includes/specials/SpecialRandomInCategory.php
<?php
/**
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
* http://www.gnu.org/copyleft/gpl.html
*
* @file
*/
namespace MediaWiki\Specials;
use BadMethodCallException;
use MediaWiki\HTMLForm\HTMLForm;
use MediaWiki\SpecialPage\FormSpecialPage;
use MediaWiki\Status\Status;
use MediaWiki\Title\Title;
use stdClass;
use Wikimedia\Rdbms\IConnectionProvider;
use Wikimedia\Rdbms\SelectQueryBuilder;
/**
* Redirect to a random page in a category
*
* @note The method used here is rather biased. It is assumed that
* the use of this page will be people wanting to get a random page
* out of a maintenance category, to fix it up. The method used by
* this page should return different pages in an unpredictable fashion
* which is hoped to be sufficient, even if some pages are selected
* more often than others.
*
* A more unbiased method could be achieved by adding a cl_random field
* to the categorylinks table.
*
* The method used here is as follows:
* * Find the smallest and largest timestamp in the category
* * Pick a random timestamp in between
* * Pick an offset between 0 and 30
* * Get the offset'ed page that is newer than the timestamp selected
* The offset is meant to counter the fact the timestamps aren't usually
* uniformly distributed, so if things are very non-uniform at least we
* won't have the same page selected 99% of the time.
*
* @ingroup SpecialPage
* @author Brian Wolff
*/
class SpecialRandomInCategory extends FormSpecialPage {
/** @var string[] Extra SQL statements */
protected $extra = [];
/** @var Title|false Title object of category */
protected $category = false;
/** @var int Max amount to fudge randomness by */
protected $maxOffset = 30;
/** @var int|null */
private $maxTimestamp = null;
/** @var int|null */
private $minTimestamp = null;
private IConnectionProvider $dbProvider;
/**
* @param IConnectionProvider $dbProvider
*/
public function __construct( IConnectionProvider $dbProvider ) {
parent::__construct( 'RandomInCategory' );
$this->dbProvider = $dbProvider;
}
/**
* Set which category to use.
* @param Title $cat
*/
public function setCategory( Title $cat ) {
$this->category = $cat;
$this->maxTimestamp = null;
$this->minTimestamp = null;
}
protected function getFormFields() {
$this->addHelpLink( 'Help:RandomInCategory' );
return [
'category' => [
'type' => 'title',
'namespace' => NS_CATEGORY,
'relative' => true,
'label-message' => 'randomincategory-category',
'required' => true,
]
];
}
public function requiresPost() {
return false;
}
protected function getDisplayFormat() {
return 'ooui';
}
protected function alterForm( HTMLForm $form ) {
$form->setSubmitTextMsg( 'randomincategory-submit' );
}
protected function getSubpageField() {
return 'category';
}
public function onSubmit( array $data ) {
$cat = false;
$categoryStr = $data['category'];
if ( $categoryStr ) {
$cat = Title::newFromText( $categoryStr, NS_CATEGORY );
}
if ( $cat && $cat->getNamespace() !== NS_CATEGORY ) {
// Someone searching for something like "Wikipedia:Foo"
$cat = Title::makeTitleSafe( NS_CATEGORY, $categoryStr );
}
if ( $cat ) {
$this->setCategory( $cat );
}
if ( !$this->category && $categoryStr ) {
$msg = $this->msg( 'randomincategory-invalidcategory',
wfEscapeWikiText( $categoryStr ) );
return Status::newFatal( $msg );
} elseif ( !$this->category ) {
return false; // no data sent
}
$title = $this->getRandomTitle();
if ( $title === null ) {
$msg = $this->msg( 'randomincategory-nopages',
$this->category->getText() );
return Status::newFatal( $msg );
}
$query = $this->getRequest()->getQueryValues();
unset( $query['title'] );
$this->getOutput()->redirect( $title->getFullURL( $query ) );
}
/**
* Choose a random title.
* @return Title|null Title object or null if nothing to choose from
*/
public function getRandomTitle() {
// Convert to float, since we do math with the random number.
$rand = (float)wfRandom();
// Given that timestamps are rather unevenly distributed, we also
// use an offset between 0 and 30 to make any biases less noticeable.
$offset = mt_rand( 0, $this->maxOffset );
if ( mt_rand( 0, 1 ) ) {
$up = true;
} else {
$up = false;
}
$row = $this->selectRandomPageFromDB( $rand, $offset, $up, __METHOD__ );
// Try again without the timestamp offset (wrap around the end)
if ( !$row ) {
$row = $this->selectRandomPageFromDB( false, $offset, $up, __METHOD__ );
}
// Maybe the category is really small and offset too high
if ( !$row ) {
$row = $this->selectRandomPageFromDB( $rand, 0, $up, __METHOD__ );
}
// Just get the first entry.
if ( !$row ) {
$row = $this->selectRandomPageFromDB( false, 0, true, __METHOD__ );
}
if ( $row ) {
return Title::makeTitle( $row->page_namespace, $row->page_title );
}
return null;
}
/**
* @note The $up parameter is supposed to counteract what would happen if there
* was a large gap in the distribution of cl_timestamp values. This way instead
* of things to the right of the gap being favoured, both sides of the gap
* are favoured.
*
* @param float|false $rand Random number between 0 and 1
* @param int $offset Extra offset to fudge randomness
* @param bool $up True to get the result above the random number, false for below
* @return SelectQueryBuilder
*/
protected function getQueryBuilder( $rand, $offset, $up ) {
if ( !$this->category instanceof Title ) {
throw new BadMethodCallException( 'No category set' );
}
$dbr = $this->dbProvider->getReplicaDatabase();
$queryBuilder = $dbr->newSelectQueryBuilder()
->select( [ 'page_title', 'page_namespace' ] )
->from( 'categorylinks' )
->join( 'page', null, 'cl_from = page_id' )
->where( [ 'cl_to' => $this->category->getDBkey() ] )
->andWhere( $this->extra )
->orderBy( 'cl_timestamp', $up ? SelectQueryBuilder::SORT_ASC : SelectQueryBuilder::SORT_DESC )
->limit( 1 )
->offset( $offset );
$minClTime = $this->getTimestampOffset( $rand );
if ( $minClTime ) {
$op = $up ? '>=' : '<=';
$queryBuilder->andWhere(
$dbr->expr( 'cl_timestamp', $op, $dbr->timestamp( $minClTime ) )
);
}
return $queryBuilder;
}
/**
* @param float|false $rand Random number between 0 and 1
* @return int|false A random (unix) timestamp from the range of the category or false on failure
*/
protected function getTimestampOffset( $rand ) {
if ( $rand === false ) {
return false;
}
if ( !$this->minTimestamp || !$this->maxTimestamp ) {
$minAndMax = $this->getMinAndMaxForCat();
if ( $minAndMax === null ) {
// No entries in this category.
return false;
}
[ $this->minTimestamp, $this->maxTimestamp ] = $minAndMax;
}
$ts = ( $this->maxTimestamp - $this->minTimestamp ) * $rand + $this->minTimestamp;
return intval( $ts );
}
/**
* Get the lowest and highest timestamp for a category.
*
* @return array|null The lowest and highest timestamp, or null if the category has no entries.
*/
protected function getMinAndMaxForCat() {
$dbr = $this->dbProvider->getReplicaDatabase();
$res = $dbr->newSelectQueryBuilder()
->select( [ 'low' => 'MIN( cl_timestamp )', 'high' => 'MAX( cl_timestamp )' ] )
->from( 'categorylinks' )
->where( [ 'cl_to' => $this->category->getDBkey(), ] )
->caller( __METHOD__ )->fetchRow();
if ( !$res ) {
return null;
}
return [ (int)wfTimestamp( TS_UNIX, $res->low ), (int)wfTimestamp( TS_UNIX, $res->high ) ];
}
/**
* @param float|false $rand A random number that is converted to a random timestamp
* @param int $offset A small offset to make the result seem more "random"
* @param bool $up Get the result above the random value
* @param string $fname The name of the calling method
* @return stdClass|false Info for the title selected.
*/
private function selectRandomPageFromDB( $rand, $offset, $up, $fname = __METHOD__ ) {
return $this->getQueryBuilder( $rand, $offset, $up )->caller( $fname )->fetchRow();
}
protected function getGroupName() {
return 'redirects';
}
}
/**
* Retain the old class name for backwards compatibility.
* @deprecated since 1.41
*/
class_alias( SpecialRandomInCategory::class, 'SpecialRandomInCategory' );