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\Linker\LinkTarget;
  26 use MediaWiki\MediaWikiServices;
  27 use MediaWiki\Navigation\PrevNextNavigationRenderer;
  28 use Wikimedia\Rdbms\IDatabase;
  29 use Wikimedia\Rdbms\IResultWrapper;
  30
  31 /**
  32  * IndexPager is an efficient pager which uses a (roughly unique) index in the
  33  * data set to implement paging, rather than a "LIMIT offset,limit" clause.
  34  * In MySQL, such a limit/offset clause requires counting through the
  35  * specified number of offset rows to find the desired data, which can be
  36  * expensive for large offsets.
  37  *
  38  * ReverseChronologicalPager is a child class of the abstract IndexPager, and
  39  * contains  some formatting and display code which is specific to the use of
  40  * timestamps as  indexes. Here is a synopsis of its operation:
  41  *
  42  *    * The query is specified by the offset, limit and direction (dir)
  43  *      parameters, in addition to any subclass-specific parameters.
  44  *    * The offset is the non-inclusive start of the DB query. A row with an
  45  *      index value equal to the offset will never be shown.
  46  *    * The query may either be done backwards, where the rows are returned by
  47  *      the database in the opposite order to which they are displayed to the
  48  *      user, or forwards. This is specified by the "dir" parameter, dir=prev
  49  *      means backwards, anything else means forwards. The offset value
  50  *      specifies the start of the database result set, which may be either
  51  *      the start or end of the displayed data set. This allows "previous"
  52  *      links to be implemented without knowledge of the index value at the
  53  *      start of the previous page.
  54  *    * An additional row beyond the user-specified limit is always requested.
  55  *      This allows us to tell whether we should display a "next" link in the
  56  *      case of forwards mode, or a "previous" link in the case of backwards
  57  *      mode. Determining whether to display the other link (the one for the
  58  *      page before the start of the database result set) can be done
  59  *      heuristically by examining the offset.
  60  *
  61  *    * An empty offset indicates that the offset condition should be omitted
  62  *      from the query. This naturally produces either the first page or the
  63  *      last page depending on the dir parameter.
  64  *
  65  *  Subclassing the pager to implement concrete functionality should be fairly
  66  *  simple, please see the examples in HistoryAction.php and
  67  *  SpecialBlockList.php. You just need to override formatRow(),
  68  *  getQueryInfo() and getIndexField(). Don't forget to call the parent
  69  *  constructor if you override it.
  70  *
  71  * @ingroup Pager
  72  */
  73 abstract class IndexPager extends ContextSource implements Pager {
  74         /** Backwards-compatible constant for $mDefaultDirection field (do not change) */
  75         const DIR_ASCENDING = false;
  76         /** Backwards-compatible constant for $mDefaultDirection field (do not change) */
  77         const DIR_DESCENDING = true;
  78
  79         /** Backwards-compatible constant for reallyDoQuery() (do not change) */
  80         const QUERY_ASCENDING = true;
  81         /** Backwards-compatible constant for reallyDoQuery() (do not change) */
  82         const QUERY_DESCENDING = false;
  83
  84         /** @var WebRequest */
  85         public $mRequest;
  86         /** @var int[] List of default entry limit options to be presented to clients */
  87         public $mLimitsShown = [ 20, 50, 100, 250, 500 ];
  88         /** @var int The default entry limit choosen for clients */
  89         public $mDefaultLimit = 50;
  90         /** @var mixed The starting point to enumerate entries */
  91         public $mOffset;
  92         /** @var int The maximum number of entries to show */
  93         public $mLimit;
  94         /** @var bool Whether the listing query completed */
  95         public $mQueryDone = false;
  96         /** @var IDatabase */
  97         public $mDb;
  98         /** @var stdClass|bool|null Extra row fetched at the end to see if the end was reached */
  99         public $mPastTheEndRow;
 100
 101         /**
 102          * The index to actually be used for ordering. This is a single column,
 103          * for one ordering, even if multiple orderings are supported.
 104          * @var string
 105          */
 106         protected $mIndexField;
 107         /**
 108          * An array of secondary columns to order by. These fields are not part of the offset.
 109          * This is a column list for one ordering, even if multiple orderings are supported.
 110          * @var string[]
 111          */
 112         protected $mExtraSortFields;
 113         /** For pages that support multiple types of ordering, which one to use.
 114          * @var string|null
 115          */
 116         protected $mOrderType;
 117         /**
 118          * $mDefaultDirection gives the direction to use when sorting results:
 119          * DIR_ASCENDING or DIR_DESCENDING. If $mIsBackwards is set, we start from
 120          * the opposite end, but we still sort the page itself according to
 121          * $mDefaultDirection. For example, if $mDefaultDirection is DIR_ASCENDING
 122          * but we're going backwards, we'll display the last page of results, but
 123          * the last result will be at the bottom, not the top.
 124          *
 125          * Like $mIndexField, $mDefaultDirection will be a single value even if the
 126          * class supports multiple default directions for different order types.
 127          * @var bool
 128          */
 129         public $mDefaultDirection;
 130         /** @var bool */
 131         public $mIsBackwards;
 132
 133         /** @var bool True if the current result set is the first one */
 134         public $mIsFirst;
 135         /** @var bool */
 136         public $mIsLast;
 137
 138         /** @var mixed */
 139         protected $mLastShown;
 140         /** @var mixed */
 141         protected $mFirstShown;
 142         /** @var mixed */
 143         protected $mPastTheEndIndex;
 144         /** @var array */
 145         protected $mDefaultQuery;
 146         /** @var string */
 147         protected $mNavigationBar;
 148
 149         /**
 150          * Whether to include the offset in the query
 151          * @var bool
 152          */
 153         protected $mIncludeOffset = false;
 154
 155         /**
 156          * Result object for the query. Warning: seek before use.
 157          *
 158          * @var IResultWrapper
 159          */
 160         public $mResult;
 161
 162         /** @var LinkRenderer */
 163         private $linkRenderer;
 164
 165         public function __construct( IContextSource $context = null, LinkRenderer $linkRenderer = null ) {
 166                 if ( $context ) {
 167                         $this->setContext( $context );
 168                 }
 169
 170                 $this->mRequest = $this->getRequest();
 171
 172                 # NB: the offset is quoted, not validated. It is treated as an
 173                 # arbitrary string to support the widest variety of index types. Be
 174                 # careful outputting it into HTML!
 175                 $this->mOffset = $this->mRequest->getText( 'offset' );
 176
 177                 # Use consistent behavior for the limit options
 178                 $this->mDefaultLimit = $this->getUser()->getIntOption( 'rclimit' );
 179                 if ( !$this->mLimit ) {
 180                         // Don't override if a subclass calls $this->setLimit() in its constructor.
 181                         list( $this->mLimit, /* $offset */ ) = $this->mRequest->getLimitOffset();
 182                 }
 183
 184                 $this->mIsBackwards = ( $this->mRequest->getVal( 'dir' ) == 'prev' );
 185                 # Let the subclass set the DB here; otherwise use a replica DB for the current wiki
 186                 $this->mDb = $this->mDb ?: wfGetDB( DB_REPLICA );
 187
 188                 $index = $this->getIndexField(); // column to sort on
 189                 $extraSort = $this->getExtraSortFields(); // extra columns to sort on for query planning
 190                 $order = $this->mRequest->getVal( 'order' );
 191                 if ( is_array( $index ) && isset( $index[$order] ) ) {
 192                         $this->mOrderType = $order;
 193                         $this->mIndexField = $index[$order];
 194                         $this->mExtraSortFields = isset( $extraSort[$order] )
 195                                 ? (array)$extraSort[$order]
 196                                 : [];
 197                 } elseif ( is_array( $index ) ) {
 198                         # First element is the default
 199                         $this->mIndexField = reset( $index );
 200                         $this->mOrderType = key( $index );
 201                         $this->mExtraSortFields = isset( $extraSort[$this->mOrderType] )
 202                                 ? (array)$extraSort[$this->mOrderType]
 203                                 : [];
 204                 } else {
 205                         # $index is not an array
 206                         $this->mOrderType = null;
 207                         $this->mIndexField = $index;
 208                         $this->mExtraSortFields = (array)$extraSort;
 209                 }
 210
 211                 if ( !isset( $this->mDefaultDirection ) ) {
 212                         $dir = $this->getDefaultDirections();
 213                         $this->mDefaultDirection = is_array( $dir )
 214                                 ? $dir[$this->mOrderType]
 215                                 : $dir;
 216                 }
 217                 $this->linkRenderer = $linkRenderer;
 218         }
 219
 220         /**
 221          * Get the Database object in use
 222          *
 223          * @return IDatabase
 224          */
 225         public function getDatabase() {
 226                 return $this->mDb;
 227         }
 228
 229         /**
 230          * Do the query, using information from the object context. This function
 231          * has been kept minimal to make it overridable if necessary, to allow for
 232          * result sets formed from multiple DB queries.
 233          */
 234         public function doQuery() {
 235                 # Use the child class name for profiling
 236                 $fname = __METHOD__ . ' (' . static::class . ')';
 237                 /** @noinspection PhpUnusedLocalVariableInspection */
 238                 $section = Profiler::instance()->scopedProfileIn( $fname );
 239
 240                 $defaultOrder = ( $this->mDefaultDirection === self::DIR_ASCENDING )
 241                         ? self::QUERY_ASCENDING
 242                         : self::QUERY_DESCENDING;
 243                 $order = $this->mIsBackwards ? self::oppositeOrder( $defaultOrder ) : $defaultOrder;
 244
 245                 # Plus an extra row so that we can tell the "next" link should be shown
 246                 $queryLimit = $this->mLimit + 1;
 247
 248                 if ( $this->mOffset == '' ) {
 249                         $isFirst = true;
 250                 } else {
 251                         // If there's an offset, we may or may not be at the first entry.
 252                         // The only way to tell is to run the query in the opposite
 253                         // direction see if we get a row.
 254                         $oldIncludeOffset = $this->mIncludeOffset;
 255                         $this->mIncludeOffset = !$this->mIncludeOffset;
 256                         $oppositeOrder = self::oppositeOrder( $order );
 257                         $isFirst = !$this->reallyDoQuery( $this->mOffset, 1, $oppositeOrder )->numRows();
 258                         $this->mIncludeOffset = $oldIncludeOffset;
 259                 }
 260
 261                 $this->mResult = $this->reallyDoQuery(
 262                         $this->mOffset,
 263                         $queryLimit,
 264                         $order
 265                 );
 266
 267                 $this->extractResultInfo( $isFirst, $queryLimit, $this->mResult );
 268                 $this->mQueryDone = true;
 269
 270                 $this->preprocessResults( $this->mResult );
 271                 $this->mResult->rewind(); // Paranoia
 272         }
 273
 274         /**
 275          * @param bool $order One of the IndexPager::QUERY_* class constants
 276          * @return bool The opposite query order as an IndexPager::QUERY_ constant
 277          */
 278         final protected static function oppositeOrder( $order ) {
 279                 return ( $order === self::QUERY_ASCENDING )
 280                         ? self::QUERY_DESCENDING
 281                         : self::QUERY_ASCENDING;
 282         }
 283
 284         /**
 285          * @return IResultWrapper The result wrapper.
 286          */
 287         function getResult() {
 288                 return $this->mResult;
 289         }
 290
 291         /**
 292          * Set the offset from an other source than the request
 293          *
 294          * @param int|string $offset
 295          */
 296         function setOffset( $offset ) {
 297                 $this->mOffset = $offset;
 298         }
 299
 300         /**
 301          * Set the limit from an other source than the request
 302          *
 303          * Verifies limit is between 1 and 5000
 304          *
 305          * @param int|string $limit
 306          */
 307         function setLimit( $limit ) {
 308                 $limit = (int)$limit;
 309                 // WebRequest::getLimitOffset() puts a cap of 5000, so do same here.
 310                 if ( $limit > 5000 ) {
 311                         $limit = 5000;
 312                 }
 313                 if ( $limit > 0 ) {
 314                         $this->mLimit = $limit;
 315                 }
 316         }
 317
 318         /**
 319          * Get the current limit
 320          *
 321          * @return int
 322          */
 323         function getLimit() {
 324                 return $this->mLimit;
 325         }
 326
 327         /**
 328          * Set whether a row matching exactly the offset should be also included
 329          * in the result or not. By default this is not the case, but when the
 330          * offset is user-supplied this might be wanted.
 331          *
 332          * @param bool $include
 333          */
 334         public function setIncludeOffset( $include ) {
 335                 $this->mIncludeOffset = $include;
 336         }
 337
 338         /**
 339          * Extract some useful data from the result object for use by
 340          * the navigation bar, put it into $this
 341          *
 342          * @param bool $isFirst False if there are rows before those fetched (i.e.
 343          *     if a "previous" link would make sense)
 344          * @param int $limit Exact query limit
 345          * @param IResultWrapper $res
 346          */
 347         function extractResultInfo( $isFirst, $limit, IResultWrapper $res ) {
 348                 $numRows = $res->numRows();
 349                 if ( $numRows ) {
 350                         # Remove any table prefix from index field
 351                         $parts = explode( '.', $this->mIndexField );
 352                         $indexColumn = end( $parts );
 353
 354                         $row = $res->fetchRow();
 355                         $firstIndex = $row[$indexColumn];
 356
 357                         # Discard the extra result row if there is one
 358                         if ( $numRows > $this->mLimit && $numRows > 1 ) {
 359                                 $res->seek( $numRows - 1 );
 360                                 $this->mPastTheEndRow = $res->fetchObject();
 361                                 $this->mPastTheEndIndex = $this->mPastTheEndRow->$indexColumn;
 362                                 $res->seek( $numRows - 2 );
 363                                 $row = $res->fetchRow();
 364                                 $lastIndex = $row[$indexColumn];
 365                         } else {
 366                                 $this->mPastTheEndRow = null;
 367                                 # Setting indexes to an empty string means that they will be
 368                                 # omitted if they would otherwise appear in URLs. It just so
 369                                 # happens that this  is the right thing to do in the standard
 370                                 # UI, in all the relevant cases.
 371                                 $this->mPastTheEndIndex = '';
 372                                 $res->seek( $numRows - 1 );
 373                                 $row = $res->fetchRow();
 374                                 $lastIndex = $row[$indexColumn];
 375                         }
 376                 } else {
 377                         $firstIndex = '';
 378                         $lastIndex = '';
 379                         $this->mPastTheEndRow = null;
 380                         $this->mPastTheEndIndex = '';
 381                 }
 382
 383                 if ( $this->mIsBackwards ) {
 384                         $this->mIsFirst = ( $numRows < $limit );
 385                         $this->mIsLast = $isFirst;
 386                         $this->mLastShown = $firstIndex;
 387                         $this->mFirstShown = $lastIndex;
 388                 } else {
 389                         $this->mIsFirst = $isFirst;
 390                         $this->mIsLast = ( $numRows < $limit );
 391                         $this->mLastShown = $lastIndex;
 392                         $this->mFirstShown = $firstIndex;
 393                 }
 394         }
 395
 396         /**
 397          * Get some text to go in brackets in the "function name" part of the SQL comment
 398          *
 399          * @return string
 400          */
 401         function getSqlComment() {
 402                 return static::class;
 403         }
 404
 405         /**
 406          * Do a query with specified parameters, rather than using the object context
 407          *
 408          * @note For b/c, query direction is true for ascending and false for descending
 409          *
 410          * @param string $offset Index offset, inclusive
 411          * @param int $limit Exact query limit
 412          * @param bool $order IndexPager::QUERY_ASCENDING or IndexPager::QUERY_DESCENDING
 413          * @return IResultWrapper
 414          */
 415         public function reallyDoQuery( $offset, $limit, $order ) {
 416                 list( $tables, $fields, $conds, $fname, $options, $join_conds ) =
 417                         $this->buildQueryInfo( $offset, $limit, $order );
 418
 419                 return $this->mDb->select( $tables, $fields, $conds, $fname, $options, $join_conds );
 420         }
 421
 422         /**
 423          * Build variables to use by the database wrapper.
 424          *
 425          * @note For b/c, query direction is true for ascending and false for descending
 426          *
 427          * @param string $offset Index offset, inclusive
 428          * @param int $limit Exact query limit
 429          * @param bool $order IndexPager::QUERY_ASCENDING or IndexPager::QUERY_DESCENDING
 430          * @return array
 431          */
 432         protected function buildQueryInfo( $offset, $limit, $order ) {
 433                 $fname = __METHOD__ . ' (' . $this->getSqlComment() . ')';
 434                 $info = $this->getQueryInfo();
 435                 $tables = $info['tables'];
 436                 $fields = $info['fields'];
 437                 $conds = $info['conds'] ?? [];
 438                 $options = $info['options'] ?? [];
 439                 $join_conds = $info['join_conds'] ?? [];
 440                 $sortColumns = array_merge( [ $this->mIndexField ], $this->mExtraSortFields );
 441                 if ( $order === self::QUERY_ASCENDING ) {
 442                         $options['ORDER BY'] = $sortColumns;
 443                         $operator = $this->mIncludeOffset ? '>=' : '>';
 444                 } else {
 445                         $orderBy = [];
 446                         foreach ( $sortColumns as $col ) {
 447                                 $orderBy[] = $col . ' DESC';
 448                         }
 449                         $options['ORDER BY'] = $orderBy;
 450                         $operator = $this->mIncludeOffset ? '<=' : '<';
 451                 }
 452                 if ( $offset != '' ) {
 453                         $conds[] = $this->mIndexField . $operator . $this->mDb->addQuotes( $offset );
 454                 }
 455                 $options['LIMIT'] = intval( $limit );
 456                 return [ $tables, $fields, $conds, $fname, $options, $join_conds ];
 457         }
 458
 459         /**
 460          * Pre-process results; useful for performing batch existence checks, etc.
 461          *
 462          * @param IResultWrapper $result
 463          */
 464         protected function preprocessResults( $result ) {
 465         }
 466
 467         /**
 468          * Get the formatted result list. Calls getStartBody(), formatRow() and
 469          * getEndBody(), concatenates the results and returns them.
 470          *
 471          * @return string
 472          */
 473         public function getBody() {
 474                 if ( !$this->mQueryDone ) {
 475                         $this->doQuery();
 476                 }
 477
 478                 if ( $this->mResult->numRows() ) {
 479                         # Do any special query batches before display
 480                         $this->doBatchLookups();
 481                 }
 482
 483                 # Don't use any extra rows returned by the query
 484                 $numRows = min( $this->mResult->numRows(), $this->mLimit );
 485
 486                 $s = $this->getStartBody();
 487                 if ( $numRows ) {
 488                         if ( $this->mIsBackwards ) {
 489                                 for ( $i = $numRows - 1; $i >= 0; $i-- ) {
 490                                         $this->mResult->seek( $i );
 491                                         $row = $this->mResult->fetchObject();
 492                                         $s .= $this->formatRow( $row );
 493                                 }
 494                         } else {
 495                                 $this->mResult->seek( 0 );
 496                                 for ( $i = 0; $i < $numRows; $i++ ) {
 497                                         $row = $this->mResult->fetchObject();
 498                                         $s .= $this->formatRow( $row );
 499                                 }
 500                         }
 501                 } else {
 502                         $s .= $this->getEmptyBody();
 503                 }
 504                 $s .= $this->getEndBody();
 505                 return $s;
 506         }
 507
 508         /**
 509          * Make a self-link
 510          *
 511          * @param string $text Text displayed on the link
 512          * @param array|null $query Associative array of parameter to be in the query string
 513          * @param string|null $type Link type used to create additional attributes, like "rel", "class" or
 514          *  "title". Valid values (non-exhaustive list): 'first', 'last', 'prev', 'next', 'asc', 'desc'.
 515          * @return string HTML fragment
 516          */
 517         function makeLink( $text, array $query = null, $type = null ) {
 518                 if ( $query === null ) {
 519                         return $text;
 520                 }
 521
 522                 $attrs = [];
 523                 if ( in_array( $type, [ 'prev', 'next' ] ) ) {
 524                         $attrs['rel'] = $type;
 525                 }
 526
 527                 if ( in_array( $type, [ 'asc', 'desc' ] ) ) {
 528                         $attrs['title'] = $this->msg( $type == 'asc' ? 'sort-ascending' : 'sort-descending' )->text();
 529                 }
 530
 531                 if ( $type ) {
 532                         $attrs['class'] = "mw-{$type}link";
 533                 }
 534
 535                 return $this->getLinkRenderer()->makeKnownLink(
 536                         $this->getTitle(),
 537                         new HtmlArmor( $text ),
 538                         $attrs,
 539                         $query + $this->getDefaultQuery()
 540                 );
 541         }
 542
 543         /**
 544          * Called from getBody(), before getStartBody() is called and
 545          * after doQuery() was called. This will be called only if there
 546          * are rows in the result set.
 547          *
 548          * @return void
 549          */
 550         protected function doBatchLookups() {
 551         }
 552
 553         /**
 554          * Hook into getBody(), allows text to be inserted at the start. This
 555          * will be called even if there are no rows in the result set.
 556          *
 557          * @return string
 558          */
 559         protected function getStartBody() {
 560                 return '';
 561         }
 562
 563         /**
 564          * Hook into getBody() for the end of the list
 565          *
 566          * @return string
 567          */
 568         protected function getEndBody() {
 569                 return '';
 570         }
 571
 572         /**
 573          * Hook into getBody(), for the bit between the start and the
 574          * end when there are no rows
 575          *
 576          * @return string
 577          */
 578         protected function getEmptyBody() {
 579                 return '';
 580         }
 581
 582         /**
 583          * Get an array of query parameters that should be put into self-links.
 584          * By default, all parameters passed in the URL are used, except for a
 585          * short blacklist.
 586          *
 587          * @return array Associative array
 588          */
 589         function getDefaultQuery() {
 590                 if ( !isset( $this->mDefaultQuery ) ) {
 591                         $this->mDefaultQuery = $this->getRequest()->getQueryValues();
 592                         unset( $this->mDefaultQuery['title'] );
 593                         unset( $this->mDefaultQuery['dir'] );
 594                         unset( $this->mDefaultQuery['offset'] );
 595                         unset( $this->mDefaultQuery['limit'] );
 596                         unset( $this->mDefaultQuery['order'] );
 597                         unset( $this->mDefaultQuery['month'] );
 598                         unset( $this->mDefaultQuery['year'] );
 599                 }
 600                 return $this->mDefaultQuery;
 601         }
 602
 603         /**
 604          * Get the number of rows in the result set
 605          *
 606          * @return int
 607          */
 608         function getNumRows() {
 609                 if ( !$this->mQueryDone ) {
 610                         $this->doQuery();
 611                 }
 612                 return $this->mResult->numRows();
 613         }
 614
 615         /**
 616          * Get a URL query array for the prev, next, first and last links.
 617          *
 618          * @return array
 619          */
 620         function getPagingQueries() {
 621                 if ( !$this->mQueryDone ) {
 622                         $this->doQuery();
 623                 }
 624
 625                 # Don't announce the limit everywhere if it's the default
 626                 $urlLimit = $this->mLimit == $this->mDefaultLimit ? null : $this->mLimit;
 627
 628                 if ( $this->mIsFirst ) {
 629                         $prev = false;
 630                         $first = false;
 631                 } else {
 632                         $prev = [
 633                                 'dir' => 'prev',
 634                                 'offset' => $this->mFirstShown,
 635                                 'limit' => $urlLimit
 636                         ];
 637                         $first = [ 'limit' => $urlLimit ];
 638                 }
 639                 if ( $this->mIsLast ) {
 640                         $next = false;
 641                         $last = false;
 642                 } else {
 643                         $next = [ 'offset' => $this->mLastShown, 'limit' => $urlLimit ];
 644                         $last = [ 'dir' => 'prev', 'limit' => $urlLimit ];
 645                 }
 646                 return [
 647                         'prev' => $prev,
 648                         'next' => $next,
 649                         'first' => $first,
 650                         'last' => $last
 651                 ];
 652         }
 653
 654         /**
 655          * Returns whether to show the "navigation bar"
 656          *
 657          * @return bool
 658          */
 659         function isNavigationBarShown() {
 660                 if ( !$this->mQueryDone ) {
 661                         $this->doQuery();
 662                 }
 663                 // Hide navigation by default if there is nothing to page
 664                 return !( $this->mIsFirst && $this->mIsLast );
 665         }
 666
 667         /**
 668          * Get paging links. If a link is disabled, the item from $disabledTexts
 669          * will be used. If there is no such item, the unlinked text from
 670          * $linkTexts will be used. Both $linkTexts and $disabledTexts are arrays
 671          * of HTML.
 672          *
 673          * @param array $linkTexts
 674          * @param array $disabledTexts
 675          * @return array
 676          */
 677         function getPagingLinks( $linkTexts, $disabledTexts = [] ) {
 678                 $queries = $this->getPagingQueries();
 679                 $links = [];
 680
 681                 foreach ( $queries as $type => $query ) {
 682                         if ( $query !== false ) {
 683                                 $links[$type] = $this->makeLink(
 684                                         $linkTexts[$type],
 685                                         $queries[$type],
 686                                         $type
 687                                 );
 688                         } elseif ( isset( $disabledTexts[$type] ) ) {
 689                                 $links[$type] = $disabledTexts[$type];
 690                         } else {
 691                                 $links[$type] = $linkTexts[$type];
 692                         }
 693                 }
 694
 695                 return $links;
 696         }
 697
 698         function getLimitLinks() {
 699                 $links = [];
 700                 if ( $this->mIsBackwards ) {
 701                         $offset = $this->mPastTheEndIndex;
 702                 } else {
 703                         $offset = $this->mOffset;
 704                 }
 705                 foreach ( $this->mLimitsShown as $limit ) {
 706                         $links[] = $this->makeLink(
 707                                 $this->getLanguage()->formatNum( $limit ),
 708                                 [ 'offset' => $offset, 'limit' => $limit ],
 709                                 'num'
 710                         );
 711                 }
 712                 return $links;
 713         }
 714
 715         /**
 716          * Abstract formatting function. This should return an HTML string
 717          * representing the result row $row. Rows will be concatenated and
 718          * returned by getBody()
 719          *
 720          * @param array|stdClass $row Database row
 721          * @return string
 722          */
 723         abstract function formatRow( $row );
 724
 725         /**
 726          * This function should be overridden to provide all parameters
 727          * needed for the main paged query. It returns an associative
 728          * array with the following elements:
 729          *    tables => Table(s) for passing to Database::select()
 730          *    fields => Field(s) for passing to Database::select(), may be *
 731          *    conds => WHERE conditions
 732          *    options => option array
 733          *    join_conds => JOIN conditions
 734          *
 735          * @return array
 736          */
 737         abstract function getQueryInfo();
 738
 739         /**
 740          * This function should be overridden to return the name of the index fi-
 741          * eld.  If the pager supports multiple orders, it may return an array of
 742          * 'querykey' => 'indexfield' pairs, so that a request with &count=querykey
 743          * will use indexfield to sort.  In this case, the first returned key is
 744          * the default.
 745          *
 746          * Needless to say, it's really not a good idea to use a non-unique index
 747          * for this!  That won't page right.
 748          *
 749          * @return string|string[]
 750          */
 751         abstract function getIndexField();
 752
 753         /**
 754          * This function should be overridden to return the names of secondary columns
 755          * to order by in addition to the column in getIndexField(). These fields will
 756          * not be used in the pager offset or in any links for users.
 757          *
 758          * If getIndexField() returns an array of 'querykey' => 'indexfield' pairs then
 759          * this must return a corresponding array of 'querykey' => [ fields... ] pairs
 760          * in order for a request with &count=querykey to use [ fields... ] to sort.
 761          *
 762          * This is useful for pagers that GROUP BY a unique column (say page_id)
 763          * and ORDER BY another (say page_len). Using GROUP BY and ORDER BY both on
 764          * page_len,page_id avoids temp tables (given a page_len index). This would
 765          * also work if page_id was non-unique but we had a page_len,page_id index.
 766          *
 767          * @return string[]|array[]
 768          */
 769         protected function getExtraSortFields() {
 770                 return [];
 771         }
 772
 773         /**
 774          * Return the default sorting direction: DIR_ASCENDING or DIR_DESCENDING.
 775          * You can also have an associative array of ordertype => dir,
 776          * if multiple order types are supported.  In this case getIndexField()
 777          * must return an array, and the keys of that must exactly match the keys
 778          * of this.
 779          *
 780          * For backward compatibility, this method's return value will be ignored
 781          * if $this->mDefaultDirection is already set when the constructor is
 782          * called, for instance if it's statically initialized.  In that case the
 783          * value of that variable (which must be a boolean) will be used.
 784          *
 785          * Note that despite its name, this does not return the value of the
 786          * $this->mDefaultDirection member variable.  That's the default for this
 787          * particular instantiation, which is a single value.  This is the set of
 788          * all defaults for the class.
 789          *
 790          * @return bool
 791          */
 792         protected function getDefaultDirections() {
 793                 return self::DIR_ASCENDING;
 794         }
 795
 796         /**
 797          * Generate (prev x| next x) (20|50|100...) type links for paging
 798          *
 799          * @param LinkTarget $title
 800          * @param int $offset
 801          * @param int $limit
 802          * @param array $query Optional URL query parameter string
 803          * @param bool $atend Optional param for specified if this is the last page
 804          * @return string
 805          */
 806         protected function buildPrevNextNavigation( LinkTarget $title, $offset, $limit,
 807                                                                                                 array $query = [], $atend = false
 808         ) {
 809                 $prevNext = new PrevNextNavigationRenderer( $this );
 810
 811                 return $prevNext->buildPrevNextNavigation( $title, $offset, $limit, $query,  $atend );
 812         }
 813
 814         protected function getLinkRenderer() {
 815                 if ( $this->linkRenderer === null ) {
 816                          $this->linkRenderer = MediaWikiServices::getInstance()->getLinkRenderer();
 817                 }
 818                 return $this->linkRenderer;
 819         }
 820 }