wikimedia/mediawiki-extensions-Wikibase

<?php

namespace Wikibase\Lib\Store;

use Wikibase\DataModel\Entity\EntityId;
use Wikibase\DataModel\Services\Lookup\LabelDescriptionLookupException;
use Wikibase\DataModel\Term\TermFallback;
use Wikibase\Lib\TermFallbackCache\TermFallbackCacheFacade;
use Wikibase\Lib\TermLanguageFallbackChain;

/**
 * Wraps another label description lookup to resolve redirects and add caching.
 * Use {@link FallbackLabelDescriptionLookupFactory} instead of using this class directly.
 *
 * @license GPL-2.0-or-later
 *
 * @note The class uses immutable cache approach: cached data never changes once persisted.
 *       For this purpose we not only include Item ID in cache key construction, but also
 *       Item's current revision ID. Revisions never change, the cached data does not need
 *       to change either, which means that we don't need to purge caches. As soon as new revision
 *       is created, cache key will change and old cache data will eventually be purged by
 *       the caching system (eg. APC, Memcached, ...) based on a Least Recently Used strategy
 *       as soon as no code will request it anymore.
 */
class CachingFallbackLabelDescriptionLookup implements FallbackLabelDescriptionLookup {

    use TermCacheKeyBuilder;

    private const LABEL = 'label';
    private const DESCRIPTION = 'description';

    /**
     * @var TermFallbackCacheFacade
     */
    private $cache;

    /**
     * @var RedirectResolvingLatestRevisionLookup
     */
    private $redirectResolvingRevisionLookup;

    /**
     * @var FallbackLabelDescriptionLookup
     */
    private $labelDescriptionLookup;

    /**
     * @var TermLanguageFallbackChain
     */
    private $termLanguageFallbackChain;

    /**
     * @param TermFallbackCacheFacade $fallbackCache
     * @param RedirectResolvingLatestRevisionLookup $redirectResolvingRevisionLookup
     * @param FallbackLabelDescriptionLookup $labelDescriptionLookup
     * @param TermLanguageFallbackChain $termLanguageFallbackChain
     */
    public function __construct(
        TermFallbackCacheFacade $fallbackCache,
        RedirectResolvingLatestRevisionLookup $redirectResolvingRevisionLookup,
        FallbackLabelDescriptionLookup $labelDescriptionLookup,
        TermLanguageFallbackChain $termLanguageFallbackChain
    ) {
        $this->cache = $fallbackCache;
        $this->redirectResolvingRevisionLookup = $redirectResolvingRevisionLookup;
        $this->labelDescriptionLookup = $labelDescriptionLookup;
        $this->termLanguageFallbackChain = $termLanguageFallbackChain;
    }

    /**
     * @param EntityId $entityId
     *
     * @throws LabelDescriptionLookupException
     * @return TermFallback|null
     */
    public function getDescription( EntityId $entityId ) {
        $languageCodes = $this->termLanguageFallbackChain->getFetchLanguageCodes();
        if ( !$languageCodes ) {
            // Can happen when the current interface language is not a valid term language, e.g. "de-formal"
            return null;
        }

        $languageCode = $languageCodes[0];
        $description = $this->getTerm( $entityId, $languageCode, self::DESCRIPTION );

        return $description;
    }

    /**
     * @param EntityId $entityId
     *
     * @throws LabelDescriptionLookupException
     * @return TermFallback|null
     */
    public function getLabel( EntityId $entityId ) {
        $languageCodes = $this->termLanguageFallbackChain->getFetchLanguageCodes();
        if ( !$languageCodes ) {
            // Can happen when the current interface language is not a valid term language, e.g. "de-formal"
            return null;
        }

        $languageCode = $languageCodes[0];
        $label = $this->getTerm( $entityId, $languageCode, self::LABEL );

        return $label;
    }

    private function getTerm( EntityId $entityId, $languageCode, $termName = self::LABEL ) {
        $resolutionResult = $this->redirectResolvingRevisionLookup->lookupLatestRevisionResolvingRedirect( $entityId );
        if ( $resolutionResult === null ) {
            return null;
        }

        [ $revisionId, $targetEntityId ] = $resolutionResult;

        $termFallback = $this->cache->get( $targetEntityId, $revisionId, $languageCode, $termName );
        if ( $termFallback === TermFallbackCacheFacade::NO_VALUE ) {
            $termFallback = $termName === self::LABEL
                ? $this->labelDescriptionLookup->getLabel( $targetEntityId )
                : $this->labelDescriptionLookup->getDescription( $targetEntityId );

            $this->cache->set( $termFallback, $targetEntityId, $revisionId, $languageCode, $termName );

            return $termFallback;
        }

        return $termFallback;
    }
}