Fix for r47482: put the RELEASE-NOTES entry in the "bug fixes" section and not the...

[mediawiki.git] / includes / Pager.php

<?php
/**
 * @defgroup Pager Pager
 *
 * @file
 * @ingroup Pager
 */

/**
 * Basic pager interface.
 * @ingroup Pager
 */
interface Pager {
        function getNavigationBar();
        function getBody();
}

/**
 * IndexPager is an efficient pager which uses a (roughly unique) index in the
 * data set to implement paging, rather than a "LIMIT offset,limit" clause.
 * In MySQL, such a limit/offset clause requires counting through the
 * specified number of offset rows to find the desired data, which can be
 * expensive for large offsets.
 *
 * ReverseChronologicalPager is a child class of the abstract IndexPager, and
 * contains  some formatting and display code which is specific to the use of
 * timestamps as  indexes. Here is a synopsis of its operation:
 *
 *    * The query is specified by the offset, limit and direction (dir)
 *      parameters, in addition to any subclass-specific parameters.
 *    * The offset is the non-inclusive start of the DB query. A row with an
 *      index value equal to the offset will never be shown.
 *    * The query may either be done backwards, where the rows are returned by
 *      the database in the opposite order to which they are displayed to the
 *      user, or forwards. This is specified by the "dir" parameter, dir=prev
 *      means backwards, anything else means forwards. The offset value
 *      specifies the start of the database result set, which may be either
 *      the start or end of the displayed data set. This allows "previous"
 *      links to be implemented without knowledge of the index value at the
 *      start of the previous page.
 *    * An additional row beyond the user-specified limit is always requested.
 *      This allows us to tell whether we should display a "next" link in the
 *      case of forwards mode, or a "previous" link in the case of backwards
 *      mode. Determining whether to display the other link (the one for the
 *      page before the start of the database result set) can be done
 *      heuristically by examining the offset.
 *
 *    * An empty offset indicates that the offset condition should be omitted
 *      from the query. This naturally produces either the first page or the
 *      last page depending on the dir parameter.
 *
 *  Subclassing the pager to implement concrete functionality should be fairly
 *  simple, please see the examples in PageHistory.php and
 *  SpecialIpblocklist.php. You just need to override formatRow(),
 *  getQueryInfo() and getIndexField(). Don't forget to call the parent
 *  constructor if you override it.
 *
 * @ingroup Pager
 */
abstract class IndexPager implements Pager {
        public $mRequest;
        public $mLimitsShown = array( 20, 50, 100, 250, 500 );
        public $mDefaultLimit = 50;
        public $mOffset, $mLimit;
        public $mQueryDone = false;
        public $mDb;
        public $mPastTheEndRow;

        /**
         * The index to actually be used for ordering.  This is a single string e-
         * ven if multiple orderings are supported.
         */
        protected $mIndexField;
        /** For pages that support multiple types of ordering, which one to use. */
        protected $mOrderType;
        /**
         * $mDefaultDirection gives the direction to use when sorting results:
         * false for ascending, true for descending.  If $mIsBackwards is set, we
         * start from the opposite end, but we still sort the page itself according
         * to $mDefaultDirection.  E.g., if $mDefaultDirection is false but we're
         * going backwards, we'll display the last page of results, but the last
         * result will be at the bottom, not the top.
         *
         * Like $mIndexField, $mDefaultDirection will be a single value even if the
         * class supports multiple default directions for different order types.
         */
        public $mDefaultDirection;
        public $mIsBackwards;

        /**
         * Result object for the query. Warning: seek before use.
         */
        public $mResult;

        public function __construct() {
                global $wgRequest, $wgUser;
                $this->mRequest = $wgRequest;

                # NB: the offset is quoted, not validated. It is treated as an
                # arbitrary string to support the widest variety of index types. Be
                # careful outputting it into HTML!
                $this->mOffset = $this->mRequest->getText( 'offset' );

                # Use consistent behavior for the limit options
                $this->mDefaultLimit = intval( $wgUser->getOption( 'rclimit' ) );
                list( $this->mLimit, /* $offset */ ) = $this->mRequest->getLimitOffset();

                $this->mIsBackwards = ( $this->mRequest->getVal( 'dir' ) == 'prev' );
                $this->mDb = wfGetDB( DB_SLAVE );

                $index = $this->getIndexField();
                $order = $this->mRequest->getVal( 'order' );
                if( is_array( $index ) && isset( $index[$order] ) ) {
                        $this->mOrderType = $order;
                        $this->mIndexField = $index[$order];
                } elseif( is_array( $index ) ) {
                        # First element is the default
                        reset( $index );
                        list( $this->mOrderType, $this->mIndexField ) = each( $index );
                } else {
                        # $index is not an array
                        $this->mOrderType = null;
                        $this->mIndexField = $index;
                }

                if( !isset( $this->mDefaultDirection ) ) {
                        $dir = $this->getDefaultDirections();
                        $this->mDefaultDirection = is_array( $dir )
                                ? $dir[$this->mOrderType]
                                : $dir;
                }
        }

        /**
         * Do the query, using information from the object context. This function
         * has been kept minimal to make it overridable if necessary, to allow for
         * result sets formed from multiple DB queries.
         */
        function doQuery() {
                # Use the child class name for profiling
                $fname = __METHOD__ . ' (' . get_class( $this ) . ')';
                wfProfileIn( $fname );

                $descending = ( $this->mIsBackwards == $this->mDefaultDirection );
                # Plus an extra row so that we can tell the "next" link should be shown
                $queryLimit = $this->mLimit + 1;

                $this->mResult = $this->reallyDoQuery( $this->mOffset, $queryLimit, $descending );
                $this->extractResultInfo( $this->mOffset, $queryLimit, $this->mResult );
                $this->mQueryDone = true;

                $this->preprocessResults( $this->mResult );
                $this->mResult->rewind(); // Paranoia

                wfProfileOut( $fname );
        }
        
        /**
         * Return the result wrapper.
         */
        function getResult() {
                return $this->mResult;
        }
        
        /**
         * Set the offset from an other source than $wgRequest
         */
        function setOffset( $offset ) {
                $this->mOffset = $offset;
        }
        /**
         * Set the limit from an other source than $wgRequest
         */
        function setLimit( $limit ) {
                $this->mLimit = $limit;
        }

        /**
         * Extract some useful data from the result object for use by
         * the navigation bar, put it into $this
         */
        function extractResultInfo( $offset, $limit, ResultWrapper $res ) {
                $numRows = $res->numRows();
                if ( $numRows ) {
                        $row = $res->fetchRow();
                        $firstIndex = $row[$this->mIndexField];

                        # Discard the extra result row if there is one
                        if ( $numRows > $this->mLimit && $numRows > 1 ) {
                                $res->seek( $numRows - 1 );
                                $this->mPastTheEndRow = $res->fetchObject();
                                $indexField = $this->mIndexField;
                                $this->mPastTheEndIndex = $this->mPastTheEndRow->$indexField;
                                $res->seek( $numRows - 2 );
                                $row = $res->fetchRow();
                                $lastIndex = $row[$this->mIndexField];
                        } else {
                                $this->mPastTheEndRow = null;
                                # Setting indexes to an empty string means that they will be
                                # omitted if they would otherwise appear in URLs. It just so
                                # happens that this  is the right thing to do in the standard
                                # UI, in all the relevant cases.
                                $this->mPastTheEndIndex = '';
                                $res->seek( $numRows - 1 );
                                $row = $res->fetchRow();
                                $lastIndex = $row[$this->mIndexField];
                        }
                } else {
                        $firstIndex = '';
                        $lastIndex = '';
                        $this->mPastTheEndRow = null;
                        $this->mPastTheEndIndex = '';
                }

                if ( $this->mIsBackwards ) {
                        $this->mIsFirst = ( $numRows < $limit );
                        $this->mIsLast = ( $offset == '' );
                        $this->mLastShown = $firstIndex;
                        $this->mFirstShown = $lastIndex;
                } else {
                        $this->mIsFirst = ( $offset == '' );
                        $this->mIsLast = ( $numRows < $limit );
                        $this->mLastShown = $lastIndex;
                        $this->mFirstShown = $firstIndex;
                }
        }

        /**
         * Do a query with specified parameters, rather than using the object
         * context
         *
         * @param string $offset Index offset, inclusive
         * @param integer $limit Exact query limit
         * @param boolean $descending Query direction, false for ascending, true for descending
         * @return ResultWrapper
         */
        function reallyDoQuery( $offset, $limit, $descending ) {
                $fname = __METHOD__ . ' (' . get_class( $this ) . ')';
                $info = $this->getQueryInfo();
                $tables = $info['tables'];
                $fields = $info['fields'];
                $conds = isset( $info['conds'] ) ? $info['conds'] : array();
                $options = isset( $info['options'] ) ? $info['options'] : array();
                $join_conds = isset( $info['join_conds'] ) ? $info['join_conds'] : array();
                if ( $descending ) {
                        $options['ORDER BY'] = $this->mIndexField;
                        $operator = '>';
                } else {
                        $options['ORDER BY'] = $this->mIndexField . ' DESC';
                        $operator = '<';
                }
                if ( $offset != '' ) {
                        $conds[] = $this->mIndexField . $operator . $this->mDb->addQuotes( $offset );
                }
                $options['LIMIT'] = intval( $limit );
                $res = $this->mDb->select( $tables, $fields, $conds, $fname, $options, $join_conds );
                return new ResultWrapper( $this->mDb, $res );
        }

        /**
         * Pre-process results; useful for performing batch existence checks, etc.
         *
         * @param ResultWrapper $result Result wrapper
         */
        protected function preprocessResults( $result ) {}

        /**
         * Get the formatted result list. Calls getStartBody(), formatRow() and
         * getEndBody(), concatenates the results and returns them.
         */
        function getBody() {
                if ( !$this->mQueryDone ) {
                        $this->doQuery();
                }
                # Don't use any extra rows returned by the query
                $numRows = min( $this->mResult->numRows(), $this->mLimit );

                $s = $this->getStartBody();
                if ( $numRows ) {
                        if ( $this->mIsBackwards ) {
                                for ( $i = $numRows - 1; $i >= 0; $i-- ) {
                                        $this->mResult->seek( $i );
                                        $row = $this->mResult->fetchObject();
                                        $s .= $this->formatRow( $row );
                                }
                        } else {
                                $this->mResult->seek( 0 );
                                for ( $i = 0; $i < $numRows; $i++ ) {
                                        $row = $this->mResult->fetchObject();
                                        $s .= $this->formatRow( $row );
                                }
                        }
                } else {
                        $s .= $this->getEmptyBody();
                }
                $s .= $this->getEndBody();
                return $s;
        }

        /**
         * Make a self-link
         */
        function makeLink($text, $query = null, $type=null) {
                if ( $query === null ) {
                        return $text;
                }

                $attrs = array();
                if( in_array( $type, array( 'first', 'prev', 'next', 'last' ) ) ) {
                        # HTML5 rel attributes
                        $attrs['rel'] = $type;
                }

                if( $type ) {
                        $attrs['class'] = "mw-{$type}link";
                }
                return $this->getSkin()->link( $this->getTitle(), $text,
                        $attrs, $query + $this->getDefaultQuery(), array('noclasses','known') );
        }

        /**
         * Hook into getBody(), allows text to be inserted at the start. This
         * will be called even if there are no rows in the result set.
         */
        function getStartBody() {
                return '';
        }

        /**
         * Hook into getBody() for the end of the list
         */
        function getEndBody() {
                return '';
        }

        /**
         * Hook into getBody(), for the bit between the start and the
         * end when there are no rows
         */
        function getEmptyBody() {
                return '';
        }

        /**
         * Title used for self-links. Override this if you want to be able to
         * use a title other than $wgTitle
         */
        function getTitle() {
                return $GLOBALS['wgTitle'];
        }

        /**
         * Get the current skin. This can be overridden if necessary.
         */
        function getSkin() {
                if ( !isset( $this->mSkin ) ) {
                        global $wgUser;
                        $this->mSkin = $wgUser->getSkin();
                }
                return $this->mSkin;
        }

        /**
         * Get an array of query parameters that should be put into self-links.
         * By default, all parameters passed in the URL are used, except for a
         * short blacklist.
         */
        function getDefaultQuery() {
                if ( !isset( $this->mDefaultQuery ) ) {
                        $this->mDefaultQuery = $_GET;
                        unset( $this->mDefaultQuery['title'] );
                        unset( $this->mDefaultQuery['dir'] );
                        unset( $this->mDefaultQuery['offset'] );
                        unset( $this->mDefaultQuery['limit'] );
                        unset( $this->mDefaultQuery['order'] );
                        unset( $this->mDefaultQuery['month'] );
                        unset( $this->mDefaultQuery['year'] );
                }
                return $this->mDefaultQuery;
        }

        /**
         * Get the number of rows in the result set
         */
        function getNumRows() {
                if ( !$this->mQueryDone ) {
                        $this->doQuery();
                }
                return $this->mResult->numRows();
        }

        /**
         * Get a URL query array for the prev, next, first and last links.
         */
        function getPagingQueries() {
                if ( !$this->mQueryDone ) {
                        $this->doQuery();
                }

                # Don't announce the limit everywhere if it's the default
                $urlLimit = $this->mLimit == $this->mDefaultLimit ? '' : $this->mLimit;

                if ( $this->mIsFirst ) {
                        $prev = false;
                        $first = false;
                } else {
                        $prev = array( 'dir' => 'prev', 'offset' => $this->mFirstShown, 'limit' => $urlLimit );
                        $first = array( 'limit' => $urlLimit );
                }
                if ( $this->mIsLast ) {
                        $next = false;
                        $last = false;
                } else {
                        $next = array( 'offset' => $this->mLastShown, 'limit' => $urlLimit );
                        $last = array( 'dir' => 'prev', 'limit' => $urlLimit );
                }
                return array( 'prev' => $prev, 'next' => $next, 'first' => $first, 'last' => $last );
        }

        /**
         * Get paging links. If a link is disabled, the item from $disabledTexts
         * will be used. If there is no such item, the unlinked text from
         * $linkTexts will be used. Both $linkTexts and $disabledTexts are arrays
         * of HTML.
         */
        function getPagingLinks( $linkTexts, $disabledTexts = array() ) {
                $queries = $this->getPagingQueries();
                $links = array();
                foreach ( $queries as $type => $query ) {
                        if ( $query !== false ) {
                                $links[$type] = $this->makeLink( $linkTexts[$type], $queries[$type], $type );
                        } elseif ( isset( $disabledTexts[$type] ) ) {
                                $links[$type] = $disabledTexts[$type];
                        } else {
                                $links[$type] = $linkTexts[$type];
                        }
                }
                return $links;
        }

        function getLimitLinks() {
                global $wgLang;
                $links = array();
                if ( $this->mIsBackwards ) {
                        $offset = $this->mPastTheEndIndex;
                } else {
                        $offset = $this->mOffset;
                }
                foreach ( $this->mLimitsShown as $limit ) {
                        $links[] = $this->makeLink( $wgLang->formatNum( $limit ),
                                array( 'offset' => $offset, 'limit' => $limit ), 'num' );
                }
                return $links;
        }

        /**
         * Abstract formatting function. This should return an HTML string
         * representing the result row $row. Rows will be concatenated and
         * returned by getBody()
         */
        abstract function formatRow( $row );

        /**
         * This function should be overridden to provide all parameters
         * needed for the main paged query. It returns an associative
         * array with the following elements:
         *    tables => Table(s) for passing to Database::select()
         *    fields => Field(s) for passing to Database::select(), may be *
         *    conds => WHERE conditions
         *    options => option array
         */
        abstract function getQueryInfo();

        /**
         * This function should be overridden to return the name of the index fi-
         * eld.  If the pager supports multiple orders, it may return an array of
         * 'querykey' => 'indexfield' pairs, so that a request with &count=querykey
         * will use indexfield to sort.  In this case, the first returned key is
         * the default.
         *
         * Needless to say, it's really not a good idea to use a non-unique index
         * for this!  That won't page right.
         */
        abstract function getIndexField();

        /**
         * Return the default sorting direction: false for ascending, true for de-
         * scending.  You can also have an associative array of ordertype => dir,
         * if multiple order types are supported.  In this case getIndexField()
         * must return an array, and the keys of that must exactly match the keys
         * of this.
         *
         * For backward compatibility, this method's return value will be ignored
         * if $this->mDefaultDirection is already set when the constructor is
         * called, for instance if it's statically initialized.  In that case the
         * value of that variable (which must be a boolean) will be used.
         *
         * Note that despite its name, this does not return the value of the
         * $this->mDefaultDirection member variable.  That's the default for this
         * particular instantiation, which is a single value.  This is the set of
         * all defaults for the class.
         */
        protected function getDefaultDirections() { return false; }
}


/**
 * IndexPager with an alphabetic list and a formatted navigation bar
 * @ingroup Pager
 */
abstract class AlphabeticPager extends IndexPager {
        /**
         * Shamelessly stolen bits from ReverseChronologicalPager,
         * didn't want to do class magic as may be still revamped
         */
        function getNavigationBar() {
                global $wgLang;

                if( isset( $this->mNavigationBar ) ) {
                        return $this->mNavigationBar;
                }

                $opts = array( 'parsemag', 'escapenoentities' );
                $linkTexts = array(
                        'prev' => wfMsgExt( 'prevn', $opts, $wgLang->formatNum( $this->mLimit ) ),
                        'next' => wfMsgExt( 'nextn', $opts, $wgLang->formatNum($this->mLimit ) ),
                        'first' => wfMsgExt( 'page_first', $opts ),
                        'last' => wfMsgExt( 'page_last', $opts )
                );

                $pagingLinks = $this->getPagingLinks( $linkTexts );
                $limitLinks = $this->getLimitLinks();
                $limits = $wgLang->pipeList( $limitLinks );

                $this->mNavigationBar =
                        "(" . $wgLang->pipeList( array( $pagingLinks['first'], $pagingLinks['last'] ) ) . ") " .
                        wfMsgHtml( 'viewprevnext', $pagingLinks['prev'],
                        $pagingLinks['next'], $limits );

                if( !is_array( $this->getIndexField() ) ) {
                        # Early return to avoid undue nesting
                        return $this->mNavigationBar;
                }

                $extra = '';
                $first = true;
                $msgs = $this->getOrderTypeMessages();
                foreach( array_keys( $msgs ) as $order ) {
                        if( $first ) {
                                $first = false;
                        } else {
                                $extra .= wfMsgExt( 'pipe-separator' , 'escapenoentities' );
                        }

                        if( $order == $this->mOrderType ) {
                                $extra .= wfMsgHTML( $msgs[$order] );
                        } else {
                                $extra .= $this->makeLink(
                                        wfMsgHTML( $msgs[$order] ),
                                        array( 'order' => $order )
                                );
                        }
                }

                if( $extra !== '' ) {
                        $this->mNavigationBar .= " ($extra)";
                }

                return $this->mNavigationBar;
        }

        /**
         * If this supports multiple order type messages, give the message key for
         * enabling each one in getNavigationBar.  The return type is an associa-
         * tive array whose keys must exactly match the keys of the array returned
         * by getIndexField(), and whose values are message keys.
         * @return array
         */
        protected function getOrderTypeMessages() {
                return null;
        }
}

/**
 * IndexPager with a formatted navigation bar
 * @ingroup Pager
 */
abstract class ReverseChronologicalPager extends IndexPager {
        public $mDefaultDirection = true;
        public $mYear;
        public $mMonth;

        function __construct() {
                parent::__construct();
        }

        function getNavigationBar() {
                global $wgLang;

                if ( isset( $this->mNavigationBar ) ) {
                        return $this->mNavigationBar;
                }
                $nicenumber = $wgLang->formatNum( $this->mLimit );
                $linkTexts = array(
                        'prev' => wfMsgExt( 'pager-newer-n', array( 'parsemag' ), $nicenumber ),
                        'next' => wfMsgExt( 'pager-older-n', array( 'parsemag' ), $nicenumber ),
                        'first' => wfMsgHtml( 'histlast' ),
                        'last' => wfMsgHtml( 'histfirst' )
                );

                $pagingLinks = $this->getPagingLinks( $linkTexts );
                $limitLinks = $this->getLimitLinks();
                $limits = $wgLang->pipeList( $limitLinks );

                $this->mNavigationBar = "({$pagingLinks['first']}" . wfMsgExt( 'pipe-separator' , 'escapenoentities' ) . "{$pagingLinks['last']}) " .
                        wfMsgHtml("viewprevnext", $pagingLinks['prev'], $pagingLinks['next'], $limits);
                return $this->mNavigationBar;
        }
        
        function getDateCond( $year, $month ) {
                $year = intval($year);
                $month = intval($month);
                // Basic validity checks
                $this->mYear = $year > 0 ? $year : false;
                $this->mMonth = ($month > 0 && $month < 13) ? $month : false;
                // Given an optional year and month, we need to generate a timestamp
                // to use as "WHERE rev_timestamp <= result"
                // Examples: year = 2006 equals < 20070101 (+000000)
                // year=2005, month=1    equals < 20050201
                // year=2005, month=12   equals < 20060101
                if ( !$this->mYear && !$this->mMonth ) {
                        return;
                }
                if ( $this->mYear ) {
                        $year = $this->mYear;
                } else {
                        // If no year given, assume the current one
                        $year = gmdate( 'Y' );
                        // If this month hasn't happened yet this year, go back to last year's month
                        if( $this->mMonth > gmdate( 'n' ) ) {
                                $year--;
                        }
                }
                if ( $this->mMonth ) {
                        $month = $this->mMonth + 1;
                        // For December, we want January 1 of the next year
                        if ($month > 12) {
                                $month = 1;
                                $year++;
                        }
                } else {
                        // No month implies we want up to the end of the year in question
                        $month = 1;
                        $year++;
                }
                // Y2K38 bug
                if ( $year > 2032 ) {
                        $year = 2032;
                }
                $ymd = (int)sprintf( "%04d%02d01", $year, $month );
                if ( $ymd > 20320101 ) {
                        $ymd = 20320101;
                }
                $this->mOffset = $this->mDb->timestamp( "${ymd}000000" );
        }
}

/**
 * Table-based display with a user-selectable sort order
 * @ingroup Pager
 */
abstract class TablePager extends IndexPager {
        var $mSort;
        var $mCurrentRow;

        function __construct() {
                global $wgRequest;
                $this->mSort = $wgRequest->getText( 'sort' );
                if ( !array_key_exists( $this->mSort, $this->getFieldNames() ) ) {
                        $this->mSort = $this->getDefaultSort();
                }
                if ( $wgRequest->getBool( 'asc' ) ) {
                        $this->mDefaultDirection = false;
                } elseif ( $wgRequest->getBool( 'desc' ) ) {
                        $this->mDefaultDirection = true;
                } /* Else leave it at whatever the class default is */

                parent::__construct();
        }

        function getStartBody() {
                global $wgStylePath;
                $tableClass = htmlspecialchars( $this->getTableClass() );
                $sortClass = htmlspecialchars( $this->getSortHeaderClass() );

                $s = "<table border='1' class=\"$tableClass\"><thead><tr>\n";
                $fields = $this->getFieldNames();

                # Make table header
                foreach ( $fields as $field => $name ) {
                        if ( strval( $name ) == '' ) {
                                $s .= "<th>&nbsp;</th>\n";
                        } elseif ( $this->isFieldSortable( $field ) ) {
                                $query = array( 'sort' => $field, 'limit' => $this->mLimit );
                                if ( $field == $this->mSort ) {
                                        # This is the sorted column
                                        # Prepare a link that goes in the other sort order
                                        if ( $this->mDefaultDirection ) {
                                                # Descending
                                                $image = 'Arr_u.png';
                                                $query['asc'] = '1';
                                                $query['desc'] = '';
                                                $alt = htmlspecialchars( wfMsg( 'descending_abbrev' ) );
                                        } else {
                                                # Ascending
                                                $image = 'Arr_d.png';
                                                $query['asc'] = '';
                                                $query['desc'] = '1';
                                                $alt = htmlspecialchars( wfMsg( 'ascending_abbrev' ) );
                                        }
                                        $image = htmlspecialchars( "$wgStylePath/common/images/$image" );
                                        $link = $this->makeLink(
                                                "<img width=\"12\" height=\"12\" alt=\"$alt\" src=\"$image\" />" .
                                                htmlspecialchars( $name ), $query );
                                        $s .= "<th class=\"$sortClass\">$link</th>\n";
                                } else {
                                        $s .= '<th>' . $this->makeLink( htmlspecialchars( $name ), $query ) . "</th>\n";
                                }
                        } else {
                                $s .= '<th>' . htmlspecialchars( $name ) . "</th>\n";
                        }
                }
                $s .= "</tr></thead><tbody>\n";
                return $s;
        }

        function getEndBody() {
                return "</tbody></table>\n";
        }

        function getEmptyBody() {
                $colspan = count( $this->getFieldNames() );
                $msgEmpty = wfMsgHtml( 'table_pager_empty' );
                return "<tr><td colspan=\"$colspan\">$msgEmpty</td></tr>\n";
        }

        function formatRow( $row ) {
                $rowClass = $this->getRowClass( $row );
                $s = "<tr class=\"$rowClass\">\n";
                $fieldNames = $this->getFieldNames();
                $this->mCurrentRow = $row;  # In case formatValue needs to know
                foreach ( $fieldNames as $field => $name ) {
                        $value = isset( $row->$field ) ? $row->$field : null;
                        $formatted = strval( $this->formatValue( $field, $value ) );
                        if ( $formatted == '' ) {
                                $formatted = '&nbsp;';
                        }
                        $class = 'TablePager_col_' . htmlspecialchars( $field );
                        $s .= "<td class=\"$class\">$formatted</td>\n";
                }
                $s .= "</tr>\n";
                return $s;
        }

        function getRowClass($row) {
                return '';
        }

        function getIndexField() {
                return $this->mSort;
        }

        function getTableClass() {
                return 'TablePager';
        }

        function getNavClass() {
                return 'TablePager_nav';
        }

        function getSortHeaderClass() {
                return 'TablePager_sort';
        }

        /**
         * A navigation bar with images
         */
        function getNavigationBar() {
                global $wgStylePath, $wgContLang;
                $path = "$wgStylePath/common/images";
                $labels = array(
                        'first' => 'table_pager_first',
                        'prev' => 'table_pager_prev',
                        'next' => 'table_pager_next',
                        'last' => 'table_pager_last',
                );
                $images = array(
                        'first' => $wgContLang->isRTL() ? 'arrow_last_25.png' : 'arrow_first_25.png',
                        'prev' =>  $wgContLang->isRTL() ? 'arrow_right_25.png' : 'arrow_left_25.png',
                        'next' =>  $wgContLang->isRTL() ? 'arrow_left_25.png' : 'arrow_right_25.png',
                        'last' =>  $wgContLang->isRTL() ? 'arrow_first_25.png' : 'arrow_last_25.png',
                );
                $disabledImages = array(
                        'first' => $wgContLang->isRTL() ? 'arrow_disabled_last_25.png' : 'arrow_disabled_first_25.png',
                        'prev' =>  $wgContLang->isRTL() ? 'arrow_disabled_right_25.png' : 'arrow_disabled_left_25.png',
                        'next' =>  $wgContLang->isRTL() ? 'arrow_disabled_left_25.png' : 'arrow_disabled_right_25.png',
                        'last' =>  $wgContLang->isRTL() ? 'arrow_disabled_first_25.png' : 'arrow_disabled_last_25.png',
                );

                $linkTexts = array();
                $disabledTexts = array();
                foreach ( $labels as $type => $label ) {
                        $msgLabel = wfMsgHtml( $label );
                        $linkTexts[$type] = "<img src=\"$path/{$images[$type]}\" alt=\"$msgLabel\"/><br/>$msgLabel";
                        $disabledTexts[$type] = "<img src=\"$path/{$disabledImages[$type]}\" alt=\"$msgLabel\"/><br/>$msgLabel";
                }
                $links = $this->getPagingLinks( $linkTexts, $disabledTexts );

                $navClass = htmlspecialchars( $this->getNavClass() );
                $s = "<table class=\"$navClass\" align=\"center\" cellpadding=\"3\"><tr>\n";
                $cellAttrs = 'valign="top" align="center" width="' . 100 / count( $links ) . '%"';
                foreach ( $labels as $type => $label ) {
                        $s .= "<td $cellAttrs>{$links[$type]}</td>\n";
                }
                $s .= "</tr></table>\n";
                return $s;
        }

        /**
         * Get a <select> element which has options for each of the allowed limits
         */
        function getLimitSelect() {
                global $wgLang;
                $s = "<select name=\"limit\">";
                foreach ( $this->mLimitsShown as $limit ) {
                        $selected = $limit == $this->mLimit ? 'selected="selected"' : '';
                        $formattedLimit = $wgLang->formatNum( $limit );
                        $s .= "<option value=\"$limit\" $selected>$formattedLimit</option>\n";
                }
                $s .= "</select>";
                return $s;
        }

        /**
         * Get <input type="hidden"> elements for use in a method="get" form.
         * Resubmits all defined elements of the $_GET array, except for a
         * blacklist, passed in the $blacklist parameter.
         */
        function getHiddenFields( $blacklist = array() ) {
                $blacklist = (array)$blacklist;
                $query = $_GET;
                foreach ( $blacklist as $name ) {
                        unset( $query[$name] );
                }
                $s = '';
                foreach ( $query as $name => $value ) {
                        $encName = htmlspecialchars( $name );
                        $encValue = htmlspecialchars( $value );
                        $s .= "<input type=\"hidden\" name=\"$encName\" value=\"$encValue\"/>\n";
                }
                return $s;
        }

        /**
         * Get a form containing a limit selection dropdown
         */
        function getLimitForm() {
                # Make the select with some explanatory text
                $url = $this->getTitle()->escapeLocalURL();
                $msgSubmit = wfMsgHtml( 'table_pager_limit_submit' );
                return
                        "<form method=\"get\" action=\"$url\">" .
                        wfMsgHtml( 'table_pager_limit', $this->getLimitSelect() ) .
                        "\n<input type=\"submit\" value=\"$msgSubmit\"/>\n" .
                        $this->getHiddenFields( array('limit','title') ) .
                        "</form>\n";
        }

        /**
         * Return true if the named field should be sortable by the UI, false
         * otherwise
         *
         * @param string $field
         */
        abstract function isFieldSortable( $field );

        /**
         * Format a table cell. The return value should be HTML, but use an empty
         * string not &nbsp; for empty cells. Do not include the <td> and </td>.
         *
         * The current result row is available as $this->mCurrentRow, in case you
         * need more context.
         *
         * @param string $name The database field name
         * @param string $value The value retrieved from the database
         */
        abstract function formatValue( $name, $value );

        /**
         * The database field name used as a default sort order
         */
        abstract function getDefaultSort();

        /**
         * An array mapping database field names to a textual description of the
         * field name, for use in the table header. The description should be plain
         * text, it will be HTML-escaped later.
         */
        abstract function getFieldNames();
}