SpecialRandomInCategory.php

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<?php
class SpecialRandomInCategory extends SpecialPage {
    protected $extra = array(); // Extra SQL statements
    protected $category = false; // Title object of category
    protected $maxOffset = 30; // Max amount to fudge randomness by.
    private $maxTimestamp = null;
    private $minTimestamp = null;
 
    public function __construct( $name = 'RandomInCategory' ) {
        parent::__construct( $name );
    }
 
    public function setCategory( Title $cat ) {
        $this->category = $cat;
        $this->maxTimestamp = null;
        $this->minTimestamp = null;
    }
 
    public function execute( $par ) {
        global $wgScript;
 
        $cat = false;
 
        $categoryStr = $this->getRequest()->getText( 'category', $par );
 
        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 ) {
            $this->setHeaders();
            $this->getOutput()->addWikiMsg( 'randomincategory-invalidcategory',
                wfEscapeWikiText( $categoryStr ) );
 
            return;
        } elseif ( !$this->category ) {
            $this->setHeaders();
            $input = Html::input( 'category' );
            $submitText = $this->msg( 'randomincategory-selectcategory-submit' )->text();
            $submit = Html::input( '', $submitText, 'submit' );
 
            $msg = $this->msg( 'randomincategory-selectcategory' );
            $form = Html::rawElement( 'form', array( 'action' => $wgScript ),
                Html::hidden( 'title', $this->getPageTitle()->getPrefixedText() ) .
                $msg->rawParams( $input, $submit )->parse()
            );
            $this->getOutput()->addHtml( $form );
 
            return;
        }
 
        $title = $this->getRandomTitle();
 
        if ( is_null( $title ) ) {
            $this->setHeaders();
            $this->getOutput()->addWikiMsg( 'randomincategory-nopages',
                $this->category->getText() );
 
            return;
        }
 
        $query = $this->getRequest()->getValues();
        unset( $query['title'] );
        unset( $query['category'] );
        $this->getOutput()->redirect( $title->getFullURL( $query ) );
    }
 
    public function getRandomTitle() {
        // Convert to float, since we do math with the random number.
        $rand = (float)wfRandom();
        $title = null;
 
        // 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 );
 
        // Try again without the timestamp offset (wrap around the end)
        if ( !$row ) {
            $row = $this->selectRandomPageFromDB( false, $offset, $up );
        }
 
        // Maybe the category is really small and offset too high
        if ( !$row ) {
            $row = $this->selectRandomPageFromDB( $rand, 0, $up );
        }
 
        // Just get the first entry.
        if ( !$row ) {
            $row = $this->selectRandomPageFromDB( false, 0, true );
        }
 
        if ( $row ) {
            return Title::makeTitle( $row->page_namespace, $row->page_title );
        }
 
        return null;
    }
 
    protected function getQueryInfo( $rand, $offset, $up ) {
        $op = $up ? '>=' : '<=';
        $dir = $up ? 'ASC' : 'DESC';
        if ( !$this->category instanceof Title ) {
            throw new MWException( 'No category set' );
        }
        $qi = array(
            'tables' => array( 'categorylinks', 'page' ),
            'fields' => array( 'page_title', 'page_namespace' ),
            'conds' => array_merge( array(
                'cl_to' => $this->category->getDBKey(),
            ), $this->extra ),
            'options' => array(
                'ORDER BY' => 'cl_timestamp ' . $dir,
                'LIMIT' => 1,
                'OFFSET' => $offset
            ),
            'join_conds' => array(
                'page' => array( 'INNER JOIN', 'cl_from = page_id' )
            )
        );
 
        $dbr = wfGetDB( DB_SLAVE );
        $minClTime = $this->getTimestampOffset( $rand );
        if ( $minClTime ) {
            $qi['conds'][] = 'cl_timestamp ' . $op . ' ' .
                $dbr->addQuotes( $dbr->timestamp( $minClTime ) );
        }
 
        return $qi;
    }
 
    protected function getTimestampOffset( $rand ) {
        if ( $rand === false ) {
            return false;
        }
        if ( !$this->minTimestamp || !$this->maxTimestamp ) {
            try {
                list( $this->minTimestamp, $this->maxTimestamp ) = $this->getMinAndMaxForCat( $this->category );
            } catch ( MWException $e ) {
                // Possibly no entries in category.
                return false;
            }
        }
 
        $ts = ( $this->maxTimestamp - $this->minTimestamp ) * $rand + $this->minTimestamp;
 
        return intval( $ts );
    }
 
    protected function getMinAndMaxForCat( Title $category ) {
        $dbr = wfGetDB( DB_SLAVE );
        $res = $dbr->selectRow(
            'categorylinks',
            array(
                'low' => 'MIN( cl_timestamp )',
                'high' => 'MAX( cl_timestamp )'
            ),
            array(
                'cl_to' => $this->category->getDBKey(),
            ),
            __METHOD__,
            array(
                'LIMIT' => 1
            )
        );
        if ( !$res ) {
            throw new MWException( 'No entries in category' );
        }
 
        return array( wfTimestamp( TS_UNIX, $res->low ), wfTimestamp( TS_UNIX, $res->high ) );
    }
 
    private function selectRandomPageFromDB( $rand, $offset, $up, $fname = __METHOD__ ) {
        $dbr = wfGetDB( DB_SLAVE );
 
        $query = $this->getQueryInfo( $rand, $offset, $up );
        $res = $dbr->select(
            $query['tables'],
            $query['fields'],
            $query['conds'],
            $fname,
            $query['options'],
            $query['join_conds']
        );
 
        return $res->fetchObject();
    }
 
    protected function getGroupName() {
        return 'redirects';
    }
}