includes/pager/IndexPager.php

   1 <?php
   2 /**
   3  * Efficient paging for SQL queries.
   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 Pager
  22  */
  23
  24 use MediaWiki\Linker\LinkRenderer;
  25 use MediaWiki\MediaWikiServices;
  26 use MediaWiki\Navigation\PrevNextNavigationRenderer;
  27 use Wikimedia\Rdbms\IDatabase;
  28 use Wikimedia\Rdbms\IResultWrapper;
  29
  30 /**
  31  * IndexPager is an efficient pager which uses a (roughly unique) index in the
  32  * data set to implement paging, rather than a "LIMIT offset,limit" clause.
  33  * In MySQL, such a limit/offset clause requires counting through the
  34  * specified number of offset rows to find the desired data, which can be
  35  * expensive for large offsets.
  36  *
  37  * ReverseChronologicalPager is a child class of the abstract IndexPager, and
  38  * contains  some formatting and display code which is specific to the use of
  39  * timestamps as  indexes. Here is a synopsis of its operation:
  40  *
  41  *    * The query is specified by the offset, limit and direction (dir)
  42  *      parameters, in addition to any subclass-specific parameters.
  43  *    * The offset is the non-inclusive start of the DB query. A row with an
  44  *      index value equal to the offset will never be shown.
  45  *    * The query may either be done backwards, where the rows are returned by
  46  *      the database in the opposite order to which they are displayed to the
  47  *      user, or forwards. This is specified by the "dir" parameter, dir=prev
  48  *      means backwards, anything else means forwards. The offset value
  49  *      specifies the start of the database result set, which may be either
  50  *      the start or end of the displayed data set. This allows "previous"
  51  *      links to be implemented without knowledge of the index value at the
  52  *      start of the previous page.
  53  *    * An additional row beyond the user-specified limit is always requested.
  54  *      This allows us to tell whether we should display a "next" link in the
  55  *      case of forwards mode, or a "previous" link in the case of backwards
  56  *      mode. Determining whether to display the other link (the one for the
  57  *      page before the start of the database result set) can be done
  58  *      heuristically by examining the offset.
  59  *
  60  *    * An empty offset indicates that the offset condition should be omitted
  61  *      from the query. This naturally produces either the first page or the
  62  *      last page depending on the dir parameter.
  63  *
  64  *  Subclassing the pager to implement concrete functionality should be fairly
  65  *  simple, please see the examples in HistoryAction.php and
  66  *  SpecialBlockList.php. You just need to override formatRow(),
  67  *  getQueryInfo() and getIndexField(). Don't forget to call the parent
  68  *  constructor if you override it.
  69  *
  70  * @ingroup Pager
  71  */
  72 abstract class IndexPager extends ContextSource implements Pager {
  73         /** Backwards-compatible constant for $mDefaultDirection field (do not change) */
  74         const DIR_ASCENDING = false;
  75         /** Backwards-compatible constant for $mDefaultDirection field (do not change) */
  76         const DIR_DESCENDING = true;
  77
  78         /** Backwards-compatible constant for reallyDoQuery() (do not change) */
  79         const QUERY_ASCENDING = true;
  80         /** Backwards-compatible constant for reallyDoQuery() (do not change) */
  81         const QUERY_DESCENDING = false;
  82
  83         /** @var WebRequest */
  84         public $mRequest;
  85         /** @var int[] List of default entry limit options to be presented to clients */
  86         public $mLimitsShown = [ 20, 50, 100, 250, 500 ];
  87         /** @var int The default entry limit choosen for clients */
  88         public $mDefaultLimit = 50;
  89         /** @var mixed The starting point to enumerate entries */
  90         public $mOffset;
  91         /** @var int The maximum number of entries to show */
  92         public $mLimit;
  93         /** @var bool Whether the listing query completed */
  94         public $mQueryDone = false;
  95         /** @var IDatabase */
  96         public $mDb;
  97         /** @var stdClass|bool|null Extra row fetched at the end to see if the end was reached */
  98         public $mPastTheEndRow;
  99
 100         /**
 101          * The index to actually be used for ordering. This is a single column,
 102          * for one ordering, even if multiple orderings are supported.
 103          * @var string
 104          */
 105         protected $mIndexField;
 106         /**
 107          * An array of secondary columns to order by. These fields are not part of the offset.
 108          * This is a column list for one ordering, even if multiple orderings are supported.
 109          * @var string[]
 110          */
 111         protected $mExtraSortFields;
 112         /** For pages that support multiple types of ordering, which one to use.
 113          * @var string|null
 114          */
 115         protected $mOrderType;
 116         /**
 117          * $mDefaultDirection gives the direction to use when sorting results:
 118          * DIR_ASCENDING or DIR_DESCENDING. If $mIsBackwards is set, we start from
 119          * the opposite end, but we still sort the page itself according to
 120          * $mDefaultDirection. For example, if $mDefaultDirection is DIR_ASCENDING
 121          * but we're going backwards, we'll display the last page of results, but
 122          * the last result will be at the bottom, not the top.
 123          *
 124          * Like $mIndexField, $mDefaultDirection will be a single value even if the
 125          * class supports multiple default directions for different order types.
 126          * @var bool
 127          */
 128         public $mDefaultDirection;
 129         /** @var bool */
 130         public $mIsBackwards;
 131
 132         /** @var bool True if the current result set is the first one */
 133         public $mIsFirst;
 134         /** @var bool */
 135         public $mIsLast;
 136
 137         /** @var mixed */
 138         protected $mLastShown;
 139         /** @var mixed */
 140         protected $mFirstShown;
 141         /** @var mixed */
 142         protected $mPastTheEndIndex;
 143         /** @var array */
 144         protected $mDefaultQuery;
 145         /** @var string */
 146         protected $mNavigationBar;
 147
 148         /**
 149          * Whether to include the offset in the query
 150          * @var bool
 151          */
 152         protected $mIncludeOffset = false;
 153
 154         /**
 155          * Result object for the query. Warning: seek before use.
 156          *
 157          * @var IResultWrapper
 158          */
 159         public $mResult;
 160
 161         /** @var LinkRenderer */
 162         private $linkRenderer;
 163
 164         public function __construct( IContextSource $context = null, LinkRenderer $linkRenderer = null ) {
 165                 if ( $context ) {
 166                         $this->setContext( $context );
 167                 }
 168
 169                 $this->mRequest = $this->getRequest();
 170
 171                 # NB: the offset is quoted, not validated. It is treated as an
 172                 # arbitrary string to support the widest variety of index types. Be
 173                 # careful outputting it into HTML!
 174                 $this->mOffset = $this->mRequest->getText( 'offset' );
 175
 176                 # Use consistent behavior for the limit options
 177                 $this->mDefaultLimit = $this->getUser()->getIntOption( 'rclimit' );
 178                 if ( !$this->mLimit ) {
 179                         // Don't override if a subclass calls $this->setLimit() in its constructor.
 180                         list( $this->mLimit, /* $offset */ ) = $this->mRequest->getLimitOffset();
 181                 }
 182
 183                 $this->mIsBackwards = ( $this->mRequest->getVal( 'dir' ) == 'prev' );
 184                 # Let the subclass set the DB here; otherwise use a replica DB for the current wiki
 185                 $this->mDb = $this->mDb ?: wfGetDB( DB_REPLICA );
 186
 187                 $index = $this->getIndexField(); // column to sort on
 188                 $extraSort = $this->getExtraSortFields(); // extra columns to sort on for query planning
 189                 $order = $this->mRequest->getVal( 'order' );
 190                 if ( is_array( $index ) && isset( $index[$order] ) ) {
 191                         $this->mOrderType = $order;
 192                         $this->mIndexField = $index[$order];
 193                         $this->mExtraSortFields = isset( $extraSort[$order] )
 194                                 ? (array)$extraSort[$order]
 195                                 : [];
 196                 } elseif ( is_array( $index ) ) {
 197                         # First element is the default
 198                         $this->mIndexField = reset( $index );
 199                         $this->mOrderType = key( $index );
 200                         $this->mExtraSortFields = isset( $extraSort[$this->mOrderType] )
 201                                 ? (array)$extraSort[$this->mOrderType]
 202                                 : [];
 203                 } else {
 204                         # $index is not an array
 205                         $this->mOrderType = null;
 206                         $this->mIndexField = $index;
 207                         $this->mExtraSortFields = (array)$extraSort;
 208                 }
 209
 210                 if ( !isset( $this->mDefaultDirection ) ) {
 211                         $dir = $this->getDefaultDirections();
 212                         $this->mDefaultDirection = is_array( $dir )
 213                                 ? $dir[$this->mOrderType]
 214                                 : $dir;
 215                 }
 216                 $this->linkRenderer = $linkRenderer;
 217         }
 218
 219         /**
 220          * Get the Database object in use
 221          *
 222          * @return IDatabase
 223          */
 224         public function getDatabase() {
 225                 return $this->mDb;
 226         }
 227
 228         /**
 229          * Do the query, using information from the object context. This function
 230          * has been kept minimal to make it overridable if necessary, to allow for
 231          * result sets formed from multiple DB queries.
 232          */
 233         public function doQuery() {
 234                 # Use the child class name for profiling
 235                 $fname = __METHOD__ . ' (' . static::class . ')';
 236                 /** @noinspection PhpUnusedLocalVariableInspection */
 237                 $section = Profiler::instance()->scopedProfileIn( $fname );
 238
 239                 $defaultOrder = ( $this->mDefaultDirection === self::DIR_ASCENDING )
 240                         ? self::QUERY_ASCENDING
 241                         : self::QUERY_DESCENDING;
 242                 $order = $this->mIsBackwards ? self::oppositeOrder( $defaultOrder ) : $defaultOrder;
 243
 244                 # Plus an extra row so that we can tell the "next" link should be shown
 245                 $queryLimit = $this->mLimit + 1;
 246
 247                 if ( $this->mOffset == '' ) {
 248                         $isFirst = true;
 249                 } else {
 250                         // If there's an offset, we may or may not be at the first entry.
 251                         // The only way to tell is to run the query in the opposite
 252                         // direction see if we get a row.
 253                         $oldIncludeOffset = $this->mIncludeOffset;
 254                         $this->mIncludeOffset = !$this->mIncludeOffset;
 255                         $oppositeOrder = self::oppositeOrder( $order );
 256                         $isFirst = !$this->reallyDoQuery( $this->mOffset, 1, $oppositeOrder )->numRows();
 257                         $this->mIncludeOffset = $oldIncludeOffset;
 258                 }
 259
 260                 $this->mResult = $this->reallyDoQuery(
 261                         $this->mOffset,
 262                         $queryLimit,
 263                         $order
 264                 );
 265
 266                 $this->extractResultInfo( $isFirst, $queryLimit, $this->mResult );
 267                 $this->mQueryDone = true;
 268
 269                 $this->preprocessResults( $this->mResult );
 270                 $this->mResult->rewind(); // Paranoia
 271         }
 272
 273         /**
 274          * @param bool $order One of the IndexPager::QUERY_* class constants
 275          * @return bool The opposite query order as an IndexPager::QUERY_ constant
 276          */
 277         final protected static function oppositeOrder( $order ) {
 278                 return ( $order === self::QUERY_ASCENDING )
 279                         ? self::QUERY_DESCENDING
 280                         : self::QUERY_ASCENDING;
 281         }
 282
 283         /**
 284          * @return IResultWrapper The result wrapper.
 285          */
 286         function getResult() {
 287                 return $this->mResult;
 288         }
 289
 290         /**
 291          * Set the offset from an other source than the request
 292          *
 293          * @param int|string $offset
 294          */
 295         function setOffset( $offset ) {
 296                 $this->mOffset = $offset;
 297         }
 298
 299         /**
 300          * Set the limit from an other source than the request
 301          *
 302          * Verifies limit is between 1 and 5000
 303          *
 304          * @param int|string $limit
 305          */
 306         function setLimit( $limit ) {
 307                 $limit = (int)$limit;
 308                 // WebRequest::getLimitOffset() puts a cap of 5000, so do same here.
 309                 if ( $limit > 5000 ) {
 310                         $limit = 5000;
 311                 }
 312                 if ( $limit > 0 ) {
 313                         $this->mLimit = $limit;
 314                 }
 315         }
 316
 317         /**
 318          * Get the current limit
 319          *
 320          * @return int
 321          */
 322         function getLimit() {
 323                 return $this->mLimit;
 324         }
 325
 326         /**
 327          * Set whether a row matching exactly the offset should be also included
 328          * in the result or not. By default this is not the case, but when the
 329          * offset is user-supplied this might be wanted.
 330          *
 331          * @param bool $include
 332          */
 333         public function setIncludeOffset( $include ) {
 334                 $this->mIncludeOffset = $include;
 335         }
 336
 337         /**
 338          * Extract some useful data from the result object for use by
 339          * the navigation bar, put it into $this
 340          *
 341          * @param bool $isFirst False if there are rows before those fetched (i.e.
 342          *     if a "previous" link would make sense)
 343          * @param int $limit Exact query limit
 344          * @param IResultWrapper $res
 345          */
 346         function extractResultInfo( $isFirst, $limit, IResultWrapper $res ) {
 347                 $numRows = $res->numRows();
 348                 if ( $numRows ) {
 349                         # Remove any table prefix from index field
 350                         $parts = explode( '.', $this->mIndexField );
 351                         $indexColumn = end( $parts );
 352
 353                         $row = $res->fetchRow();
 354                         $firstIndex = $row[$indexColumn];
 355
 356                         # Discard the extra result row if there is one
 357                         if ( $numRows > $this->mLimit && $numRows > 1 ) {
 358                                 $res->seek( $numRows - 1 );
 359                                 $this->mPastTheEndRow = $res->fetchObject();
 360                                 $this->mPastTheEndIndex = $this->mPastTheEndRow->$indexColumn;
 361                                 $res->seek( $numRows - 2 );
 362                                 $row = $res->fetchRow();
 363                                 $lastIndex = $row[$indexColumn];
 364                         } else {
 365                                 $this->mPastTheEndRow = null;
 366                                 # Setting indexes to an empty string means that they will be
 367                                 # omitted if they would otherwise appear in URLs. It just so
 368                                 # happens that this  is the right thing to do in the standard
 369                                 # UI, in all the relevant cases.
 370                                 $this->mPastTheEndIndex = '';
 371                                 $res->seek( $numRows - 1 );
 372                                 $row = $res->fetchRow();
 373                                 $lastIndex = $row[$indexColumn];
 374                         }
 375                 } else {
 376                         $firstIndex = '';
 377                         $lastIndex = '';
 378                         $this->mPastTheEndRow = null;
 379                         $this->mPastTheEndIndex = '';
 380                 }
 381
 382                 if ( $this->mIsBackwards ) {
 383                         $this->mIsFirst = ( $numRows < $limit );
 384                         $this->mIsLast = $isFirst;
 385                         $this->mLastShown = $firstIndex;
 386                         $this->mFirstShown = $lastIndex;
 387                 } else {
 388                         $this->mIsFirst = $isFirst;
 389                         $this->mIsLast = ( $numRows < $limit );
 390                         $this->mLastShown = $lastIndex;
 391                         $this->mFirstShown = $firstIndex;
 392                 }
 393         }
 394
 395         /**
 396          * Get some text to go in brackets in the "function name" part of the SQL comment
 397          *
 398          * @return string
 399          */
 400         function getSqlComment() {
 401                 return static::class;
 402         }
 403
 404         /**
 405          * Do a query with specified parameters, rather than using the object context
 406          *
 407          * @note For b/c, query direction is true for ascending and false for descending
 408          *
 409          * @param string $offset Index offset, inclusive
 410          * @param int $limit Exact query limit
 411          * @param bool $order IndexPager::QUERY_ASCENDING or IndexPager::QUERY_DESCENDING
 412          * @return IResultWrapper
 413          */
 414         public function reallyDoQuery( $offset, $limit, $order ) {
 415                 list( $tables, $fields, $conds, $fname, $options, $join_conds ) =
 416                         $this->buildQueryInfo( $offset, $limit, $order );
 417
 418                 return $this->mDb->select( $tables, $fields, $conds, $fname, $options, $join_conds );
 419         }
 420
 421         /**
 422          * Build variables to use by the database wrapper.
 423          *
 424          * @note For b/c, query direction is true for ascending and false for descending
 425          *
 426          * @param string $offset Index offset, inclusive
 427          * @param int $limit Exact query limit
 428          * @param bool $order IndexPager::QUERY_ASCENDING or IndexPager::QUERY_DESCENDING
 429          * @return array
 430          */
 431         protected function buildQueryInfo( $offset, $limit, $order ) {
 432                 $fname = __METHOD__ . ' (' . $this->getSqlComment() . ')';
 433                 $info = $this->getQueryInfo();
 434                 $tables = $info['tables'];
 435                 $fields = $info['fields'];
 436                 $conds = $info['conds'] ?? [];
 437                 $options = $info['options'] ?? [];
 438                 $join_conds = $info['join_conds'] ?? [];
 439                 $sortColumns = array_merge( [ $this->mIndexField ], $this->mExtraSortFields );
 440                 if ( $order === self::QUERY_ASCENDING ) {
 441                         $options['ORDER BY'] = $sortColumns;
 442                         $operator = $this->mIncludeOffset ? '>=' : '>';
 443                 } else {
 444                         $orderBy = [];
 445                         foreach ( $sortColumns as $col ) {
 446                                 $orderBy[] = $col . ' DESC';
 447                         }
 448                         $options['ORDER BY'] = $orderBy;
 449                         $operator = $this->mIncludeOffset ? '<=' : '<';
 450                 }
 451                 if ( $offset != '' ) {
 452                         $conds[] = $this->mIndexField . $operator . $this->mDb->addQuotes( $offset );
 453                 }
 454                 $options['LIMIT'] = intval( $limit );
 455                 return [ $tables, $fields, $conds, $fname, $options, $join_conds ];
 456         }
 457
 458         /**
 459          * Pre-process results; useful for performing batch existence checks, etc.
 460          *
 461          * @param IResultWrapper $result
 462          */
 463         protected function preprocessResults( $result ) {
 464         }
 465
 466         /**
 467          * Get the formatted result list. Calls getStartBody(), formatRow() and
 468          * getEndBody(), concatenates the results and returns them.
 469          *
 470          * @return string
 471          */
 472         public function getBody() {
 473                 if ( !$this->mQueryDone ) {
 474                         $this->doQuery();
 475                 }
 476
 477                 if ( $this->mResult->numRows() ) {
 478                         # Do any special query batches before display
 479                         $this->doBatchLookups();
 480                 }
 481
 482                 # Don't use any extra rows returned by the query
 483                 $numRows = min( $this->mResult->numRows(), $this->mLimit );
 484
 485                 $s = $this->getStartBody();
 486                 if ( $numRows ) {
 487                         if ( $this->mIsBackwards ) {
 488                                 for ( $i = $numRows - 1; $i >= 0; $i-- ) {
 489                                         $this->mResult->seek( $i );
 490                                         $row = $this->mResult->fetchObject();
 491                                         $s .= $this->formatRow( $row );
 492                                 }
 493                         } else {
 494                                 $this->mResult->seek( 0 );
 495                                 for ( $i = 0; $i < $numRows; $i++ ) {
 496                                         $row = $this->mResult->fetchObject();
 497                                         $s .= $this->formatRow( $row );
 498                                 }
 499                         }
 500                 } else {
 501                         $s .= $this->getEmptyBody();
 502                 }
 503                 $s .= $this->getEndBody();
 504                 return $s;
 505         }
 506
 507         /**
 508          * Make a self-link
 509          *
 510          * @param string $text Text displayed on the link
 511          * @param array|null $query Associative array of parameter to be in the query string
 512          * @param string|null $type Link type used to create additional attributes, like "rel", "class" or
 513          *  "title". Valid values (non-exhaustive list): 'first', 'last', 'prev', 'next', 'asc', 'desc'.
 514          * @return string HTML fragment
 515          */
 516         function makeLink( $text, array $query = null, $type = null ) {
 517                 if ( $query === null ) {
 518                         return $text;
 519                 }
 520
 521                 $attrs = [];
 522                 if ( in_array( $type, [ 'prev', 'next' ] ) ) {
 523                         $attrs['rel'] = $type;
 524                 }
 525
 526                 if ( in_array( $type, [ 'asc', 'desc' ] ) ) {
 527                         $attrs['title'] = $this->msg( $type == 'asc' ? 'sort-ascending' : 'sort-descending' )->text();
 528                 }
 529
 530                 if ( $type ) {
 531                         $attrs['class'] = "mw-{$type}link";
 532                 }
 533
 534                 return $this->getLinkRenderer()->makeKnownLink(
 535                         $this->getTitle(),
 536                         new HtmlArmor( $text ),
 537                         $attrs,
 538                         $query + $this->getDefaultQuery()
 539                 );
 540         }
 541
 542         /**
 543          * Called from getBody(), before getStartBody() is called and
 544          * after doQuery() was called. This will be called only if there
 545          * are rows in the result set.
 546          *
 547          * @return void
 548          */
 549         protected function doBatchLookups() {
 550         }
 551
 552         /**
 553          * Hook into getBody(), allows text to be inserted at the start. This
 554          * will be called even if there are no rows in the result set.
 555          *
 556          * @return string
 557          */
 558         protected function getStartBody() {
 559                 return '';
 560         }
 561
 562         /**
 563          * Hook into getBody() for the end of the list
 564          *
 565          * @return string
 566          */
 567         protected function getEndBody() {
 568                 return '';
 569         }
 570
 571         /**
 572          * Hook into getBody(), for the bit between the start and the
 573          * end when there are no rows
 574          *
 575          * @return string
 576          */
 577         protected function getEmptyBody() {
 578                 return '';
 579         }
 580
 581         /**
 582          * Get an array of query parameters that should be put into self-links.
 583          * By default, all parameters passed in the URL are used, except for a
 584          * short blacklist.
 585          *
 586          * @return array Associative array
 587          */
 588         function getDefaultQuery() {
 589                 if ( !isset( $this->mDefaultQuery ) ) {
 590                         $this->mDefaultQuery = $this->getRequest()->getQueryValues();
 591                         unset( $this->mDefaultQuery['title'] );
 592                         unset( $this->mDefaultQuery['dir'] );
 593                         unset( $this->mDefaultQuery['offset'] );
 594                         unset( $this->mDefaultQuery['limit'] );
 595                         unset( $this->mDefaultQuery['order'] );
 596                         unset( $this->mDefaultQuery['month'] );
 597                         unset( $this->mDefaultQuery['year'] );
 598                 }
 599                 return $this->mDefaultQuery;
 600         }
 601
 602         /**
 603          * Get the number of rows in the result set
 604          *
 605          * @return int
 606          */
 607         function getNumRows() {
 608                 if ( !$this->mQueryDone ) {
 609                         $this->doQuery();
 610                 }
 611                 return $this->mResult->numRows();
 612         }
 613
 614         /**
 615          * Get a URL query array for the prev, next, first and last links.
 616          *
 617          * @return array
 618          */
 619         function getPagingQueries() {
 620                 if ( !$this->mQueryDone ) {
 621                         $this->doQuery();
 622                 }
 623
 624                 # Don't announce the limit everywhere if it's the default
 625                 $urlLimit = $this->mLimit == $this->mDefaultLimit ? null : $this->mLimit;
 626
 627                 if ( $this->mIsFirst ) {
 628                         $prev = false;
 629                         $first = false;
 630                 } else {
 631                         $prev = [
 632                                 'dir' => 'prev',
 633                                 'offset' => $this->mFirstShown,
 634                                 'limit' => $urlLimit
 635                         ];
 636                         $first = [ 'limit' => $urlLimit ];
 637                 }
 638                 if ( $this->mIsLast ) {
 639                         $next = false;
 640                         $last = false;
 641                 } else {
 642                         $next = [ 'offset' => $this->mLastShown, 'limit' => $urlLimit ];
 643                         $last = [ 'dir' => 'prev', 'limit' => $urlLimit ];
 644                 }
 645                 return [
 646                         'prev' => $prev,
 647                         'next' => $next,
 648                         'first' => $first,
 649                         'last' => $last
 650                 ];
 651         }
 652
 653         /**
 654          * Returns whether to show the "navigation bar"
 655          *
 656          * @return bool
 657          */
 658         function isNavigationBarShown() {
 659                 if ( !$this->mQueryDone ) {
 660                         $this->doQuery();
 661                 }
 662                 // Hide navigation by default if there is nothing to page
 663                 return !( $this->mIsFirst && $this->mIsLast );
 664         }
 665
 666         /**
 667          * Get paging links. If a link is disabled, the item from $disabledTexts
 668          * will be used. If there is no such item, the unlinked text from
 669          * $linkTexts will be used. Both $linkTexts and $disabledTexts are arrays
 670          * of HTML.
 671          *
 672          * @param array $linkTexts
 673          * @param array $disabledTexts
 674          * @return array
 675          */
 676         function getPagingLinks( $linkTexts, $disabledTexts = [] ) {
 677                 $queries = $this->getPagingQueries();
 678                 $links = [];
 679
 680                 foreach ( $queries as $type => $query ) {
 681                         if ( $query !== false ) {
 682                                 $links[$type] = $this->makeLink(
 683                                         $linkTexts[$type],
 684                                         $queries[$type],
 685                                         $type
 686                                 );
 687                         } elseif ( isset( $disabledTexts[$type] ) ) {
 688                                 $links[$type] = $disabledTexts[$type];
 689                         } else {
 690                                 $links[$type] = $linkTexts[$type];
 691                         }
 692                 }
 693
 694                 return $links;
 695         }
 696
 697         function getLimitLinks() {
 698                 $links = [];
 699                 if ( $this->mIsBackwards ) {
 700                         $offset = $this->mPastTheEndIndex;
 701                 } else {
 702                         $offset = $this->mOffset;
 703                 }
 704                 foreach ( $this->mLimitsShown as $limit ) {
 705                         $links[] = $this->makeLink(
 706                                 $this->getLanguage()->formatNum( $limit ),
 707                                 [ 'offset' => $offset, 'limit' => $limit ],
 708                                 'num'
 709                         );
 710                 }
 711                 return $links;
 712         }
 713
 714         /**
 715          * Abstract formatting function. This should return an HTML string
 716          * representing the result row $row. Rows will be concatenated and
 717          * returned by getBody()
 718          *
 719          * @param array|stdClass $row Database row
 720          * @return string
 721          */
 722         abstract function formatRow( $row );
 723
 724         /**
 725          * This function should be overridden to provide all parameters
 726          * needed for the main paged query. It returns an associative
 727          * array with the following elements:
 728          *    tables => Table(s) for passing to Database::select()
 729          *    fields => Field(s) for passing to Database::select(), may be *
 730          *    conds => WHERE conditions
 731          *    options => option array
 732          *    join_conds => JOIN conditions
 733          *
 734          * @return array
 735          */
 736         abstract function getQueryInfo();
 737
 738         /**
 739          * This function should be overridden to return the name of the index fi-
 740          * eld.  If the pager supports multiple orders, it may return an array of
 741          * 'querykey' => 'indexfield' pairs, so that a request with &count=querykey
 742          * will use indexfield to sort.  In this case, the first returned key is
 743          * the default.
 744          *
 745          * Needless to say, it's really not a good idea to use a non-unique index
 746          * for this!  That won't page right.
 747          *
 748          * @return string|string[]
 749          */
 750         abstract function getIndexField();
 751
 752         /**
 753          * This function should be overridden to return the names of secondary columns
 754          * to order by in addition to the column in getIndexField(). These fields will
 755          * not be used in the pager offset or in any links for users.
 756          *
 757          * If getIndexField() returns an array of 'querykey' => 'indexfield' pairs then
 758          * this must return a corresponding array of 'querykey' => [ fields... ] pairs
 759          * in order for a request with &count=querykey to use [ fields... ] to sort.
 760          *
 761          * This is useful for pagers that GROUP BY a unique column (say page_id)
 762          * and ORDER BY another (say page_len). Using GROUP BY and ORDER BY both on
 763          * page_len,page_id avoids temp tables (given a page_len index). This would
 764          * also work if page_id was non-unique but we had a page_len,page_id index.
 765          *
 766          * @return string[]|array[]
 767          */
 768         protected function getExtraSortFields() {
 769                 return [];
 770         }
 771
 772         /**
 773          * Return the default sorting direction: DIR_ASCENDING or DIR_DESCENDING.
 774          * You can also have an associative array of ordertype => dir,
 775          * if multiple order types are supported.  In this case getIndexField()
 776          * must return an array, and the keys of that must exactly match the keys
 777          * of this.
 778          *
 779          * For backward compatibility, this method's return value will be ignored
 780          * if $this->mDefaultDirection is already set when the constructor is
 781          * called, for instance if it's statically initialized.  In that case the
 782          * value of that variable (which must be a boolean) will be used.
 783          *
 784          * Note that despite its name, this does not return the value of the
 785          * $this->mDefaultDirection member variable.  That's the default for this
 786          * particular instantiation, which is a single value.  This is the set of
 787          * all defaults for the class.
 788          *
 789          * @return bool
 790          */
 791         protected function getDefaultDirections() {
 792                 return self::DIR_ASCENDING;
 793         }
 794
 795         /**
 796          * Generate (prev x| next x) (20|50|100...) type links for paging
 797          *
 798          * @param Title $title
 799          * @param int $offset
 800          * @param int $limit
 801          * @param array $query Optional URL query parameter string
 802          * @param bool $atend Optional param for specified if this is the last page
 803          * @return string
 804          */
 805         protected function buildPrevNextNavigation( Title $title, $offset, $limit,
 806                                                                                                 array $query = [], $atend = false
 807         ) {
 808                 $prevNext = new PrevNextNavigationRenderer( $this );
 809
 810                 return $prevNext->buildPrevNextNavigation( $title, $offset, $limit, $query,  $atend );
 811         }
 812
 813         protected function getLinkRenderer() {
 814                 if ( $this->linkRenderer === null ) {
 815                          $this->linkRenderer = MediaWikiServices::getInstance()->getLinkRenderer();
 816                 }
 817                 return $this->linkRenderer;
 818         }
 819 }