);

            } else {
                // Warn admins on admin/index.php page.
                $result = $value;
            }

        } else {
            $result = @iconv('UTF-8', 'UTF-8//IGNORE', $value);
        }

        return $result;

    } else if (is_array($value)) {
        foreach ($value as $k => $v) {
            $value[$k] = fix_utf8($v);
        }
        return $value;

    } else if (is_object($value)) {
        // Do not modify original.
        $value = clone($value);
        foreach ($value as $k => $v) {
            $value->$k = fix_utf8($v);
        }
        return $value;

    } else {
        // This is some other type, no utf-8 here.
        return $value;
    }
}

/**
 * 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.
 *
 * NOTE: this function is called from lib/db/upgrade.php
 *
 * @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 {
                // Settings from db are always strings.
                $CFG->$name = (string)$value;
            }
        }

        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 stdClass();
                $config->name  = $name;
                $config->value = $value;
                $DB->insert_record('config', $config, false);
            }
        }
        if ($name === 'siteidentifier') {
            cache_helper::update_site_identifier($value);
        }
        cache_helper::invalidate_by_definition('core', 'config', array(), 'core');
    } else {
        // Plugin scope.
        if ($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 stdClass();
                $config->plugin = $plugin;
                $config->name   = $name;
                $config->value  = $value;
                $DB->insert_record('config_plugins', $config, false);
            }
        }
        cache_helper::invalidate_by_definition('core', 'config', array(), $plugin);
    }

    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.
 *
 * NOTE: this function is called from lib/db/upgrade.php
 *
 * @static string|false $siteidentifier The site identifier is not cached. We use this static cache so
 *     that we need only fetch it once per request.
 * @param string $plugin full component name
 * @param string $name default null
 * @return mixed hash-like object or single value, return false no config found
 * @throws dml_exception
 */
function get_config($plugin, $name = null) {
    global $CFG, $DB;

    static $siteidentifier = null;

    if ($plugin === 'moodle' || $plugin === 'core' || empty($plugin)) {
        $forced =& $CFG->config_php_settings;
        $iscore = true;
        $plugin = 'core';
    } else {
        if (array_key_exists($plugin, $CFG->forced_plugin_settings)) {
            $forced =& $CFG->forced_plugin_settings[$plugin];
        } else {
            $forced = array();
        }
        $iscore = false;
    }

    if ($siteidentifier === null) {
        try {
            // This may fail during installation.
            // If you have a look at {@link initialise_cfg()} you will see that this is how we detect the need to
            // install the database.
            $siteidentifier = $DB->get_field('config', 'value', array('name' => 'siteidentifier'));
        } catch (dml_exception $ex) {
            // Set siteidentifier to false. We don't want to trip this continually.
            $siteidentifier = false;
            throw $ex;
        }
    }

    if (!empty($name)) {
        if (array_key_exists($name, $forced)) {
            return (string)$forced[$name];
        } else if ($name === 'siteidentifier' && $plugin == 'core') {
            return $siteidentifier;
        }
    }

    $cache = cache::make('core', 'config');
    $result = $cache->get($plugin);
    if ($result === false) {
        // The user is after a recordset.
        if (!$iscore) {
            $result = $DB->get_records_menu('config_plugins', array('plugin' => $plugin), '', 'name,value');
        } else {
            // This part is not really used any more, but anyway...
            $result = $DB->get_records_menu('config', array(), '', 'name,value');;
        }
        $cache->set($plugin, $result);
    }

    if (!empty($name)) {
        if (array_key_exists($name, $result)) {
            return $result[$name];
        }
        return false;
    }

    if ($plugin === 'core') {
        $result['siteidentifier'] = $siteidentifier;
    }

    foreach ($forced as $key => $value) {
        if (is_null($value) or is_array($value) or is_object($value)) {
            // We do not want any extra mess here, just real settings that could be saved in db.
            unset($result[$key]);
        } else {
            // Convert to string as if it went through the DB.
            $result[$key] = (string)$value;
        }
    }

    return (object)$result;
}

/**
 * Removes a key from global configuration.
 *
 * NOTE: this function is called from lib/db/upgrade.php
 *
 * @param string $name the key to set
 * @param string $plugin (optional) the plugin scope
 * @return boolean whether the operation succeeded.
 */
function unset_config($name, $plugin=null) {
    global $CFG, $DB;

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

    return true;
}

/**
 * Remove all the config variables for a given plugin.
 *
 * NOTE: this function is called from lib/db/upgrade.php
 *
 * @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;
    // Delete from the obvious config_plugins first.
    $DB->delete_records('config_plugins', array('plugin' => $plugin));
    // Next delete any suspect settings from config.
    $like = $DB->sql_like('name', '?', true, true, false, '|');
    $params = array($DB->sql_like_escape($plugin.'_', '|') . '%');
    $DB->delete_records_select('config', $like, $params);
    // Finally clear both the plugin cache and the core cache (suspect settings now removed from core).
    cache_helper::invalidate_by_definition('core', 'config', array(), array('core', $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 $includeadmins include administrators.
 * @return array of user objects.
 */
function get_users_from_config($value, $capability, $includeadmins = true) {
    if (empty($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(context_system::instance(), $capability);
    if ($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;
}


/**
 * Invalidates browser caches and cached data in temp.
 *
 * IMPORTANT - If you are adding anything here to do with the cache directory you should also have a look at
 * {@link phpunit_util::reset_dataroot()}
 *
 * @return void
 */
function purge_all_caches() {
    global $CFG, $DB;

    reset_text_filters_cache();
    js_reset_all_caches();
    theme_reset_all_caches();
    get_string_manager()->reset_caches();
    core_text::reset_caches();
    if (class_exists('core_plugin_manager')) {
        core_plugin_manager::reset_caches();
    }

    // Bump up cacherev field for all courses.
    try {
        increment_revision_number('course', 'cacherev', '');
    } catch (moodle_exception $e) {
        // Ignore exception since this function is also called before upgrade script when field course.cacherev does not exist yet.
    }

    $DB->reset_caches();
    cache_helper::purge_all();

    // Purge all other caches: rss, simplepie, etc.
    remove_dir($CFG->cachedir.'', true);

    // Make sure cache dir is writable, throws exception if not.
    make_cache_directory('');

    // This is the only place where we purge local caches, we are only adding files there.
    // The $CFG->localcachedirpurged flag forces local directories to be purged on cluster nodes.
    remove_dir($CFG->localcachedir, true);
    set_config('localcachedirpurged', time());
    make_localcache_directory('', true);
    \core\task\manager::clear_static_caches();
}

/**
 * Get volatile flags
 *
 * @param string $type
 * @param int $changedsince default null
 * @return array records array
 */
function get_cache_flags($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 $changedsince default null
 * @return string|false The cache flag value or false
 */
function get_cache_flag($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' => $type), '*', IGNORE_MULTIPLE)) {
        // This is a potential problem in DEBUG_DEVELOPER.
        if ($f->value == $value and $f->expiry == $expiry and $f->timemodified == $timemodified) {
            return true; // No need to update.
        }
        $f->value        = $value;
        $f->expiry       = $expiry;
        $f->timemodified = $timemodified;
        $DB->update_record('cache_flags', $f);
    } else {
        $f = new stdClass();
        $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
 *
 * @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;
}

// USER PREFERENCE API.

/**
 * Refresh user preference cache. This is used most often for $USER
 * object that is stored in session, but it also helps with performance in cron script.
 *
 * Preferences for each user are loaded on first use on every page, then again after the timeout expires.
 *
 * @package  core
 * @category preference
 * @access   public
 * @param    stdClass         $user          User object. Preferences are preloaded into 'preference' property
 * @param    int              $cachelifetime Cache life time on the current page (in seconds)
 * @throws   coding_exception
 * @return   null
 */
function check_user_preferences_loaded(stdClass $user, $cachelifetime = 120) {
    global $DB;
    // Static cache, we need to check on each page load, not only every 2 minutes.
    static $loadedusers = array();

    if (!isset($user->id)) {
        throw new coding_exception('Invalid $user parameter in check_user_preferences_loaded() call, missing id field');
    }

    if (empty($user->id) or isguestuser($user->id)) {
        // No permanent storage for not-logged-in users and guest.
        if (!isset($user->preference)) {
            $user->preference = array();
        }
        return;
    }

    $timenow = time();

    if (isset($loadedusers[$user->id]) and isset($user->preference) and isset($user->preference['_lastloaded'])) {
        // Already loaded at least once on this page. Are we up to date?
        if ($user->preference['_lastloaded'] + $cachelifetime > $timenow) {
            // No need to reload - we are on the same page and we loaded prefs just a moment ago.
            return;

        } else if (!get_cache_flag('userpreferenceschanged', $user->id, $user->preference['_lastloaded'])) {
            // No change since the lastcheck on this page.
            $user->preference['_lastloaded'] = $timenow;
            return;
        }
    }

    // OK, so we have to reload all preferences.
    $loadedusers[$user->id] = true;
    $user->preference = $DB->get_records_menu('user_preferences', array('userid' => $user->id), '', 'name,value'); // All values.
    $user->preference['_lastloaded'] = $timenow;
}

/**
 * Called from set/unset_user_preferences, so that the prefs can be correctly reloaded in different sessions.
 *
 * NOTE: internal function, do not call from other code.
 *
 * @package core
 * @access private
 * @param integer $userid the user whose prefs were changed.
 */
function mark_user_preferences_changed($userid) {
    global $CFG;

    if (empty($userid) or isguestuser($userid)) {
        // No cache flags for guest and not-logged-in users.
        return;
    }

    set_cache_flag('userpreferenceschanged', $userid, 1, time() + $CFG->sessiontimeout);
}

/**
 * Sets a preference for the specified user.
 *
 * If a $user object is submitted it's 'preference' property is used for the preferences cache.
 *
 * @package  core
 * @category preference
 * @access   public
 * @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, null means delete current value.
 * @param    stdClass|int|null $user  A moodle user object or id, null means current user
 * @throws   coding_exception
 * @return   bool                     Always true or exception
 */
function set_user_preference($name, $value, $user = null) {
    global $USER, $DB;

    if (empty($name) or is_numeric($name) or $name === '_lastloaded') {
        throw new coding_exception('Invalid preference name in set_user_preference() call');
    }

    if (is_null($value)) {
        // Null means delete current.
        return unset_user_preference($name, $user);
    } else if (is_object($value)) {
        throw new coding_exception('Invalid value in set_user_preference() call, objects are not allowed');
    } else if (is_array($value)) {
        throw new coding_exception('Invalid value in set_user_preference() call, arrays are not allowed');
    }
    // Value column maximum length is 1333 characters.
    $value = (string)$value;
    if (core_text::strlen($value) > 1333) {
        throw new coding_exception('Invalid value in set_user_preference() call, value is is too long for the value column');
    }

    if (is_null($user)) {
        $user = $USER;
    } else if (isset($user->id)) {
        // It is a valid object.
    } else if (is_numeric($user)) {
        $user = (object)array('id' => (int)$user);
    } else {
        throw new coding_exception('Invalid $user parameter in set_user_preference() call');
    }

    check_user_preferences_loaded($user);

    if (empty($user->id) or isguestuser($user->id)) {
        // No permanent storage for not-logged-in users and guest.
        $user->preference[$name] = $value;
        return true;
    }

    if ($preference = $DB->get_record('user_preferences', array('userid' => $user->id, 'name' => $name))) {
        if ($preference->value === $value and isset($user->preference[$name]) and $user->preference[$name] === $value) {
            // Preference already set to this value.
            return true;
        }
        $DB->set_field('user_preferences', 'value', $value, array('id' => $preference->id));

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

    // Update value in cache.
    $user->preference[$name] = $value;

    // Set reload flag for other sessions.
    mark_user_preferences_changed($user->id);

    return true;
}

/**
 * Sets a whole array of preferences for the current user
 *
 * If a $user object is submitted it's 'preference' property is used for the preferences cache.
 *
 * @package  core
 * @category preference
 * @access   public
 * @param    array             $prefarray An array of key/value pairs to be set
 * @param    stdClass|int|null $user      A moodle user object or id, null means current user
 * @return   bool                         Always true or exception
 */
function set_user_preferences(array $prefarray, $user = null) {
    foreach ($prefarray as $name => $value) {
        set_user_preference($name, $value, $user);
    }
    return true;
}

/**
 * Unsets a preference completely by deleting it from the database
 *
 * If a $user object is submitted it's 'preference' property is used for the preferences cache.
 *
 * @package  core
 * @category preference
 * @access   public
 * @param    string            $name The key to unset as preference for the specified user
 * @param    stdClass|int|null $user A moodle user object or id, null means current user
 * @throws   coding_exception
 * @return   bool                    Always true or exception
 */
function unset_user_preference($name, $user = null) {
    global $USER, $DB;

    if (empty($name) or is_numeric($name) or $name === '_lastloaded') {
        throw new coding_exception('Invalid preference name in unset_user_preference() call');
    }

    if (is_null($user)) {
        $user = $USER;
    } else if (isset($user->id)) {
        // It is a valid object.
    } else if (is_numeric($user)) {
        $user = (object)array('id' => (int)$user);
    } else {
        throw new coding_exception('Invalid $user parameter in unset_user_preference() call');
    }

    check_user_preferences_loaded($user);

    if (empty($user->id) or isguestuser($user->id)) {
        // No permanent storage for not-logged-in user and guest.
        unset($user->preference[$name]);
        return true;
    }

    // Delete from DB.
    $DB->delete_records('user_preferences', array('userid' => $user->id, 'name' => $name));

    // Delete the preference from cache.
    unset($user->preference[$name]);

    // Set reload flag for other sessions.
    mark_user_preferences_changed($user->id);

    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.
 *
 * If a $user object is submitted it's 'preference' property is used for the preferences cache.
 *
 * @package  core
 * @category preference
 * @access   public
 * @param    string            $name    Name of the key to use in finding a preference value
 * @param    mixed|null        $default Value to be returned if the $name key is not set in the user preferences
 * @param    stdClass|int|null $user    A moodle user object or id, null means current user
 * @throws   coding_exception
 * @return   string|mixed|null          A string containing the value of a single preference. An
 *                                      array with all of the preferences or null
 */
function get_user_preferences($name = null, $default = null, $user = null) {
    global $USER;

    if (is_null($name)) {
        // All prefs.
    } else if (is_numeric($name) or $name === '_lastloaded') {
        throw new coding_exception('Invalid preference name in get_user_preferences() call');
    }

    if (is_null($user)) {
        $user = $USER;
    } else if (isset($user->id)) {
        // Is a valid object.
    } else if (is_numeric($user)) {
        $user = (object)array('id' => (int)$user);
    } else {
        throw new coding_exception('Invalid $user parameter in get_user_preferences() call');
    }

    check_user_preferences_loaded($user);

    if (empty($name)) {
        // All values.
        return $user->preference;
    } else if (isset($user->preference[$name])) {
        // The single string value.
        return $user->preference[$name];
    } else {
        // Default value (null if not specified).
        return $default;
    }
}

// FUNCTIONS FOR HANDLING TIME.

/**
 * Given date parts in user time produce a GMT timestamp.
 *
 * @package core
 * @category time
 * @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 int|float|string $timezone Timezone modifier, used to calculate GMT time offset.
 *             if 99 then default user's timezone is used {@link http://docs.moodle.org/dev/Time_API#Timezone}
 * @param bool $applydst Toggle Daylight Saving Time, default true, will be
 *             applied only if timezone is 99 or string.
 * @return int GMT timestamp
 */
function make_timestamp($year, $month=1, $day=1, $hour=0, $minute=0, $second=0, $timezone=99, $applydst=true) {
    $date = new DateTime('now', core_date::get_user_timezone_object($timezone));
    $date->setDate((int)$year, (int)$month, (int)$day);
    $date->setTime((int)$hour, (int)$minute, (int)$second);

    $time = $date->getTimestamp();

    // Moodle BC DST stuff.
    if (!$applydst) {
        $time += dst_offset_on($time, $timezone);
    }

    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
 *
 * @package core
 * @category time
 * @uses MINSECS
 * @uses HOURSECS
 * @uses DAYSECS
 * @uses YEARSECS
 * @param int $totalsecs Time in seconds
 * @param stdClass $str Should be a time object
 * @return string A nicely formatted date/time string
 */
function format_time($totalsecs, $str = null) {

    $totalsecs = abs($totalsecs);

    if (!$str) {
        // Create the str structure the slow way.
        $str = new stdClass();
        $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.
 *
 * @package core
 * @category time
 * @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 int|float|string $timezone by default, uses the user's time zone. if numeric and
 *        not 99 then daylight saving will not be added.
 *        {@link http://docs.moodle.org/dev/Time_API#Timezone}
 * @param bool $fixday If true (default) then the leading zero from %d is removed.
 *        If false then the leading zero is maintained.
 * @param bool $fixhour If true (default) then the leading zero from %I is removed.
 * @return string the formatted date/time.
 */
function userdate($date, $format = '', $timezone = 99, $fixday = true, $fixhour = true) {
    $calendartype = \core_calendar\type_factory::get_calendar_instance();
    return $calendartype->timestamp_to_date_string($date, $format, $timezone, $fixday, $fixhour);
}

/**
 * Returns a formatted date ensuring it is UTF-8.
 *
 * If we are running under Windows convert to Windows encoding and then back to UTF-8
 * (because it's impossible to specify UTF-8 to fetch locale info in Win32).
 *
 * @param int $date the timestamp - since Moodle 2.9 this is a real UTC timestamp
 * @param string $format strftime format.
 * @param int|float|string $tz the user timezone
 * @return string the formatted date/time.
 * @since Moodle 2.3.3
 */
function date_format_string($date, $format, $tz = 99) {
    global $CFG;

    $localewincharset = null;
    // Get the calendar type user is using.
    if ($CFG->ostype == 'WINDOWS') {
        $calendartype = \core_calendar\type_factory::get_calendar_instance();
        $localewincharset = $calendartype->locale_win_charset();
    }

    if ($localewincharset) {
        $format = core_text::convert($format, 'utf-8', $localewincharset);
    }

    date_default_timezone_set(core_date::get_user_timezone($tz));
    $datestring = strftime($format, $date);
    core_date::set_default_server_timezone();

    if ($localewincharset) {
        $datestring = core_text::convert($datestring, $localewincharset, 'utf-8');
    }

    return $datestring;
}

/**
 * Given a $time timestamp in GMT (seconds since epoch),
 * returns an array that represents the Gregorian date in user time
 *
 * @package core
 * @category time
 * @param int $time Timestamp in GMT
 * @param float|int|string $timezone user timezone
 * @return array An array that represents the date in user time
 */
function usergetdate($time, $timezone=99) {
    date_default_timezone_set(core_date::get_user_timezone($timezone));
    $result = getdate($time);
    core_date::set_default_server_timezone();

    return $result;
}

/**
 * Given a GMT timestamp (seconds since epoch), offsets it by
 * the timezone.  eg 3pm in India is 3pm GMT - 7 * 3600 seconds
 *
 * NOTE: this function does not include DST properly,
 *       you should use the PHP date stuff instead!
 *
 * @package core
 * @category time
 * @param int $date Timestamp in GMT
 * @param float|int|string $timezone user timezone
 * @return int
 */
function usertime($date, $timezone=99) {
    $userdate = new DateTime('@' . $date);
    $userdate->setTimezone(core_date::get_user_timezone_object($timezone));
    $dst = dst_offset_on($date, $timezone);

    return $date - $userdate->getOffset() + $dst;
}

/**
 * Given a time, return the GMT timestamp of the most recent midnight
 * for the current user.
 *
 * @package core
 * @category time
 * @param int $date Timestamp in GMT
 * @param float|int|string $timezone user timezone
 * @return int Returns a GMT timestamp
 */
function usergetmidnight($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
 *
 * @package core
 * @category time
 * @param float|int|string $timezone user timezone
 * @return string
 */
function usertimezone($timezone=99) {
    $tz = core_date::get_user_timezone($timezone);
    return core_date::get_localised_timezone($tz);
}

/**
 * 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
 *
 * @package core
 * @category time
 * @param float|int|string $tz timezone to calculate GMT time offset before
 *        calculating user timezone, 99 is default user timezone
 *        {@link http://docs.moodle.org/dev/Time_API#Timezone}
 * @return float|string
 */
function get_user_timezone($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;

    // Loop while $tz is, empty but not zero, or 99, and there is another timezone is the array.
    while (((empty($tz) && !is_numeric($tz)) || $tz == 99) && $next = each($timezones)) {
        $tz = $next['value'];
    }
    return is_numeric($tz) ? (float) $tz : $tz;
}

/**
 * Calculates the Daylight Saving Offset for a given date/time (timestamp)
 * - Note: Daylight saving only works for string timezones and not for float.
 *
 * @package core
 * @category time
 * @param int $time must NOT be compensated at all, it has to be a pure timestamp
 * @param int|float|string $strtimezone user timezone
 * @return int
 */
function dst_offset_on($time, $strtimezone = null) {
    $tz = core_date::get_user_timezone($strtimezone);
    $date = new DateTime('@' . $time);
    $date->setTimezone(new DateTimeZone($tz));
    if ($date->format('I') == '1') {
        if ($tz === 'Australia/Lord_Howe') {
            return 1800;
        }
        return 3600;
    }
    return 0;
}

/**
 * Calculates when the day appears in specific month
 *
 * @package core
 * @category time
 * @param int $startday starting day of the month
 * @param int $weekday The day when week starts (normally taken from user preferences)
 * @param int $month The month whose day is sought
 * @param int $year The year of the month whose day is sought
 * @return int
 */
function find_day_in_month($startday, $weekday, $month, $year) {
    $calendartype = \core_calendar\type_factory::get_calendar_instance();

    $daysinmonth = days_in_month($month, $year);
    $daysinweek = count($calendartype->get_weekdays());

    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);
        $lastmonthweekday = dayofweek($daysinmonth, $month, $year);

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

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

        return $lastinmonth;
    } else {
        $indexweekday = dayofweek($startday, $month, $year);

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

        // 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
 *
 * @package core
 * @category time
 * @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) {
    $calendartype = \core_calendar\type_factory::get_calendar_instance();
    return $calendartype->get_num_days_in_month($year, $month);
}

/**
 * Calculate the position in the week of a specific calendar day
 *
 * @package core
 * @category time
 * @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) {
    $calendartype = \core_calendar\type_factory::get_calendar_instance();
    return $calendartype->get_weekday($year, $month, $day);
}

// USER AUTHENTICATION AND LOGIN.

/**
 * Returns full login url.
 *
 * @return string login url
 */
function get_login_url() {
    global $CFG;

    $url = "$CFG->wwwroot/login/index.php";

    if (!empty($CFG->loginhttps)) {
        $url = str_replace('http:', 'https:', $url);
    }

    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.
 *
 * @package    core_access
 * @category   access
 *
 * @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 $preventredirect set to true in scripts that can not redirect (CLI, rss feeds, etc.), throws exceptions
 * @return mixed Void, exit, and die depending on path
 * @throws coding_exception
 * @throws require_login_exception
 */
function require_login($courseorid = null, $autologinguest = true, $cm = null, $setwantsurltome = true, $preventredirect = false) {
    global $CFG, $SESSION, $USER, $PAGE, $SITE, $DB, $OUTPUT;

    // Must not redirect when byteserving already started.
    if (!empty($_SERVER['HTTP_RANGE'])) {
        $preventredirect = true;
    }

    if (AJAX_SCRIPT) {
        // We cannot redirect for AJAX scripts either.
        $preventredirect = true;
    }

    // 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!!');
            }
            // Make sure we have a $cm from get_fast_modinfo as this contains activity access details.
            if (!($cm instanceof cm_info)) {
                // Note: nearly all pages call get_fast_modinfo anyway and it does not make any
                // db queries so this is not really a performance concern, however it is obviously
                // better if you use get_fast_modinfo to get the cm before calling this.
                $modinfo = get_fast_modinfo($course);
                $cm = $modinfo->get_cm($cm->id);
            }
        }
    } 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 this is an AJAX request and $setwantsurltome is true then we need to override it and set it to false.
    // Otherwise the AJAX request URL will be set to $SESSION->wantsurl and events such as self enrolment in the future
    // risk leading the user back to the AJAX request URL.
    if ($setwantsurltome && defined('AJAX_SCRIPT') && AJAX_SCRIPT) {
        $setwantsurltome = false;
    }

    // Redirect to the login page if session has expired, only with dbsessions enabled (MDL-35029) to maintain current behaviour.
    if ((!isloggedin() or isguestuser()) && !empty($SESSION->has_timed_out) && !empty($CFG->dbsessions)) {
        if ($preventredirect) {
            throw new require_login_session_timeout_exception();
        } else {
            if ($setwantsurltome) {
                $SESSION->wantsurl = qualified_me();
            }
            redirect(get_login_url());
        }
    }

    // If the user is not even logged in yet then make sure they are.
    if (!isloggedin()) {
        if ($autologinguest and !empty($CFG->guestloginbutton) and !empty($CFG->autologinguests)) {
            if (!$guest = get_complete_user_data('id', $CFG->siteguest)) {
                // Misconfigured site guest, just redirect to login page.
                redirect(get_login_url());
                exit; // Never reached.
            }
            $lang = isset($SESSION->lang) ? $SESSION->lang : $CFG->lang;
            complete_user_login($guest);
            $USER->autologinguest = true;
            $SESSION->lang = $lang;
        } else {
            // 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 = qualified_me();
            }

            $referer = get_local_referer(false);
            if (!empty($referer)) {
                $SESSION->fromurl = $referer;
            }

            // Give auth plugins an opportunity to authenticate or redirect to an external login page
            $authsequence = get_enabled_auth_plugins(true); // auths, in sequence
            foreach($authsequence as $authname) {
                $authplugin = get_auth_plugin($authname);
                $authplugin->pre_loginpage_hook();
                if (isloggedin()) {
                    break;
                }
            }

            // If we're still not logged in then go to the login page
            if (!isloggedin()) {
                redirect(get_login_url());
                exit; // Never reached.
            }
        }
    }

    // Loginas as redirection if needed.
    if ($course->id != SITEID and \core\session\manager::is_loggedinas()) {
        if ($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') && !\core\session\manager::is_loggedinas()) {
        $userauth = get_auth_plugin($USER->auth);
        if ($userauth->can_change_password() and !$preventredirect) {
            if ($setwantsurltome) {
                $SESSION->wantsurl = qualified_me();
            }
            if ($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');
        }
        if ($setwantsurltome) {
            $SESSION->wantsurl = qualified_me();
        }
        redirect($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 the global $COURSE.
        if ($cm) {
            $PAGE->set_cm($cm, $course);
            $PAGE->set_pagelayout('incourse');
        } else if (!empty($courseorid)) {
            $PAGE->set_course($course);
        }
        // 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 - do not test in case of admins.
    if (!$USER->policyagreed and !is_siteadmin()) {
        if (!empty($CFG->sitepolicy) and !isguestuser()) {
            if ($preventredirect) {
                throw new require_login_exception('Policy not agreed');
            }
            if ($setwantsurltome) {
                $SESSION->wantsurl = qualified_me();
            }
            redirect($CFG->wwwroot .'/user/policy.php');
        } else if (!empty($CFG->sitepolicyguest) and isguestuser()) {
            if ($preventredirect) {
                throw new require_login_exception('Policy not agreed');
            }
            if ($setwantsurltome) {
                $SESSION->wantsurl = qualified_me();
            }
            redirect($CFG->wwwroot .'/user/policy.php');
        }
    }

    // Fetch the system context, the course context, and prefetch its child contexts.
    $sysctx = context_system::instance();
    $coursecontext = context_course::instance($course->id, MUST_EXIST);
    if ($cm) {
        $cmcontext = context_module::instance($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 ($course->id == SITEID) {
        // Frontpage can not be hidden.
    } else {
        if (is_role_switched($course->id)) {
            // 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');
                }
                $PAGE->set_context(null);
                // We need to override the navigation URL as the course won't have been added to the navigation and thus
                // the navigation will mess up when trying to find it.
                navigation_node::override_active_url(new moodle_url('/'));
                notice(get_string('coursehidden'), $CFG->wwwroot .'/');
            }
        }
    }

    // Is the user enrolled?
    if ($course->id == SITEID) {
        // Everybody is enrolled on the frontpage.
    } else {
        if (\core\session\manager::is_loggedinas()) {
            // Make sure the REAL person can access this course first.
            $realuser = \core\session\manager::get_realuser();
            if (!is_enrolled($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');
                }
                $PAGE->set_context(null);
                echo $OUTPUT->header();
                notice(get_string('studentnotallowed', '', fullname($USER, true)), $CFG->wwwroot .'/');
            }
        }

        $access = false;

        if (is_role_switched($course->id)) {
            // Ok, user had to be inside this course before the switch.
            $access = true;

        } else 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] > time()) {
                    $access = true;
                    if (isset($USER->enrol['tempguest'][$course->id])) {
                        unset($USER->enrol['tempguest'][$course->id]);
                        remove_temp_course_roles($coursecontext);
                    }
                } 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'][$course->id]);
                    remove_temp_course_roles($coursecontext);
                }
            }

            if (!$access) {
                // Cache not ok.
                $until = enrol_get_enrolment_end($coursecontext->instanceid, $USER->id);
                if ($until !== false) {
                    // Active participants may always access, a timestamp in the future, 0 (always) or false.
                    if ($until == 0) {
                        $until = ENROL_MAX_TIMESTAMP;
                    }
                    $USER->enrol['enrolled'][$course->id] = $until;
                    $access = true;

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

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

    // Check visibility of activity to current user; includes visible flag, conditional availability, etc.
    if ($cm && !$cm->uservisible) {
        if ($preventredirect) {
            throw new require_login_exception('Activity is hidden');
        }
        if ($course->id != SITEID) {
            $url = new moodle_url('/course/view.php', array('id' => $course->id));
        } else {
            $url = new moodle_url('/');
        }
        redirect($url, get_string('activityiscurrentlyhidden'));
    }

    // Set the global $COURSE.
    if ($cm) {
        $PAGE->set_cm($cm, $course);
        $PAGE->set_pagelayout('incourse');
    } else if (!empty($courseorid)) {
        $PAGE->set_course($course);
    }

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


/**
 * This function just makes sure a user is logged out.
 *
 * @package    core_access
 * @category   access
 */
function require_logout() {
    global $USER, $DB;

    if (!isloggedin()) {
        // This should not happen often, no need for hooks or events here.
        \core\session\manager::terminate_current();
        return;
    }

    // Execute hooks before action.
    $authplugins = array();
    $authsequence = get_enabled_auth_plugins();
    foreach ($authsequence as $authname) {
        $authplugins[$authname] = get_auth_plugin($authname);
        $authplugins[$authname]->prelogout_hook();
    }

    // Store info that gets removed during logout.
    $sid = session_id();
    $event = \core\event\user_loggedout::create(
        array(
            'userid' => $USER->id,
            'objectid' => $USER->id,
            'other' => array('sessionid' => $sid),
        )
    );
    if ($session = $DB->get_record('sessions', array('sid'=>$sid))) {
        $event->add_record_snapshot('sessions', $session);
    }

    // Clone of $USER object to be used by auth plugins.
    $user = fullclone($USER);

    // Delete session record and drop $_SESSION content.
    \core\session\manager::terminate_current();

    // Trigger event AFTER action.
    $event->trigger();

    // Hook to execute auth plugins redirection after event trigger.
    foreach ($authplugins as $authplugin) {
        $authplugin->postlogout_hook($user);
    }
}

/**
 * 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()
 *
 * @package    core_access
 * @category   access
 *
 * @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 $preventredirect set to true in scripts that can not redirect (CLI, rss feeds, etc.), throws exceptions
 * @return void
 * @throws coding_exception
 */
function require_course_login($courseorid, $autologinguest = true, $cm = null, $setwantsurltome = true, $preventredirect = false) {
    global $CFG, $PAGE, $SITE;
    $issite = ((is_object($courseorid) and $courseorid->id == SITEID)
          or (!is_object($courseorid) and $courseorid == SITEID));
    if ($issite && !empty($cm) && !($cm instanceof cm_info)) {
        // Note: nearly all pages call get_fast_modinfo anyway and it does not make any
        // db queries so this is not really a performance concern, however it is obviously
        // better if you use get_fast_modinfo to get the cm before calling this.
        if (is_object($courseorid)) {
            $course = $courseorid;
        } else {
            $course = clone($SITE);
        }
        $modinfo = get_fast_modinfo($course);
        $cm = $modinfo->get_cm($cm->id);
    }
    if (!empty($CFG->forcelogin)) {
        // Login required for both SITE and courses.
        require_login($courseorid, $autologinguest, $cm, $setwantsurltome, $preventredirect);

    } else if ($issite && !empty($cm) and !$cm->uservisible) {
        // Always login for hidden activities.
        require_login($courseorid, $autologinguest, $cm, $setwantsurltome, $preventredirect);

    } else if ($issite) {
        // Login for SITE not required.
        // We still need to instatiate PAGE vars properly so that things that rely on it like navigation function correctly.
        if (!empty($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);
        }
        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.
 *
 * @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 $DB;

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

    // Extra safety.
    \core\session\manager::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.
    enrol_check_plugins($user);
    \core\session\manager::set_user($user);

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

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

/**
 * Creates a new private user access key.
 *
 * @param string $script unique target identifier
 * @param int $userid
 * @param 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 stdClass();
    $key->script        = $script;
    $key->userid        = $userid;
    $key->instance      = $instance;
    $key->iprestriction = $iprestriction;
    $key->validuntil    = $validuntil;
    $key->timecreated   = time();

    // Something long and unique.
    $key->value         = md5($userid.'_'.time().random_string(40));
    while ($DB->record_exists('user_private_key', array('value' => $key->value))) {
        // Must be unique.