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[mediawiki.git] / includes / specials / SpecialRandomInCategory.php

<?php
/**
 * Implements Special:RandomInCategory
 *
 * 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
 * @ingroup SpecialPage
 * @author Brian Wolff
 */

/**
 * Special page to direct the user to a random page
 *
 * @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
 */
class SpecialRandomInCategory extends FormSpecialPage {
        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 );
        }

        /**
         * 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() {
                $form = array(
                        'category' => array(
                                'type' => 'text',
                                'label-message' => 'randomincategory-category',
                                'required' => true,
                        )
                );

                return $form;
        }

        public function requiresWrite() {
                return false;
        }

        public function requiresUnblock() {
                return false;
        }

        protected function setParameter( $par ) {
                // if subpage present, fake form submission
                $this->onSubmit( array( 'category' => $par ) );
        }

        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; // no data sent
                }

                $title = $this->getRandomTitle();

                if ( is_null( $title ) ) {
                        $msg = $this->msg( 'randomincategory-nopages',
                                $this->category->getText() );

                        return Status::newFatal( $msg );
                }

                $this->getOutput()->redirect( $title->getFullURL() );
        }

        /**
         * 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();
                $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;
        }

        /**
         * @param float $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
         *
         * @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.
         * @return array Query information.
         */
        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;
        }

        /**
         * @param float $rand Random number between 0 and 1
         *
         * @return int|bool 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 ) {
                        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 );
        }

        /**
         * Get the lowest and highest timestamp for a category.
         *
         * @param Title $category
         * @return array The lowest and highest timestamp
         * @throws MWException If category has no entries.
         */
        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 ) );
        }

        /**
         * @param float $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 array Info for the title selected.
         */
        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';
        }
}