Revert r106545 and pass a null variable by ref (also updated the documentation) so...

[mediawiki.git] / includes / Revision.php

<?php

/**
 * @todo document
 */
class Revision {
        protected $mId;
        protected $mPage;
        protected $mUserText;
        protected $mOrigUserText;
        protected $mUser;
        protected $mMinorEdit;
        protected $mTimestamp;
        protected $mDeleted;
        protected $mSize;
        protected $mSha1;
        protected $mParentId;
        protected $mComment;
        protected $mText;
        protected $mTextRow;
        protected $mTitle;
        protected $mCurrent;

        const DELETED_TEXT = 1;
        const DELETED_COMMENT = 2;
        const DELETED_USER = 4;
        const DELETED_RESTRICTED = 8;
        // Convenience field
        const SUPPRESSED_USER = 12;
        // Audience options for Revision::getText()
        const FOR_PUBLIC = 1;
        const FOR_THIS_USER = 2;
        const RAW = 3;

        /**
         * Load a page revision from a given revision ID number.
         * Returns null if no such revision can be found.
         *
         * @param $id Integer
         * @return Revision or null
         */
        public static function newFromId( $id ) {
                return Revision::newFromConds( array( 'rev_id' => intval( $id ) ) );
        }

        /**
         * Load either the current, or a specified, revision
         * that's attached to a given title. If not attached
         * to that title, will return null.
         *
         * @param $title Title
         * @param $id Integer (optional)
         * @return Revision or null
         */
        public static function newFromTitle( $title, $id = 0 ) {
                $conds = array(
                        'page_namespace' => $title->getNamespace(),
                        'page_title'     => $title->getDBkey()
                );
                if ( $id ) {
                        // Use the specified ID
                        $conds['rev_id'] = $id;
                } elseif ( wfGetLB()->getServerCount() > 1 ) {
                        // Get the latest revision ID from the master
                        $dbw = wfGetDB( DB_MASTER );
                        $latest = $dbw->selectField( 'page', 'page_latest', $conds, __METHOD__ );
                        if ( $latest === false ) {
                                return null; // page does not exist
                        }
                        $conds['rev_id'] = $latest;
                } else {
                        // Use a join to get the latest revision
                        $conds[] = 'rev_id=page_latest';
                }
                return Revision::newFromConds( $conds );
        }

        /**
         * Load either the current, or a specified, revision
         * that's attached to a given page ID.
         * Returns null if no such revision can be found.
         *
         * @param $revId Integer
         * @param $pageId Integer (optional)
         * @return Revision or null
         */
        public static function newFromPageId( $pageId, $revId = 0 ) {
                $conds = array( 'page_id' => $pageId );
                if ( $revId ) {
                        $conds['rev_id'] = $revId;
                } elseif ( wfGetLB()->getServerCount() > 1 ) {
                        // Get the latest revision ID from the master
                        $dbw = wfGetDB( DB_MASTER );
                        $latest = $dbw->selectField( 'page', 'page_latest', $conds, __METHOD__ );
                        if ( $latest === false ) {
                                return null; // page does not exist
                        }
                        $conds['rev_id'] = $latest;
                } else {
                        $conds[] = 'rev_id = page_latest';
                }
                return Revision::newFromConds( $conds );
        }

        /**
         * Make a fake revision object from an archive table row. This is queried
         * for permissions or even inserted (as in Special:Undelete)
         * @todo FIXME: Should be a subclass for RevisionDelete. [TS]
         *
         * @param $row
         * @param $overrides array
         *
         * @return Revision
         */
        public static function newFromArchiveRow( $row, $overrides = array() ) {
                $attribs = $overrides + array(
                        'page'       => isset( $row->ar_page_id ) ? $row->ar_page_id : null,
                        'id'         => isset( $row->ar_rev_id ) ? $row->ar_rev_id : null,
                        'comment'    => $row->ar_comment,
                        'user'       => $row->ar_user,
                        'user_text'  => $row->ar_user_text,
                        'timestamp'  => $row->ar_timestamp,
                        'minor_edit' => $row->ar_minor_edit,
                        'text_id'    => isset( $row->ar_text_id ) ? $row->ar_text_id : null,
                        'deleted'    => $row->ar_deleted,
                        'len'        => $row->ar_len,
                        'sha1'       => isset( $row->ar_sha1 ) ? $row->ar_sha1 : null,
                );
                if ( isset( $row->ar_text ) && !$row->ar_text_id ) {
                        // Pre-1.5 ar_text row
                        $attribs['text'] = self::getRevisionText( $row, 'ar_' );
                        if ( $attribs['text'] === false ) {
                                throw new MWException( 'Unable to load text from archive row (possibly bug 22624)' );
                        }
                }
                return new self( $attribs );
        }

        /**
         * @since 1.19
         *
         * @param $row
         * @return Revision
         */
        public static function newFromRow( $row ) {
                return new self( $row );
        }

        /**
         * Load a page revision from a given revision ID number.
         * Returns null if no such revision can be found.
         *
         * @param $db DatabaseBase
         * @param $id Integer
         * @return Revision or null
         */
        public static function loadFromId( $db, $id ) {
                return Revision::loadFromConds( $db, array( 'rev_id' => intval( $id ) ) );
        }

        /**
         * Load either the current, or a specified, revision
         * that's attached to a given page. If not attached
         * to that page, will return null.
         *
         * @param $db DatabaseBase
         * @param $pageid Integer
         * @param $id Integer
         * @return Revision or null
         */
        public static function loadFromPageId( $db, $pageid, $id = 0 ) {
                $conds = array( 'rev_page' => intval( $pageid ), 'page_id'  => intval( $pageid ) );
                if( $id ) {
                        $conds['rev_id'] = intval( $id );
                } else {
                        $conds[] = 'rev_id=page_latest';
                }
                return Revision::loadFromConds( $db, $conds );
        }

        /**
         * Load either the current, or a specified, revision
         * that's attached to a given page. If not attached
         * to that page, will return null.
         *
         * @param $db DatabaseBase
         * @param $title Title
         * @param $id Integer
         * @return Revision or null
         */
        public static function loadFromTitle( $db, $title, $id = 0 ) {
                if( $id ) {
                        $matchId = intval( $id );
                } else {
                        $matchId = 'page_latest';
                }
                return Revision::loadFromConds( $db,
                        array( "rev_id=$matchId",
                                   'page_namespace' => $title->getNamespace(),
                                   'page_title'     => $title->getDBkey() )
                );
        }

        /**
         * Load the revision for the given title with the given timestamp.
         * WARNING: Timestamps may in some circumstances not be unique,
         * so this isn't the best key to use.
         *
         * @param $db DatabaseBase
         * @param $title Title
         * @param $timestamp String
         * @return Revision or null
         */
        public static function loadFromTimestamp( $db, $title, $timestamp ) {
                return Revision::loadFromConds( $db,
                        array( 'rev_timestamp'  => $db->timestamp( $timestamp ),
                                   'page_namespace' => $title->getNamespace(),
                                   'page_title'     => $title->getDBkey() )
                );
        }

        /**
         * Given a set of conditions, fetch a revision.
         *
         * @param $conditions Array
         * @return Revision or null
         */
        public static function newFromConds( $conditions ) {
                $db = wfGetDB( DB_SLAVE );
                $rev = Revision::loadFromConds( $db, $conditions );
                if( is_null( $rev ) && wfGetLB()->getServerCount() > 1 ) {
                        $dbw = wfGetDB( DB_MASTER );
                        $rev = Revision::loadFromConds( $dbw, $conditions );
                }
                return $rev;
        }

        /**
         * Given a set of conditions, fetch a revision from
         * the given database connection.
         *
         * @param $db DatabaseBase
         * @param $conditions Array
         * @return Revision or null
         */
        private static function loadFromConds( $db, $conditions ) {
                $res = Revision::fetchFromConds( $db, $conditions );
                if( $res ) {
                        $row = $res->fetchObject();
                        if( $row ) {
                                $ret = new Revision( $row );
                                return $ret;
                        }
                }
                $ret = null;
                return $ret;
        }

        /**
         * Return a wrapper for a series of database rows to
         * fetch all of a given page's revisions in turn.
         * Each row can be fed to the constructor to get objects.
         *
         * @param $title Title
         * @return ResultWrapper
         */
        public static function fetchRevision( $title ) {
                return Revision::fetchFromConds(
                        wfGetDB( DB_SLAVE ),
                        array( 'rev_id=page_latest',
                                   'page_namespace' => $title->getNamespace(),
                                   'page_title'     => $title->getDBkey() )
                );
        }

        /**
         * Given a set of conditions, return a ResultWrapper
         * which will return matching database rows with the
         * fields necessary to build Revision objects.
         *
         * @param $db DatabaseBase
         * @param $conditions Array
         * @return ResultWrapper
         */
        private static function fetchFromConds( $db, $conditions ) {
                $fields = array_merge(
                        self::selectFields(),
                        self::selectPageFields(),
                        self::selectUserFields()
                );
                return $db->select(
                        array( 'revision', 'page', 'user' ),
                        $fields,
                        $conditions,
                        __METHOD__,
                        array( 'LIMIT' => 1 ),
                        array( 'page' => self::pageJoinCond(), 'user' => self::userJoinCond() )
                );
        }

        /**
         * Return the value of a select() JOIN conds array for the user table.
         * This will get user table rows for logged-in users.
         * @return Array
         */
        public static function userJoinCond() {
                return array( 'LEFT JOIN', array( 'rev_user != 0', 'user_id = rev_user' ) );
        }

        /**
         * Return the value of a select() page conds array for the paeg table.
         * This will assure that the revision(s) are not orphaned from live pages.
         * @return Array
         */
        public static function pageJoinCond() {
                return array( 'INNER JOIN', array( 'page_id = rev_page' ) );
        }

        /**
         * Return the list of revision fields that should be selected to create
         * a new revision.
         */
        public static function selectFields() {
                return array(
                        'rev_id',
                        'rev_page',
                        'rev_text_id',
                        'rev_timestamp',
                        'rev_comment',
                        'rev_user_text',
                        'rev_user',
                        'rev_minor_edit',
                        'rev_deleted',
                        'rev_len',
                        'rev_parent_id',
                        'rev_sha1'
                );
        }

        /**
         * Return the list of text fields that should be selected to read the
         * revision text
         */
        public static function selectTextFields() {
                return array(
                        'old_text',
                        'old_flags'
                );
        }

        /**
         * Return the list of page fields that should be selected from page table
         */
        public static function selectPageFields() {
                return array(
                        'page_namespace',
                        'page_title',
                        'page_latest'
                );
        }

        /**
         * Return the list of user fields that should be selected from user table
         */
        public static function selectUserFields() {
                return array( 'user_name' );
        }

        /**
         * Constructor
         *
         * @param $row Mixed: either a database row or an array
         * @access private
         */
        function __construct( $row ) {
                if( is_object( $row ) ) {
                        $this->mId        = intval( $row->rev_id );
                        $this->mPage      = intval( $row->rev_page );
                        $this->mTextId    = intval( $row->rev_text_id );
                        $this->mComment   =         $row->rev_comment;
                        $this->mUser      = intval( $row->rev_user );
                        $this->mMinorEdit = intval( $row->rev_minor_edit );
                        $this->mTimestamp =         $row->rev_timestamp;
                        $this->mDeleted   = intval( $row->rev_deleted );

                        if( !isset( $row->rev_parent_id ) ) {
                                $this->mParentId = is_null( $row->rev_parent_id ) ? null : 0;
                        } else {
                                $this->mParentId  = intval( $row->rev_parent_id );
                        }

                        if( !isset( $row->rev_len ) || is_null( $row->rev_len ) ) {
                                $this->mSize = null;
                        } else {
                                $this->mSize = intval( $row->rev_len );
                        }

                        if ( !isset( $row->rev_sha1 ) ) {
                                $this->mSha1 = null;
                        } else {
                                $this->mSha1 = $row->rev_sha1;
                        }

                        if( isset( $row->page_latest ) ) {
                                $this->mCurrent = ( $row->rev_id == $row->page_latest );
                                $this->mTitle = Title::newFromRow( $row );
                        } else {
                                $this->mCurrent = false;
                                $this->mTitle = null;
                        }

                        // Lazy extraction...
                        $this->mText      = null;
                        if( isset( $row->old_text ) ) {
                                $this->mTextRow = $row;
                        } else {
                                // 'text' table row entry will be lazy-loaded
                                $this->mTextRow = null;
                        }

                        // Use user_name for users and rev_user_text for IPs...
                        $this->mUserText = null; // lazy load if left null
                        if ( $this->mUser == 0 ) {
                                $this->mUserText = $row->rev_user_text; // IP user
                        } elseif ( isset( $row->user_name ) ) {
                                $this->mUserText = $row->user_name; // logged-in user
                        }
                        $this->mOrigUserText = $row->rev_user_text;
                } elseif( is_array( $row ) ) {
                        // Build a new revision to be saved...
                        global $wgUser; // ugh

                        $this->mId        = isset( $row['id']         ) ? intval( $row['id']         ) : null;
                        $this->mPage      = isset( $row['page']       ) ? intval( $row['page']       ) : null;
                        $this->mTextId    = isset( $row['text_id']    ) ? intval( $row['text_id']    ) : null;
                        $this->mUserText  = isset( $row['user_text']  ) ? strval( $row['user_text']  ) : $wgUser->getName();
                        $this->mUser      = isset( $row['user']       ) ? intval( $row['user']       ) : $wgUser->getId();
                        $this->mMinorEdit = isset( $row['minor_edit'] ) ? intval( $row['minor_edit'] ) : 0;
                        $this->mTimestamp = isset( $row['timestamp']  ) ? strval( $row['timestamp']  ) : wfTimestamp( TS_MW );
                        $this->mDeleted   = isset( $row['deleted']    ) ? intval( $row['deleted']    ) : 0;
                        $this->mSize      = isset( $row['len']        ) ? intval( $row['len']        ) : null;
                        $this->mParentId  = isset( $row['parent_id']  ) ? intval( $row['parent_id']  ) : null;
                        $this->mSha1      = isset( $row['sha1']  )      ? strval( $row['sha1']  )      : null;

                        // Enforce spacing trimming on supplied text
                        $this->mComment   = isset( $row['comment']    ) ?  trim( strval( $row['comment'] ) ) : null;
                        $this->mText      = isset( $row['text']       ) ? rtrim( strval( $row['text']    ) ) : null;
                        $this->mTextRow   = null;

                        $this->mTitle     = null; # Load on demand if needed
                        $this->mCurrent   = false;
                        # If we still have no length, see it we have the text to figure it out
                        if ( !$this->mSize ) {
                                $this->mSize = is_null( $this->mText ) ? null : strlen( $this->mText );
                        }
                        # Same for sha1
                        if ( $this->mSha1 === null ) {
                                $this->mSha1 = is_null( $this->mText ) ? null : self::base36Sha1( $this->mText );
                        }
                } else {
                        throw new MWException( 'Revision constructor passed invalid row format.' );
                }
                $this->mUnpatrolled = null;
        }

        /**
         * Get revision ID
         *
         * @return Integer
         */
        public function getId() {
                return $this->mId;
        }

        /**
         * Get text row ID
         *
         * @return Integer
         */
        public function getTextId() {
                return $this->mTextId;
        }

        /**
         * Get parent revision ID (the original previous page revision)
         *
         * @return Integer
         */
        public function getParentId() {
                return $this->mParentId;
        }

        /**
         * Returns the length of the text in this revision, or null if unknown.
         *
         * @return Integer
         */
        public function getSize() {
                return $this->mSize;
        }

        /**
         * Returns the base36 sha1 of the text in this revision, or null if unknown.
         *
         * @return String
         */
        public function getSha1() {
                return $this->mSha1;
        }

        /**
         * Returns the title of the page associated with this entry.
         *
         * @return Title
         */
        public function getTitle() {
                if( isset( $this->mTitle ) ) {
                        return $this->mTitle;
                }
                $dbr = wfGetDB( DB_SLAVE );
                $row = $dbr->selectRow(
                        array( 'page', 'revision' ),
                        array( 'page_namespace', 'page_title' ),
                        array( 'page_id=rev_page',
                                   'rev_id' => $this->mId ),
                        'Revision::getTitle' );
                if( $row ) {
                        $this->mTitle = Title::makeTitle( $row->page_namespace, $row->page_title );
                }
                return $this->mTitle;
        }

        /**
         * Set the title of the revision
         *
         * @param $title Title
         */
        public function setTitle( $title ) {
                $this->mTitle = $title;
        }

        /**
         * Get the page ID
         *
         * @return Integer
         */
        public function getPage() {
                return $this->mPage;
        }

        /**
         * Fetch revision's user id if it's available to the specified audience.
         * If the specified audience does not have access to it, zero will be
         * returned.
         *
         * @param $audience Integer: one of:
         *      Revision::FOR_PUBLIC       to be displayed to all users
         *      Revision::FOR_THIS_USER    to be displayed to $wgUser
         *      Revision::RAW              get the ID regardless of permissions
         * @param $user User object to check for, only if FOR_THIS_USER is passed
         *              to the $audience parameter
         * @return Integer
         */
        public function getUser( $audience = self::FOR_PUBLIC, User $user = null ) {
                if( $audience == self::FOR_PUBLIC && $this->isDeleted( self::DELETED_USER ) ) {
                        return 0;
                } elseif( $audience == self::FOR_THIS_USER && !$this->userCan( self::DELETED_USER, $user ) ) {
                        return 0;
                } else {
                        return $this->mUser;
                }
        }

        /**
         * Fetch revision's user id without regard for the current user's permissions
         *
         * @return String
         */
        public function getRawUser() {
                return $this->mUser;
        }

        /**
         * Fetch revision's username if it's available to the specified audience.
         * If the specified audience does not have access to the username, an
         * empty string will be returned.
         *
         * @param $audience Integer: one of:
         *      Revision::FOR_PUBLIC       to be displayed to all users
         *      Revision::FOR_THIS_USER    to be displayed to $wgUser
         *      Revision::RAW              get the text regardless of permissions
         * @param $user User object to check for, only if FOR_THIS_USER is passed
         *              to the $audience parameter
         * @return string
         */
        public function getUserText( $audience = self::FOR_PUBLIC, User $user = null ) {
                if( $audience == self::FOR_PUBLIC && $this->isDeleted( self::DELETED_USER ) ) {
                        return '';
                } elseif( $audience == self::FOR_THIS_USER && !$this->userCan( self::DELETED_USER, $user ) ) {
                        return '';
                } else {
                        return $this->getRawUserText();
                }
        }

        /**
         * Fetch revision's username without regard for view restrictions
         *
         * @return String
         */
        public function getRawUserText() {
                if ( $this->mUserText === null ) {
                        $this->mUserText = User::whoIs( $this->mUser ); // load on demand
                        if ( $this->mUserText === false ) {
                                # This shouldn't happen, but it can if the wiki was recovered
                                # via importing revs and there is no user table entry yet.
                                $this->mUserText = $this->mOrigUserText;
                        }
                }
                return $this->mUserText;
        }

        /**
         * Fetch revision comment if it's available to the specified audience.
         * If the specified audience does not have access to the comment, an
         * empty string will be returned.
         *
         * @param $audience Integer: one of:
         *      Revision::FOR_PUBLIC       to be displayed to all users
         *      Revision::FOR_THIS_USER    to be displayed to $wgUser
         *      Revision::RAW              get the text regardless of permissions
         * @param $user User object to check for, only if FOR_THIS_USER is passed
         *              to the $audience parameter
         * @return String
         */
        function getComment( $audience = self::FOR_PUBLIC, User $user = null ) {
                if( $audience == self::FOR_PUBLIC && $this->isDeleted( self::DELETED_COMMENT ) ) {
                        return '';
                } elseif( $audience == self::FOR_THIS_USER && !$this->userCan( self::DELETED_COMMENT, $user ) ) {
                        return '';
                } else {
                        return $this->mComment;
                }
        }

        /**
         * Fetch revision comment without regard for the current user's permissions
         *
         * @return String
         */
        public function getRawComment() {
                return $this->mComment;
        }

        /**
         * @return Boolean
         */
        public function isMinor() {
                return (bool)$this->mMinorEdit;
        }

        /**
         * @return Integer rcid of the unpatrolled row, zero if there isn't one
         */
        public function isUnpatrolled() {
                if( $this->mUnpatrolled !== null ) {
                        return $this->mUnpatrolled;
                }
                $dbr = wfGetDB( DB_SLAVE );
                $this->mUnpatrolled = $dbr->selectField( 'recentchanges',
                        'rc_id',
                        array( // Add redundant user,timestamp condition so we can use the existing index
                                'rc_user_text'  => $this->getRawUserText(),
                                'rc_timestamp'  => $dbr->timestamp( $this->getTimestamp() ),
                                'rc_this_oldid' => $this->getId(),
                                'rc_patrolled'  => 0
                        ),
                        __METHOD__
                );
                return (int)$this->mUnpatrolled;
        }

        /**
         * @param $field int one of DELETED_* bitfield constants
         *
         * @return Boolean
         */
        public function isDeleted( $field ) {
                return ( $this->mDeleted & $field ) == $field;
        }

        /**
         * Get the deletion bitfield of the revision
         *
         * @return int
         */
        public function getVisibility() {
                return (int)$this->mDeleted;
        }

        /**
         * Fetch revision text if it's available to the specified audience.
         * If the specified audience does not have the ability to view this
         * revision, an empty string will be returned.
         *
         * @param $audience Integer: one of:
         *      Revision::FOR_PUBLIC       to be displayed to all users
         *      Revision::FOR_THIS_USER    to be displayed to $wgUser
         *      Revision::RAW              get the text regardless of permissions
         * @param $user User object to check for, only if FOR_THIS_USER is passed
         *              to the $audience parameter
         * @return String
         */
        public function getText( $audience = self::FOR_PUBLIC, User $user = null ) {
                if( $audience == self::FOR_PUBLIC && $this->isDeleted( self::DELETED_TEXT ) ) {
                        return '';
                } elseif( $audience == self::FOR_THIS_USER && !$this->userCan( self::DELETED_TEXT, $user ) ) {
                        return '';
                } else {
                        return $this->getRawText();
                }
        }

        /**
         * Alias for getText(Revision::FOR_THIS_USER)
         *
         * @deprecated since 1.17
         * @return String
         */
        public function revText() {
                wfDeprecated( __METHOD__, '1.17' );
                return $this->getText( self::FOR_THIS_USER );
        }

        /**
         * Fetch revision text without regard for view restrictions
         *
         * @return String
         */
        public function getRawText() {
                if( is_null( $this->mText ) ) {
                        // Revision text is immutable. Load on demand:
                        $this->mText = $this->loadText();
                }
                return $this->mText;
        }

        /**
         * @return String
         */
        public function getTimestamp() {
                return wfTimestamp( TS_MW, $this->mTimestamp );
        }

        /**
         * @return Boolean
         */
        public function isCurrent() {
                return $this->mCurrent;
        }

        /**
         * Get previous revision for this title
         *
         * @return Revision or null
         */
        public function getPrevious() {
                if( $this->getTitle() ) {
                        $prev = $this->getTitle()->getPreviousRevisionID( $this->getId() );
                        if( $prev ) {
                                return Revision::newFromTitle( $this->getTitle(), $prev );
                        }
                }
                return null;
        }

        /**
         * Get next revision for this title
         *
         * @return Revision or null
         */
        public function getNext() {
                if( $this->getTitle() ) {
                        $next = $this->getTitle()->getNextRevisionID( $this->getId() );
                        if ( $next ) {
                                return Revision::newFromTitle( $this->getTitle(), $next );
                        }
                }
                return null;
        }

        /**
         * Get previous revision Id for this page_id
         * This is used to populate rev_parent_id on save
         *
         * @param $db DatabaseBase
         * @return Integer
         */
        private function getPreviousRevisionId( $db ) {
                if( is_null( $this->mPage ) ) {
                        return 0;
                }
                # Use page_latest if ID is not given
                if( !$this->mId ) {
                        $prevId = $db->selectField( 'page', 'page_latest',
                                array( 'page_id' => $this->mPage ),
                                __METHOD__ );
                } else {
                        $prevId = $db->selectField( 'revision', 'rev_id',
                                array( 'rev_page' => $this->mPage, 'rev_id < ' . $this->mId ),
                                __METHOD__,
                                array( 'ORDER BY' => 'rev_id DESC' ) );
                }
                return intval( $prevId );
        }

        /**
          * Get revision text associated with an old or archive row
          * $row is usually an object from wfFetchRow(), both the flags and the text
          * field must be included
          *
          * @param $row Object: the text data
          * @param $prefix String: table prefix (default 'old_')
          * @return String: text the text requested or false on failure
          */
        public static function getRevisionText( $row, $prefix = 'old_' ) {
                wfProfileIn( __METHOD__ );

                # Get data
                $textField = $prefix . 'text';
                $flagsField = $prefix . 'flags';

                if( isset( $row->$flagsField ) ) {
                        $flags = explode( ',', $row->$flagsField );
                } else {
                        $flags = array();
                }

                if( isset( $row->$textField ) ) {
                        $text = $row->$textField;
                } else {
                        wfProfileOut( __METHOD__ );
                        return false;
                }

                # Use external methods for external objects, text in table is URL-only then
                if ( in_array( 'external', $flags ) ) {
                        $url = $text;
                        $parts = explode( '://', $url, 2 );
                        if( count( $parts ) == 1 || $parts[1] == '' ) {
                                wfProfileOut( __METHOD__ );
                                return false;
                        }
                        $text = ExternalStore::fetchFromURL( $url );
                }

                // If the text was fetched without an error, convert it
                if ( $text !== false ) {
                        if( in_array( 'gzip', $flags ) ) {
                                # Deal with optional compression of archived pages.
                                # This can be done periodically via maintenance/compressOld.php, and
                                # as pages are saved if $wgCompressRevisions is set.
                                $text = gzinflate( $text );
                        }

                        if( in_array( 'object', $flags ) ) {
                                # Generic compressed storage
                                $obj = unserialize( $text );
                                if ( !is_object( $obj ) ) {
                                        // Invalid object
                                        wfProfileOut( __METHOD__ );
                                        return false;
                                }
                                $text = $obj->getText();
                        }

                        global $wgLegacyEncoding;
                        if( $text !== false && $wgLegacyEncoding
                                && !in_array( 'utf-8', $flags ) && !in_array( 'utf8', $flags ) )
                        {
                                # Old revisions kept around in a legacy encoding?
                                # Upconvert on demand.
                                # ("utf8" checked for compatibility with some broken
                                #  conversion scripts 2008-12-30)
                                global $wgContLang;
                                $text = $wgContLang->iconv( $wgLegacyEncoding, 'UTF-8', $text );
                        }
                }
                wfProfileOut( __METHOD__ );
                return $text;
        }

        /**
         * If $wgCompressRevisions is enabled, we will compress data.
         * The input string is modified in place.
         * Return value is the flags field: contains 'gzip' if the
         * data is compressed, and 'utf-8' if we're saving in UTF-8
         * mode.
         *
         * @param $text Mixed: reference to a text
         * @return String
         */
        public static function compressRevisionText( &$text ) {
                global $wgCompressRevisions;
                $flags = array();

                # Revisions not marked this way will be converted
                # on load if $wgLegacyCharset is set in the future.
                $flags[] = 'utf-8';

                if( $wgCompressRevisions ) {
                        if( function_exists( 'gzdeflate' ) ) {
                                $text = gzdeflate( $text );
                                $flags[] = 'gzip';
                        } else {
                                wfDebug( "Revision::compressRevisionText() -- no zlib support, not compressing\n" );
                        }
                }
                return implode( ',', $flags );
        }

        /**
         * Insert a new revision into the database, returning the new revision ID
         * number on success and dies horribly on failure.
         *
         * @param $dbw DatabaseBase: (master connection)
         * @return Integer
         */
        public function insertOn( $dbw ) {
                global $wgDefaultExternalStore;

                wfProfileIn( __METHOD__ );

                $data = $this->mText;
                $flags = Revision::compressRevisionText( $data );

                # Write to external storage if required
                if( $wgDefaultExternalStore ) {
                        // Store and get the URL
                        $data = ExternalStore::insertToDefault( $data );
                        if( !$data ) {
                                throw new MWException( "Unable to store text to external storage" );
                        }
                        if( $flags ) {
                                $flags .= ',';
                        }
                        $flags .= 'external';
                }

                # Record the text (or external storage URL) to the text table
                if( !isset( $this->mTextId ) ) {
                        $old_id = $dbw->nextSequenceValue( 'text_old_id_seq' );
                        $dbw->insert( 'text',
                                array(
                                        'old_id'    => $old_id,
                                        'old_text'  => $data,
                                        'old_flags' => $flags,
                                ), __METHOD__
                        );
                        $this->mTextId = $dbw->insertId();
                }

                if ( $this->mComment === null ) $this->mComment = "";

                # Record the edit in revisions
                $rev_id = isset( $this->mId )
                        ? $this->mId
                        : $dbw->nextSequenceValue( 'revision_rev_id_seq' );
                $dbw->insert( 'revision',
                        array(
                                'rev_id'         => $rev_id,
                                'rev_page'       => $this->mPage,
                                'rev_text_id'    => $this->mTextId,
                                'rev_comment'    => $this->mComment,
                                'rev_minor_edit' => $this->mMinorEdit ? 1 : 0,
                                'rev_user'       => $this->mUser,
                                'rev_user_text'  => $this->mUserText,
                                'rev_timestamp'  => $dbw->timestamp( $this->mTimestamp ),
                                'rev_deleted'    => $this->mDeleted,
                                'rev_len'        => $this->mSize,
                                'rev_parent_id'  => is_null( $this->mParentId )
                                        ? $this->getPreviousRevisionId( $dbw )
                                        : $this->mParentId,
                                'rev_sha1'       => is_null( $this->mSha1 )
                                        ? Revision::base36Sha1( $this->mText )
                                        : $this->mSha1
                        ), __METHOD__
                );

                $this->mId = !is_null( $rev_id ) ? $rev_id : $dbw->insertId();

                wfRunHooks( 'RevisionInsertComplete', array( &$this, $data, $flags ) );

                wfProfileOut( __METHOD__ );
                return $this->mId;
        }

        /**
         * Get the base 36 SHA-1 value for a string of text
         * @param $text String
         * @return String
         */
        public static function base36Sha1( $text ) {
                return wfBaseConvert( sha1( $text ), 16, 36, 31 );
        }

        /**
         * Lazy-load the revision's text.
         * Currently hardcoded to the 'text' table storage engine.
         *
         * @return String
         */
        protected function loadText() {
                wfProfileIn( __METHOD__ );

                // Caching may be beneficial for massive use of external storage
                global $wgRevisionCacheExpiry, $wgMemc;
                $textId = $this->getTextId();
                $key = wfMemcKey( 'revisiontext', 'textid', $textId );
                if( $wgRevisionCacheExpiry ) {
                        $text = $wgMemc->get( $key );
                        if( is_string( $text ) ) {
                                wfDebug( __METHOD__ . ": got id $textId from cache\n" );
                                wfProfileOut( __METHOD__ );
                                return $text;
                        }
                }

                // If we kept data for lazy extraction, use it now...
                if ( isset( $this->mTextRow ) ) {
                        $row = $this->mTextRow;
                        $this->mTextRow = null;
                } else {
                        $row = null;
                }

                if( !$row ) {
                        // Text data is immutable; check slaves first.
                        $dbr = wfGetDB( DB_SLAVE );
                        $row = $dbr->selectRow( 'text',
                                array( 'old_text', 'old_flags' ),
                                array( 'old_id' => $this->getTextId() ),
                                __METHOD__ );
                }

                if( !$row && wfGetLB()->getServerCount() > 1 ) {
                        // Possible slave lag!
                        $dbw = wfGetDB( DB_MASTER );
                        $row = $dbw->selectRow( 'text',
                                array( 'old_text', 'old_flags' ),
                                array( 'old_id' => $this->getTextId() ),
                                __METHOD__ );
                }

                $text = self::getRevisionText( $row );

                # No negative caching -- negative hits on text rows may be due to corrupted slave servers
                if( $wgRevisionCacheExpiry && $text !== false ) {
                        $wgMemc->set( $key, $text, $wgRevisionCacheExpiry );
                }

                wfProfileOut( __METHOD__ );

                return $text;
        }

        /**
         * Create a new null-revision for insertion into a page's
         * history. This will not re-save the text, but simply refer
         * to the text from the previous version.
         *
         * Such revisions can for instance identify page rename
         * operations and other such meta-modifications.
         *
         * @param $dbw DatabaseBase
         * @param $pageId Integer: ID number of the page to read from
         * @param $summary String: revision's summary
         * @param $minor Boolean: whether the revision should be considered as minor
         * @return Revision|null on error
         */
        public static function newNullRevision( $dbw, $pageId, $summary, $minor ) {
                wfProfileIn( __METHOD__ );

                $current = $dbw->selectRow(
                        array( 'page', 'revision' ),
                        array( 'page_latest', 'rev_text_id', 'rev_len', 'rev_sha1' ),
                        array(
                                'page_id' => $pageId,
                                'page_latest=rev_id',
                                ),
                        __METHOD__ );

                if( $current ) {
                        $revision = new Revision( array(
                                'page'       => $pageId,
                                'comment'    => $summary,
                                'minor_edit' => $minor,
                                'text_id'    => $current->rev_text_id,
                                'parent_id'  => $current->page_latest,
                                'len'        => $current->rev_len,
                                'sha1'       => $current->rev_sha1
                                ) );
                } else {
                        $revision = null;
                }

                wfProfileOut( __METHOD__ );
                return $revision;
        }

        /**
         * Determine if the current user is allowed to view a particular
         * field of this revision, if it's marked as deleted.
         *
         * @param $field Integer:one of self::DELETED_TEXT,
         *                              self::DELETED_COMMENT,
         *                              self::DELETED_USER
         * @param $user User object to check, or null to use $wgUser
         * @return Boolean
         */
        public function userCan( $field, User $user = null ) {
                return self::userCanBitfield( $this->mDeleted, $field, $user );
        }

        /**
         * Determine if the current user is allowed to view a particular
         * field of this revision, if it's marked as deleted. This is used
         * by various classes to avoid duplication.
         *
         * @param $bitfield Integer: current field
         * @param $field Integer: one of self::DELETED_TEXT = File::DELETED_FILE,
         *                               self::DELETED_COMMENT = File::DELETED_COMMENT,
         *                               self::DELETED_USER = File::DELETED_USER
         * @param $user User object to check, or null to use $wgUser
         * @return Boolean
         */
        public static function userCanBitfield( $bitfield, $field, User $user = null ) {
                if( $bitfield & $field ) { // aspect is deleted
                        if ( $bitfield & self::DELETED_RESTRICTED ) {
                                $permission = 'suppressrevision';
                        } elseif ( $field & self::DELETED_TEXT ) {
                                $permission = 'deletedtext';
                        } else {
                                $permission = 'deletedhistory';
                        }
                        wfDebug( "Checking for $permission due to $field match on $bitfield\n" );
                        if ( $user === null ) {
                                global $wgUser;
                                $user = $wgUser;
                        }
                        return $user->isAllowed( $permission );
                } else {
                        return true;
                }
        }

        /**
         * Get rev_timestamp from rev_id, without loading the rest of the row
         *
         * @param $title Title
         * @param $id Integer
         * @return String
         */
        static function getTimestampFromId( $title, $id ) {
                $dbr = wfGetDB( DB_SLAVE );
                // Casting fix for DB2
                if ( $id == '' ) {
                        $id = 0;
                }
                $conds = array( 'rev_id' => $id );
                $conds['rev_page'] = $title->getArticleId();
                $timestamp = $dbr->selectField( 'revision', 'rev_timestamp', $conds, __METHOD__ );
                if ( $timestamp === false && wfGetLB()->getServerCount() > 1 ) {
                        # Not in slave, try master
                        $dbw = wfGetDB( DB_MASTER );
                        $timestamp = $dbw->selectField( 'revision', 'rev_timestamp', $conds, __METHOD__ );
                }
                return wfTimestamp( TS_MW, $timestamp );
        }

        /**
         * Get count of revisions per page...not very efficient
         *
         * @param $db DatabaseBase
         * @param $id Integer: page id
         * @return Integer
         */
        static function countByPageId( $db, $id ) {
                $row = $db->selectRow( 'revision', 'COUNT(*) AS revCount',
                        array( 'rev_page' => $id ), __METHOD__ );
                if( $row ) {
                        return $row->revCount;
                }
                return 0;
        }

        /**
         * Get count of revisions per page...not very efficient
         *
         * @param $db DatabaseBase
         * @param $title Title
         * @return Integer
         */
        static function countByTitle( $db, $title ) {
                $id = $title->getArticleId();
                if( $id ) {
                        return Revision::countByPageId( $db, $id );
                }
                return 0;
        }
}