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 FormSpecialPage {
  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         protected function getFormFields() {
  71                 $this->addHelpLink( 'Help:RandomInCategory' );
  72
  73                 $form = array(
  74                         'category' => array(
  75                                 'type' => 'text',
  76                                 'label-message' => 'randomincategory-category',
  77                                 'required' => true,
  78                         )
  79                 );
  80
  81                 return $form;
  82         }
  83
  84         public function requiresWrite() {
  85                 return false;
  86         }
  87
  88         public function requiresUnblock() {
  89                 return false;
  90         }
  91
  92         protected function setParameter( $par ) {
  93                 // if subpage present, fake form submission
  94                 $this->onSubmit( array( 'category' => $par ) );
  95         }
  96
  97         public function onSubmit( array $data ) {
  98                 $cat = false;
  99
 100                 $categoryStr = $data['category'];
 101
 102                 if ( $categoryStr ) {
 103                         $cat = Title::newFromText( $categoryStr, NS_CATEGORY );
 104                 }
 105
 106                 if ( $cat && $cat->getNamespace() !== NS_CATEGORY ) {
 107                         // Someone searching for something like "Wikipedia:Foo"
 108                         $cat = Title::makeTitleSafe( NS_CATEGORY, $categoryStr );
 109                 }
 110
 111                 if ( $cat ) {
 112                         $this->setCategory( $cat );
 113                 }
 114
 115                 if ( !$this->category && $categoryStr ) {
 116                         $msg = $this->msg( 'randomincategory-invalidcategory',
 117                                 wfEscapeWikiText( $categoryStr ) );
 118
 119                         return Status::newFatal( $msg );
 120
 121                 } elseif ( !$this->category ) {
 122                         return false; // no data sent
 123                 }
 124
 125                 $title = $this->getRandomTitle();
 126
 127                 if ( is_null( $title ) ) {
 128                         $msg = $this->msg( 'randomincategory-nopages',
 129                                 $this->category->getText() );
 130
 131                         return Status::newFatal( $msg );
 132                 }
 133
 134                 $this->getOutput()->redirect( $title->getFullURL() );
 135         }
 136
 137         /**
 138          * Choose a random title.
 139          * @return Title|null Title object (or null if nothing to choose from)
 140          */
 141         public function getRandomTitle() {
 142                 // Convert to float, since we do math with the random number.
 143                 $rand = (float)wfRandom();
 144                 $title = null;
 145
 146                 // Given that timestamps are rather unevenly distributed, we also
 147                 // use an offset between 0 and 30 to make any biases less noticeable.
 148                 $offset = mt_rand( 0, $this->maxOffset );
 149
 150                 if ( mt_rand( 0, 1 ) ) {
 151                         $up = true;
 152                 } else {
 153                         $up = false;
 154                 }
 155
 156                 $row = $this->selectRandomPageFromDB( $rand, $offset, $up );
 157
 158                 // Try again without the timestamp offset (wrap around the end)
 159                 if ( !$row ) {
 160                         $row = $this->selectRandomPageFromDB( false, $offset, $up );
 161                 }
 162
 163                 // Maybe the category is really small and offset too high
 164                 if ( !$row ) {
 165                         $row = $this->selectRandomPageFromDB( $rand, 0, $up );
 166                 }
 167
 168                 // Just get the first entry.
 169                 if ( !$row ) {
 170                         $row = $this->selectRandomPageFromDB( false, 0, true );
 171                 }
 172
 173                 if ( $row ) {
 174                         return Title::makeTitle( $row->page_namespace, $row->page_title );
 175                 }
 176
 177                 return null;
 178         }
 179
 180         /**
 181          * @param float $rand Random number between 0 and 1
 182          * @param int $offset Extra offset to fudge randomness
 183          * @param bool $up True to get the result above the random number, false for below
 184          * @return array Query information.
 185          * @throws MWException
 186          * @note The $up parameter is supposed to counteract what would happen if there
 187          *   was a large gap in the distribution of cl_timestamp values. This way instead
 188          *   of things to the right of the gap being favoured, both sides of the gap
 189          *   are favoured.
 190          */
 191         protected function getQueryInfo( $rand, $offset, $up ) {
 192                 $op = $up ? '>=' : '<=';
 193                 $dir = $up ? 'ASC' : 'DESC';
 194                 if ( !$this->category instanceof Title ) {
 195                         throw new MWException( 'No category set' );
 196                 }
 197                 $qi = array(
 198                         'tables' => array( 'categorylinks', 'page' ),
 199                         'fields' => array( 'page_title', 'page_namespace' ),
 200                         'conds' => array_merge( array(
 201                                 'cl_to' => $this->category->getDBKey(),
 202                         ), $this->extra ),
 203                         'options' => array(
 204                                 'ORDER BY' => 'cl_timestamp ' . $dir,
 205                                 'LIMIT' => 1,
 206                                 'OFFSET' => $offset
 207                         ),
 208                         'join_conds' => array(
 209                                 'page' => array( 'INNER JOIN', 'cl_from = page_id' )
 210                         )
 211                 );
 212
 213                 $dbr = wfGetDB( DB_SLAVE );
 214                 $minClTime = $this->getTimestampOffset( $rand );
 215                 if ( $minClTime ) {
 216                         $qi['conds'][] = 'cl_timestamp ' . $op . ' ' .
 217                                 $dbr->addQuotes( $dbr->timestamp( $minClTime ) );
 218                 }
 219
 220                 return $qi;
 221         }
 222
 223         /**
 224          * @param float $rand Random number between 0 and 1
 225          *
 226          * @return int|bool A random (unix) timestamp from the range of the category or false on failure
 227          */
 228         protected function getTimestampOffset( $rand ) {
 229                 if ( $rand === false ) {
 230                         return false;
 231                 }
 232                 if ( !$this->minTimestamp || !$this->maxTimestamp ) {
 233                         try {
 234                                 list( $this->minTimestamp, $this->maxTimestamp ) = $this->getMinAndMaxForCat( $this->category );
 235                         } catch ( Exception $e ) {
 236                                 // Possibly no entries in category.
 237                                 return false;
 238                         }
 239                 }
 240
 241                 $ts = ( $this->maxTimestamp - $this->minTimestamp ) * $rand + $this->minTimestamp;
 242
 243                 return intval( $ts );
 244         }
 245
 246         /**
 247          * Get the lowest and highest timestamp for a category.
 248          *
 249          * @param Title $category
 250          * @return array The lowest and highest timestamp
 251          * @throws MWException If category has no entries.
 252          */
 253         protected function getMinAndMaxForCat( Title $category ) {
 254                 $dbr = wfGetDB( DB_SLAVE );
 255                 $res = $dbr->selectRow(
 256                         'categorylinks',
 257                         array(
 258                                 'low' => 'MIN( cl_timestamp )',
 259                                 'high' => 'MAX( cl_timestamp )'
 260                         ),
 261                         array(
 262                                 'cl_to' => $this->category->getDBKey(),
 263                         ),
 264                         __METHOD__,
 265                         array(
 266                                 'LIMIT' => 1
 267                         )
 268                 );
 269                 if ( !$res ) {
 270                         throw new MWException( 'No entries in category' );
 271                 }
 272
 273                 return array( wfTimestamp( TS_UNIX, $res->low ), wfTimestamp( TS_UNIX, $res->high ) );
 274         }
 275
 276         /**
 277          * @param float $rand A random number that is converted to a random timestamp
 278          * @param int $offset A small offset to make the result seem more "random"
 279          * @param bool $up Get the result above the random value
 280          * @param string $fname The name of the calling method
 281          * @return array Info for the title selected.
 282          */
 283         private function selectRandomPageFromDB( $rand, $offset, $up, $fname = __METHOD__ ) {
 284                 $dbr = wfGetDB( DB_SLAVE );
 285
 286                 $query = $this->getQueryInfo( $rand, $offset, $up );
 287                 $res = $dbr->select(
 288                         $query['tables'],
 289                         $query['fields'],
 290                         $query['conds'],
 291                         $fname,
 292                         $query['options'],
 293                         $query['join_conds']
 294                 );
 295
 296                 return $res->fetchObject();
 297         }
 298
 299         protected function getGroupName() {
 300                 return 'redirects';
 301         }
 302 }