wikimedia/mediawiki-extensions-Wikibase

<?php

namespace Wikibase\Lib\Store;

use Wikibase\DataModel\Entity\EntityId;
use Wikimedia\Assert\Assert;

/**
 * EntityRevisionLookup implementation that checks an EntityRevisionCache for cached revisions (but
 * doesn't cache on its own). Falls back to a given EntityRevisionLookup.
 *
 * @license GPL-2.0-or-later
 * @author Daniel Kinzler
 * @author Marius Hoch
 */
class CacheRetrievingEntityRevisionLookup implements EntityRevisionLookup {

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

    /**
     * @var EntityRevisionLookup
     */
    private $lookup;

    /**
     * @var bool
     */
    private $shouldVerifyRevision = false;

    public function __construct( EntityRevisionCache $cache, EntityRevisionLookup $lookup ) {
        $this->cache = $cache;
        $this->lookup = $lookup;
    }

    /**
     * Determine whether the revision of the cached entity should be verified against the
     * current revision in the underlying lookup.
     *
     * @param bool $shouldVerifyRevision
     */
    public function setVerifyRevision( $shouldVerifyRevision ) {
        $this->shouldVerifyRevision = $shouldVerifyRevision;
    }

    /**
     * Get an EntityRevision from cache or (otherwise) from the underlying EntityRevisionLookup.
     *
     * @see EntityRevisionLookup::getEntityRevision
     *
     * @note If this lookup is configured to verify revisions, getLatestRevisionId()
     * will be called on the underlying lookup to check whether the cached revision is
     * still the latest. Otherwise, any cached revision will be used if $revisionId=0.
     *
     * @param EntityId $entityId
     * @param int $revisionId The desired revision id, or 0 for the latest revision.
     * @param string $mode One of the EntityRevisionLookup::LATEST_* constants.
     *
     * @throws StorageException
     * @return EntityRevision|null
     */
    public function getEntityRevision(
        EntityId $entityId,
        $revisionId = 0,
        $mode = LookupConstants::LATEST_FROM_REPLICA
    ) {
        Assert::parameterType( 'integer', $revisionId, '$revisionId' );
        Assert::parameterType( 'string', $mode, '$mode' );

        $entityRevision = $this->getEntityRevisionFromCache( $entityId, $revisionId, $mode );

        if ( $entityRevision === null ) {
            $entityRevision = $this->lookup->getEntityRevision( $entityId, $revisionId, $mode );
        }

        return $entityRevision;
    }

    /**
     * Try to get an EntityRevision from cache.
     *
     * @note If this lookup is configured to verify revisions, getLatestRevisionId()
     * will be called on the underlying lookup to check whether the cached revision is
     * still the latest. Otherwise, any cached revision will be used if $revisionId=0.
     *
     * @param EntityId $entityId
     * @param int $revisionId The desired revision id, or 0 for the latest revision.
     * @param string $mode LATEST_FROM_REPLICA, LATEST_FROM_REPLICA_WITH_FALLBACK or
     *        LATEST_FROM_MASTER.
     *
     * @throws StorageException
     * @return EntityRevision|null Null if the EntityRevision in question is not cached.
     */
    public function getEntityRevisionFromCache(
        EntityId $entityId,
        $revisionId = 0,
        $mode = LookupConstants::LATEST_FROM_REPLICA
    ) {
        Assert::parameterType( 'integer', $revisionId, '$revisionId' );
        Assert::parameterType( 'string', $mode, '$mode' );

        $entityRevision = $this->cache->get( $entityId );

        if ( $entityRevision !== null ) {
            if ( $revisionId === 0 && $this->shouldVerifyRevision ) {
                $latestRevisionIdResult = $this->lookup->getLatestRevisionId( $entityId, $mode );
                $returnFalse = function () {
                    return false;
                };

                $latestRevision = $latestRevisionIdResult->onConcreteRevision( function ( $revId ) {
                    return $revId;
                } )
                    ->onRedirect( $returnFalse )
                    ->onNonexistentEntity( $returnFalse )
                    ->map();

                if ( $latestRevision === false ) {
                    // entity no longer exists!
                    return null;
                } else {
                    $revisionId = $latestRevision;
                }
            }

            if ( $revisionId > 0 && $entityRevision && $entityRevision->getRevisionId() !== $revisionId ) {
                $entityRevision = null;
            }
        }

        return $entityRevision;
    }

    /**
     * @see EntityRevisionLookup::getLatestRevisionId
     *
     * @note If this lookup is configured to verify revisions, this just delegates
     * to the underlying lookup. Otherwise, it may return the ID of a cached
     * revision.
     *
     * @param EntityId $entityId
     * @param string $mode
     *
     * @return LatestRevisionIdResult
     */
    public function getLatestRevisionId( EntityId $entityId, $mode = LookupConstants::LATEST_FROM_REPLICA ) {
        // If we do not need to verify the revision, and the revision isn't
        // needed for an update, we can get the revision from the cached object.
        // XXX: whether this is actually quicker depends on the cache.
        if ( !$this->shouldVerifyRevision && $mode !== LookupConstants::LATEST_FROM_MASTER ) {
            $entityRevision = $this->cache->get( $entityId );

            if ( $entityRevision ) {
                return LatestRevisionIdResult::concreteRevision( $entityRevision->getRevisionId(), $entityRevision->getTimestamp() );
            }
        }

        return $this->lookup->getLatestRevisionId( $entityId, $mode );
    }

}