Proyectos de Subversion Moodle

<?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/>.

/**

 * Environment class to aid with the detection and establishment of the working environment.

 *

 * @package    core

 * @copyright  2013 Sam Hemelryk

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

/**

 * The user agent class.

 *

 * It's important to note that we do not like browser sniffing and its use in core code is highly discouraged.

 * No new uses of this API will be integrated unless there is absolutely no alternative.

 *

 * This API supports the few browser checks we do have in core, all of which one day will hopefully be removed.

 * The API will remain to support any third party use out there, however at some point like all code it will be deprecated.

 *

 * Use sparingly and only with good cause!

 *

 * @package    core

 * @copyright  2013 Sam Hemelryk

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

class core_useragent {

    /**

     * The default for devices, think of as a computer.

     */

    const DEVICETYPE_DEFAULT = 'default';

    /**

     * Legacy devices, or at least legacy browsers. These are older devices/browsers

     * that don't support standards.

     */

    const DEVICETYPE_LEGACY = 'legacy';

    /**

     * Mobile devices like your cell phone or hand held gaming device.

     */

    const DEVICETYPE_MOBILE = 'mobile';

    /**

     * Tables, larger than hand held, but still easily portable and smaller than a laptop.

     */

    const DEVICETYPE_TABLET = 'tablet';

    /**

     * An instance of this class.

     * @var core_useragent

     */

    protected static $instance = null;

    /**

     * The device types we track.

     * @var array

     */

    public static $devicetypes = array(

        self::DEVICETYPE_DEFAULT,

        self::DEVICETYPE_LEGACY,

        self::DEVICETYPE_MOBILE,

        self::DEVICETYPE_TABLET,

    );

    /**

     * The current requests user agent string if there was one.

     * @var string|bool|null Null until initialised, false if none available, or string when available.

     */

    protected $useragent = null;

    /**

     * The users device type, one of self::DEVICETYPE_*.

     * @var string null until initialised

     */

    protected $devicetype = null;

    /**

     * True if the user agent supports the display of svg images. False if not.

     * @var bool|null Null until initialised, then true or false.

     */

    protected $supportssvg = null;

    /**

     * Get an instance of the user agent object.

     *

     * @param bool $reload If set to true the user agent will be reset and all ascertations remade.

     * @param string $forceuseragent The string to force as the user agent, don't use unless absolutely unavoidable.

     * @return core_useragent

     */

    public static function instance($reload = false, $forceuseragent = null) {

        if (!self::$instance || $reload) {

            self::$instance = new core_useragent($forceuseragent);

        }

        return self::$instance;

    }

    /**

     * Constructs a new user agent object. Publically you must use the instance method above.

     *

     * @param string|null $forceuseragent Optional a user agent to force.

     */

    protected function __construct($forceuseragent = null) {

        if ($forceuseragent !== null) {

            $this->useragent = $forceuseragent;

        } else if (!empty($_SERVER['HTTP_USER_AGENT'])) {

            $this->useragent = $_SERVER['HTTP_USER_AGENT'];

        } else {

            $this->useragent = false;

            $this->devicetype = self::DEVICETYPE_DEFAULT;

        }

    }

    /**

     * Get the MoodleBot UserAgent for this site.

     *

     * @return string UserAgent

     */

    public static function get_moodlebot_useragent() {

        global $CFG;

        $version = moodle_major_version(); // Only major version for security.

        return "MoodleBot/$version (+{$CFG->wwwroot})";

    }

    /**

     * Returns the user agent string.

     * @return bool|string The user agent string or false if one isn't available.

     */

    public static function get_user_agent_string() {

        $instance = self::instance();

        return $instance->useragent;

    }

    /**

     * Returns the device type we believe is being used.

     * @return string

     */

    public static function get_device_type() {

        $instance = self::instance();

        if ($instance->devicetype === null) {

            return $instance->guess_device_type();

        }

        return $instance->devicetype;

    }

    /**

     * Guesses the device type the user agent is running on.

     *

     * @return string

     */

    protected function guess_device_type() {

        if ($this->is_useragent_mobile()) {

            $this->devicetype = self::DEVICETYPE_MOBILE;

        } else if ($this->is_useragent_tablet()) {

            $this->devicetype = self::DEVICETYPE_TABLET;

        } else if (self::check_ie_version('0') && !self::check_ie_version('7.0')) {

            // IE 6 and before are considered legacy.

            $this->devicetype = self::DEVICETYPE_LEGACY;

        } else {

            $this->devicetype = self::DEVICETYPE_DEFAULT;

        }

        return $this->devicetype;

    }

    /**

     * Returns true if the user appears to be on a mobile device.

     * @return bool

     */

    protected function is_useragent_mobile() {

        // Mobile detection PHP direct copy from open source detectmobilebrowser.com.

        $phonesregex = '/android .+ mobile|avantgo|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|symbian|treo|up\.(browser|link)|vodafone|wap|windows (ce|phone)|xda|xiino/i';

        $modelsregex = '/1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|e\-|e\/|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(di|rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|xda(\-|2|g)|yas\-|your|zeto|zte\-/i';

        return (preg_match($phonesregex, $this->useragent) || preg_match($modelsregex, substr($this->useragent, 0, 4)));

    }

    /**

     * Returns true if the user appears to be on a tablet.

     *

     * @return int

     */

    protected function is_useragent_tablet() {

        $tabletregex = '/Tablet browser|android|iPad|iProd|GT-P1000|GT-I9000|SHW-M180S|SGH-T849|SCH-I800|Build\/ERE27|sholest/i';

        return (preg_match($tabletregex, $this->useragent));

    }

    /**

     * Whether the user agent relates to a web crawler.

     * This includes all types of web crawler.

     * @return bool

     */

    protected function is_useragent_web_crawler() {

        $regex = '/MoodleBot|Googlebot|google\.com|Yahoo! Slurp|\[ZSEBOT\]|msnbot|bingbot|BingPreview|Yandex|AltaVista'

                .'|Baiduspider|Teoma/i';

        return (preg_match($regex, $this->useragent));

    }

    /**

     * Gets a list of known device types.

     *

     * @deprecated Moodle 4.3 MDL-78468 - No longer used. Please use core_useragent::devicetypes instead.

     * @todo Final deprecation on Moodle 4.7 MDL-79052

     * @param bool $includecustomtypes If set to true we'll include types that have been added by the admin.

     * @return array

     */

    public static function get_device_type_list($includecustomtypes = true) {

        debugging(

            __FUNCTION__ . '() is deprecated.' .

                'All functions associated with devicedetectregex theme setting are being removed.

                Please use core_useragent::devicetypes instead',

            DEBUG_DEVELOPER

        );

        $types = self::$devicetypes;

        if ($includecustomtypes) {

            $instance = self::instance();

            $types = array_merge($types, array_keys($instance->devicetypecustoms));

        }

        return $types;

    }

    /**

     * Returns the theme to use for the given device type.

     *

     * This used to be get_selected_theme_for_device_type.

     * @param null|string $devicetype The device type to find out for. Defaults to the device the user is using,

     * @deprecated since 4.3.

     * @return bool

     */

    public static function get_device_type_theme($devicetype = null) {

        debugging(

            __FUNCTION__ . '() is deprecated.' .

                'All functions associated with device specific themes are being removed.',

            DEBUG_DEVELOPER

        );

        global $CFG;

        if ($devicetype === null) {

            $devicetype = self::get_device_type();

        }

        $themevarname = self::get_device_type_cfg_var_name($devicetype);

        if (empty($CFG->$themevarname)) {

            return false;

        }

        return $CFG->$themevarname;

    }

    /**

     * Returns the CFG var used to find the theme to use for the given device.

     *

     * Used to be get_device_cfg_var_name.

     *

     * @param null|string $devicetype The device type to find out for. Defaults to the device the user is using,

     * @deprecated since 4.3.

     * @return string

     */

    public static function get_device_type_cfg_var_name($devicetype = null) {

        debugging(

            __FUNCTION__ . '() is deprecated.' .

                'All functions associated with device specific themes are being removed.',

            DEBUG_DEVELOPER

        );

        if ($devicetype == self::DEVICETYPE_DEFAULT || empty($devicetype)) {

            return 'theme';

        }

        return 'theme' . $devicetype;

    }

    /**

     * Gets the device type the user is currently using.

     * @return string

     */

    public static function get_user_device_type() {

        $device = self::get_device_type();

        $switched = get_user_preferences('switchdevice'.$device, false);

        if ($switched != false) {

            return $switched;

        }

        return $device;

    }

    /**

     * Switches the device type we think the user is using to what ever was given.

     * @param string $newdevice

     * @return bool

     * @throws coding_exception

     */

    public static function set_user_device_type($newdevice) {

        $devicetype = self::get_device_type();

        if ($newdevice == $devicetype) {

            unset_user_preference('switchdevice'.$devicetype);

            return true;

        } else {

            $devicetypes = self::$devicetypes;

            if (in_array($newdevice, $devicetypes)) {

                set_user_preference('switchdevice'.$devicetype, $newdevice);

                return true;

            }

        }

        throw new coding_exception('Invalid device type provided to set_user_device_type');

    }

    /**

     * Returns true if the user agent matches the given brand and the version is equal to or greater than that specified.

     *

     * @param string $brand The branch to check for.

     * @param scalar $version The version if we need to find out if it is equal to or greater than that specified.

     * @return bool

     */

    public static function check_browser_version($brand, $version = null) {

        switch ($brand) {

            case 'MSIE':

                // Internet Explorer.

                return self::check_ie_version($version);

            case 'Edge':

                // Microsoft Edge.

                return self::check_edge_version($version);

            case 'Firefox':

                // Mozilla Firefox browsers.

                return self::check_firefox_version($version);

            case 'Chrome':

                return self::check_chrome_version($version);

            case 'Opera':

                // Opera.

                return self::check_opera_version($version);

            case 'Safari':

                // Desktop version of Apple Safari browser - no mobile or touch devices.

                return self::check_safari_version($version);

            case 'Safari iOS':

                // Safari on iPhone, iPad and iPod touch.

                return self::check_safari_ios_version($version);

            case 'WebKit':

                // WebKit based browser - everything derived from it (Safari, Chrome, iOS, Android and other mobiles).

                return self::check_webkit_version($version);

            case 'Gecko':

                // Gecko based browsers.

                return self::check_gecko_version($version);

            case 'WebKit Android':

                // WebKit browser on Android.

                return self::check_webkit_android_version($version);

            case 'Camino':

                // OSX browser using Gecke engine.

                return self::check_camino_version($version);

        }

        // Who knows?! doesn't pass anyway.

        return false;

    }

    /**

     * Checks the user agent is camino based and that the version is equal to or greater than that specified.

     *

     * Camino browser is at the end of its life, its no longer being developed or supported, just don't worry about it.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    protected static function check_camino_version($version = null) {

        // OSX browser using Gecko engine.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'Camino') === false) {

            return false;

        }

        if (empty($version)) {

            return true; // No version specified.

        }

        if (preg_match("/Camino\/([0-9\.]+)/i", $useragent, $match)) {

            if (version_compare($match[1], $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks the user agent is Firefox (of any version).

     *

     * @return bool true if firefox

     */

    public static function is_firefox() {

        return self::check_firefox_version();

    }

    /**

     * Checks the user agent is Firefox based and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_firefox_version($version = null) {

        // Mozilla Firefox browsers.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'Firefox') === false && strpos($useragent, 'Iceweasel') === false) {

            return false;

        }

        if (empty($version)) {

            return true; // No version specified..

        }

        if (preg_match("/(Iceweasel|Firefox)\/([0-9\.]+)/i", $useragent, $match)) {

            if (version_compare($match[2], $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks the user agent is Gecko based (of any version).

     *

     * @return bool true if Gecko based.

     */

    public static function is_gecko() {

        return self::check_gecko_version();

    }

    /**

     * Checks the user agent is Gecko based and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_gecko_version($version = null) {

        // Gecko based browsers.

        // Do not look for dates any more, we expect real Firefox version here.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (empty($version)) {

            $version = 1;

        } else if ($version > 20000000) {

            // This is just a guess, it is not supposed to be 100% accurate!

            if (preg_match('/^201/', $version)) {

                $version = 3.6;

            } else if (preg_match('/^200[7-9]/', $version)) {

                $version = 3;

            } else if (preg_match('/^2006/', $version)) {

                $version = 2;

            } else {

                $version = 1.5;

            }

        }

        if (preg_match("/(Iceweasel|Firefox)\/([0-9\.]+)/i", $useragent, $match)) {

            // Use real Firefox version if specified in user agent string.

            if (version_compare($match[2], $version) >= 0) {

                return true;

            }

        } else if (preg_match("/Gecko\/([0-9\.]+)/i", $useragent, $match)) {

            // Gecko might contain date or Firefox revision, let's just guess the Firefox version from the date.

            $browserver = $match[1];

            if ($browserver > 20000000) {

                // This is just a guess, it is not supposed to be 100% accurate!

                if (preg_match('/^201/', $browserver)) {

                    $browserver = 3.6;

                } else if (preg_match('/^200[7-9]/', $browserver)) {

                    $browserver = 3;

                } else if (preg_match('/^2006/', $version)) {

                    $browserver = 2;

                } else {

                    $browserver = 1.5;

                }

            }

            if (version_compare($browserver, $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks the user agent is Edge (of any version).

     *

     * @return bool true if Edge

     */

    public static function is_edge() {

        return self::check_edge_version();

    }

    /**

     * Check the User Agent for the version of Edge.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_edge_version($version = null) {

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            // No User Agent found.

            return false;

        }

        if (strpos($useragent, 'Edge/') === false) {

            // Edge was not found in the UA - this is not Edge.

            return false;

        }

        if (empty($version)) {

            // No version to check.

            return true;

        }

        // Find the version.

        // Edge versions are always in the format:

        //      Edge/<version>.<OS build number>

        preg_match('%Edge/([\d]+)\.(.*)$%', $useragent, $matches);

        // Just to be safe, round the version being tested.

        // Edge only uses integer versions - the second component is the OS build number.

        $version = round($version);

        // Check whether the version specified is >= the version found.

        return version_compare($matches[1], $version, '>=');

    }

    /**

     * Checks the user agent is IE (of any version).

     *

     * @return bool true if internet exporeer

     */

    public static function is_ie() {

        return self::check_ie_version();

    }

    /**

     * Checks the user agent is IE and returns its main properties:

     * - browser version;

     * - whether running in compatibility view.

     *

     * @return bool|array False if not IE, otherwise an associative array of properties.

     */

    public static function check_ie_properties() {

        // Internet Explorer.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'Opera') !== false) {

            // Reject Opera.

            return false;

        }

        // See: http://www.useragentstring.com/pages/Internet%20Explorer/.

        if (preg_match("/MSIE ([0-9\.]+)/", $useragent, $match)) {

            $browser = $match[1];

        // See: http://msdn.microsoft.com/en-us/library/ie/bg182625%28v=vs.85%29.aspx for IE11+ useragent details.

        } else if (preg_match("/Trident\/[0-9\.]+/", $useragent) && preg_match("/rv:([0-9\.]+)/", $useragent, $match)) {

            $browser = $match[1];

        } else {

            return false;

        }

        $compatview = false;

        // IE8 and later versions may pretend to be IE7 for intranet sites, use Trident version instead,

        // the Trident should always describe the capabilities of IE in any emulation mode.

        if ($browser === '7.0' and preg_match("/Trident\/([0-9\.]+)/", $useragent, $match)) {

            $compatview = true;

            $browser = $match[1] + 4; // NOTE: Hopefully this will work also for future IE versions.

        }

        $browser = round($browser, 1);

        return array(

            'version'    => $browser,

            'compatview' => $compatview

        );

    }

    /**

     * Checks the user agent is IE and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_ie_version($version = null) {

        // Internet Explorer.

        $properties = self::check_ie_properties();

        if (!is_array($properties)) {

            return false;

        }

        // In case of IE we have to deal with BC of the version parameter.

        if (is_null($version)) {

            $version = 5.5; // Anything older is not considered a browser at all!

        }

        // IE uses simple versions, let's cast it to float to simplify the logic here.

        $version = round($version, 1);

        return ($properties['version'] >= $version);

    }

    /**

     * Checks the user agent is IE and that IE is running under Compatibility View setting.

     *

     * @return bool true if internet explorer runs in Compatibility View mode.

     */

    public static function check_ie_compatibility_view() {

        // IE User Agent string when in Compatibility View:

        // - IE  8: "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/4.0; ...)".

        // - IE  9: "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/5.0; ...)".

        // - IE 10: "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/6.0; ...)".

        // - IE 11: "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.3; Trident/7.0; ...)".

        // Refs:

        // - http://blogs.msdn.com/b/ie/archive/2009/01/09/the-internet-explorer-8-user-agent-string-updated-edition.aspx.

        // - http://blogs.msdn.com/b/ie/archive/2010/03/23/introducing-ie9-s-user-agent-string.aspx.

        // - http://blogs.msdn.com/b/ie/archive/2011/04/15/the-ie10-user-agent-string.aspx.

        // - http://msdn.microsoft.com/en-us/library/ie/hh869301%28v=vs.85%29.aspx.

        $properties = self::check_ie_properties();

        if (!is_array($properties)) {

            return false;

        }

        return $properties['compatview'];

    }

    /**

     * Checks the user agent is Opera (of any version).

     *

     * @return bool true if opera

     */

    public static function is_opera() {

        return self::check_opera_version();

    }

    /**

     * Checks the user agent is Opera and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_opera_version($version = null) {

        // Opera.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'Opera') === false) {

            return false;

        }

        if (empty($version)) {

            return true; // No version specified.

        }

        // Recent Opera useragents have Version/ with the actual version, e.g.:

        // Opera/9.80 (Windows NT 6.1; WOW64; U; en) Presto/2.10.289 Version/12.01

        // That's Opera 12.01, not 9.8.

        if (preg_match("/Version\/([0-9\.]+)/i", $useragent, $match)) {

            if (version_compare($match[1], $version) >= 0) {

                return true;

            }

        } else if (preg_match("/Opera\/([0-9\.]+)/i", $useragent, $match)) {

            if (version_compare($match[1], $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks the user agent is webkit based

     *

     * @return bool true if webkit

     */

    public static function is_webkit() {

        return self::check_webkit_version();

    }

    /**

     * Checks the user agent is Webkit based and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_webkit_version($version = null) {

        // WebKit based browser - everything derived from it (Safari, Chrome, iOS, Android and other mobiles).

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'AppleWebKit') === false) {

            return false;

        }

        if (empty($version)) {

            return true; // No version specified.

        }

        if (preg_match("/AppleWebKit\/([0-9.]+)/i", $useragent, $match)) {

            if (version_compare($match[1], $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks the user agent is Safari

     *

     * @return bool true if safari

     */

    public static function is_safari() {

        return self::check_safari_version();

    }

    /**

     * Checks the user agent is Safari based and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_safari_version($version = null) {

        // Desktop version of Apple Safari browser - no mobile or touch devices.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'AppleWebKit') === false) {

            return false;

        }

        // Look for AppleWebKit, excluding strings with OmniWeb, Shiira and SymbianOS and any other mobile devices.

        if (strpos($useragent, 'OmniWeb')) {

            // Reject OmniWeb.

            return false;

        }

        if (strpos($useragent, 'Shiira')) {

            // Reject Shiira.

            return false;

        }

        if (strpos($useragent, 'SymbianOS')) {

            // Reject SymbianOS.

            return false;

        }

        if (strpos($useragent, 'Android')) {

            // Reject Androids too.

            return false;

        }

        if (strpos($useragent, 'iPhone') or strpos($useragent, 'iPad') or strpos($useragent, 'iPod')) {

            // No Apple mobile devices here - editor does not work, course ajax is not touch compatible, etc.

            return false;

        }

        if (strpos($useragent, 'Chrome')) {

            // Reject chrome browsers - it needs to be tested explicitly.

            // This will also reject Edge, which pretends to be both Chrome, and Safari.

            return false;

        }

        if (empty($version)) {

            return true; // No version specified.

        }

        if (preg_match("/AppleWebKit\/([0-9.]+)/i", $useragent, $match)) {

            if (version_compare($match[1], $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks the user agent is Chrome

     *

     * @return bool true if chrome

     */

    public static function is_chrome() {

        return self::check_chrome_version();

    }

    /**

     * Checks the user agent is Chrome based and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_chrome_version($version = null) {

        // Chrome.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'Chrome') === false) {

            return false;

        }

        if (empty($version)) {

            return true; // No version specified.

        }

        if (preg_match("/Chrome\/(.*)[ ]+/i", $useragent, $match)) {

            if (version_compare($match[1], $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks the user agent is webkit android based.

     *

     * @return bool true if webkit based and on Android

     */

    public static function is_webkit_android() {

        return self::check_webkit_android_version();

    }

    /**

     * Checks the user agent is Webkit based and on Android and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_webkit_android_version($version = null) {

        // WebKit browser on Android.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'Android') === false) {

            return false;

        }

        if (empty($version)) {

            return true; // No version specified.

        }

        if (preg_match("/AppleWebKit\/([0-9]+)/i", $useragent, $match)) {

            if (version_compare($match[1], $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks the user agent is Safari on iOS

     *

     * @return bool true if Safari on iOS

     */

    public static function is_safari_ios() {

        return self::check_safari_ios_version();

    }

    /**

     * Checks the user agent is Safari on iOS and that the version is equal to or greater than that specified.

     *

     * @param string|int $version A version to check for, returns true if its equal to or greater than that specified.

     * @return bool

     */

    public static function check_safari_ios_version($version = null) {

        // Safari on iPhone, iPad and iPod touch.

        $useragent = self::get_user_agent_string();

        if ($useragent === false) {

            return false;

        }

        if (strpos($useragent, 'AppleWebKit') === false or strpos($useragent, 'Safari') === false) {

            return false;

        }

        if (!strpos($useragent, 'iPhone') and !strpos($useragent, 'iPad') and !strpos($useragent, 'iPod')) {

            return false;

        }

        if (empty($version)) {

            return true; // No version specified.

        }

        if (preg_match("/AppleWebKit\/([0-9]+)/i", $useragent, $match)) {

            if (version_compare($match[1], $version) >= 0) {

                return true;

            }

        }

        return false;

    }

    /**

     * Checks if the user agent is MS Word.

     * Not perfect, as older versions of Word use standard IE6/7 user agents without any identifying traits.

     *

     * @return bool true if user agent could be identified as MS Word.

     */

    public static function is_msword() {

        $useragent = self::get_user_agent_string();

        if (!preg_match('/(\bWord\b|ms-office|MSOffice|Microsoft Office)/i', $useragent)) {

            return false;

        } else if (strpos($useragent, 'Outlook') !== false) {

            return false;

        } else if (strpos($useragent, 'Meridio') !== false) {

            return false;

        }

        // It's Office, not Outlook and not Meridio - so it's probably Word, but we can't really be sure in most cases.

        return true;

    }

    /**

     * Check if the user agent matches a given brand.

     *

     * Known brand: 'Windows','Linux','Macintosh','SGI','SunOS','HP-UX'

     *

     * @param string $brand

     * @return bool

     */

    public static function check_browser_operating_system($brand) {

        $useragent = self::get_user_agent_string();

        return ($useragent !== false && preg_match("/$brand/i", $useragent));

    }

    /**

     * Gets an array of CSS classes to represent the user agent.

     * @return array

     */

    public static function get_browser_version_classes() {

        $classes = array();

        if (self::is_edge()) {

            $classes[] = 'edge';

        } else if (self::is_ie()) {

            $classes[] = 'ie';

            for ($i = 12; $i >= 6; $i--) {

                if (self::check_ie_version($i)) {

                    $classes[] = 'ie'.$i;

                    break;

                }

            }

        } else if (self::is_firefox() || self::is_gecko() || self::check_camino_version()) {

            $classes[] = 'gecko';

            if (preg_match('/rv\:([1-2])\.([0-9])/', self::get_user_agent_string(), $matches)) {

                $classes[] = "gecko{$matches[1]}{$matches[2]}";

            }

        } else if (self::is_chrome()) {

            $classes[] = 'chrome';

            if (self::is_webkit_android()) {

                $classes[] = 'android';

            }

        } else if (self::is_webkit()) {

            if (self::is_safari()) {

                $classes[] = 'safari';

            }

            if (self::is_safari_ios()) {

                $classes[] = 'ios';

            } else if (self::is_webkit_android()) {

                $classes[] = 'android'; // Old pre-Chrome android browsers.

            }

        } else if (self::is_opera()) {

            $classes[] = 'opera';

        }

        return $classes;

    }

    /**

     * Returns true if the user agent supports the display of SVG images.

     *

     * @return bool

     */

    public static function supports_svg() {

        $instance = self::instance();

        if ($instance->supportssvg === null) {

            if (preg_match('#Android +[0-2]\.#', $instance->useragent)) {

                // Android < 3 doesn't support SVG.

                $instance->supportssvg = false;

            } else {

                // With widespread SVG support in modern browsers, default to returning true (even when useragent is false).

                $instance->supportssvg = true;

            }

        }

        return $instance->supportssvg;

    }

    /**

     * Returns true if the user agent supports the MIME media type for JSON text, as defined in RFC 4627.

     *

     * @return bool

     */

    public static function supports_json_contenttype() {

        // Modern browsers other than IE correctly supports 'application/json' media type.

        if (!self::check_ie_version('0')) {

            return true;

        }

        // IE8+ supports 'application/json' media type, when NOT in Compatibility View mode.

        // Refs:

        // - http://blogs.msdn.com/b/ie/archive/2008/09/10/native-json-in-ie8.aspx;

        // - MDL-39810: issues when using 'text/plain' in Compatibility View for the body of an HTTP POST response.

        if (self::check_ie_version(8) && !self::check_ie_compatibility_view()) {

            return true;

        }

        // This browser does not support json.

        return false;

    }

    /**