wikimedia/mediawiki-extensions-MobileFrontend

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includes/MobileContext.php

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2 days
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<?php

use MediaWiki\Config\Config;
use MediaWiki\Context\ContextSource;
use MediaWiki\Context\IContextSource;
use MediaWiki\Context\RequestContext;
use MediaWiki\MediaWikiServices;
use MediaWiki\Utils\UrlUtils;
use MobileFrontend\Devices\DeviceDetectorService;
use MobileFrontend\WMFBaseDomainExtractor;

/**
 * Provide various request-dependant methods to use in mobile context
 */
class MobileContext extends ContextSource {
    public const MODE_BETA = 'beta';
    public const MODE_STABLE = 'stable';
    public const OPTIN_COOKIE_NAME = 'optin';
    public const STOP_MOBILE_REDIRECT_COOKIE_NAME = 'stopMobileRedirect';
    public const USEFORMAT_COOKIE_NAME = 'mf_useformat';
    public const USER_MODE_PREFERENCE_NAME = 'mfMode';

    // Keep in sync with https://wikitech.wikimedia.org/wiki/X-Analytics.
    private const ANALYTICS_HEADER_KEY = 'mf-m';
    private const ANALYTICS_HEADER_DELIMITER = ',';
    private const ANALYTICS_HEADER_VALUE_BETA = 'b';
    private const ANALYTICS_HEADER_VALUE_AMC = 'amc';

    /**
     * Saves the testing mode user has opted in: 'beta' or 'stable'
     * @var string|null
     */
    protected $mobileMode = null;

    /**
     * Save explicitly requested format
     * @var string|null
     */
    protected $useFormat = null;

    /**
     * Key/value pairs of things to add to X-Analytics response header for analytics
     * @var array[]
     */
    protected $analyticsLogItems = [];

    /**
     * The memoized result of `MobileContext#isMobileDevice`.
     *
     * This defaults to `null`, meaning that `MobileContext#isMobileDevice` has
     * yet to be called.
     *
     * @see MobileContext#isMobileDevice
     *
     * @var bool|null
     */
    private $isMobileDevice = null;

    /**
     * Saves requested Mobile action
     * @var string|null
     */
    protected $mobileAction = null;

    /**
     * Save whether mobile view is explicitly requested
     * @var bool
     */
    private $forceMobileView = false;

    /**
     * Save whether or not we should display the mobile view
     * @var bool|null
     */
    private $mobileView = null;

    /**
     * Have we already checked for desktop/mobile view toggling?
     * @var bool
     */
    private $toggleViewChecked = false;

    /**
     * @var self|null
     */
    private static $instance = null;

    /**
     * @var string|null What to switch the view to
     */
    private $viewChange = null;

    /**
     * @var string|null Domain to use for the stopMobileRedirect cookie
     */
    public static $mfStopRedirectCookieHost = null;

    /**
     * In-process cache for checking whether the current wiki has a mobile URL that's
     * different from the desktop one.
     * @var bool|null
     */
    private $hasMobileUrl = null;

    /**
     * @var Config
     */
    private $config;

    /**
     * Returns the actual MobileContext Instance or create a new if no exists
     * @deprecated use MediaWikiServices::getInstance()->getService( 'MobileFrontend.Context' );
     * @return self
     */
    public static function singleton() {
        if ( !self::$instance ) {
            self::$instance = new self(
                RequestContext::getMain(),
                MediaWikiServices::getInstance()->getService( 'MobileFrontend.Config' )
            );
        }
        return self::$instance;
    }

    /**
     * Resets the singleton instance.
     */
    public static function resetInstanceForTesting() {
        self::$instance = null;
    }

    /**
     * @param IContextSource $context
     * @param Config $config
     */
    protected function __construct( IContextSource $context, Config $config ) {
        $this->setContext( $context );
        $this->config = $config;
    }

    /**
     * Detects whether the UA is sending the request from a device and, if so,
     * whether to display the mobile view to that device.
     *
     * The mobile view will always be displayed to mobile devices. However, it
     * will only be displayed to tablet devices if `$wgMFShowMobileViewToTablets`
     * is truthy.
     *
     * @fixme This should be renamed to something more appropriate, e.g.
     * `shouldDisplayMobileViewToDevice`.
     *
     * @see MobileContext::shouldDisplayMobileView
     *
     * @return bool
     */
    public function isMobileDevice() {
        if ( $this->isMobileDevice !== null ) {
            return $this->isMobileDevice;
        }

        $this->isMobileDevice = false;

        $properties = DeviceDetectorService::factory( $this->config )
            ->detectDeviceProperties( $this->getRequest(), $_SERVER );

        if ( $properties ) {
            $showMobileViewToTablets = $this->config->get( 'MFShowMobileViewToTablets' );

            $this->isMobileDevice =
                $properties->isMobileDevice()
                || ( $properties->isTabletDevice() && $showMobileViewToTablets );
        }

        return $this->isMobileDevice;
    }

    /**
     * Save whether mobile view should always be enforced
     * @param bool $value should mobile view be enforced?
     */
    public function setForceMobileView( $value ) {
        $this->forceMobileView = $value;
    }

    /**
     * Sets the value of $this->mobileMode property to the value of the 'optin' cookie.
     * If the cookie is not set the value will be an empty string.
     */
    private function loadMobileModeCookie() {
        $this->mobileMode = $this->getRequest()->getCookie( self::OPTIN_COOKIE_NAME, '' );
    }

    /**
     * Returns the testing mode user has opted in: 'beta' or any other value for stable
     * @return string
     */
    private function getMobileMode() {
        $enableBeta = $this->config->get( 'MFEnableBeta' );

        if ( !$enableBeta ) {
            return '';
        }
        if ( $this->mobileMode === null ) {
            $mobileAction = $this->getMobileAction();
            if ( $mobileAction === self::MODE_BETA || $mobileAction === self::MODE_STABLE ) {
                $this->mobileMode = $mobileAction;
            } else {
                $user = $this->getUser();
                if ( !$user->isRegistered() ) {
                    $this->loadMobileModeCookie();
                } else {
                    $userOptionManager = MediaWikiServices::getInstance()->getUserOptionsManager();
                    $mode = $userOptionManager->getOption( $user, self::USER_MODE_PREFERENCE_NAME );
                    $this->mobileMode = $mode;
                    // Edge case where preferences are corrupt or the user opted
                    // in before change.
                    if ( $mode === null ) {
                        // Should we set the user option here?
                        $this->loadMobileModeCookie();
                    }
                }
            }
        }
        return $this->mobileMode;
    }

    /**
     * Sets testing group membership, both cookie and this class variables
     *
     * WARNING: Does not persist the updated user preference to the database.
     * The caller must handle this by calling User::saveSettings() after all
     * preference updates associated with this web request are made.
     *
     * @param string $mode Mode to set
     */
    public function setMobileMode( $mode ) {
        if ( $mode !== self::MODE_BETA ) {
            $mode = '';
        }
        $services = MediaWikiServices::getInstance();
        $this->mobileMode = $mode;

        $user = $this->getUser();
        if ( $user->getId() ) {
            $userOptionsManager = $services->getUserOptionsManager();
            $userOptionsManager->setOption(
                $user,
                self::USER_MODE_PREFERENCE_NAME,
                $mode
            );
        }

        $this->getRequest()->response()->setCookie( self::OPTIN_COOKIE_NAME, $mode, 0, [
            'prefix' => '',
            'domain' => $this->getCookieDomain()
        ] );
    }

    /**
     * Whether user is Beta group member
     * @return bool
     */
    public function isBetaGroupMember() {
        return $this->getMobileMode() === self::MODE_BETA;
    }

    /**
     * Whether the current user is has advanced mobile contributions enabled.
     * @return bool
     */
    private static function isAmcUser() {
        $services = MediaWikiServices::getInstance();
        /** @var \MobileFrontend\Amc\UserMode $userMode */
        $userMode = $services->getService( 'MobileFrontend.AMC.UserMode' );
        return $userMode->isEnabled();
    }

    /**
     * Determine whether or not we should display the mobile view
     *
     * Step through the hierarchy of what should or should not trigger
     * the mobile view.
     *
     * Primacy is given to the page action - we will never show mobile view
     * for page edits or page history. 'userformat' request param is then
     * honored, followed by cookie settings, then actual device detection,
     * finally falling back on false.
     * @return bool
     */
    public function shouldDisplayMobileView() {
        if ( $this->mobileView !== null ) {
            return $this->mobileView;
        }
        // check if we need to toggle between mobile/desktop view
        $this->checkToggleView();
        $this->mobileView = $this->shouldDisplayMobileViewInternal();
        return $this->mobileView;
    }

    /**
     * Value for shouldDisplayMobileView()
     * @return bool
     */
    private function shouldDisplayMobileViewInternal() {
        // May be overridden programmatically
        if ( $this->forceMobileView ) {
            return true;
        }

        // always display desktop or mobile view if it's explicitly requested
        $useFormat = $this->getUseFormat();
        if ( $useFormat == 'desktop' ) {
            return false;
        } elseif ( $useFormat == 'mobile' ) {
            return true;
        }

        if ( $this->getRequest()->getRawVal( 'mobileformat' ) !== null ) {
            return true;
        }

        /**
         * If a user is accessing the site from a mobile domain, then we should
         * always display the mobile version of the site (otherwise, the cache
         * may get polluted). See
         * https://phabricator.wikimedia.org/T48473
         */
        if ( $this->usingMobileDomain() ) {
            return true;
        }

        // check cookies for what to display
        $useMobileFormat = $this->getUseFormatCookie();
        if ( $useMobileFormat == 'true' ) {
            return true;
        }
        $stopMobileRedirect = $this->getStopMobileRedirectCookie();
        if ( $stopMobileRedirect == 'true' ) {
            return false;
        }

        // do device detection
        if ( $this->isMobileDevice() ) {
            return true;
        }

        return false;
    }

    /**
     * Get requested mobile action
     * @return string
     */
    public function getMobileAction() {
        if ( $this->mobileAction === null ) {
            $this->mobileAction = $this->getRequest()->getRawVal( 'mobileaction' );
        }

        return $this->mobileAction;
    }

    /**
     * Gets the value of the `useformat` query string parameter.
     *
     * @return string Typically "desktop" or "mobile"
     */
    private function getUseFormat() {
        if ( $this->useFormat === null ) {
            $this->useFormat = $this->getRequest()->getRawVal( 'useformat' );
        }
        return $this->useFormat;
    }

    /**
     * Set Cookie to stop automatically redirect to mobile page
     * @param int|null $expiry Expire time of cookie
     */
    public function setStopMobileRedirectCookie( $expiry = null ) {
        $stopMobileRedirectCookieSecureValue =
            $this->config->get( 'MFStopMobileRedirectCookieSecureValue' );

        $this->getRequest()->response()->setCookie(
            self::STOP_MOBILE_REDIRECT_COOKIE_NAME,
            'true',
            $expiry ?? $this->getUseFormatCookieExpiry(),
            [
                'domain' => $this->getStopMobileRedirectCookieDomain(),
                'prefix' => '',
                'secure' => (bool)$stopMobileRedirectCookieSecureValue,
            ]
        );
    }

    /**
     * Remove cookie and continue automatic redirect to mobile page
     */
    public function unsetStopMobileRedirectCookie() {
        if ( $this->getStopMobileRedirectCookie() === null ) {
            return;
        }
        $expire = $this->getUseFormatCookieExpiry( time(), -3600 );
        $this->setStopMobileRedirectCookie( $expire );
    }

    /**
     * Read cookie for stop automatic mobile redirect
     * @return string
     */
    public function getStopMobileRedirectCookie() {
        $stopMobileRedirectCookie = $this->getRequest()
            ->getCookie( self::STOP_MOBILE_REDIRECT_COOKIE_NAME, '' );

        return $stopMobileRedirectCookie;
    }

    /**
     * This cookie can determine whether or not a user should see the mobile
     * version of a page.
     *
     * @return string|null
     */
    public function getUseFormatCookie() {
        $useFormatFromCookie = $this->getRequest()->getCookie( self::USEFORMAT_COOKIE_NAME, '' );

        return $useFormatFromCookie;
    }

    /**
     * Return the base level domain or IP address
     *
     * @return string|null
     */
    public function getCookieDomain() {
        $helper = new WMFBaseDomainExtractor();
        return $helper->getCookieDomain( $this->config->get( 'Server' ) );
    }

    /**
     * Determine the correct domain to use for the stopMobileRedirect cookie
     *
     * Will use $wgMFStopRedirectCookieHost if it's set, otherwise will use
     * result of getCookieDomain()
     * @return string|null
     */
    public function getStopMobileRedirectCookieDomain() {
        $mfStopRedirectCookieHost = $this->config->get( 'MFStopRedirectCookieHost' );

        if ( !$mfStopRedirectCookieHost ) {
            self::$mfStopRedirectCookieHost = $this->getCookieDomain();
        } else {
            self::$mfStopRedirectCookieHost = $mfStopRedirectCookieHost;
        }

        return self::$mfStopRedirectCookieHost;
    }

    /**
     * Set the mf_useformat cookie
     *
     * This cookie can determine whether or not a user should see the mobile
     * version of pages.
     *
     * @param string $cookieFormat should user see mobile version of pages?
     * @param int|null $expiry Expiration of cookie
     */
    public function setUseFormatCookie( $cookieFormat = 'true', $expiry = null ) {
        $this->getRequest()->response()->setCookie(
            self::USEFORMAT_COOKIE_NAME,
            $cookieFormat,
            $expiry ?? $this->getUseFormatCookieExpiry(),
            [
                'prefix' => '',
                'httpOnly' => true,
            ]
        );
        $stats = MediaWikiServices::getInstance()->getStatsdDataFactory();
        $stats->updateCount( 'mobile.useformat_' . $cookieFormat . '_cookie_set', 1 );
    }

    /**
     * Remove cookie based saved useformat value
     */
    public function unsetUseFormatCookie() {
        if ( $this->getUseFormatCookie() === null ) {
            return;
        }

        // set expiration date in the past
        $expire = $this->getUseFormatCookieExpiry( time(), -3600 );
        $this->setUseFormatCookie( '', $expire );
    }

    /**
     * Get the expiration time for the mf_useformat cookie
     *
     * @param int|null $startTime The base time (in seconds since Epoch) from which to calculate
     *         cookie expiration. If null, time() is used.
     * @param int|null $cookieDuration The time (in seconds) the cookie should last
     * @return int The time (in seconds since Epoch) that the cookie should expire
     */
    protected function getUseFormatCookieExpiry( $startTime = null, $cookieDuration = null ) {
        // use $cookieDuration if it's valid
        if ( intval( $cookieDuration ) === 0 ) {
            $cookieDuration = $this->getUseFormatCookieDuration();
        }

        // use $startTime if it's valid
        if ( intval( $startTime ) === 0 ) {
            $startTime = time();
        }

        $expiry = $startTime + $cookieDuration;
        return $expiry;
    }

    /**
     * Determine the duration the cookie should last.
     *
     * If $wgMobileFrontendFormatcookieExpiry has a non-0 value, use that
     * for the duration. Otherwise, fall back to $wgCookieExpiration.
     *
     * @return int The number of seconds for which the cookie should last.
     */
    public function getUseFormatCookieDuration() {
        $mobileFrontendFormatCookieExpiry =
            $this->config->get( 'MobileFrontendFormatCookieExpiry' );

        $cookieExpiration = $this->getConfig()->get( 'CookieExpiration' );

        $cookieDuration = ( abs( intval( $mobileFrontendFormatCookieExpiry ) ) > 0 ) ?
            $mobileFrontendFormatCookieExpiry : $cookieExpiration;
        return $cookieDuration;
    }

    /**
     * Returns the callback from $wgMobileUrlCallback, which changes
     *   a desktop domain into a mobile domain.
     * @return callable|null
     * @phan-return callable(string):string|null
     */
    private function getMobileUrlCallback(): ?callable {
        return $this->config->get( 'MobileUrlCallback' );
    }

    /**
     * True if the current wiki has separate mobile and desktop domains (regardless
     * of which domain is used by the current request).
     * @return bool
     */
    public function hasMobileDomain(): bool {
        if ( $this->hasMobileUrl === null ) {
            $mobileUrlCallback = $this->getMobileUrlCallback();
            if ( $mobileUrlCallback ) {
                $urlUtils = MediaWikiServices::getInstance()->getUrlUtils();
                $server = $urlUtils->expand( $this->getConfig()->get( 'Server' ), PROTO_CANONICAL ) ?? '';
                $host = $urlUtils->parse( $server )['host'] ?? '';
                $mobileDomain = call_user_func( $mobileUrlCallback, $host );
                $this->hasMobileUrl = $mobileDomain !== $host;
            } else {
                $this->hasMobileUrl = false;
            }
        }
        return $this->hasMobileUrl;
    }

    /**
     * Take a URL and return the equivalent mobile URL (ie. replace the domain with the
     * mobile domain).
     *
     * Typically this is a URL for the current wiki, but it can be anything as long as
     * $wgMobileUrlCallback can convert its domain (so e.g. interwiki links can be
     * converted). If the domain is already a mobile domain, or not recognized by
     * $wgMobileUrlCallback, or the wiki does not use mobile domains and so
     * $wgMobileUrlCallback is not set, the URL will be returned unchanged (except
     * $forceHttps will still be applied).
     *
     * @param string $url URL to convert
     * @param bool $forceHttps Force HTTPS, even if the original URL used HTTP
     * @return string|bool
     */
    public function getMobileUrl( $url, $forceHttps = false ) {
        $urlUtils = MediaWikiServices::getInstance()->getUrlUtils();
        $parsedUrl = $urlUtils->parse( $url );
        // if parsing failed, maybe it's a local Url, try to expand and reparse it - task T107505
        if ( !$parsedUrl ) {
            $expandedUrl = $urlUtils->expand( $url, PROTO_CURRENT );
            if ( $expandedUrl ) {
                $parsedUrl = $urlUtils->parse( $expandedUrl );
            }
            if ( !$expandedUrl || !$parsedUrl ) {
                return false;
            }
        }

        $mobileUrlCallback = $this->getMobileUrlCallback();
        if ( $mobileUrlCallback ) {
            $parsedUrl['host'] = call_user_func( $mobileUrlCallback, $parsedUrl['host'] );
        }
        if ( $forceHttps ) {
            $parsedUrl['scheme'] = 'https';
            $parsedUrl['delimiter'] = '://';
        }

        $assembleUrl = UrlUtils::assemble( $parsedUrl );
        return $assembleUrl;
    }

    /**
     * Checks whether the current request is using the mobile domain.
     *
     * This assumes that some infrastructure outside MediaWiki will set a
     * header (specified by $wgMFMobileHeader) on requests which use the
     * mobile domain. This means that the traffic routing layer can rewrite
     * hostnames to be canonical, so non-MobileFrontend-aware code can still
     * work.
     *
     * @return bool
     */
    public function usingMobileDomain() {
        $mobileHeader = $this->config->get( 'MFMobileHeader' );
        return ( $this->hasMobileDomain()
            && $mobileHeader
            && $this->getRequest()->getHeader( $mobileHeader ) !== false
        );
    }

    /**
     * Take a URL and return a copy that removes any mobile tokens.
     *
     * This only works with URLs of the current wiki.
     *
     * @param string $url representing a page on the mobile domain e.g. `https://en.m.wikipedia.org/`
     * @return string (absolute url)
     */
    public function getDesktopUrl( $url ) {
        $urlUtils = MediaWikiServices::getInstance()->getUrlUtils();
        $parsedUrl = $urlUtils->parse( $url ) ?? [];
        $this->updateDesktopUrlHost( $parsedUrl );
        $this->updateDesktopUrlQuery( $parsedUrl );
        $desktopUrl = UrlUtils::assemble( $parsedUrl );
        return $desktopUrl;
    }

    /**
     * Update the host of a given URL to strip out any mobile tokens
     * @param array &$parsedUrl Result of parseUrl() or UrlUtils::parse()
     */
    protected function updateDesktopUrlHost( array &$parsedUrl ) {
        $server = $this->getConfig()->get( 'Server' );

        if ( !$this->hasMobileDomain() ) {
            return;
        }

        $urlUtils = MediaWikiServices::getInstance()->getUrlUtils();
        $parsedWgServer = $urlUtils->parse( $server );
        $parsedUrl['host'] = $parsedWgServer['host'] ?? '';
    }

    /**
     * Update the query portion of a given URL to remove any 'useformat' params
     * @param array &$parsedUrl Result of parseUrl() or UrlUtils::parse()
     */
    protected function updateDesktopUrlQuery( array &$parsedUrl ) {
        if ( isset( $parsedUrl['query'] ) && strpos( $parsedUrl['query'], 'useformat' ) !== false ) {
            $query = wfCgiToArray( $parsedUrl['query'] );
            unset( $query['useformat'] );
            $parsedUrl['query'] = wfArrayToCgi( $query );
        }
    }

    /**
     * Toggles view to one specified by the user
     *
     * If a user has requested a particular view (eg clicked 'Desktop' from
     * a mobile page), set the requested view for this particular request
     * and set a cookie to keep them on that view for subsequent requests.
     *
     * @param string $view User requested particular view
     */
    public function toggleView( $view ) {
        $this->viewChange = $view;
        if ( !$this->hasMobileDomain() ) {
            $this->useFormat = $view;
        }
    }

    /**
     * Performs view change as requested vy toggleView()
     */
    public function doToggling() {
        // make sure viewChange is set
        $this->shouldDisplayMobileView();

        if ( !$this->viewChange ) {
            return;
        }

        $title = $this->getTitle();
        if ( !$title ) {
            return;
        }

        $query = $this->getRequest()->getQueryValues();
        unset( $query['mobileaction'] );
        unset( $query['useformat'] );
        unset( $query['title'] );
        $url = $title->getFullURL( $query, false, PROTO_CURRENT );

        if ( $this->viewChange == 'mobile' ) {
            // unset stopMobileRedirect cookie
            // @TODO is this necessary with unsetting the cookie via JS?
            $this->unsetStopMobileRedirectCookie();

            // if no mobile domain support, set mobile cookie
            if ( !$this->hasMobileDomain() ) {
                $this->setUseFormatCookie();
            } else {
                // else redirect to mobile domain
                $mobileUrl = $this->getMobileUrl( $url );
                $this->getOutput()->redirect( $mobileUrl, 301 );
            }
        } elseif ( $this->viewChange == 'desktop' ) {
            // set stopMobileRedirect cookie
            $this->setStopMobileRedirectCookie();
            // unset useformat cookie
            if ( $this->getUseFormatCookie() == "true" ) {
                $this->unsetUseFormatCookie();
            }

            if ( $this->hasMobileDomain() ) {
                // if there is mobile domain support, redirect to desktop domain
                $desktopUrl = $this->getDesktopUrl( $url );
                $this->getOutput()->redirect( $desktopUrl, 301 );
            }
        }
    }

    /**
     * Determine whether or not we need to toggle the view, and toggle it
     */
    public function checkToggleView() {
        if ( !$this->toggleViewChecked ) {
            $this->toggleViewChecked = true;
            $mobileAction = $this->getMobileAction();
            if ( $mobileAction == 'toggle_view_desktop' ) {
                $this->toggleView( 'desktop' );
            } elseif ( $mobileAction == 'toggle_view_mobile' ) {
                $this->toggleView( 'mobile' );
            }
        }
    }

    /**
     * Determine whether or not a given URL is local
     *
     * @param string $url URL to check against
     * @return bool
     */
    public function isLocalUrl( $url ) {
        $urlUtils = MediaWikiServices::getInstance()->getUrlUtils();
        $parsedTargetHost = $urlUtils->parse( $url )['host'] ?? '';
        $parsedServerHost = $urlUtils->parse( $this->config->get( 'Server' ) )['host'] ?? '';
        return $parsedTargetHost === $parsedServerHost;
    }

    /**
     * Add key/value pairs for analytics purposes to $this->analyticsLogItems. Pre-existing entries
     * are appended to as sets delimited by commas.
     * @param string $key for <key> in `X-Analytics: <key>=<value>`
     * @param string $val for <value> in `X-Analytics: <key>=<value>`
     */
    public function addAnalyticsLogItem( $key, $val ) {
        $key = trim( $key );
        $val = trim( $val );
        $items = $this->analyticsLogItems[$key] ?? [];
        if ( !in_array( $val, $items ) ) {
            $items[] = $val;
            $this->analyticsLogItems[$key] = $items;
        }
    }

    /**
     * Read key/value pairs for analytics purposes from $this->analyticsLogItems
     * @return array
     */
    public function getAnalyticsLogItems() {
        return array_map(
            static function ( $val ) {
                return implode( self::ANALYTICS_HEADER_DELIMITER, $val );
            },
            $this->analyticsLogItems
        );
    }

    /**
     * Get HTTP header string for X-Analytics
     *
     * This is made up of key/value pairs and is used for analytics purposes.
     *
     * @return string|bool
     */
    public function getXAnalyticsHeader() {
        $response = $this->getRequest()->response();
        $currentHeader = method_exists( $response, 'getHeader' ) ?
            (string)$response->getHeader( 'X-Analytics' ) : '';
        parse_str( preg_replace( '/; */', '&', $currentHeader ), $logItems );
        $logItems += $this->getAnalyticsLogItems();
        if ( count( $logItems ) ) {
            $xanalytics_items = [];
            foreach ( $logItems as $key => $val ) {
                $xanalytics_items[] = urlencode( $key ) . "=" . urlencode( $val );
            }
            $headerValue = implode( ';', $xanalytics_items );
            return "X-Analytics: $headerValue";
        } else {
            return false;
        }
    }

    /**
     * Take a key/val pair in string format and add it to $this->analyticsLogItems
     *
     * @param string $xanalytics_item In the format key=value
     */
    public function addAnalyticsLogItemFromXAnalytics( $xanalytics_item ) {
        [ $key, $val ] = explode( '=', $xanalytics_item, 2 );
        $this->addAnalyticsLogItem( urldecode( $key ), urldecode( $val ) );
    }

    /**
     * Adds analytics log items depending on which modes are enabled for the user
     *
     * Invoked from MobileFrontendHooks::onRequestContextCreateSkin()
     *
     * Making changes to what this method logs? Make sure you update the
     * documentation for the X-Analytics header: https://wikitech.wikimedia.org/wiki/X-Analytics
     */
    public function logMobileMode() {
        if ( $this->isBetaGroupMember() ) {
            $this->addAnalyticsLogItem( self::ANALYTICS_HEADER_KEY, self::ANALYTICS_HEADER_VALUE_BETA );
        }
        if ( self::isAmcUser() ) {
            $this->addAnalyticsLogItem( self::ANALYTICS_HEADER_KEY, self::ANALYTICS_HEADER_VALUE_AMC );
        }
    }

    /**
     * Gets whether Wikibase descriptions should be shown in search results,
     * and watchlists; or as taglines on article pages.
     * Doesn't take into account whether the wikidata descriptions
     * feature has been enabled.
     *
     * @param string $feature which description to show?
     * @param Config $config
     * @return bool
     * @throws DomainException If `feature` isn't one that shows Wikidata descriptions. See the
     *  `wgMFDisplayWikibaseDescriptions` configuration variable for detail
     */
    public function shouldShowWikibaseDescriptions( $feature, Config $config ) {
        $displayWikibaseDescriptions = $config->get( 'MFDisplayWikibaseDescriptions' );
        if ( !isset( $displayWikibaseDescriptions[$feature] ) ) {
            throw new DomainException(
                "\"{$feature}\" isn't a feature that shows Wikidata descriptions."
            );
        }

        return $displayWikibaseDescriptions[$feature];
    }
}