includes/search/SearchEngine.php

   1 <?php
   2 /**
   3  * Basic search engine
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Search
  22  */
  23
  24 /**
  25  * @defgroup Search Search
  26  */
  27
  28 /**
  29  * Contain a class for special pages
  30  * @ingroup Search
  31  */
  32 class SearchEngine {
  33         /** @var string */
  34         public $prefix = '';
  35
  36         /** @var int[]|null */
  37         public $namespaces = [ NS_MAIN ];
  38
  39         /** @var int */
  40         protected $limit = 10;
  41
  42         /** @var int */
  43         protected $offset = 0;
  44
  45         /** @var array|string */
  46         protected $searchTerms = [];
  47
  48         /** @var bool */
  49         protected $showSuggestion = true;
  50         private $sort = 'relevance';
  51
  52         /** @var array Feature values */
  53         protected $features = [];
  54
  55         /**
  56          * Perform a full text search query and return a result set.
  57          * If full text searches are not supported or disabled, return null.
  58          * STUB
  59          *
  60          * @param string $term Raw search term
  61          * @return SearchResultSet|Status|null
  62          */
  63         function searchText( $term ) {
  64                 return null;
  65         }
  66
  67         /**
  68          * Perform a title-only search query and return a result set.
  69          * If title searches are not supported or disabled, return null.
  70          * STUB
  71          *
  72          * @param string $term Raw search term
  73          * @return SearchResultSet|null
  74          */
  75         function searchTitle( $term ) {
  76                 return null;
  77         }
  78
  79         /**
  80          * @since 1.18
  81          * @param string $feature
  82          * @return bool
  83          */
  84         public function supports( $feature ) {
  85                 switch ( $feature ) {
  86                 case 'search-update':
  87                         return true;
  88                 case 'title-suffix-filter':
  89                 default:
  90                         return false;
  91                 }
  92         }
  93
  94         /**
  95          * Way to pass custom data for engines
  96          * @since 1.18
  97          * @param string $feature
  98          * @param mixed $data
  99          * @return bool
 100          */
 101         public function setFeatureData( $feature, $data ) {
 102                 $this->features[$feature] = $data;
 103         }
 104
 105         /**
 106          * When overridden in derived class, performs database-specific conversions
 107          * on text to be used for searching or updating search index.
 108          * Default implementation does nothing (simply returns $string).
 109          *
 110          * @param string $string String to process
 111          * @return string
 112          */
 113         public function normalizeText( $string ) {
 114                 global $wgContLang;
 115
 116                 // Some languages such as Chinese require word segmentation
 117                 return $wgContLang->segmentByWord( $string );
 118         }
 119
 120         /**
 121          * Transform search term in cases when parts of the query came as different
 122          * GET params (when supported), e.g. for prefix queries:
 123          * search=test&prefix=Main_Page/Archive -> test prefix:Main Page/Archive
 124          * @param string $term
 125          * @return string
 126          */
 127         function transformSearchTerm( $term ) {
 128                 return $term;
 129         }
 130
 131         /**
 132          * If an exact title match can be found, or a very slightly close match,
 133          * return the title. If no match, returns NULL.
 134          *
 135          * @param string $searchterm
 136          * @return Title
 137          */
 138         public static function getNearMatch( $searchterm ) {
 139                 $title = self::getNearMatchInternal( $searchterm );
 140
 141                 Hooks::run( 'SearchGetNearMatchComplete', [ $searchterm, &$title ] );
 142                 return $title;
 143         }
 144
 145         /**
 146          * Do a near match (see SearchEngine::getNearMatch) and wrap it into a
 147          * SearchResultSet.
 148          *
 149          * @param string $searchterm
 150          * @return SearchResultSet
 151          */
 152         public static function getNearMatchResultSet( $searchterm ) {
 153                 return new SearchNearMatchResultSet( self::getNearMatch( $searchterm ) );
 154         }
 155
 156         /**
 157          * Really find the title match.
 158          * @param string $searchterm
 159          * @return null|Title
 160          */
 161         private static function getNearMatchInternal( $searchterm ) {
 162                 global $wgContLang, $wgEnableSearchContributorsByIP;
 163
 164                 $allSearchTerms = [ $searchterm ];
 165
 166                 if ( $wgContLang->hasVariants() ) {
 167                         $allSearchTerms = array_unique( array_merge(
 168                                 $allSearchTerms,
 169                                 $wgContLang->autoConvertToAllVariants( $searchterm )
 170                         ) );
 171                 }
 172
 173                 $titleResult = null;
 174                 if ( !Hooks::run( 'SearchGetNearMatchBefore', [ $allSearchTerms, &$titleResult ] ) ) {
 175                         return $titleResult;
 176                 }
 177
 178                 foreach ( $allSearchTerms as $term ) {
 179
 180                         # Exact match? No need to look further.
 181                         $title = Title::newFromText( $term );
 182                         if ( is_null( $title ) ) {
 183                                 return null;
 184                         }
 185
 186                         # Try files if searching in the Media: namespace
 187                         if ( $title->getNamespace() == NS_MEDIA ) {
 188                                 $title = Title::makeTitle( NS_FILE, $title->getText() );
 189                         }
 190
 191                         if ( $title->isSpecialPage() || $title->isExternal() || $title->exists() ) {
 192                                 return $title;
 193                         }
 194
 195                         # See if it still otherwise has content is some sane sense
 196                         $page = WikiPage::factory( $title );
 197                         if ( $page->hasViewableContent() ) {
 198                                 return $title;
 199                         }
 200
 201                         if ( !Hooks::run( 'SearchAfterNoDirectMatch', [ $term, &$title ] ) ) {
 202                                 return $title;
 203                         }
 204
 205                         # Now try all lower case (i.e. first letter capitalized)
 206                         $title = Title::newFromText( $wgContLang->lc( $term ) );
 207                         if ( $title && $title->exists() ) {
 208                                 return $title;
 209                         }
 210
 211                         # Now try capitalized string
 212                         $title = Title::newFromText( $wgContLang->ucwords( $term ) );
 213                         if ( $title && $title->exists() ) {
 214                                 return $title;
 215                         }
 216
 217                         # Now try all upper case
 218                         $title = Title::newFromText( $wgContLang->uc( $term ) );
 219                         if ( $title && $title->exists() ) {
 220                                 return $title;
 221                         }
 222
 223                         # Now try Word-Caps-Breaking-At-Word-Breaks, for hyphenated names etc
 224                         $title = Title::newFromText( $wgContLang->ucwordbreaks( $term ) );
 225                         if ( $title && $title->exists() ) {
 226                                 return $title;
 227                         }
 228
 229                         // Give hooks a chance at better match variants
 230                         $title = null;
 231                         if ( !Hooks::run( 'SearchGetNearMatch', [ $term, &$title ] ) ) {
 232                                 return $title;
 233                         }
 234                 }
 235
 236                 $title = Title::newFromText( $searchterm );
 237
 238                 # Entering an IP address goes to the contributions page
 239                 if ( $wgEnableSearchContributorsByIP ) {
 240                         if ( ( $title->getNamespace() == NS_USER && User::isIP( $title->getText() ) )
 241                                 || User::isIP( trim( $searchterm ) ) ) {
 242                                 return SpecialPage::getTitleFor( 'Contributions', $title->getDBkey() );
 243                         }
 244                 }
 245
 246                 # Entering a user goes to the user page whether it's there or not
 247                 if ( $title->getNamespace() == NS_USER ) {
 248                         return $title;
 249                 }
 250
 251                 # Go to images that exist even if there's no local page.
 252                 # There may have been a funny upload, or it may be on a shared
 253                 # file repository such as Wikimedia Commons.
 254                 if ( $title->getNamespace() == NS_FILE ) {
 255                         $image = wfFindFile( $title );
 256                         if ( $image ) {
 257                                 return $title;
 258                         }
 259                 }
 260
 261                 # MediaWiki namespace? Page may be "implied" if not customized.
 262                 # Just return it, with caps forced as the message system likes it.
 263                 if ( $title->getNamespace() == NS_MEDIAWIKI ) {
 264                         return Title::makeTitle( NS_MEDIAWIKI, $wgContLang->ucfirst( $title->getText() ) );
 265                 }
 266
 267                 # Quoted term? Try without the quotes...
 268                 $matches = [];
 269                 if ( preg_match( '/^"([^"]+)"$/', $searchterm, $matches ) ) {
 270                         return SearchEngine::getNearMatch( $matches[1] );
 271                 }
 272
 273                 return null;
 274         }
 275
 276         public static function legalSearchChars() {
 277                 return "A-Za-z_'.0-9\\x80-\\xFF\\-";
 278         }
 279
 280         /**
 281          * Set the maximum number of results to return
 282          * and how many to skip before returning the first.
 283          *
 284          * @param int $limit
 285          * @param int $offset
 286          */
 287         function setLimitOffset( $limit, $offset = 0 ) {
 288                 $this->limit = intval( $limit );
 289                 $this->offset = intval( $offset );
 290         }
 291
 292         /**
 293          * Set which namespaces the search should include.
 294          * Give an array of namespace index numbers.
 295          *
 296          * @param int[]|null $namespaces
 297          */
 298         function setNamespaces( $namespaces ) {
 299                 if ( $namespaces ) {
 300                         // Filter namespaces to only keep valid ones
 301                         $validNs = $this->searchableNamespaces();
 302                         $namespaces = array_filter( $namespaces, function( $ns ) use( $validNs ) {
 303                                 return $ns < 0 || isset( $validNs[$ns] );
 304                         } );
 305                 } else {
 306                         $namespaces = [];
 307                 }
 308                 $this->namespaces = $namespaces;
 309         }
 310
 311         /**
 312          * Set whether the searcher should try to build a suggestion.  Note: some searchers
 313          * don't support building a suggestion in the first place and others don't respect
 314          * this flag.
 315          *
 316          * @param bool $showSuggestion Should the searcher try to build suggestions
 317          */
 318         function setShowSuggestion( $showSuggestion ) {
 319                 $this->showSuggestion = $showSuggestion;
 320         }
 321
 322         /**
 323          * Get the valid sort directions.  All search engines support 'relevance' but others
 324          * might support more. The default in all implementations should be 'relevance.'
 325          *
 326          * @since 1.25
 327          * @return array(string) the valid sort directions for setSort
 328          */
 329         public function getValidSorts() {
 330                 return [ 'relevance' ];
 331         }
 332
 333         /**
 334          * Set the sort direction of the search results. Must be one returned by
 335          * SearchEngine::getValidSorts()
 336          *
 337          * @since 1.25
 338          * @throws InvalidArgumentException
 339          * @param string $sort sort direction for query result
 340          */
 341         public function setSort( $sort ) {
 342                 if ( !in_array( $sort, $this->getValidSorts() ) ) {
 343                         throw new InvalidArgumentException( "Invalid sort: $sort. " .
 344                                 "Must be one of: " . implode( ', ', $this->getValidSorts() ) );
 345                 }
 346                 $this->sort = $sort;
 347         }
 348
 349         /**
 350          * Get the sort direction of the search results
 351          *
 352          * @since 1.25
 353          * @return string
 354          */
 355         public function getSort() {
 356                 return $this->sort;
 357         }
 358
 359         /**
 360          * Parse some common prefixes: all (search everything)
 361          * or namespace names
 362          *
 363          * @param string $query
 364          * @return string
 365          */
 366         function replacePrefixes( $query ) {
 367                 global $wgContLang;
 368
 369                 $parsed = $query;
 370                 if ( strpos( $query, ':' ) === false ) { // nothing to do
 371                         return $parsed;
 372                 }
 373
 374                 $allkeyword = wfMessage( 'searchall' )->inContentLanguage()->text() . ":";
 375                 if ( strncmp( $query, $allkeyword, strlen( $allkeyword ) ) == 0 ) {
 376                         $this->namespaces = null;
 377                         $parsed = substr( $query, strlen( $allkeyword ) );
 378                 } elseif ( strpos( $query, ':' ) !== false ) {
 379                         $prefix = str_replace( ' ', '_', substr( $query, 0, strpos( $query, ':' ) ) );
 380                         $index = $wgContLang->getNsIndex( $prefix );
 381                         if ( $index !== false ) {
 382                                 $this->namespaces = [ $index ];
 383                                 $parsed = substr( $query, strlen( $prefix ) + 1 );
 384                         }
 385                 }
 386                 if ( trim( $parsed ) == '' ) {
 387                         $parsed = $query; // prefix was the whole query
 388                 }
 389
 390                 return $parsed;
 391         }
 392
 393         /**
 394          * Make a list of searchable namespaces and their canonical names.
 395          * @return array
 396          */
 397         public static function searchableNamespaces() {
 398                 global $wgContLang;
 399                 $arr = [];
 400                 foreach ( $wgContLang->getNamespaces() as $ns => $name ) {
 401                         if ( $ns >= NS_MAIN ) {
 402                                 $arr[$ns] = $name;
 403                         }
 404                 }
 405
 406                 Hooks::run( 'SearchableNamespaces', [ &$arr ] );
 407                 return $arr;
 408         }
 409
 410         /**
 411          * Extract default namespaces to search from the given user's
 412          * settings, returning a list of index numbers.
 413          *
 414          * @param user $user
 415          * @return array
 416          */
 417         public static function userNamespaces( $user ) {
 418                 $arr = [];
 419                 foreach ( SearchEngine::searchableNamespaces() as $ns => $name ) {
 420                         if ( $user->getOption( 'searchNs' . $ns ) ) {
 421                                 $arr[] = $ns;
 422                         }
 423                 }
 424
 425                 return $arr;
 426         }
 427
 428         /**
 429          * Find snippet highlight settings for all users
 430          *
 431          * @return array Contextlines, contextchars
 432          */
 433         public static function userHighlightPrefs() {
 434                 $contextlines = 2; // Hardcode this. Old defaults sucked. :)
 435                 $contextchars = 75; // same as above.... :P
 436                 return [ $contextlines, $contextchars ];
 437         }
 438
 439         /**
 440          * An array of namespaces indexes to be searched by default
 441          *
 442          * @return array
 443          */
 444         public static function defaultNamespaces() {
 445                 global $wgNamespacesToBeSearchedDefault;
 446
 447                 return array_keys( $wgNamespacesToBeSearchedDefault, true );
 448         }
 449
 450         /**
 451          * Get a list of namespace names useful for showing in tooltips
 452          * and preferences
 453          *
 454          * @param array $namespaces
 455          * @return array
 456          */
 457         public static function namespacesAsText( $namespaces ) {
 458                 global $wgContLang;
 459
 460                 $formatted = array_map( [ $wgContLang, 'getFormattedNsText' ], $namespaces );
 461                 foreach ( $formatted as $key => $ns ) {
 462                         if ( empty( $ns ) ) {
 463                                 $formatted[$key] = wfMessage( 'blanknamespace' )->text();
 464                         }
 465                 }
 466                 return $formatted;
 467         }
 468
 469         /**
 470          * Load up the appropriate search engine class for the currently
 471          * active database backend, and return a configured instance.
 472          *
 473          * @param string $type Type of search backend, if not the default
 474          * @return SearchEngine
 475          */
 476         public static function create( $type = null ) {
 477                 global $wgSearchType;
 478                 $dbr = null;
 479
 480                 $alternatives = self::getSearchTypes();
 481
 482                 if ( $type && in_array( $type, $alternatives ) ) {
 483                         $class = $type;
 484                 } elseif ( $wgSearchType !== null ) {
 485                         $class = $wgSearchType;
 486                 } else {
 487                         $dbr = wfGetDB( DB_SLAVE );
 488                         $class = $dbr->getSearchEngine();
 489                 }
 490
 491                 $search = new $class( $dbr );
 492                 return $search;
 493         }
 494
 495         /**
 496          * Return the search engines we support. If only $wgSearchType
 497          * is set, it'll be an array of just that one item.
 498          *
 499          * @return array
 500          */
 501         public static function getSearchTypes() {
 502                 global $wgSearchType, $wgSearchTypeAlternatives;
 503
 504                 $alternatives = $wgSearchTypeAlternatives ?: [];
 505                 array_unshift( $alternatives, $wgSearchType );
 506
 507                 return $alternatives;
 508         }
 509
 510         /**
 511          * Create or update the search index record for the given page.
 512          * Title and text should be pre-processed.
 513          * STUB
 514          *
 515          * @param int $id
 516          * @param string $title
 517          * @param string $text
 518          */
 519         function update( $id, $title, $text ) {
 520                 // no-op
 521         }
 522
 523         /**
 524          * Update a search index record's title only.
 525          * Title should be pre-processed.
 526          * STUB
 527          *
 528          * @param int $id
 529          * @param string $title
 530          */
 531         function updateTitle( $id, $title ) {
 532                 // no-op
 533         }
 534
 535         /**
 536          * Delete an indexed page
 537          * Title should be pre-processed.
 538          * STUB
 539          *
 540          * @param int $id Page id that was deleted
 541          * @param string $title Title of page that was deleted
 542          */
 543         function delete( $id, $title ) {
 544                 // no-op
 545         }
 546
 547         /**
 548          * Get OpenSearch suggestion template
 549          *
 550          * @deprecated since 1.25
 551          * @return string
 552          */
 553         public static function getOpenSearchTemplate() {
 554                 wfDeprecated( __METHOD__, '1.25' );
 555                 return ApiOpenSearch::getOpenSearchTemplate( 'application/x-suggestions+json' );
 556         }
 557
 558         /**
 559          * Get the raw text for updating the index from a content object
 560          * Nicer search backends could possibly do something cooler than
 561          * just returning raw text
 562          *
 563          * @todo This isn't ideal, we'd really like to have content-specific handling here
 564          * @param Title $t Title we're indexing
 565          * @param Content $c Content of the page to index
 566          * @return string
 567          */
 568         public function getTextFromContent( Title $t, Content $c = null ) {
 569                 return $c ? $c->getTextForSearchIndex() : '';
 570         }
 571
 572         /**
 573          * If an implementation of SearchEngine handles all of its own text processing
 574          * in getTextFromContent() and doesn't require SearchUpdate::updateText()'s
 575          * rather silly handling, it should return true here instead.
 576          *
 577          * @return bool
 578          */
 579         public function textAlreadyUpdatedForIndex() {
 580                 return false;
 581         }
 582
 583         /**
 584          * Makes search simple string if it was namespaced.
 585          * Sets namespaces of the search to namespaces extracted from string.
 586          * @param string $search
 587          * @return $string Simplified search string
 588          */
 589         protected function normalizeNamespaces( $search ) {
 590                 // Find a Title which is not an interwiki and is in NS_MAIN
 591                 $title = Title::newFromText( $search );
 592                 $ns = $this->namespaces;
 593                 if ( $title && !$title->isExternal() ) {
 594                         $ns = [ $title->getNamespace() ];
 595                         $search = $title->getText();
 596                         if ( $ns[0] == NS_MAIN ) {
 597                                 $ns = $this->namespaces; // no explicit prefix, use default namespaces
 598                                 Hooks::run( 'PrefixSearchExtractNamespace', [ &$ns, &$search ] );
 599                         }
 600                 } else {
 601                         $title = Title::newFromText( $search . 'Dummy' );
 602                         if ( $title && $title->getText() == 'Dummy'
 603                                         && $title->getNamespace() != NS_MAIN
 604                                         && !$title->isExternal() )
 605                         {
 606                                 $ns = [ $title->getNamespace() ];
 607                                 $search = '';
 608                         } else {
 609                                 Hooks::run( 'PrefixSearchExtractNamespace', [ &$ns, &$search ] );
 610                         }
 611                 }
 612
 613                 $ns = array_map( function( $space ) {
 614                         return $space == NS_MEDIA ? NS_FILE : $space;
 615                 }, $ns );
 616
 617                 $this->setNamespaces( $ns );
 618                 return $search;
 619         }
 620
 621         /**
 622          * Perform a completion search.
 623          * Does not resolve namespaces and does not check variants.
 624          * Search engine implementations may want to override this function.
 625          * @param string $search
 626          * @return SearchSuggestionSet
 627          */
 628         protected function completionSearchBackend( $search ) {
 629                 $results = [];
 630
 631                 $search = trim( $search );
 632
 633                 if ( !in_array( NS_SPECIAL, $this->namespaces ) && // We do not run hook on Special: search
 634                          !Hooks::run( 'PrefixSearchBackend',
 635                                 [ $this->namespaces, $search, $this->limit, &$results, $this->offset ]
 636                 ) ) {
 637                         // False means hook worked.
 638                         // FIXME: Yes, the API is weird. That's why it is going to be deprecated.
 639
 640                         return SearchSuggestionSet::fromStrings( $results );
 641                 } else {
 642                         // Hook did not do the job, use default simple search
 643                         $results = $this->simplePrefixSearch( $search );
 644                         return SearchSuggestionSet::fromTitles( $results );
 645                 }
 646         }
 647
 648         /**
 649          * Perform a completion search.
 650          * @param string $search
 651          * @return SearchSuggestionSet
 652          */
 653         public function completionSearch( $search ) {
 654                 if ( trim( $search ) === '' ) {
 655                         return SearchSuggestionSet::emptySuggestionSet(); // Return empty result
 656                 }
 657                 $search = $this->normalizeNamespaces( $search );
 658                 return $this->processCompletionResults( $search, $this->completionSearchBackend( $search ) );
 659         }
 660
 661         /**
 662          * Perform a completion search with variants.
 663          * @param string $search
 664          * @return SearchSuggestionSet
 665          */
 666         public function completionSearchWithVariants( $search ) {
 667                 if ( trim( $search ) === '' ) {
 668                         return SearchSuggestionSet::emptySuggestionSet(); // Return empty result
 669                 }
 670                 $search = $this->normalizeNamespaces( $search );
 671
 672                 $results = $this->completionSearchBackend( $search );
 673                 $fallbackLimit = $this->limit - $results->getSize();
 674                 if ( $fallbackLimit > 0 ) {
 675                         global $wgContLang;
 676
 677                         $fallbackSearches = $wgContLang->autoConvertToAllVariants( $search );
 678                         $fallbackSearches = array_diff( array_unique( $fallbackSearches ), [ $search ] );
 679
 680                         foreach ( $fallbackSearches as $fbs ) {
 681                                 $this->setLimitOffset( $fallbackLimit );
 682                                 $fallbackSearchResult = $this->completionSearch( $fbs );
 683                                 $results->appendAll( $fallbackSearchResult );
 684                                 $fallbackLimit -= count( $fallbackSearchResult );
 685                                 if ( $fallbackLimit <= 0 ) {
 686                                         break;
 687                                 }
 688                         }
 689                 }
 690                 return $this->processCompletionResults( $search, $results );
 691         }
 692
 693         /**
 694          * Extract titles from completion results
 695          * @param SearchSuggestionSet $completionResults
 696          * @return Title[]
 697          */
 698         public function extractTitles( SearchSuggestionSet $completionResults ) {
 699                 return $completionResults->map( function( SearchSuggestion $sugg ) {
 700                         return $sugg->getSuggestedTitle();
 701                 } );
 702         }
 703
 704         /**
 705          * Process completion search results.
 706          * Resolves the titles and rescores.
 707          * @param SearchSuggestionSet $suggestions
 708          * @return SearchSuggestionSet
 709          */
 710         protected function processCompletionResults( $search, SearchSuggestionSet $suggestions ) {
 711                 $search = trim( $search );
 712                 // preload the titles with LinkBatch
 713                 $titles = $suggestions->map( function( SearchSuggestion $sugg ) {
 714                         return $sugg->getSuggestedTitle();
 715                 } );
 716                 $lb = new LinkBatch( $titles );
 717                 $lb->setCaller( __METHOD__ );
 718                 $lb->execute();
 719
 720                 $results = $suggestions->map( function( SearchSuggestion $sugg ) {
 721                         return $sugg->getSuggestedTitle()->getPrefixedText();
 722                 } );
 723
 724                 // Rescore results with an exact title match
 725                 // NOTE: in some cases like cross-namespace redirects
 726                 // (frequently used as shortcuts e.g. WP:WP on huwiki) some
 727                 // backends like Cirrus will return no results. We should still
 728                 // try an exact title match to workaround this limitation
 729                 $rescorer = new SearchExactMatchRescorer();
 730                 $rescoredResults = $rescorer->rescore( $search, $this->namespaces, $results, $this->limit );
 731
 732                 if ( count( $rescoredResults ) > 0 ) {
 733                         $found = array_search( $rescoredResults[0], $results );
 734                         if ( $found === false ) {
 735                                 // If the first result is not in the previous array it
 736                                 // means that we found a new exact match
 737                                 $exactMatch = SearchSuggestion::fromTitle( 0, Title::newFromText( $rescoredResults[0] ) );
 738                                 $suggestions->prepend( $exactMatch );
 739                                 $suggestions->shrink( $this->limit );
 740                         } else {
 741                                 // if the first result is not the same we need to rescore
 742                                 if ( $found > 0 ) {
 743                                         $suggestions->rescore( $found );
 744                                 }
 745                         }
 746                 }
 747
 748                 return $suggestions;
 749         }
 750
 751         /**
 752          * Simple prefix search for subpages.
 753          * @param string $search
 754          * @return Title[]
 755          */
 756         public function defaultPrefixSearch( $search ) {
 757                 if ( trim( $search ) === '' ) {
 758                         return [];
 759                 }
 760
 761                 $search = $this->normalizeNamespaces( $search );
 762                 return $this->simplePrefixSearch( $search );
 763         }
 764
 765         /**
 766          * Call out to simple search backend.
 767          * Defaults to TitlePrefixSearch.
 768          * @param string $search
 769          * @return Title[]
 770          */
 771         protected function simplePrefixSearch( $search ) {
 772                 // Use default database prefix search
 773                 $backend = new TitlePrefixSearch;
 774                 return $backend->defaultSearchBackend( $this->namespaces, $search, $this->limit, $this->offset );
 775         }
 776
 777 }
 778
 779 /**
 780  * Dummy class to be used when non-supported Database engine is present.
 781  * @todo FIXME: Dummy class should probably try something at least mildly useful,
 782  * such as a LIKE search through titles.
 783  * @ingroup Search
 784  */
 785 class SearchEngineDummy extends SearchEngine {
 786         // no-op
 787 }