ElasticSearchTTMServer.php

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<?php
use Elastica\Aggregation\Terms;
use Elastica\Client;
use Elastica\Document;
use Elastica\Exception\ExceptionInterface;
use Elastica\Query;
use Elastica\Query\BoolQuery;
use Elastica\Query\FunctionScore;
use Elastica\Query\MatchQuery;
use Elastica\Query\Term;
use MediaWiki\Extension\Elastica\MWElasticUtils;
use MediaWiki\Extension\Translate\TranslatorInterface\TranslationHelperException;
use MediaWiki\Logger\LoggerFactory;
use MediaWiki\MediaWikiServices;
 
class ElasticSearchTTMServer
    extends TTMServer
    implements ReadableTTMServer, WritableTTMServer, SearchableTTMServer
{
    private const BULK_INDEX_RETRY_ATTEMPTS = 5;
 
    private const WAIT_UNTIL_READY_TIMEOUT = 3600;
 
    protected $client;
    protected $logger;
    protected $updateMapping = false;
 
    public function isLocalSuggestion( array $suggestion ) {
        return $suggestion['wiki'] === WikiMap::getCurrentWikiId();
    }
 
    public function expandLocation( array $suggestion ) {
        return $suggestion['uri'];
    }
 
    public function query( $sourceLanguage, $targetLanguage, $text ) {
        try {
            return $this->doQuery( $sourceLanguage, $targetLanguage, $text );
        } catch ( Exception $e ) {
            throw new TranslationHelperException( 'Elastica exception: ' . $e );
        }
    }
 
    protected function doQuery( $sourceLanguage, $targetLanguage, $text ) {
        if ( !$this->useWikimediaExtraPlugin() ) {
            // ElasticTTM is currently not compatible with elasticsearch 2.x/5.x
            // It needs FuzzyLikeThis ported via the wmf extra plugin
            throw new RuntimeException( 'The wikimedia extra plugin is mandatory.' );
        }
        /* Two query system:
         * 1) Find all strings in source language that match text
         * 2) Do another query for translations for those strings
         */
        $connection = $this->getClient()->getConnection();
        $oldTimeout = $connection->getTimeout();
        $connection->setTimeout( 10 );
 
        $fuzzyQuery = new FuzzyLikeThis();
        $fuzzyQuery->setLikeText( $text );
        $fuzzyQuery->addFields( [ 'content' ] );
 
        $boostQuery = new FunctionScore();
        $boostQuery->addFunction(
            'levenshtein_distance_score',
            [
                'text' => $text,
                'field' => 'content'
            ]
        );
        $boostQuery->setBoostMode( FunctionScore::BOOST_MODE_REPLACE );
 
        // Wrap the fuzzy query so it can be used as a filter.
        // This is slightly faster, as ES can throw away the scores by this query.
        $bool = new BoolQuery();
        $bool->addFilter( $fuzzyQuery );
        $bool->addMust( $boostQuery );
 
        $languageFilter = new Term();
        $languageFilter->setTerm( 'language', $sourceLanguage );
        $bool->addFilter( $languageFilter );
 
        // The whole query
        $query = new Query();
        $query->setQuery( $bool );
 
        // The interface usually displays three best candidates. These might
        // come from more than three source things, if the translations are
        // the same. In other words suggestions are grouped by the suggested
        // translation. This algorithm might not find all suggestions, if the
        // top N best matching source texts don't have equivalent translations
        // in the target language, but worse matches which we did not fetch do.
        // This code tries to balance between doing too many or too big queries
        // and not fetching enough results to show all possible suggestions.
        $sizeFirst = 100;
        $sizeSecond = $sizeFirst * 5;
 
        $query->setFrom( 0 );
        $query->setSize( $sizeFirst );
        $query->setParam( '_source', [ 'content' ] );
        $cutoff = $this->config['cutoff'] ?? 0.65;
        $query->setParam( 'min_score', $cutoff );
        $query->setSort( [ '_score', 'wiki', 'localid' ] );
 
        /* This query is doing two unrelated things:
         * 1) Collect the message contents and scores so that they can
         *    be accessed later for the translations we found.
         * 2) Build the query string for the query that fetches the translations.
         */
        $contents = $scores = $terms = [];
        do {
            $resultset = $this->getIndex()->search( $query );
 
            if ( count( $resultset ) === 0 ) {
                break;
            }
 
            foreach ( $resultset->getResults() as $result ) {
                $data = $result->getData();
                $score = $result->getScore();
 
                $sourceId = preg_replace( '~/[^/]+$~', '', $result->getId() );
                $contents[$sourceId] = $data['content'];
                $scores[$sourceId] = $score;
                $terms[] = "$sourceId/$targetLanguage";
            }
 
            // Check if it looks like that we are hitting the long tail already.
            // Otherwise, we'll do a query to fetch some more to reach a "sane"
            // breaking point, i.e. include all suggestions with same content
            // for reliable used X times statistics.
            if ( count( array_unique( $scores ) ) > 5 ) {
                break;
            }
 
            // Okay, We are now in second iteration of the loop. We already got
            // lots of suggestions. We will give up for now even if it means we
            // return in some sense incomplete results.
            if ( count( $resultset ) === $sizeSecond ) {
                break;
            }
 
            // After the first query, the smallest score is the new threshold.
            // @phan-suppress-next-line PhanPossiblyUndeclaredVariable
            $query->setParam( 'min_score', $score );
            $query->setFrom( $query->getParam( 'size' ) + $query->getParam( 'from' ) );
            $query->setSize( $sizeSecond );
 
            // Break if we already got all hits
        } while ( $resultset->getTotalHits() > count( $contents ) );
 
        $suggestions = [];
 
        // Skip second query if first query found nothing. Keeping only one return
        // statement in this method to avoid forgetting to reset connection timeout
        if ( $terms !== [] ) {
            $idQuery = new Query\Terms( '_id', $terms );
 
            $query = new Query( $idQuery );
            $query->setSize( 25 );
            $query->setParam( '_source', [ 'wiki', 'uri', 'content', 'localid' ] );
            $resultset = $this->getIndex()->search( $query );
 
            foreach ( $resultset->getResults() as $result ) {
                $data = $result->getData();
 
                // Construct the matching source id
                $sourceId = preg_replace( '~/[^/]+$~', '', $result->getId() );
 
                $suggestions[] = [
                    'source' => $contents[$sourceId],
                    'target' => $data['content'],
                    'context' => $data['localid'],
                    'quality' => $scores[$sourceId],
                    'wiki' => $data['wiki'],
                    'location' => $data['localid'] . '/' . $targetLanguage,
                    'uri' => $data['uri'],
                ];
            }
 
            // Ensure results are in quality order
            uasort( $suggestions, static function ( $a, $b ) {
                if ( $a['quality'] === $b['quality'] ) {
                    return 0;
                }
 
                return ( $a['quality'] < $b['quality'] ) ? 1 : -1;
            } );
        }
 
        $connection->setTimeout( $oldTimeout );
 
        return $suggestions;
    }
 
    /* Write functions */
 
    public function update( MessageHandle $handle, $targetText ) {
        if ( !$handle->isValid() || $handle->getCode() === '' ) {
            return false;
        }
 
        /* There are various different cases here:
         * [new or updated] [fuzzy|non-fuzzy] [translation|definition]
         * 1) We don't distinguish between new or updated here.
         * 2) Delete old translation, but not definition
         * 3) Insert new translation or definition, if non-fuzzy
         * The definition should never be fuzzied anyway.
         *
         * These only apply to known messages.
         */
 
        $sourceLanguage = $handle->getGroup()->getSourceLanguage();
 
        // Do not delete definitions, because the translations are attached to that
        if ( $handle->getCode() !== $sourceLanguage ) {
            $localid = $handle->getTitleForBase()->getPrefixedText();
            $this->deleteByQuery( $this->getIndex(), Query::create(
                ( new BoolQuery() )
                ->addFilter( new Term( [ 'wiki' => WikiMap::getCurrentWikiId() ] ) )
                ->addFilter( new Term( [ 'language' => $handle->getCode() ] ) )
                ->addFilter( new Term( [ 'localid' => $localid ] ) ) ) );
        }
 
        // If translation was made fuzzy, we do not need to add anything
        if ( $targetText === null ) {
            return true;
        }
 
        // source language is null, skip doing rest of the stuff
        if ( $sourceLanguage === null ) {
            return true;
        }
 
        $revId = $handle->getTitleForLanguage( $sourceLanguage )->getLatestRevID();
        $doc = $this->createDocument( $handle, $targetText, $revId );
        $fname = __METHOD__;
 
        MWElasticUtils::withRetry( self::BULK_INDEX_RETRY_ATTEMPTS,
            function () use ( $doc ) {
                $this->getIndex()->addDocuments( [ $doc ] );
            },
            static function ( $e, $errors ) use ( $fname ) {
                $c = get_class( $e );
                $msg = $e->getMessage();
                error_log( $fname . ": update failed ($c: $msg); retrying." );
                sleep( 10 );
            }
        );
 
        return true;
    }
 
    protected function createDocument( MessageHandle $handle, $text, $revId ) {
        $language = $handle->getCode();
 
        $localid = $handle->getTitleForBase()->getPrefixedText();
        $wiki = WikiMap::getCurrentWikiId();
        $globalid = "$wiki-$localid-$revId/$language";
 
        $data = [
            'wiki' => $wiki,
            'uri' => $handle->getTitle()->getCanonicalURL(),
            'localid' => $localid,
            'language' => $language,
            'content' => $text,
            'group' => $handle->getGroupIds(),
        ];
 
        return new Document( $globalid, $data, '_doc' );
    }
 
    public function createIndex( $rebuild ) {
        $indexSettings = [
            'settings' => [
                'index' => [
                    'number_of_shards' => $this->getShardCount(),
                    'analysis' => [
                        'filter' => [
                            'prefix_filter' => [
                                'type' => 'edge_ngram',
                                'min_gram' => 2,
                                'max_gram' => 20
                            ]
                        ],
                        'analyzer' => [
                            'prefix' => [
                                'type' => 'custom',
                                'tokenizer' => 'standard',
                                'filter' => [ 'lowercase', 'prefix_filter' ]
                            ],
                            'casesensitive' => [
                                'tokenizer' => 'standard'
                            ]
                        ]
                    ]
                ],
            ],
        ];
        $replicas = $this->getReplicaCount();
        if ( strpos( $replicas, '-' ) === false ) {
            $indexSettings['settings']['index']['number_of_replicas'] = $replicas;
        } else {
            $indexSettings['settings']['index']['auto_expand_replicas'] = $replicas;
        }
 
        $this->getIndex()->create( $indexSettings, $rebuild );
    }
 
    public function beginBootstrap() {
        $this->checkElasticsearchVersion();
        $index = $this->getIndex();
        if ( $this->updateMapping ) {
            $this->logOutput( 'Updating the index mappings...' );
            $this->createIndex( true );
        } elseif ( !$index->exists() ) {
            $this->createIndex( false );
        }
 
        $settings = $index->getSettings();
        $settings->setRefreshInterval( '-1' );
 
        $this->deleteByQuery( $this->getIndex(), Query::create(
            ( new Term() )->setTerm( 'wiki', WikiMap::getCurrentWikiId() ) ) );
 
        $properties = [
            'wiki' => [ 'type' => 'keyword' ],
            'localid' => [ 'type' => 'keyword' ],
            'uri' => [ 'type' => 'keyword' ],
            'language' => [ 'type' => 'keyword' ],
            'group' => [ 'type' => 'keyword' ],
            'content' => [
                'type' => 'text',
                'fields' => [
                    'content' => [
                        'type' => 'text',
                        'term_vector' => 'yes'
                    ],
                    'prefix_complete' => [
                        'type' => 'text',
                        'analyzer' => 'prefix',
                        'search_analyzer' => 'standard',
                        'term_vector' => 'yes'
                    ],
                    'case_sensitive' => [
                        'type' => 'text',
                        'analyzer' => 'casesensitive',
                        'term_vector' => 'yes'
                    ]
                ]
            ],
        ];
        if ( $this->useElastica6() ) {
            // Elastica 6 support
            // @phan-suppress-next-line PhanUndeclaredClassMethod
            $mapping = new \Elastica\Type\Mapping();
            // @phan-suppress-next-line PhanUndeclaredMethod, PhanUndeclaredClassMethod
            $mapping->setType( $index->getType( '_doc' ) );
            // @phan-suppress-next-line PhanUndeclaredClassMethod
            $mapping->setProperties( $properties );
            // @phan-suppress-next-line PhanUndeclaredClassMethod
            $mapping->send( [ 'include_type_name' => 'true' ] );
        } else {
            // Elastica 7
            $mapping = new \Elastica\Mapping( $properties );
            $mapping->send( $index, [ 'include_type_name' => 'false' ] );
        }
 
        $this->waitUntilReady();
    }
 
    public function beginBatch() {
        // I hate the rule that forbids {}
    }
 
    public function batchInsertDefinitions( array $batch ) {
        $lb = MediaWikiServices::getInstance()->getLinkBatchFactory()->newLinkBatch();
        foreach ( $batch as $data ) {
            $lb->addObj( $data[0]->getTitle() );
        }
        $lb->execute();
 
        $this->batchInsertTranslations( $batch );
    }
 
    public function batchInsertTranslations( array $batch ) {
        $docs = [];
        foreach ( $batch as $data ) {
            [ $handle, $sourceLanguage, $text ] = $data;
            $revId = $handle->getTitleForLanguage( $sourceLanguage )->getLatestRevID();
            $docs[] = $this->createDocument( $handle, $text, $revId );
        }
 
        MWElasticUtils::withRetry( self::BULK_INDEX_RETRY_ATTEMPTS,
            function () use ( $docs ) {
                $this->getIndex()->addDocuments( $docs );
            },
            function ( $e, $errors ) {
                $c = get_class( $e );
                $msg = $e->getMessage();
                $this->logOutput( "Batch failed ($c: $msg), trying again in 10 seconds" );
                sleep( 10 );
            }
        );
    }
 
    public function endBatch() {
        // I hate the rule that forbids {}
    }
 
    public function endBootstrap() {
        $index = $this->getIndex();
        $index->refresh();
        $index->forcemerge();
        $index->getSettings()->setRefreshInterval( '5s' );
    }
 
    public function getClient() {
        if ( !$this->client ) {
            if ( isset( $this->config['config'] ) ) {
                $this->client = new Client( $this->config['config'] );
            } else {
                $this->client = new Client();
            }
        }
        return $this->client;
    }
 
    public function useWikimediaExtraPlugin() {
        return isset( $this->config['use_wikimedia_extra'] ) && $this->config['use_wikimedia_extra'];
    }
 
    private function getIndexName() {
        return $this->config['index'] ?? 'ttmserver';
    }
 
    public function getIndex() {
        return $this->getClient()
            ->getIndex( $this->getIndexName() );
    }
 
    protected function getShardCount() {
        return $this->config['shards'] ?? 1;
    }
 
    protected function getReplicaCount() {
        return $this->config['replicas'] ?? '0-2';
    }
 
    protected function getIndexHealth( $indexName ) {
        $path = "_cluster/health/$indexName";
        $response = $this->getClient()->request( $path );
        if ( $response->hasError() ) {
            throw new Exception( "Error while fetching index health status: " . $response->getError() );
        }
        return $response->getData();
    }
 
    protected function waitForGreen( $indexName, $timeout ) {
        $startTime = time();
        while ( ( $startTime + $timeout ) > time() ) {
            try {
                $response = $this->getIndexHealth( $indexName );
                $status = $response['status'] ?? 'unknown';
                if ( $status === 'green' ) {
                    $this->logOutput( "\tGreen!" );
                    return true;
                }
                $this->logOutput( "\tIndex is $status retrying..." );
                sleep( 5 );
            } catch ( Exception $e ) {
                $this->logOutput( "Error while waiting for green ({$e->getMessage()}), retrying..." );
            }
        }
        return false;
    }
 
    protected function waitUntilReady() {
        $statuses = MWElasticUtils::waitForGreen(
            $this->getClient(),
            $this->getIndexName(),
            self::WAIT_UNTIL_READY_TIMEOUT );
        $this->logOutput( "Waiting for the index to go green..." );
        foreach ( $statuses as $message ) {
            $this->logOutput( $message );
        }
 
        if ( !$statuses->getReturn() ) {
            die( "Timeout! Please check server logs for {$this->getIndexName()}." );
        }
    }
 
    public function setLogger( $logger ) {
        $this->logger = $logger;
    }
 
    // Can it get any uglier?
    protected function logOutput( $text ) {
        if ( $this->logger ) {
            $this->logger->statusLine( "$text\n" );
        }
    }
 
    public function setDoReIndex() {
        $this->updateMapping = true;
    }
 
    protected function parseQueryString( $queryString, array $opts ) {
        $fields = $highlights = [];
        $terms = preg_split( '/\s+/', $queryString );
        $match = $opts['match'];
        $case = $opts['case'];
 
        // Map each word in the query string with its corresponding field
        foreach ( $terms as $term ) {
            $prefix = strstr( $term, '*', true );
            if ( $prefix ) {
                // For wildcard search
                $fields['content.prefix_complete'][] = $prefix;
            } elseif ( $case === '1' ) {
                // For case sensitive search
                $fields['content.case_sensitive'][] = $term;
            } else {
                $fields['content'][] = $term;
            }
        }
 
        // Allow searching either by message content or message id (page name
        // without language subpage) with exact match only.
        $searchQuery = new BoolQuery();
        foreach ( $fields as $analyzer => $words ) {
            foreach ( $words as $word ) {
                $boolQuery = new BoolQuery();
                $contentQuery = new MatchQuery();
                $contentQuery->setFieldQuery( $analyzer, $word );
                $boolQuery->addShould( $contentQuery );
                $messageQuery = new Term();
                $messageQuery->setTerm( 'localid', $word );
                $boolQuery->addShould( $messageQuery );
 
                if ( $match === 'all' ) {
                    $searchQuery->addMust( $boolQuery );
                } else {
                    $searchQuery->addShould( $boolQuery );
                }
 
                // Fields for highlighting
                $highlights[$analyzer] = [
                    'number_of_fragments' => 0
                ];
 
                // Allow searching by exact message title (page name with
                // language subpage).
                $title = Title::newFromText( $word );
                if ( !$title ) {
                    continue;
                }
                $handle = new MessageHandle( $title );
                if ( $handle->isValid() && $handle->getCode() !== '' ) {
                    $localid = $handle->getTitleForBase()->getPrefixedText();
                    $boolQuery = new BoolQuery();
                    $messageId = new Term();
                    $messageId->setTerm( 'localid', $localid );
                    $boolQuery->addMust( $messageId );
                    $searchQuery->addShould( $boolQuery );
                }
            }
        }
 
        return [ $searchQuery, $highlights ];
    }
 
    public function createSearch( $queryString, $opts, $highlight ) {
        $query = new Query();
 
        [ $searchQuery, $highlights ] = $this->parseQueryString( $queryString, $opts );
        $query->setQuery( $searchQuery );
 
        $language = new Terms( 'language' );
        $language->setField( 'language' );
        $language->setSize( 500 );
        $query->addAggregation( $language );
 
        $group = new Terms( 'group' );
        $group->setField( 'group' );
        // Would like to prioritize the top level groups and not show subgroups
        // if the top group has only few hits, but that doesn't seem to be possile.
        $group->setSize( 500 );
        $query->addAggregation( $group );
 
        $query->setSize( $opts['limit'] );
        $query->setFrom( $opts['offset'] );
 
        // BoolAnd filters are executed in sequence per document. Bool filters with
        // multiple must clauses are executed by converting each filter into a bit
        // field then anding them together. The latter is normally faster if either
        // of the subfilters are reused. May not make a difference in this context.
        $filters = new BoolQuery();
 
        $language = $opts['language'];
        if ( $language !== '' ) {
            $languageFilter = new Term();
            $languageFilter->setTerm( 'language', $language );
            $filters->addFilter( $languageFilter );
        }
 
        $group = $opts['group'];
        if ( $group !== '' ) {
            $groupFilter = new Term();
            $groupFilter->setTerm( 'group', $group );
            $filters->addFilter( $groupFilter );
        }
 
        // Check that we have at least one filter to avoid invalid query errors.
        if ( $language !== '' || $group !== '' ) {
            // TODO: This seems wrong, but perhaps for aggregation purposes?
            // should make $search a must clause and use the bool query
            // as main.
            $query->setPostFilter( $filters );
        }
 
        [ $pre, $post ] = $highlight;
        $query->setHighlight( [
            // The value must be an object
            'pre_tags' => [ $pre ],
            'post_tags' => [ $post ],
            'fields' => $highlights,
        ] );
 
        return $this->getIndex()->createSearch( $query );
    }
 
    public function search( $queryString, $opts, $highlight ) {
        $search = $this->createSearch( $queryString, $opts, $highlight );
 
        try {
            return $search->search();
        } catch ( ExceptionInterface $e ) {
            throw new TTMServerException( $e->getMessage() );
        }
    }
 
    public function getFacets( $resultset ) {
        $aggs = $resultset->getAggregations();
        '@phan-var array[][][] $aggs';
 
        $ret = [
            'language' => [],
            'group' => []
        ];
 
        foreach ( $aggs as $type => $info ) {
            foreach ( $info['buckets'] as $row ) {
                $ret[$type][$row['key']] = $row['doc_count'];
            }
        }
 
        return $ret;
    }
 
    public function getTotalHits( $resultset ) {
        return $resultset->getTotalHits();
    }
 
    public function getDocuments( $resultset ) {
        $ret = [];
        foreach ( $resultset->getResults() as $document ) {
            $data = $document->getData();
            $hl = $document->getHighlights();
            if ( isset( $hl['content.prefix_complete'][0] ) ) {
                $data['content'] = $hl['content.prefix_complete'][0];
            } elseif ( isset( $hl['content.case_sensitive'][0] ) ) {
                $data['content'] = $hl['content.case_sensitive'][0];
            } elseif ( isset( $hl['content'][0] ) ) {
                $data['content'] = $hl['content'][0];
            }
            $ret[] = $data;
        }
 
        return $ret;
    }
 
    private function deleteByQuery( \Elastica\Index $index, Query $query ) {
        try {
            MWElasticUtils::deleteByQuery( $index, $query, /* $allowConflicts = */ true );
        } catch ( Exception $e ) {
            LoggerFactory::getInstance( 'ElasticSearchTTMServer' )->error(
                'Problem encountered during deletion.',
                [ 'exception' => $e ]
            );
 
            throw new RuntimeException( "Problem encountered during deletion.\n" . $e );
        }
    }
 
    /* @throws RuntimeException */
    private function getElasticsearchVersion(): string {
        $response = $this->getClient()->request( '' );
        if ( !$response->isOK() ) {
            throw new \RuntimeException( "Cannot fetch elasticsearch version: " . $response->getError() );
        }
 
        $result = $response->getData();
        if ( !isset( $result['version']['number'] ) ) {
            throw new \RuntimeException( 'Unable to determine elasticsearch version, aborting.' );
        }
 
        return $result[ 'version' ][ 'number' ];
    }
 
    private function checkElasticsearchVersion() {
        $version = $this->getElasticsearchVersion();
        if ( strpos( $version, '6.8' ) !== 0 && strpos( $version, '7.' ) !== 0 ) {
            throw new \RuntimeException( "Only Elasticsearch 6.8.x and 7.x are supported. Your version: $version." );
        }
    }
 
    private function useElastica6(): bool {
        return class_exists( '\Elastica\Type' );
    }
}