SpecialRandompage.php

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<?php
class RandomPage extends SpecialPage {
    private $namespaces; // namespaces to select pages from
    protected $isRedir = false; // should the result be a redirect?
    protected $extra = array(); // Extra SQL statements

    public function __construct( $name = 'Randompage' ) {
        $this->namespaces = MWNamespace::getContentNamespaces();
        parent::__construct( $name );
    }

    public function getNamespaces() {
        return $this->namespaces;
    }

    public function setNamespace( $ns ) {
        if ( !$ns || $ns < NS_MAIN ) {
            $ns = NS_MAIN;
        }
        $this->namespaces = array( $ns );
    }

    // select redirects instead of normal pages?
    public function isRedirect() {
        return $this->isRedir;
    }

    public function execute( $par ) {
        global $wgContLang;

        if ( $par ) {
            $this->setNamespace( $wgContLang->getNsIndex( $par ) );
        }

        $title = $this->getRandomTitle();

        if ( is_null( $title ) ) {
            $this->setHeaders();
            // Message: randompage-nopages, randomredirect-nopages
            $this->getOutput()->addWikiMsg( strtolower( $this->getName() ) . '-nopages',
                $this->getNsList(), count( $this->namespaces ) );

            return;
        }

        $redirectParam = $this->isRedirect() ? array( 'redirect' => 'no' ) : array();
        $query = array_merge( $this->getRequest()->getValues(), $redirectParam );
        unset( $query['title'] );
        $this->getOutput()->redirect( $title->getFullURL( $query ) );
    }

    private function getNsList() {
        global $wgContLang;
        $nsNames = array();
        foreach ( $this->namespaces as $n ) {
            if ( $n === NS_MAIN ) {
                $nsNames[] = $this->msg( 'blanknamespace' )->plain();
            } else {
                $nsNames[] = $wgContLang->getNsText( $n );
            }
        }

        return $wgContLang->commaList( $nsNames );
    }

    public function getRandomTitle() {
        $randstr = wfRandom();
        $title = null;

        if ( !wfRunHooks(
            'SpecialRandomGetRandomTitle',
            array( &$randstr, &$this->isRedir, &$this->namespaces, &$this->extra, &$title )
        ) ) {
            return $title;
        }

        $row = $this->selectRandomPageFromDB( $randstr );

        /* If we picked a value that was higher than any in
         * the DB, wrap around and select the page with the
         * lowest value instead!  One might think this would
         * skew the distribution, but in fact it won't cause
         * any more bias than what the page_random scheme
         * causes anyway.  Trust me, I'm a mathematician. :)
         */
        if ( !$row ) {
            $row = $this->selectRandomPageFromDB( "0" );
        }

        if ( $row ) {
            return Title::makeTitleSafe( $row->page_namespace, $row->page_title );
        }

        return null;
    }

    protected function getQueryInfo( $randstr ) {
        $redirect = $this->isRedirect() ? 1 : 0;

        return array(
            'tables' => array( 'page' ),
            'fields' => array( 'page_title', 'page_namespace' ),
            'conds' => array_merge( array(
                'page_namespace' => $this->namespaces,
                'page_is_redirect' => $redirect,
                'page_random >= ' . $randstr
            ), $this->extra ),
            'options' => array(
                'ORDER BY' => 'page_random',
                'USE INDEX' => 'page_random',
                'LIMIT' => 1,
            ),
            'join_conds' => array()
        );
    }

    private function selectRandomPageFromDB( $randstr, $fname = __METHOD__ ) {
        $dbr = wfGetDB( DB_SLAVE );

        $query = $this->getQueryInfo( $randstr );
        $res = $dbr->select(
            $query['tables'],
            $query['fields'],
            $query['conds'],
            $fname,
            $query['options'],
            $query['join_conds']
        );

        return $dbr->fetchObject( $res );
    }

    protected function getGroupName() {
        return 'redirects';
    }
}