includes/specials/SpecialRandomInCategory.php

   1 <?php
   2 /**
   3  * Implements Special:RandomInCategory
   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 SpecialPage
  22  * @author Brian Wolff
  23  */
  24
  25 /**
  26  * Special page to direct the user to a random page
  27  *
  28  * @note The method used here is rather biased. It is assumed that
  29  * the use of this page will be people wanting to get a random page
  30  * out of a maintenance category, to fix it up. The method used by
  31  * this page should return different pages in an unpredictable fashion
  32  * which is hoped to be sufficient, even if some pages are selected
  33  * more often than others.
  34  *
  35  * A more unbiased method could be achieved by adding a cl_random field
  36  * to the categorylinks table.
  37  *
  38  * The method used here is as follows:
  39  *  * Find the smallest and largest timestamp in the category
  40  *  * Pick a random timestamp in between
  41  *  * Pick an offset between 0 and 30
  42  *  * Get the offset'ed page that is newer than the timestamp selected
  43  * The offset is meant to counter the fact the timestamps aren't usually
  44  * uniformly distributed, so if things are very non-uniform at least we
  45  * won't have the same page selected 99% of the time.
  46  *
  47  * @ingroup SpecialPage
  48  */
  49 class SpecialRandomInCategory extends SpecialPage {
  50         protected $extra = array(); // Extra SQL statements
  51         protected $category = false; // Title object of category
  52         protected $maxOffset = 30; // Max amount to fudge randomness by.
  53         private $maxTimestamp = null;
  54         private $minTimestamp = null;
  55
  56         public function __construct( $name = 'RandomInCategory' ) {
  57                 parent::__construct( $name );
  58         }
  59
  60         /**
  61          * Set which category to use.
  62          * @param Title $cat
  63          */
  64         public function setCategory( Title $cat ) {
  65                 $this->category = $cat;
  66                 $this->maxTimestamp = null;
  67                 $this->minTimestamp = null;
  68         }
  69
  70         public function execute( $par ) {
  71                 $cat = false;
  72
  73                 $categoryStr = $this->getRequest()->getText( 'category', $par );
  74
  75                 if ( $categoryStr ) {
  76                         $cat = Title::newFromText( $categoryStr, NS_CATEGORY );
  77                 }
  78
  79                 if ( $cat ) {
  80                         $this->setCategory( $cat );
  81                 }
  82
  83
  84                 if ( !$this->category && $categoryStr ) {
  85                         $this->setHeaders();
  86                         $this->getOutput()->addWikiMsg( 'randomincategory-invalidcategory',
  87                                 wfEscapeWikiText( $categoryStr ) );
  88
  89                         return;
  90                 } elseif ( !$this->category ) {
  91                         $this->setHeaders();
  92                         $input = Html::input( 'category' );
  93                         $submitText = $this->msg( 'randomincategory-selectcategory-submit' )->text();
  94                         $submit = Html::input( '', $submitText, 'submit' );
  95
  96                         $msg = $this->msg( 'randomincategory-selectcategory' );
  97                         $form = Html::rawElement( 'form', array( 'action' => $this->getTitle()->getLocalUrl() ),
  98                                 $msg->rawParams( $input, $submit )->parse()
  99                         );
 100                         $this->getOutput()->addHtml( $form );
 101
 102                         return;
 103                 }
 104
 105                 $title = $this->getRandomTitle();
 106
 107                 if ( is_null( $title ) ) {
 108                         $this->setHeaders();
 109                         $this->getOutput()->addWikiMsg( 'randomincategory-nopages',
 110                                 $this->category->getText() );
 111
 112                         return;
 113                 }
 114
 115                 $query = $this->getRequest()->getValues();
 116                 unset( $query['title'] );
 117                 unset( $query['category'] );
 118                 $this->getOutput()->redirect( $title->getFullURL( $query ) );
 119         }
 120
 121         /**
 122          * Choose a random title.
 123          * @return Title object (or null if nothing to choose from)
 124          */
 125         public function getRandomTitle() {
 126                 // Convert to float, since we do math with the random number.
 127                 $rand = (float) wfRandom();
 128                 $title = null;
 129
 130                 // Given that timestamps are rather unevenly distributed, we also
 131                 // use an offset between 0 and 30 to make any biases less noticeable.
 132                 $offset = mt_rand( 0, $this->maxOffset );
 133
 134                 if ( mt_rand( 0, 1 ) ) {
 135                         $up = true;
 136                 } else {
 137                         $up = false;
 138                 }
 139
 140                 $row = $this->selectRandomPageFromDB( $rand, $offset, $up );
 141
 142                 // Try again without the timestamp offset (wrap around the end)
 143                 if ( !$row ) {
 144                         $row = $this->selectRandomPageFromDB( false, $offset, $up );
 145                 }
 146
 147                 // Maybe the category is really small and offset too high
 148                 if ( !$row ) {
 149                         $row = $this->selectRandomPageFromDB( $rand, 0, $up );
 150                 }
 151
 152                 // Just get the first entry.
 153                 if ( !$row ) {
 154                         $row = $this->selectRandomPageFromDB( false, 0, true );
 155                 }
 156
 157                 if ( $row ) {
 158                         return Title::makeTitle( $row->page_namespace, $row->page_title );
 159                 }
 160
 161                 return null;
 162         }
 163
 164         /**
 165          * @param float $rand Random number between 0 and 1
 166          * @param int $offset Extra offset to fudge randomness
 167          * @param bool $up True to get the result above the random number, false for below
 168          *
 169          * @note The $up parameter is supposed to counteract what would happen if there
 170          *   was a large gap in the distribution of cl_timestamp values. This way instead
 171          *   of things to the right of the gap being favoured, both sides of the gap
 172          *   are favoured.
 173          * @return Array Query information.
 174          */
 175         protected function getQueryInfo( $rand, $offset, $up ) {
 176                 $op = $up ? '>=' : '<=';
 177                 $dir = $up ? 'ASC' : 'DESC';
 178                 if ( !$this->category instanceof Title ) {
 179                         throw new MWException( 'No category set' );
 180                 }
 181                 $qi = array(
 182                         'tables' => array( 'categorylinks', 'page' ),
 183                         'fields' => array( 'page_title', 'page_namespace' ),
 184                         'conds' => array_merge( array(
 185                                 'cl_to' => $this->category->getDBKey(),
 186                         ), $this->extra ),
 187                         'options' => array(
 188                                 'ORDER BY' => 'cl_timestamp ' . $dir,
 189                                 'LIMIT' => 1,
 190                                 'OFFSET' => $offset
 191                         ),
 192                         'join_conds' => array(
 193                                 'page' => array( 'INNER JOIN', 'cl_from = page_id' )
 194                         )
 195                 );
 196
 197                 $dbr = wfGetDB( DB_SLAVE );
 198                 $minClTime = $this->getTimestampOffset( $rand );
 199                 if ( $minClTime ) {
 200                         $qi['conds'][] = 'cl_timestamp ' . $op . ' ' .
 201                                 $dbr->addQuotes( $dbr->timestamp( $minClTime ) );
 202                 }
 203                 return $qi;
 204         }
 205
 206         /**
 207          * @param float $rand Random number between 0 and 1
 208          *
 209          * @return int|bool A random (unix) timestamp from the range of the category or false on failure
 210          */
 211         protected function getTimestampOffset( $rand ) {
 212                 if ( $rand === false ) {
 213                         return false;
 214                 }
 215                 if ( !$this->minTimestamp || !$this->maxTimestamp ) {
 216                         try {
 217                                 list( $this->minTimestamp, $this->maxTimestamp ) = $this->getMinAndMaxForCat( $this->category );
 218                         } catch( MWException $e ) {
 219                                 // Possibly no entries in category.
 220                                 return false;
 221                         }
 222                 }
 223
 224                 $ts = ( $this->maxTimestamp - $this->minTimestamp ) * $rand + $this->minTimestamp;
 225                 return intval( $ts );
 226         }
 227
 228         /**
 229          * Get the lowest and highest timestamp for a category.
 230          *
 231          * @param Title $category
 232          * @return Array The lowest and highest timestamp
 233          * @throws MWException if category has no entries.
 234          */
 235         protected function getMinAndMaxForCat( Title $category ) {
 236                 $dbr = wfGetDB( DB_SLAVE );
 237                 $res = $dbr->selectRow(
 238                         'categorylinks',
 239                         array(
 240                                 'low' => 'MIN( cl_timestamp )',
 241                                 'high' => 'MAX( cl_timestamp )'
 242                         ),
 243                         array(
 244                                 'cl_to' => $this->category->getDBKey(),
 245                         ),
 246                         __METHOD__,
 247                         array(
 248                                 'LIMIT' => 1
 249                         )
 250                 );
 251                 if ( !$res ) {
 252                         throw new MWException( 'No entries in category' );
 253                 }
 254                 return array( wfTimestamp( TS_UNIX, $res->low ), wfTimestamp( TS_UNIX, $res->high ) );
 255         }
 256
 257         /**
 258          * @param float $rand A random number that is converted to a random timestamp
 259          * @param int $offset A small offset to make the result seem more "random"
 260          * @param bool $up Get the result above the random value
 261          * @param String $fname The name of the calling method
 262          * @return Array Info for the title selected.
 263          */
 264         private function selectRandomPageFromDB( $rand, $offset, $up, $fname = __METHOD__ ) {
 265                 $dbr = wfGetDB( DB_SLAVE );
 266
 267                 $query = $this->getQueryInfo( $rand, $offset, $up );
 268                 $res = $dbr->select(
 269                         $query['tables'],
 270                         $query['fields'],
 271                         $query['conds'],
 272                         $fname,
 273                         $query['options'],
 274                         $query['join_conds']
 275                 );
 276
 277                 return $res->fetchObject();
 278         }
 279
 280         protected function getGroupName() {
 281                 return 'redirects';
 282         }
 283 }