<?php

namespace SMW\SPARQLStore;

use RuntimeException;
use SMW\DIWikiPage;
use SMW\InMemoryPoolCache;
use SMWExpNsResource as ExpNsResource;
use SMWExporter as Exporter;
use SMWExpResource as ExpResource;
use SMWTurtleSerializer as TurtleSerializer;

/**
 * @license GNU GPL v2+
 * @since 2.0
 *
 * @author Markus Krötzsch
 * @author mwjames
 */
class RepositoryRedirectLookup {

	/**
	 * ID used for the InMemoryPoolCache
	 */
	const POOLCACHE_ID = 'sparql.repository.redirectLookup';

	/**
	 * @var RepositoryConnection
	 */
	private $repositoryConnection;

	/**
	 * @since 2.0
	 *
	 * @param RepositoryConnection $repositoryConnection
	 */
	public function __construct( RepositoryConnection $repositoryConnection ) {
		$this->repositoryConnection = $repositoryConnection;
	}

	/**
	 * @since 2.1
	 */
	public static function reset() {
		InMemoryPoolCache::getInstance()->resetPoolCacheById( self::POOLCACHE_ID );
	}

	/**
	 * Find the redirect target of an ExpNsResource
	 *
	 * Returns an SMWExpNsResource object the input redirects to, the input
	 * itself if there is no redirect (or it cannot be used for making a resource
	 * with a prefix).
	 *
	 * @since 1.6
	 *
	 * @param ExpNsResource $expNsResource string URI to check
	 * @param boolean $existsthat is set to true if $expNsResource is in the
	 * store; always false for blank nodes; always true for subobjects
	 *
	 * @return ExpNsResource
	 * @throws RuntimeException
	 */
	public function findRedirectTargetResource( ExpNsResource $expNsResource, &$exists ) {

		$exists = true;

		if ( $expNsResource->isBlankNode() || $this->isNonRedirectableResource( $expNsResource ) ) {
			$exists = false;
			return $expNsResource;
		}

		if ( ( $expNsResource->getDataItem() instanceof DIWikiPage ) &&
			   $expNsResource->getDataItem()->getSubobjectName() !== '' ) {
			return $expNsResource;
		}

		$firstRow = $this->doLookupResourceUriTargetFor( $expNsResource );

		if ( $firstRow === false ) {
			$exists = false;
			return $expNsResource;
		}

		if ( is_array( $firstRow ) && count( $firstRow ) > 1 && !is_null( $firstRow[1] ) ) {
			return $this->getResourceForTargetElement( $expNsResource, $firstRow[1] );
		}

		return $expNsResource;
	}

	private function doLookupResourceUriTargetFor( ExpNsResource $expNsResource ) {

		$poolCache = InMemoryPoolCache::getInstance()->getPoolCacheById( self::POOLCACHE_ID );

		if ( !$poolCache->contains( $expNsResource->getUri() ) ) {
			$poolCache->save(
				$expNsResource->getUri(),
				$this->lookupResourceUriTargetFromDatabase( $expNsResource )
			);
		}

		return $poolCache->fetch( $expNsResource->getUri() );
	}

	private function isNonRedirectableResource( ExpNsResource $expNsResource ) {
		return $expNsResource->getNamespaceId() === 'swivt' ||
			$expNsResource->getNamespaceId() === 'rdf' ||
			$expNsResource->getNamespaceId() === 'rdfs' ||
			( $expNsResource->getNamespaceId() === 'property' && strrpos( $expNsResource->getLocalName(), 'aux' ) ) ||
			( isset( $expNsResource->isUserDefined ) && !$expNsResource->isUserDefined );
	}

	private function lookupResourceUriTargetFromDatabase( ExpNsResource $expNsResource ) {

		$resourceUri = TurtleSerializer::getTurtleNameForExpElement( $expNsResource );
		$rediUri = TurtleSerializer::getTurtleNameForExpElement( Exporter::getInstance()->getSpecialPropertyResource( '_REDI' ) );
		$skeyUri = TurtleSerializer::getTurtleNameForExpElement( Exporter::getInstance()->getSpecialPropertyResource( '_SKEY' ) );

		$respositoryResult = $this->repositoryConnection->select(
			'*',
			"$resourceUri $skeyUri ?s  OPTIONAL { $resourceUri $rediUri ?r }",
			[ 'LIMIT' => 1 ],
			[ $expNsResource->getNamespaceId() => $expNsResource->getNamespace() ]
		);

		return $respositoryResult->current();
	}

	private function getResourceForTargetElement( ExpNsResource $expNsResource, $rediTargetElement ) {

		if ( !$rediTargetElement instanceof ExpResource ) {
			throw new RuntimeException( 'Expected a ExpResource instance' );
		}

		$rediTargetUri = $rediTargetElement->getUri();
		$wikiNamespace = Exporter::getInstance()->getNamespaceUri( 'wiki' );

		if ( strpos( $rediTargetUri, $wikiNamespace ) === 0 ) {
			return new ExpNsResource( substr( $rediTargetUri, strlen( $wikiNamespace ) ), $wikiNamespace, 'wiki' );
		}

		return $expNsResource;
	}

}