<?php
/**
 * Page history
 *
 * Split off from Article.php and Skin.php, 2003-12-22
 *
 * 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
 */

/**
 * This class handles printing the history page for an article.  In order to
 * be efficient, it uses timestamps rather than offsets for paging, to avoid
 * costly LIMIT,offset queries.
 *
 * Construct it by passing in an Article, and call $h->history() to print the
 * history.
 *
 */
class HistoryAction extends FormlessAction {
	const DIR_PREV = 0;
	const DIR_NEXT = 1;

	public function getName() {
		return 'history';
	}

	public function requiresWrite() {
		return false;
	}

	public function requiresUnblock() {
		return false;
	}

	protected function getPageTitle() {
		return $this->msg( 'history-title', $this->getTitle()->getPrefixedText() )->text();
	}

	protected function getDescription() {
		// Creation of a subtitle link pointing to [[Special:Log]]
		return Linker::linkKnown(
			SpecialPage::getTitleFor( 'Log' ),
			$this->msg( 'viewpagelogs' )->escaped(),
			array(),
			array( 'page' => $this->getTitle()->getPrefixedText() )
		);
	}

	/**
	 * Get the Article object we are working on.
	 * @return Page
	 */
	public function getArticle() {
		return $this->page;
	}

	/**
	 * As we use the same small set of messages in various methods and that
	 * they are called often, we call them once and save them in $this->message
	 */
	private function preCacheMessages() {
		// Precache various messages
		if ( !isset( $this->message ) ) {
			$msgs = array( 'cur', 'last', 'pipe-separator' );
			foreach ( $msgs as $msg ) {
				$this->message[$msg] = $this->msg( $msg )->escaped();
			}
		}
	}

	/**
	 * Print the history page for an article.
	 */
	function onView() {
		global $wgScript, $wgUseFileCache;

		$out = $this->getOutput();
		$request = $this->getRequest();

		/**
		 * Allow client caching.
		 */
		if ( $out->checkLastModified( $this->page->getTouched() ) ) {
			return; // Client cache fresh and headers sent, nothing more to do.
		}

		wfProfileIn( __METHOD__ );

		$this->preCacheMessages();

		# Fill in the file cache if not set already
		if ( $wgUseFileCache && HTMLFileCache::useFileCache( $this->getContext() ) ) {
			$cache = HTMLFileCache::newFromTitle( $this->getTitle(), 'history' );
			if ( !$cache->isCacheGood( /* Assume up to date */ ) ) {
				ob_start( array( &$cache, 'saveToFileCache' ) );
			}
		}

		// Setup page variables.
		$out->setFeedAppendQuery( 'action=history' );
		$out->addModules( array( 'mediawiki.legacy.history', 'mediawiki.action.history' ) );

		// Handle atom/RSS feeds.
		$feedType = $request->getVal( 'feed' );
		if ( $feedType ) {
			$this->feed( $feedType );
			wfProfileOut( __METHOD__ );
			return;
		}

		// Fail nicely if article doesn't exist.
		if ( !$this->page->exists() ) {
			$out->addWikiMsg( 'nohistory' );
			# show deletion/move log if there is an entry
			LogEventsList::showLogExtract(
				$out,
				array( 'delete', 'move' ),
				$this->getTitle(),
				'',
				array(  'lim' => 10,
					'conds' => array( "log_action != 'revision'" ),
					'showIfEmpty' => false,
					'msgKey' => array( 'moveddeleted-notice' )
				)
			);
			wfProfileOut( __METHOD__ );
			return;
		}

		/**
		 * Add date selector to quickly get to a certain time
		 */
		$year        = $request->getInt( 'year' );
		$month       = $request->getInt( 'month' );
		$tagFilter   = $request->getVal( 'tagfilter' );
		$tagSelector = ChangeTags::buildTagFilterSelector( $tagFilter );

		/**
		 * Option to show only revisions that have been (partially) hidden via RevisionDelete
		 */
		if ( $request->getBool( 'deleted' ) ) {
			$conds = array( "rev_deleted != '0'" );
		} else {
			$conds = array();
		}
		$checkDeleted = Xml::checkLabel( $this->msg( 'history-show-deleted' )->text(),
			'deleted', 'mw-show-deleted-only', $request->getBool( 'deleted' ) ) . "\n";

		// Add the general form
		$action = htmlspecialchars( $wgScript );
		$out->addHTML(
			"<form action=\"$action\" method=\"get\" id=\"mw-history-searchform\">" .
			Xml::fieldset(
				$this->msg( 'history-fieldset-title' )->text(),
				false,
				array( 'id' => 'mw-history-search' )
			) .
			Html::hidden( 'title', $this->getTitle()->getPrefixedDBKey() ) . "\n" .
			Html::hidden( 'action', 'history' ) . "\n" .
			Xml::dateMenu( $year, $month ) . '&#160;' .
			( $tagSelector ? ( implode( '&#160;', $tagSelector ) . '&#160;' ) : '' ) .
			$checkDeleted .
			Xml::submitButton( $this->msg( 'allpagessubmit' )->text() ) . "\n" .
			'</fieldset></form>'
		);

		wfRunHooks( 'PageHistoryBeforeList', array( &$this->page ) );

		// Create and output the list.
		$pager = new HistoryPager( $this, $year, $month, $tagFilter, $conds );
		$out->addHTML(
			$pager->getNavigationBar() .
			$pager->getBody() .
			$pager->getNavigationBar()
		);
		$out->preventClickjacking( $pager->getPreventClickjacking() );

		wfProfileOut( __METHOD__ );
	}

	/**
	 * Fetch an array of revisions, specified by a given limit, offset and
	 * direction. This is now only used by the feeds. It was previously
	 * used by the main UI but that's now handled by the pager.
	 *
	 * @param $limit Integer: the limit number of revisions to get
	 * @param $offset Integer
	 * @param $direction Integer: either HistoryPage::DIR_PREV or HistoryPage::DIR_NEXT
	 * @return ResultWrapper
	 */
	function fetchRevisions( $limit, $offset, $direction ) {
		// Fail if article doesn't exist.
		if( !$this->getTitle()->exists() ) {
			return new FakeResultWrapper( array() );
		}

		$dbr = wfGetDB( DB_SLAVE );

		if ( $direction == HistoryPage::DIR_PREV ) {
			list( $dirs, $oper ) = array( "ASC", ">=" );
		} else { /* $direction == HistoryPage::DIR_NEXT */
			list( $dirs, $oper ) = array( "DESC", "<=" );
		}

		if ( $offset ) {
			$offsets = array( "rev_timestamp $oper '$offset'" );
		} else {
			$offsets = array();
		}

		$page_id = $this->page->getId();

		return $dbr->select( 'revision',
			Revision::selectFields(),
			array_merge( array( "rev_page=$page_id" ), $offsets ),
			__METHOD__,
			array( 'ORDER BY' => "rev_timestamp $dirs",
				'USE INDEX' => 'page_timestamp', 'LIMIT' => $limit )
		);
	}

	/**
	 * Output a subscription feed listing recent edits to this page.
	 *
	 * @param $type String: feed type
	 */
	function feed( $type ) {
		global $wgFeedClasses, $wgFeedLimit;
		if ( !FeedUtils::checkFeedOutput( $type ) ) {
			return;
		}
		$request = $this->getRequest();

		$feed = new $wgFeedClasses[$type](
			$this->getTitle()->getPrefixedText() . ' - ' .
			$this->msg( 'history-feed-title' )->inContentLanguage()->text(),
			$this->msg( 'history-feed-description' )->inContentLanguage()->text(),
			$this->getTitle()->getFullUrl( 'action=history' )
		);

		// Get a limit on number of feed entries. Provide a sane default
		// of 10 if none is defined (but limit to $wgFeedLimit max)
		$limit = $request->getInt( 'limit', 10 );
		if ( $limit > $wgFeedLimit || $limit < 1 ) {
			$limit = 10;
		}
		$items = $this->fetchRevisions( $limit, 0, HistoryPage::DIR_NEXT );

		// Generate feed elements enclosed between header and footer.
		$feed->outHeader();
		if ( $items->numRows() ) {
			foreach ( $items as $row ) {
				$feed->outItem( $this->feedItem( $row ) );
			}
		} else {
			$feed->outItem( $this->feedEmpty() );
		}
		$feed->outFooter();
	}

	function feedEmpty() {
		return new FeedItem(
			$this->msg( 'nohistory' )->inContentLanguage()->text(),
			$this->msg( 'history-feed-empty' )->inContentLanguage()->parseAsBlock(),
			$this->getTitle()->getFullUrl(),
			wfTimestamp( TS_MW ),
			'',
			$this->getTitle()->getTalkPage()->getFullUrl()
		);
	}

	/**
	 * Generate a FeedItem object from a given revision table row
	 * Borrows Recent Changes' feed generation functions for formatting;
	 * includes a diff to the previous revision (if any).
	 *
	 * @param $row Object: database row
	 * @return FeedItem
	 */
	function feedItem( $row ) {
		$rev = new Revision( $row );
		$rev->setTitle( $this->getTitle() );
		$text = FeedUtils::formatDiffRow(
			$this->getTitle(),
			$this->getTitle()->getPreviousRevisionID( $rev->getId() ),
			$rev->getId(),
			$rev->getTimestamp(),
			$rev->getComment()
		);
		if ( $rev->getComment() == '' ) {
			global $wgContLang;
			$title = $this->msg( 'history-feed-item-nocomment',
				$rev->getUserText(),
				$wgContLang->timeanddate( $rev->getTimestamp() ),
				$wgContLang->date( $rev->getTimestamp() ),
				$wgContLang->time( $rev->getTimestamp() ) )->inContentLanguage()->text();
		} else {
			$title = $rev->getUserText() .
			$this->msg( 'colon-separator' )->inContentLanguage()->text() .
			FeedItem::stripComment( $rev->getComment() );
		}
		return new FeedItem(
			$title,
			$text,
			$this->getTitle()->getFullUrl( 'diff=' . $rev->getId() . '&oldid=prev' ),
			$rev->getTimestamp(),
			$rev->getUserText(),
			$this->getTitle()->getTalkPage()->getFullUrl()
		);
	}
}

/**
 * @ingroup Pager
 */
class HistoryPager extends ReverseChronologicalPager {
	public $lastRow = false, $counter, $historyPage, $buttons, $conds;
	protected $oldIdChecked;
	protected $preventClickjacking = false;
	/**
	 * @var array
	 */
	protected $parentLens;

	function __construct( $historyPage, $year = '', $month = '', $tagFilter = '', $conds = array() ) {
		parent::__construct( $historyPage->getContext() );
		$this->historyPage = $historyPage;
		$this->tagFilter = $tagFilter;
		$this->getDateCond( $year, $month );
		$this->conds = $conds;
	}

	// For hook compatibility...
	function getArticle() {
		return $this->historyPage->getArticle();
	}

	function getSqlComment() {
		if ( $this->conds ) {
			return 'history page filtered'; // potentially slow, see CR r58153
		} else {
			return 'history page unfiltered';
		}
	}

	function getQueryInfo() {
		$queryInfo = array(
			'tables'  => array( 'revision', 'user' ),
			'fields'  => array_merge( Revision::selectFields(), Revision::selectUserFields() ),
			'conds'   => array_merge(
				array( 'rev_page' => $this->getWikiPage()->getId() ),
				$this->conds ),
			'options' => array( 'USE INDEX' => array( 'revision' => 'page_timestamp' ) ),
			'join_conds' => array(
				'user'        => Revision::userJoinCond(),
				'tag_summary' => array( 'LEFT JOIN', 'ts_rev_id=rev_id' ) ),
		);
		ChangeTags::modifyDisplayQuery(
			$queryInfo['tables'],
			$queryInfo['fields'],
			$queryInfo['conds'],
			$queryInfo['join_conds'],
			$queryInfo['options'],
			$this->tagFilter
		);
		wfRunHooks( 'PageHistoryPager::getQueryInfo', array( &$this, &$queryInfo ) );
		return $queryInfo;
	}

	function getIndexField() {
		return 'rev_timestamp';
	}

	function formatRow( $row ) {
		if ( $this->lastRow ) {
			$latest = ( $this->counter == 1 && $this->mIsFirst );
			$firstInList = $this->counter == 1;
			$this->counter++;
			$s = $this->historyLine( $this->lastRow, $row,
				$this->getTitle()->getNotificationTimestamp( $this->getUser() ), $latest, $firstInList );
		} else {
			$s = '';
		}
		$this->lastRow = $row;
		return $s;
	}

	function doBatchLookups() {
		# Do a link batch query
		$this->mResult->seek( 0 );
		$batch = new LinkBatch();
		$revIds = array();
		foreach ( $this->mResult as $row ) {
			if( $row->rev_parent_id ) {
				$revIds[] = $row->rev_parent_id;
			}
			if( !is_null( $row->user_name ) ) {
				$batch->add( NS_USER, $row->user_name );
				$batch->add( NS_USER_TALK, $row->user_name );
			} else { # for anons or usernames of imported revisions
				$batch->add( NS_USER, $row->rev_user_text );
				$batch->add( NS_USER_TALK, $row->rev_user_text );
			}
		}
		$this->parentLens = Revision::getParentLengths( $this->mDb, $revIds );
		$batch->execute();
		$this->mResult->seek( 0 );
	}

	/**
	 * Creates begin of history list with a submit button
	 *
	 * @return string HTML output
	 */
	function getStartBody() {
		global $wgScript;
		$this->lastRow = false;
		$this->counter = 1;
		$this->oldIdChecked = 0;

		$this->getOutput()->wrapWikiMsg( "<div class='mw-history-legend'>\n$1\n</div>", 'histlegend' );
		$s = Html::openElement( 'form', array( 'action' => $wgScript,
			'id' => 'mw-history-compare' ) ) . "\n";
		$s .= Html::hidden( 'title', $this->getTitle()->getPrefixedDbKey() ) . "\n";
		$s .= Html::hidden( 'action', 'historysubmit' ) . "\n";

		// Button container stored in $this->buttons for re-use in getEndBody()
		$this->buttons = '<div>';
		$this->buttons .= $this->submitButton( $this->msg( 'compareselectedversions' )->text(),
			array( 'class' => 'historysubmit mw-history-compareselectedversions-button' )
				+ Linker::tooltipAndAccesskeyAttribs( 'compareselectedversions' )
		) . "\n";

		if ( $this->getUser()->isAllowed( 'deleterevision' ) ) {
			$this->buttons .= $this->getRevisionButton( 'revisiondelete', 'showhideselectedversions' );
		}
		$this->buttons .= '</div>';

		$s .= $this->buttons;
		$s .= '<ul id="pagehistory">' . "\n";
		return $s;
	}

	private function getRevisionButton( $name, $msg ) {
		$this->preventClickjacking();
		# Note bug #20966, <button> is non-standard in IE<8
		$element = Html::element( 'button',
			array(
				'type' => 'submit',
				'name' => $name,
				'value' => '1',
				'class' => "historysubmit mw-history-$name-button",
			),
			$this->msg( $msg )->text()
		) . "\n";
		return $element;
	}

	function getEndBody() {
		if ( $this->lastRow ) {
			$latest = $this->counter == 1 && $this->mIsFirst;
			$firstInList = $this->counter == 1;
			if ( $this->mIsBackwards ) {
				# Next row is unknown, but for UI reasons, probably exists if an offset has been specified
				if ( $this->mOffset == '' ) {
					$next = null;
				} else {
					$next = 'unknown';
				}
			} else {
				# The next row is the past-the-end row
				$next = $this->mPastTheEndRow;
			}
			$this->counter++;
			$s = $this->historyLine( $this->lastRow, $next,
				$this->getTitle()->getNotificationTimestamp( $this->getUser() ), $latest, $firstInList );
		} else {
			$s = '';
		}
		$s .= "</ul>\n";
		# Add second buttons only if there is more than one rev
		if ( $this->getNumRows() > 2 ) {
			$s .= $this->buttons;
		}
		$s .= '</form>';
		return $s;
	}

	/**
	 * Creates a submit button
	 *
	 * @param $message String: text of the submit button, will be escaped
	 * @param $attributes Array: attributes
	 * @return String: HTML output for the submit button
	 */
	function submitButton( $message, $attributes = array() ) {
		# Disable submit button if history has 1 revision only
		if ( $this->getNumRows() > 1 ) {
			return Xml::submitButton( $message , $attributes );
		} else {
			return '';
		}
	}

	/**
	 * Returns a row from the history printout.
	 *
	 * @todo document some more, and maybe clean up the code (some params redundant?)
	 *
	 * @param $row Object: the database row corresponding to the previous line.
	 * @param $next Mixed: the database row corresponding to the next line. (chronologically previous)
	 * @param $notificationtimestamp
	 * @param $latest Boolean: whether this row corresponds to the page's latest revision.
	 * @param $firstInList Boolean: whether this row corresponds to the first displayed on this history page.
	 * @return String: HTML output for the row
	 */
	function historyLine( $row, $next, $notificationtimestamp = false,
		$latest = false, $firstInList = false )
	{
		$rev = new Revision( $row );
		$rev->setTitle( $this->getTitle() );

		if ( is_object( $next ) ) {
			$prevRev = new Revision( $next );
			$prevRev->setTitle( $this->getTitle() );
		} else {
			$prevRev = null;
		}

		$curlink = $this->curLink( $rev, $latest );
		$lastlink = $this->lastLink( $rev, $next );
		$diffButtons = $this->diffButtons( $rev, $firstInList );
		$histLinks = Html::rawElement(
				'span',
				array( 'class' => 'mw-history-histlinks' ),
				$this->msg( 'parentheses' )->rawParams( $curlink . $this->historyPage->message['pipe-separator'] . $lastlink )->escaped()
		);
		$s = $histLinks . $diffButtons;

		$link = $this->revLink( $rev );
		$classes = array();

		$del = '';
		$user = $this->getUser();
		// Show checkboxes for each revision
		if ( $user->isAllowed( 'deleterevision' ) ) {
			$this->preventClickjacking();
			// If revision was hidden from sysops, disable the checkbox
			if ( !$rev->userCan( Revision::DELETED_RESTRICTED, $user ) ) {
				$del = Xml::check( 'deleterevisions', false, array( 'disabled' => 'disabled' ) );
			// Otherwise, enable the checkbox...
			} else {
				$del = Xml::check( 'showhiderevisions', false,
					array( 'name' => 'ids[' . $rev->getId() . ']' ) );
			}
		// User can only view deleted revisions...
		} elseif ( $rev->getVisibility() && $user->isAllowed( 'deletedhistory' ) ) {
			// If revision was hidden from sysops, disable the link
			if ( !$rev->userCan( Revision::DELETED_RESTRICTED, $user ) ) {
				$cdel = Linker::revDeleteLinkDisabled( false );
			// Otherwise, show the link...
			} else {
				$query = array( 'type' => 'revision',
					'target' => $this->getTitle()->getPrefixedDbkey(), 'ids' => $rev->getId() );
				$del .= Linker::revDeleteLink( $query,
					$rev->isDeleted( Revision::DELETED_RESTRICTED ), false );
			}
		}
		if ( $del ) {
			$s .= " $del ";
		}

		$lang = $this->getLanguage();
		$dirmark = $lang->getDirMark();

		$s .= " $link";
		$s .= $dirmark;
		$s .= " <span class='history-user'>" .
			Linker::revUserTools( $rev, true ) . "</span>";
		$s .= $dirmark;

		if ( $rev->isMinor() ) {
			$s .= ' ' . ChangesList::flag( 'minor' );
		}

		# Size is always public data
		$prevSize = isset( $this->parentLens[$row->rev_parent_id] )
			? $this->parentLens[$row->rev_parent_id]
			: 0;
		$sDiff = ChangesList::showCharacterDifference( $prevSize, $rev->getSize() );
		$fSize = Linker::formatRevisionSize($rev->getSize());
		$s .= ' <span class="mw-changeslist-separator">. .</span> ' . "$fSize $sDiff";

		# Text following the character difference is added just before running hooks
		$s2 = Linker::revComment( $rev, false, true );

		if ( $notificationtimestamp && ( $row->rev_timestamp >= $notificationtimestamp ) ) {
			$s2 .= ' <span class="updatedmarker">' .  $this->msg( 'updatedmarker' )->escaped() . '</span>';
			$classes[] = 'mw-history-line-updated';
		}

		$tools = array();

		# Rollback and undo links
		if ( $prevRev && $this->getTitle()->quickUserCan( 'edit', $user ) ) {
			if ( $latest && $this->getTitle()->quickUserCan( 'rollback', $user ) ) {
				$this->preventClickjacking();
				$tools[] = '<span class="mw-rollback-link">' .
					Linker::buildRollbackLink( $rev, $this->getContext() ) . '</span>';
			}

			if ( !$rev->isDeleted( Revision::DELETED_TEXT )
				&& !$prevRev->isDeleted( Revision::DELETED_TEXT ) )
			{
				# Create undo tooltip for the first (=latest) line only
				$undoTooltip = $latest
					? array( 'title' => $this->msg( 'tooltip-undo' )->text() )
					: array();
				$undolink = Linker::linkKnown(
					$this->getTitle(),
					$this->msg( 'editundo' )->escaped(),
					$undoTooltip,
					array(
						'action'    => 'edit',
						'undoafter' => $prevRev->getId(),
						'undo'      => $rev->getId()
					)
				);
				$tools[] = "<span class=\"mw-history-undo\">{$undolink}</span>";
			}
		}

		if ( $tools ) {
			$s2 .= ' '. $this->msg( 'parentheses' )->rawParams( $lang->pipeList( $tools ) )->escaped();
		}

		# Tags
		list( $tagSummary, $newClasses ) = ChangeTags::formatSummaryRow( $row->ts_tags, 'history' );
		$classes = array_merge( $classes, $newClasses );
		if ( $tagSummary !== '' ) {
			$s2 .= " $tagSummary";
		}

		# Include separator between character difference and following text
		if ( $s2 !== '' ) {
			$s .= ' <span class="mw-changeslist-separator">. .</span> ' . $s2;
		}

		wfRunHooks( 'PageHistoryLineEnding', array( $this, &$row , &$s, &$classes ) );

		$attribs = array();
		if ( $classes ) {
			$attribs['class'] = implode( ' ', $classes );
		}

		return Xml::tags( 'li', $attribs, $s ) . "\n";
	}

	/**
	 * Create a link to view this revision of the page
	 *
	 * @param $rev Revision
	 * @return String
	 */
	function revLink( $rev ) {
		$date = $this->getLanguage()->userTimeAndDate( $rev->getTimestamp(), $this->getUser() );
		$date = htmlspecialchars( $date );
		if ( $rev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
			$link = Linker::linkKnown(
				$this->getTitle(),
				$date,
				array( 'class' => 'mw-changeslist-date' ),
				array( 'oldid' => $rev->getId() )
			);
		} else {
			$link = $date;
		}
		if ( $rev->isDeleted( Revision::DELETED_TEXT ) ) {
			$link = "<span class=\"history-deleted\">$link</span>";
		}
		return $link;
	}

	/**
	 * Create a diff-to-current link for this revision for this page
	 *
	 * @param $rev Revision
	 * @param $latest Boolean: this is the latest revision of the page?
	 * @return String
	 */
	function curLink( $rev, $latest ) {
		$cur = $this->historyPage->message['cur'];
		if ( $latest || !$rev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
			return $cur;
		} else {
			return Linker::linkKnown(
				$this->getTitle(),
				$cur,
				array(),
				array(
					'diff' => $this->getWikiPage()->getLatest(),
					'oldid' => $rev->getId()
				)
			);
		}
	}

	/**
	 * Create a diff-to-previous link for this revision for this page.
	 *
	 * @param $prevRev Revision: the previous revision
	 * @param $next Mixed: the newer revision
	 * @return String
	 */
	function lastLink( $prevRev, $next ) {
		$last = $this->historyPage->message['last'];
		# $next may either be a Row, null, or "unkown"
		$nextRev = is_object( $next ) ? new Revision( $next ) : $next;
		if ( is_null( $next ) ) {
			# Probably no next row
			return $last;
		} elseif ( $next === 'unknown' ) {
			# Next row probably exists but is unknown, use an oldid=prev link
			return Linker::linkKnown(
				$this->getTitle(),
				$last,
				array(),
				array(
					'diff' => $prevRev->getId(),
					'oldid' => 'prev'
				)
			);
		} elseif ( !$prevRev->userCan( Revision::DELETED_TEXT, $this->getUser() )
			|| !$nextRev->userCan( Revision::DELETED_TEXT, $this->getUser() ) )
		{
			return $last;
		} else {
			return Linker::linkKnown(
				$this->getTitle(),
				$last,
				array(),
				array(
					'diff' => $prevRev->getId(),
					'oldid' => $next->rev_id
				)
			);
		}
	}

	/**
	 * Create radio buttons for page history
	 *
	 * @param $rev Revision object
	 * @param $firstInList Boolean: is this version the first one?
	 *
	 * @return String: HTML output for the radio buttons
	 */
	function diffButtons( $rev, $firstInList ) {
		if ( $this->getNumRows() > 1 ) {
			$id = $rev->getId();
			$radio = array( 'type'  => 'radio', 'value' => $id );
			/** @todo: move title texts to javascript */
			if ( $firstInList ) {
				$first = Xml::element( 'input',
					array_merge( $radio, array(
						'style' => 'visibility:hidden',
						'name'  => 'oldid',
						'id' => 'mw-oldid-null' ) )
				);
				$checkmark = array( 'checked' => 'checked' );
			} else {
				# Check visibility of old revisions
				if ( !$rev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
					$radio['disabled'] = 'disabled';
					$checkmark = array(); // We will check the next possible one
				} elseif ( !$this->oldIdChecked ) {
					$checkmark = array( 'checked' => 'checked' );
					$this->oldIdChecked = $id;
				} else {
					$checkmark = array();
				}
				$first = Xml::element( 'input',
					array_merge( $radio, $checkmark, array(
						'name'  => 'oldid',
						'id' => "mw-oldid-$id" ) ) );
				$checkmark = array();
			}
			$second = Xml::element( 'input',
				array_merge( $radio, $checkmark, array(
					'name'  => 'diff',
					'id' => "mw-diff-$id" ) ) );
			return $first . $second;
		} else {
			return '';
		}
	}

	/**
	 * This is called if a write operation is possible from the generated HTML
	 */
	function preventClickjacking( $enable = true ) {
		$this->preventClickjacking = $enable;
	}

	/**
	 * Get the "prevent clickjacking" flag
	 * @return bool
	 */
	function getPreventClickjacking() {
		return $this->preventClickjacking;
	}
}

/**
 * Backwards-compatibility alias
 */
class HistoryPage extends HistoryAction {
	public function __construct( Page $article ) { # Just to make it public
		parent::__construct( $article );
	}

	public function history() {
		$this->onView();
	}
}