Merge "Remove unused messages 'edit-externally' and 'edit-externally-help'"

[mediawiki.git] / includes / cache / LocalisationCache.php

<?php
/**
 * Cache of the contents of localisation files.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

define( 'MW_LC_VERSION', 2 );

/**
 * Class for caching the contents of localisation files, Messages*.php
 * and *.i18n.php.
 *
 * An instance of this class is available using Language::getLocalisationCache().
 *
 * The values retrieved from here are merged, containing items from extension
 * files, core messages files and the language fallback sequence (e.g. zh-cn ->
 * zh-hans -> en ). Some common errors are corrected, for example namespace
 * names with spaces instead of underscores, but heavyweight processing, such
 * as grammatical transformation, is done by the caller.
 */
class LocalisationCache {
        /** Configuration associative array */
        private $conf;

        /**
         * True if recaching should only be done on an explicit call to recache().
         * Setting this reduces the overhead of cache freshness checking, which
         * requires doing a stat() for every extension i18n file.
         */
        private $manualRecache = false;

        /**
         * True to treat all files as expired until they are regenerated by this object.
         */
        private $forceRecache = false;

        /**
         * The cache data. 3-d array, where the first key is the language code,
         * the second key is the item key e.g. 'messages', and the third key is
         * an item specific subkey index. Some items are not arrays and so for those
         * items, there are no subkeys.
         */
        protected $data = array();

        /**
         * The persistent store object. An instance of LCStore.
         *
         * @var LCStore
         */
        private $store;

        /**
         * A 2-d associative array, code/key, where presence indicates that the item
         * is loaded. Value arbitrary.
         *
         * For split items, if set, this indicates that all of the subitems have been
         * loaded.
         */
        private $loadedItems = array();

        /**
         * A 3-d associative array, code/key/subkey, where presence indicates that
         * the subitem is loaded. Only used for the split items, i.e. messages.
         */
        private $loadedSubitems = array();

        /**
         * An array where presence of a key indicates that that language has been
         * initialised. Initialisation includes checking for cache expiry and doing
         * any necessary updates.
         */
        private $initialisedLangs = array();

        /**
         * An array mapping non-existent pseudo-languages to fallback languages. This
         * is filled by initShallowFallback() when data is requested from a language
         * that lacks a Messages*.php file.
         */
        private $shallowFallbacks = array();

        /**
         * An array where the keys are codes that have been recached by this instance.
         */
        private $recachedLangs = array();

        /**
         * All item keys
         */
        static public $allKeys = array(
                'fallback', 'namespaceNames', 'bookstoreList',
                'magicWords', 'messages', 'rtl', 'capitalizeAllNouns', 'digitTransformTable',
                'separatorTransformTable', 'fallback8bitEncoding', 'linkPrefixExtension',
                'linkTrail', 'linkPrefixCharset', 'namespaceAliases',
                'dateFormats', 'datePreferences', 'datePreferenceMigrationMap',
                'defaultDateFormat', 'extraUserToggles', 'specialPageAliases',
                'imageFiles', 'preloadedMessages', 'namespaceGenderAliases',
                'digitGroupingPattern', 'pluralRules', 'pluralRuleTypes', 'compiledPluralRules',
        );

        /**
         * Keys for items which consist of associative arrays, which may be merged
         * by a fallback sequence.
         */
        static public $mergeableMapKeys = array( 'messages', 'namespaceNames',
                'dateFormats', 'imageFiles', 'preloadedMessages'
        );

        /**
         * Keys for items which are a numbered array.
         */
        static public $mergeableListKeys = array( 'extraUserToggles' );

        /**
         * Keys for items which contain an array of arrays of equivalent aliases
         * for each subitem. The aliases may be merged by a fallback sequence.
         */
        static public $mergeableAliasListKeys = array( 'specialPageAliases' );

        /**
         * Keys for items which contain an associative array, and may be merged if
         * the primary value contains the special array key "inherit". That array
         * key is removed after the first merge.
         */
        static public $optionalMergeKeys = array( 'bookstoreList' );

        /**
         * Keys for items that are formatted like $magicWords
         */
        static public $magicWordKeys = array( 'magicWords' );

        /**
         * Keys for items where the subitems are stored in the backend separately.
         */
        static public $splitKeys = array( 'messages' );

        /**
         * Keys which are loaded automatically by initLanguage()
         */
        static public $preloadedKeys = array( 'dateFormats', 'namespaceNames' );

        /**
         * Associative array of cached plural rules. The key is the language code,
         * the value is an array of plural rules for that language.
         */
        private $pluralRules = null;

        /**
         * Associative array of cached plural rule types. The key is the language
         * code, the value is an array of plural rule types for that language. For
         * example, $pluralRuleTypes['ar'] = ['zero', 'one', 'two', 'few', 'many'].
         * The index for each rule type matches the index for the rule in
         * $pluralRules, thus allowing correlation between the two. The reason we
         * don't just use the type names as the keys in $pluralRules is because
         * Language::convertPlural applies the rules based on numeric order (or
         * explicit numeric parameter), not based on the name of the rule type. For
         * example, {{plural:count|wordform1|wordform2|wordform3}}, rather than
         * {{plural:count|one=wordform1|two=wordform2|many=wordform3}}.
         */
        private $pluralRuleTypes = null;

        private $mergeableKeys = null;

        /**
         * Constructor.
         * For constructor parameters, see the documentation in DefaultSettings.php
         * for $wgLocalisationCacheConf.
         *
         * @param $conf Array
         * @throws MWException
         */
        function __construct( $conf ) {
                global $wgCacheDirectory;

                $this->conf = $conf;
                $storeConf = array();
                if ( !empty( $conf['storeClass'] ) ) {
                        $storeClass = $conf['storeClass'];
                } else {
                        switch ( $conf['store'] ) {
                                case 'files':
                                case 'file':
                                        $storeClass = 'LCStoreCDB';
                                        break;
                                case 'db':
                                        $storeClass = 'LCStoreDB';
                                        break;
                                case 'accel':
                                        $storeClass = 'LCStoreAccel';
                                        break;
                                case 'detect':
                                        $storeClass = $wgCacheDirectory ? 'LCStoreCDB' : 'LCStoreDB';
                                        break;
                                default:
                                        throw new MWException(
                                                'Please set $wgLocalisationCacheConf[\'store\'] to something sensible.' );
                        }
                }

                wfDebug( get_class( $this ) . ": using store $storeClass\n" );
                if ( !empty( $conf['storeDirectory'] ) ) {
                        $storeConf['directory'] = $conf['storeDirectory'];
                }

                $this->store = new $storeClass( $storeConf );
                foreach ( array( 'manualRecache', 'forceRecache' ) as $var ) {
                        if ( isset( $conf[$var] ) ) {
                                $this->$var = $conf[$var];
                        }
                }
        }

        /**
         * Returns true if the given key is mergeable, that is, if it is an associative
         * array which can be merged through a fallback sequence.
         * @param $key
         * @return bool
         */
        public function isMergeableKey( $key ) {
                if ( $this->mergeableKeys === null ) {
                        $this->mergeableKeys = array_flip( array_merge(
                                self::$mergeableMapKeys,
                                self::$mergeableListKeys,
                                self::$mergeableAliasListKeys,
                                self::$optionalMergeKeys,
                                self::$magicWordKeys
                        ) );
                }

                return isset( $this->mergeableKeys[$key] );
        }

        /**
         * Get a cache item.
         *
         * Warning: this may be slow for split items (messages), since it will
         * need to fetch all of the subitems from the cache individually.
         * @param $code
         * @param $key
         * @return mixed
         */
        public function getItem( $code, $key ) {
                if ( !isset( $this->loadedItems[$code][$key] ) ) {
                        wfProfileIn( __METHOD__ . '-load' );
                        $this->loadItem( $code, $key );
                        wfProfileOut( __METHOD__ . '-load' );
                }

                if ( $key === 'fallback' && isset( $this->shallowFallbacks[$code] ) ) {
                        return $this->shallowFallbacks[$code];
                }

                return $this->data[$code][$key];
        }

        /**
         * Get a subitem, for instance a single message for a given language.
         * @param $code
         * @param $key
         * @param $subkey
         * @return null
         */
        public function getSubitem( $code, $key, $subkey ) {
                if ( !isset( $this->loadedSubitems[$code][$key][$subkey] ) &&
                        !isset( $this->loadedItems[$code][$key] )
                ) {
                        wfProfileIn( __METHOD__ . '-load' );
                        $this->loadSubitem( $code, $key, $subkey );
                        wfProfileOut( __METHOD__ . '-load' );
                }

                if ( isset( $this->data[$code][$key][$subkey] ) ) {
                        return $this->data[$code][$key][$subkey];
                } else {
                        return null;
                }
        }

        /**
         * Get the list of subitem keys for a given item.
         *
         * This is faster than array_keys($lc->getItem(...)) for the items listed in
         * self::$splitKeys.
         *
         * Will return null if the item is not found, or false if the item is not an
         * array.
         * @param $code
         * @param $key
         * @return bool|null|string
         */
        public function getSubitemList( $code, $key ) {
                if ( in_array( $key, self::$splitKeys ) ) {
                        return $this->getSubitem( $code, 'list', $key );
                } else {
                        $item = $this->getItem( $code, $key );
                        if ( is_array( $item ) ) {
                                return array_keys( $item );
                        } else {
                                return false;
                        }
                }
        }

        /**
         * Load an item into the cache.
         * @param $code
         * @param $key
         */
        protected function loadItem( $code, $key ) {
                if ( !isset( $this->initialisedLangs[$code] ) ) {
                        $this->initLanguage( $code );
                }

                // Check to see if initLanguage() loaded it for us
                if ( isset( $this->loadedItems[$code][$key] ) ) {
                        return;
                }

                if ( isset( $this->shallowFallbacks[$code] ) ) {
                        $this->loadItem( $this->shallowFallbacks[$code], $key );

                        return;
                }

                if ( in_array( $key, self::$splitKeys ) ) {
                        $subkeyList = $this->getSubitem( $code, 'list', $key );
                        foreach ( $subkeyList as $subkey ) {
                                if ( isset( $this->data[$code][$key][$subkey] ) ) {
                                        continue;
                                }
                                $this->data[$code][$key][$subkey] = $this->getSubitem( $code, $key, $subkey );
                        }
                } else {
                        $this->data[$code][$key] = $this->store->get( $code, $key );
                }

                $this->loadedItems[$code][$key] = true;
        }

        /**
         * Load a subitem into the cache
         * @param $code
         * @param $key
         * @param $subkey
         */
        protected function loadSubitem( $code, $key, $subkey ) {
                if ( !in_array( $key, self::$splitKeys ) ) {
                        $this->loadItem( $code, $key );

                        return;
                }

                if ( !isset( $this->initialisedLangs[$code] ) ) {
                        $this->initLanguage( $code );
                }

                // Check to see if initLanguage() loaded it for us
                if ( isset( $this->loadedItems[$code][$key] ) ||
                        isset( $this->loadedSubitems[$code][$key][$subkey] )
                ) {
                        return;
                }

                if ( isset( $this->shallowFallbacks[$code] ) ) {
                        $this->loadSubitem( $this->shallowFallbacks[$code], $key, $subkey );

                        return;
                }

                $value = $this->store->get( $code, "$key:$subkey" );
                $this->data[$code][$key][$subkey] = $value;
                $this->loadedSubitems[$code][$key][$subkey] = true;
        }

        /**
         * Returns true if the cache identified by $code is missing or expired.
         *
         * @param string $code
         *
         * @return bool
         */
        public function isExpired( $code ) {
                if ( $this->forceRecache && !isset( $this->recachedLangs[$code] ) ) {
                        wfDebug( __METHOD__ . "($code): forced reload\n" );

                        return true;
                }

                $deps = $this->store->get( $code, 'deps' );
                $keys = $this->store->get( $code, 'list' );
                $preload = $this->store->get( $code, 'preload' );
                // Different keys may expire separately, at least in LCStoreAccel
                if ( $deps === null || $keys === null || $preload === null ) {
                        wfDebug( __METHOD__ . "($code): cache missing, need to make one\n" );

                        return true;
                }

                foreach ( $deps as $dep ) {
                        // Because we're unserializing stuff from cache, we
                        // could receive objects of classes that don't exist
                        // anymore (e.g. uninstalled extensions)
                        // When this happens, always expire the cache
                        if ( !$dep instanceof CacheDependency || $dep->isExpired() ) {
                                wfDebug( __METHOD__ . "($code): cache for $code expired due to " .
                                        get_class( $dep ) . "\n" );

                                return true;
                        }
                }

                return false;
        }

        /**
         * Initialise a language in this object. Rebuild the cache if necessary.
         * @param $code
         * @throws MWException
         */
        protected function initLanguage( $code ) {
                if ( isset( $this->initialisedLangs[$code] ) ) {
                        return;
                }

                $this->initialisedLangs[$code] = true;

                # If the code is of the wrong form for a Messages*.php file, do a shallow fallback
                if ( !Language::isValidBuiltInCode( $code ) ) {
                        $this->initShallowFallback( $code, 'en' );

                        return;
                }

                # Recache the data if necessary
                if ( !$this->manualRecache && $this->isExpired( $code ) ) {
                        if ( file_exists( Language::getMessagesFileName( $code ) ) ) {
                                $this->recache( $code );
                        } elseif ( $code === 'en' ) {
                                throw new MWException( 'MessagesEn.php is missing.' );
                        } else {
                                $this->initShallowFallback( $code, 'en' );
                        }

                        return;
                }

                # Preload some stuff
                $preload = $this->getItem( $code, 'preload' );
                if ( $preload === null ) {
                        if ( $this->manualRecache ) {
                                // No Messages*.php file. Do shallow fallback to en.
                                if ( $code === 'en' ) {
                                        throw new MWException( 'No localisation cache found for English. ' .
                                                'Please run maintenance/rebuildLocalisationCache.php.' );
                                }
                                $this->initShallowFallback( $code, 'en' );

                                return;
                        } else {
                                throw new MWException( 'Invalid or missing localisation cache.' );
                        }
                }
                $this->data[$code] = $preload;
                foreach ( $preload as $key => $item ) {
                        if ( in_array( $key, self::$splitKeys ) ) {
                                foreach ( $item as $subkey => $subitem ) {
                                        $this->loadedSubitems[$code][$key][$subkey] = true;
                                }
                        } else {
                                $this->loadedItems[$code][$key] = true;
                        }
                }
        }

        /**
         * Create a fallback from one language to another, without creating a
         * complete persistent cache.
         * @param $primaryCode
         * @param $fallbackCode
         */
        public function initShallowFallback( $primaryCode, $fallbackCode ) {
                $this->data[$primaryCode] =& $this->data[$fallbackCode];
                $this->loadedItems[$primaryCode] =& $this->loadedItems[$fallbackCode];
                $this->loadedSubitems[$primaryCode] =& $this->loadedSubitems[$fallbackCode];
                $this->shallowFallbacks[$primaryCode] = $fallbackCode;
        }

        /**
         * Read a PHP file containing localisation data.
         * @param $_fileName
         * @param $_fileType
         * @throws MWException
         * @return array
         */
        protected function readPHPFile( $_fileName, $_fileType ) {
                wfProfileIn( __METHOD__ );
                // Disable APC caching
                $_apcEnabled = ini_set( 'apc.cache_by_default', '0' );
                include $_fileName;
                ini_set( 'apc.cache_by_default', $_apcEnabled );

                if ( $_fileType == 'core' || $_fileType == 'extension' ) {
                        $data = compact( self::$allKeys );
                } elseif ( $_fileType == 'aliases' ) {
                        $data = compact( 'aliases' );
                } else {
                        wfProfileOut( __METHOD__ );
                        throw new MWException( __METHOD__ . ": Invalid file type: $_fileType" );
                }
                wfProfileOut( __METHOD__ );

                return $data;
        }

        /**
         * Get the compiled plural rules for a given language from the XML files.
         * @since 1.20
         */
        public function getCompiledPluralRules( $code ) {
                $rules = $this->getPluralRules( $code );
                if ( $rules === null ) {
                        return null;
                }
                try {
                        $compiledRules = CLDRPluralRuleEvaluator::compile( $rules );
                } catch ( CLDRPluralRuleError $e ) {
                        wfDebugLog( 'l10n', $e->getMessage() . "\n" );

                        return array();
                }

                return $compiledRules;
        }

        /**
         * Get the plural rules for a given language from the XML files.
         * Cached.
         * @since 1.20
         */
        public function getPluralRules( $code ) {
                if ( $this->pluralRules === null ) {
                        $this->loadPluralFiles();
                }
                if ( !isset( $this->pluralRules[$code] ) ) {
                        return null;
                } else {
                        return $this->pluralRules[$code];
                }
        }

        /**
         * Get the plural rule types for a given language from the XML files.
         * Cached.
         * @since 1.22
         */
        public function getPluralRuleTypes( $code ) {
                if ( $this->pluralRuleTypes === null ) {
                        $this->loadPluralFiles();
                }
                if ( !isset( $this->pluralRuleTypes[$code] ) ) {
                        return null;
                } else {
                        return $this->pluralRuleTypes[$code];
                }
        }

        /**
         * Load the plural XML files.
         */
        protected function loadPluralFiles() {
                global $IP;
                $cldrPlural = "$IP/languages/data/plurals.xml";
                $mwPlural = "$IP/languages/data/plurals-mediawiki.xml";
                // Load CLDR plural rules
                $this->loadPluralFile( $cldrPlural );
                if ( file_exists( $mwPlural ) ) {
                        // Override or extend
                        $this->loadPluralFile( $mwPlural );
                }
        }

        /**
         * Load a plural XML file with the given filename, compile the relevant
         * rules, and save the compiled rules in a process-local cache.
         */
        protected function loadPluralFile( $fileName ) {
                $doc = new DOMDocument;
                $doc->load( $fileName );
                $rulesets = $doc->getElementsByTagName( "pluralRules" );
                foreach ( $rulesets as $ruleset ) {
                        $codes = $ruleset->getAttribute( 'locales' );
                        $rules = array();
                        $ruleTypes = array();
                        $ruleElements = $ruleset->getElementsByTagName( "pluralRule" );
                        foreach ( $ruleElements as $elt ) {
                                $ruleType = $elt->getAttribute( 'count' );
                                $rules[] = $elt->nodeValue;
                                $ruleTypes[] = $ruleType;
                        }
                        foreach ( explode( ' ', $codes ) as $code ) {
                                $this->pluralRules[$code] = $rules;
                                $this->pluralRuleTypes[$code] = $ruleTypes;
                        }
                }
        }

        /**
         * Read the data from the source files for a given language, and register
         * the relevant dependencies in the $deps array. If the localisation
         * exists, the data array is returned, otherwise false is returned.
         */
        protected function readSourceFilesAndRegisterDeps( $code, &$deps ) {
                global $IP;
                wfProfileIn( __METHOD__ );

                $fileName = Language::getMessagesFileName( $code );
                if ( !file_exists( $fileName ) ) {
                        wfProfileOut( __METHOD__ );

                        return false;
                }

                $deps[] = new FileDependency( $fileName );
                $data = $this->readPHPFile( $fileName, 'core' );

                # Load CLDR plural rules for JavaScript
                $data['pluralRules'] = $this->getPluralRules( $code );
                # And for PHP
                $data['compiledPluralRules'] = $this->getCompiledPluralRules( $code );
                # Load plural rule types
                $data['pluralRuleTypes'] = $this->getPluralRuleTypes( $code );

                $deps['plurals'] = new FileDependency( "$IP/languages/data/plurals.xml" );
                $deps['plurals-mw'] = new FileDependency( "$IP/languages/data/plurals-mediawiki.xml" );

                wfProfileOut( __METHOD__ );

                return $data;
        }

        /**
         * Merge two localisation values, a primary and a fallback, overwriting the
         * primary value in place.
         * @param $key
         * @param $value
         * @param $fallbackValue
         */
        protected function mergeItem( $key, &$value, $fallbackValue ) {
                if ( !is_null( $value ) ) {
                        if ( !is_null( $fallbackValue ) ) {
                                if ( in_array( $key, self::$mergeableMapKeys ) ) {
                                        $value = $value + $fallbackValue;
                                } elseif ( in_array( $key, self::$mergeableListKeys ) ) {
                                        $value = array_unique( array_merge( $fallbackValue, $value ) );
                                } elseif ( in_array( $key, self::$mergeableAliasListKeys ) ) {
                                        $value = array_merge_recursive( $value, $fallbackValue );
                                } elseif ( in_array( $key, self::$optionalMergeKeys ) ) {
                                        if ( !empty( $value['inherit'] ) ) {
                                                $value = array_merge( $fallbackValue, $value );
                                        }

                                        if ( isset( $value['inherit'] ) ) {
                                                unset( $value['inherit'] );
                                        }
                                } elseif ( in_array( $key, self::$magicWordKeys ) ) {
                                        $this->mergeMagicWords( $value, $fallbackValue );
                                }
                        }
                } else {
                        $value = $fallbackValue;
                }
        }

        /**
         * @param $value
         * @param $fallbackValue
         */
        protected function mergeMagicWords( &$value, $fallbackValue ) {
                foreach ( $fallbackValue as $magicName => $fallbackInfo ) {
                        if ( !isset( $value[$magicName] ) ) {
                                $value[$magicName] = $fallbackInfo;
                        } else {
                                $oldSynonyms = array_slice( $fallbackInfo, 1 );
                                $newSynonyms = array_slice( $value[$magicName], 1 );
                                $synonyms = array_values( array_unique( array_merge(
                                        $newSynonyms, $oldSynonyms ) ) );
                                $value[$magicName] = array_merge( array( $fallbackInfo[0] ), $synonyms );
                        }
                }
        }

        /**
         * Given an array mapping language code to localisation value, such as is
         * found in extension *.i18n.php files, iterate through a fallback sequence
         * to merge the given data with an existing primary value.
         *
         * Returns true if any data from the extension array was used, false
         * otherwise.
         * @param $codeSequence
         * @param $key
         * @param $value
         * @param $fallbackValue
         * @return bool
         */
        protected function mergeExtensionItem( $codeSequence, $key, &$value, $fallbackValue ) {
                $used = false;
                foreach ( $codeSequence as $code ) {
                        if ( isset( $fallbackValue[$code] ) ) {
                                $this->mergeItem( $key, $value, $fallbackValue[$code] );
                                $used = true;
                        }
                }

                return $used;
        }

        /**
         * Load localisation data for a given language for both core and extensions
         * and save it to the persistent cache store and the process cache
         * @param $code
         * @throws MWException
         */
        public function recache( $code ) {
                global $wgExtensionMessagesFiles;
                wfProfileIn( __METHOD__ );

                if ( !$code ) {
                        wfProfileOut( __METHOD__ );
                        throw new MWException( "Invalid language code requested" );
                }
                $this->recachedLangs[$code] = true;

                # Initial values
                $initialData = array_combine(
                        self::$allKeys,
                        array_fill( 0, count( self::$allKeys ), null ) );
                $coreData = $initialData;
                $deps = array();

                # Load the primary localisation from the source file
                $data = $this->readSourceFilesAndRegisterDeps( $code, $deps );
                if ( $data === false ) {
                        wfDebug( __METHOD__ . ": no localisation file for $code, using fallback to en\n" );
                        $coreData['fallback'] = 'en';
                } else {
                        wfDebug( __METHOD__ . ": got localisation for $code from source\n" );

                        # Merge primary localisation
                        foreach ( $data as $key => $value ) {
                                $this->mergeItem( $key, $coreData[$key], $value );
                        }
                }

                # Fill in the fallback if it's not there already
                if ( is_null( $coreData['fallback'] ) ) {
                        $coreData['fallback'] = $code === 'en' ? false : 'en';
                }
                if ( $coreData['fallback'] === false ) {
                        $coreData['fallbackSequence'] = array();
                } else {
                        $coreData['fallbackSequence'] = array_map( 'trim', explode( ',', $coreData['fallback'] ) );
                        $len = count( $coreData['fallbackSequence'] );

                        # Ensure that the sequence ends at en
                        if ( $coreData['fallbackSequence'][$len - 1] !== 'en' ) {
                                $coreData['fallbackSequence'][] = 'en';
                        }

                        # Load the fallback localisation item by item and merge it
                        foreach ( $coreData['fallbackSequence'] as $fbCode ) {
                                # Load the secondary localisation from the source file to
                                # avoid infinite cycles on cyclic fallbacks
                                $fbData = $this->readSourceFilesAndRegisterDeps( $fbCode, $deps );
                                if ( $fbData === false ) {
                                        continue;
                                }

                                foreach ( self::$allKeys as $key ) {
                                        if ( !isset( $fbData[$key] ) ) {
                                                continue;
                                        }

                                        if ( is_null( $coreData[$key] ) || $this->isMergeableKey( $key ) ) {
                                                $this->mergeItem( $key, $coreData[$key], $fbData[$key] );
                                        }
                                }
                        }
                }

                $codeSequence = array_merge( array( $code ), $coreData['fallbackSequence'] );

                # Load the extension localisations
                # This is done after the core because we know the fallback sequence now.
                # But it has a higher precedence for merging so that we can support things
                # like site-specific message overrides.
                wfProfileIn( __METHOD__ . '-extensions' );
                $allData = $initialData;
                foreach ( $wgExtensionMessagesFiles as $fileName ) {
                        $data = $this->readPHPFile( $fileName, 'extension' );
                        $used = false;

                        foreach ( $data as $key => $item ) {
                                if ( $this->mergeExtensionItem( $codeSequence, $key, $allData[$key], $item ) ) {
                                        $used = true;
                                }
                        }

                        if ( $used ) {
                                $deps[] = new FileDependency( $fileName );
                        }
                }

                # Merge core data into extension data
                foreach ( $coreData as $key => $item ) {
                        $this->mergeItem( $key, $allData[$key], $item );
                }
                wfProfileOut( __METHOD__ . '-extensions' );

                # Add cache dependencies for any referenced globals
                $deps['wgExtensionMessagesFiles'] = new GlobalDependency( 'wgExtensionMessagesFiles' );
                $deps['version'] = new ConstantDependency( 'MW_LC_VERSION' );

                # Add dependencies to the cache entry
                $allData['deps'] = $deps;

                # Replace spaces with underscores in namespace names
                $allData['namespaceNames'] = str_replace( ' ', '_', $allData['namespaceNames'] );

                # And do the same for special page aliases. $page is an array.
                foreach ( $allData['specialPageAliases'] as &$page ) {
                        $page = str_replace( ' ', '_', $page );
                }
                # Decouple the reference to prevent accidental damage
                unset( $page );

                # If there were no plural rules, return an empty array
                if ( $allData['pluralRules'] === null ) {
                        $allData['pluralRules'] = array();
                }
                if ( $allData['compiledPluralRules'] === null ) {
                        $allData['compiledPluralRules'] = array();
                }
                # If there were no plural rule types, return an empty array
                if ( $allData['pluralRuleTypes'] === null ) {
                        $allData['pluralRuleTypes'] = array();
                }

                # Set the list keys
                $allData['list'] = array();
                foreach ( self::$splitKeys as $key ) {
                        $allData['list'][$key] = array_keys( $allData[$key] );
                }
                # Run hooks
                wfRunHooks( 'LocalisationCacheRecache', array( $this, $code, &$allData ) );

                if ( is_null( $allData['namespaceNames'] ) ) {
                        wfProfileOut( __METHOD__ );
                        throw new MWException( __METHOD__ . ': Localisation data failed sanity check! ' .
                                'Check that your languages/messages/MessagesEn.php file is intact.' );
                }

                # Set the preload key
                $allData['preload'] = $this->buildPreload( $allData );

                # Save to the process cache and register the items loaded
                $this->data[$code] = $allData;
                foreach ( $allData as $key => $item ) {
                        $this->loadedItems[$code][$key] = true;
                }

                # Save to the persistent cache
                wfProfileIn( __METHOD__ . '-write' );
                $this->store->startWrite( $code );
                foreach ( $allData as $key => $value ) {
                        if ( in_array( $key, self::$splitKeys ) ) {
                                foreach ( $value as $subkey => $subvalue ) {
                                        $this->store->set( "$key:$subkey", $subvalue );
                                }
                        } else {
                                $this->store->set( $key, $value );
                        }
                }
                $this->store->finishWrite();
                wfProfileOut( __METHOD__ . '-write' );

                # Clear out the MessageBlobStore
                # HACK: If using a null (i.e. disabled) storage backend, we
                # can't write to the MessageBlobStore either
                if ( !$this->store instanceof LCStoreNull ) {
                        MessageBlobStore::clear();
                }

                wfProfileOut( __METHOD__ );
        }

        /**
         * Build the preload item from the given pre-cache data.
         *
         * The preload item will be loaded automatically, improving performance
         * for the commonly-requested items it contains.
         * @param $data
         * @return array
         */
        protected function buildPreload( $data ) {
                $preload = array( 'messages' => array() );
                foreach ( self::$preloadedKeys as $key ) {
                        $preload[$key] = $data[$key];
                }

                foreach ( $data['preloadedMessages'] as $subkey ) {
                        if ( isset( $data['messages'][$subkey] ) ) {
                                $subitem = $data['messages'][$subkey];
                        } else {
                                $subitem = null;
                        }
                        $preload['messages'][$subkey] = $subitem;
                }

                return $preload;
        }

        /**
         * Unload the data for a given language from the object cache.
         * Reduces memory usage.
         * @param $code
         */
        public function unload( $code ) {
                unset( $this->data[$code] );
                unset( $this->loadedItems[$code] );
                unset( $this->loadedSubitems[$code] );
                unset( $this->initialisedLangs[$code] );
                unset( $this->shallowFallbacks[$code] );

                foreach ( $this->shallowFallbacks as $shallowCode => $fbCode ) {
                        if ( $fbCode === $code ) {
                                $this->unload( $shallowCode );
                        }
                }
        }

        /**
         * Unload all data
         */
        public function unloadAll() {
                foreach ( $this->initialisedLangs as $lang => $unused ) {
                        $this->unload( $lang );
                }
        }

        /**
         * Disable the storage backend
         */
        public function disableBackend() {
                $this->store = new LCStoreNull;
                $this->manualRecache = false;
        }
}

/**
 * Interface for the persistence layer of LocalisationCache.
 *
 * The persistence layer is two-level hierarchical cache. The first level
 * is the language, the second level is the item or subitem.
 *
 * Since the data for a whole language is rebuilt in one operation, it needs
 * to have a fast and atomic method for deleting or replacing all of the
 * current data for a given language. The interface reflects this bulk update
 * operation. Callers writing to the cache must first call startWrite(), then
 * will call set() a couple of thousand times, then will call finishWrite()
 * to commit the operation. When finishWrite() is called, the cache is
 * expected to delete all data previously stored for that language.
 *
 * The values stored are PHP variables suitable for serialize(). Implementations
 * of LCStore are responsible for serializing and unserializing.
 */
interface LCStore {
        /**
         * Get a value.
         * @param string $code Language code
         * @param string $key Cache key
         */
        function get( $code, $key );

        /**
         * Start a write transaction.
         * @param string $code Language code
         */
        function startWrite( $code );

        /**
         * Finish a write transaction.
         */
        function finishWrite();

        /**
         * Set a key to a given value. startWrite() must be called before this
         * is called, and finishWrite() must be called afterwards.
         * @param string $key
         * @param mixed $value
         */
        function set( $key, $value );
}

/**
 * LCStore implementation which uses PHP accelerator to store data.
 * This will work if one of XCache, WinCache or APC cacher is configured.
 * (See ObjectCache.php)
 */
class LCStoreAccel implements LCStore {
        private $currentLang;
        private $keys;

        public function __construct() {
                $this->cache = wfGetCache( CACHE_ACCEL );
        }

        public function get( $code, $key ) {
                $k = wfMemcKey( 'l10n', $code, 'k', $key );
                $r = $this->cache->get( $k );

                return $r === false ? null : $r;
        }

        public function startWrite( $code ) {
                $k = wfMemcKey( 'l10n', $code, 'l' );
                $keys = $this->cache->get( $k );
                if ( $keys ) {
                        foreach ( $keys as $k ) {
                                $this->cache->delete( $k );
                        }
                }
                $this->currentLang = $code;
                $this->keys = array();
        }

        public function finishWrite() {
                if ( $this->currentLang ) {
                        $k = wfMemcKey( 'l10n', $this->currentLang, 'l' );
                        $this->cache->set( $k, array_keys( $this->keys ) );
                }
                $this->currentLang = null;
                $this->keys = array();
        }

        public function set( $key, $value ) {
                if ( $this->currentLang ) {
                        $k = wfMemcKey( 'l10n', $this->currentLang, 'k', $key );
                        $this->keys[$k] = true;
                        $this->cache->set( $k, $value );
                }
        }
}

/**
 * LCStore implementation which uses the standard DB functions to store data.
 * This will work on any MediaWiki installation.
 */
class LCStoreDB implements LCStore {
        private $currentLang;
        private $writesDone = false;

        /**
         * @var DatabaseBase
         */
        private $dbw;
        private $batch;
        private $readOnly = false;

        public function get( $code, $key ) {
                if ( $this->writesDone ) {
                        $db = wfGetDB( DB_MASTER );
                } else {
                        $db = wfGetDB( DB_SLAVE );
                }
                $row = $db->selectRow( 'l10n_cache', array( 'lc_value' ),
                        array( 'lc_lang' => $code, 'lc_key' => $key ), __METHOD__ );
                if ( $row ) {
                        return unserialize( $row->lc_value );
                } else {
                        return null;
                }
        }

        public function startWrite( $code ) {
                if ( $this->readOnly ) {
                        return;
                }

                if ( !$code ) {
                        throw new MWException( __METHOD__ . ": Invalid language \"$code\"" );
                }

                $this->dbw = wfGetDB( DB_MASTER );
                try {
                        $this->dbw->begin( __METHOD__ );
                        $this->dbw->delete( 'l10n_cache', array( 'lc_lang' => $code ), __METHOD__ );
                } catch ( DBQueryError $e ) {
                        if ( $this->dbw->wasReadOnlyError() ) {
                                $this->readOnly = true;
                                $this->dbw->rollback( __METHOD__ );

                                return;
                        } else {
                                throw $e;
                        }
                }

                $this->currentLang = $code;
                $this->batch = array();
        }

        public function finishWrite() {
                if ( $this->readOnly ) {
                        return;
                }

                if ( $this->batch ) {
                        $this->dbw->insert( 'l10n_cache', $this->batch, __METHOD__ );
                }

                $this->dbw->commit( __METHOD__ );
                $this->currentLang = null;
                $this->dbw = null;
                $this->batch = array();
                $this->writesDone = true;
        }

        public function set( $key, $value ) {
                if ( $this->readOnly ) {
                        return;
                }

                if ( is_null( $this->currentLang ) ) {
                        throw new MWException( __CLASS__ . ': must call startWrite() before calling set()' );
                }

                $this->batch[] = array(
                        'lc_lang' => $this->currentLang,
                        'lc_key' => $key,
                        'lc_value' => serialize( $value ) );

                if ( count( $this->batch ) >= 100 ) {
                        $this->dbw->insert( 'l10n_cache', $this->batch, __METHOD__ );
                        $this->batch = array();
                }
        }
}

/**
 * LCStore implementation which stores data as a collection of CDB files in the
 * directory given by $wgCacheDirectory. If $wgCacheDirectory is not set, this
 * will throw an exception.
 *
 * Profiling indicates that on Linux, this implementation outperforms MySQL if
 * the directory is on a local filesystem and there is ample kernel cache
 * space. The performance advantage is greater when the DBA extension is
 * available than it is with the PHP port.
 *
 * See Cdb.php and http://cr.yp.to/cdb.html
 */
class LCStoreCDB implements LCStore {
        private $readers;
        private $writer;
        private $currentLang;
        private $directory;

        function __construct( $conf = array() ) {
                global $wgCacheDirectory;

                if ( isset( $conf['directory'] ) ) {
                        $this->directory = $conf['directory'];
                } else {
                        $this->directory = $wgCacheDirectory;
                }
        }

        public function get( $code, $key ) {
                if ( !isset( $this->readers[$code] ) ) {
                        $fileName = $this->getFileName( $code );

                        $this->readers[$code] = false;
                        if ( file_exists( $fileName ) ) {
                                try {
                                        $this->readers[$code] = CdbReader::open( $fileName );
                                } catch ( CdbException $e ) {
                                        wfDebug( __METHOD__ . ": unable to open cdb file for reading" );
                                }
                        }
                }

                if ( !$this->readers[$code] ) {
                        return null;
                } else {
                        $value = false;
                        try {
                                $value = $this->readers[$code]->get( $key );
                        } catch ( CdbException $e ) {
                                wfDebug( __METHOD__ . ": CdbException caught, error message was "
                                        . $e->getMessage() );
                        }
                        if ( $value === false ) {
                                return null;
                        }

                        return unserialize( $value );
                }
        }

        public function startWrite( $code ) {
                if ( !file_exists( $this->directory ) ) {
                        if ( !wfMkdirParents( $this->directory, null, __METHOD__ ) ) {
                                throw new MWException( "Unable to create the localisation store " .
                                        "directory \"{$this->directory}\"" );
                        }
                }

                // Close reader to stop permission errors on write
                if ( !empty( $this->readers[$code] ) ) {
                        $this->readers[$code]->close();
                }

                try {
                        $this->writer = CdbWriter::open( $this->getFileName( $code ) );
                } catch ( CdbException $e ) {
                        throw new MWException( $e->getMessage() );
                }
                $this->currentLang = $code;
        }

        public function finishWrite() {
                // Close the writer
                try {
                        $this->writer->close();
                } catch ( CdbException $e ) {
                        throw new MWException( $e->getMessage() );
                }
                $this->writer = null;
                unset( $this->readers[$this->currentLang] );
                $this->currentLang = null;
        }

        public function set( $key, $value ) {
                if ( is_null( $this->writer ) ) {
                        throw new MWException( __CLASS__ . ': must call startWrite() before calling set()' );
                }
                try {
                        $this->writer->set( $key, serialize( $value ) );
                } catch ( CdbException $e ) {
                        throw new MWException( $e->getMessage() );
                }
        }

        protected function getFileName( $code ) {
                if ( strval( $code ) === '' || strpos( $code, '/' ) !== false ) {
                        throw new MWException( __METHOD__ . ": Invalid language \"$code\"" );
                }

                return "{$this->directory}/l10n_cache-$code.cdb";
        }
}

/**
 * Null store backend, used to avoid DB errors during install
 */
class LCStoreNull implements LCStore {
        public function get( $code, $key ) {
                return null;
        }

        public function startWrite( $code ) {
        }

        public function finishWrite() {
        }

        public function set( $key, $value ) {
        }
}

/**
 * A localisation cache optimised for loading large amounts of data for many
 * languages. Used by rebuildLocalisationCache.php.
 */
class LocalisationCacheBulkLoad extends LocalisationCache {
        /**
         * A cache of the contents of data files.
         * Core files are serialized to avoid using ~1GB of RAM during a recache.
         */
        private $fileCache = array();

        /**
         * Most recently used languages. Uses the linked-list aspect of PHP hashtables
         * to keep the most recently used language codes at the end of the array, and
         * the language codes that are ready to be deleted at the beginning.
         */
        private $mruLangs = array();

        /**
         * Maximum number of languages that may be loaded into $this->data
         */
        private $maxLoadedLangs = 10;

        /**
         * @param $fileName
         * @param $fileType
         * @return array|mixed
         */
        protected function readPHPFile( $fileName, $fileType ) {
                $serialize = $fileType === 'core';
                if ( !isset( $this->fileCache[$fileName][$fileType] ) ) {
                        $data = parent::readPHPFile( $fileName, $fileType );

                        if ( $serialize ) {
                                $encData = serialize( $data );
                        } else {
                                $encData = $data;
                        }

                        $this->fileCache[$fileName][$fileType] = $encData;

                        return $data;
                } elseif ( $serialize ) {
                        return unserialize( $this->fileCache[$fileName][$fileType] );
                } else {
                        return $this->fileCache[$fileName][$fileType];
                }
        }

        /**
         * @param $code
         * @param $key
         * @return mixed
         */
        public function getItem( $code, $key ) {
                unset( $this->mruLangs[$code] );
                $this->mruLangs[$code] = true;

                return parent::getItem( $code, $key );
        }

        /**
         * @param $code
         * @param $key
         * @param $subkey
         * @return
         */
        public function getSubitem( $code, $key, $subkey ) {
                unset( $this->mruLangs[$code] );
                $this->mruLangs[$code] = true;

                return parent::getSubitem( $code, $key, $subkey );
        }

        /**
         * @param $code
         */
        public function recache( $code ) {
                parent::recache( $code );
                unset( $this->mruLangs[$code] );
                $this->mruLangs[$code] = true;
                $this->trimCache();
        }

        /**
         * @param $code
         */
        public function unload( $code ) {
                unset( $this->mruLangs[$code] );
                parent::unload( $code );
        }

        /**
         * Unload cached languages until there are less than $this->maxLoadedLangs
         */
        protected function trimCache() {
                while ( count( $this->data ) > $this->maxLoadedLangs && count( $this->mruLangs ) ) {
                        reset( $this->mruLangs );
                        $code = key( $this->mruLangs );
                        wfDebug( __METHOD__ . ": unloading $code\n" );
                        $this->unload( $code );
                }
        }
}