const TUint KMaxMatchingEntries		= 2;        ///< Maximum number of matching directory entries scan drive can fix. Any more indicates a fault in the file system

const TUint KMaxArrayDepth			= 6;        ///< Maximum array depth for cluster storage when KMaxScanDepth is reached

/** Data structure used to store the location of a partial VFat entry */

/** Data structure used to store the locations of entries with matching start cluster numbers. */

	TUint       iCount;         ///< Count of matching entries

	TUint       iStartCluster;  ///< The matching cluster number found in more than one entry

//---------------------------------------------------------------------------------------------------------------------------------

    This class is used for checking volume for FS errors and fixing a limited set of FS artefacts introduced by Rugged FAT on write failures.

    It can operate in 2 modes:

    1. "ScanDrive" mode, scan whole volume for possible Rugged FAT artefacts and fix them if possible. 

        1.1 If there was no problem at all, then StartL() finishes normally and ProblemsDiscovered() returns ENoErrors.

        1.2 If there was Rugged FAT artefact and it had been successfully fixed, StartL() finishes normally and ProblemsDiscovered() returns EScanDriveDirError.

            In this case the client may perform volum remounting, because FAT is very likely to have been changed.

        1.3 If there was a fatal error, like media failure or unfixable FS problem, StartL() will leave with some generic error code.

    2.  "CheckDisk" mode. check file system for known artefacts and return an error if _any_ problem discovered.

        In this case StartL() _may_ leave with something like KErrCorrupt if there was a media failure or scan has stumbled across unknown FS error, 

        ProblemsDiscovered() _may_ return some code describing the problem. If StartL() did not leave, but ProblemsDiscovered() returns a code different 

        from ENoErrors, this means that there is FS corruption. 

public:

    /** description of known problems that this scanned can deal with. Mostly used in "CheckDisk " mode */

    enum TGenericError

        {

        ENoErrors = 0,          ///< 0  no errors discovered

        EBadClusterNumber,      ///< 1  cluster number that doesn't correspond to the max. amount of clusters on the volume

        EClusterAlreadyInUse,   ///< 2  cross-linked cluster chain

        EBadClusterValue,       ///< 3  also means "lost cluster"

        EInvalidEntrySize,      ///< 4  size of file/directory does not correspond to the cluster chain length

        EUnknownError = 95,     ///< unknown error

        EScanDriveDirError=100  ///< 100 ScanDrive error

        };

    TGenericError ProblemsDiscovered() const;

	/** CScanDrive mode of operation */

    enum TScanDriveMode

        {

        EScanAndFix, ///< "ScanDrive" mode, scan whole volume for possible Rugged FAT artefacts and fix them

        ECheckDisk,  ///< "CheckDisk" mode. check file system for known artefacts and return an error if _any_ problem discovered

        };

    void StartL(TScanDriveMode aMode);

	void CompareFatsL(TBool aStopOnFirstErrorFound) ;

	void CompareAndFixFatsL();

    void FixupDirErrorL();

	TBool IsClusterUsedL(TUint aCluster);

	void MarkClusterUsedL(TUint aCluster);

	TUint32 ReadFatL(TUint aClusterNum) ;

	void CheckDirL(TUint32 aCluster);

	void RecordClusterChainL(TInt aCluster,TUint aSizeInBytes);

    inline void IndicateErrorsFound(TGenericError aError);

    inline TUint32 MaxClusters() const;

    inline TBool CheckDiskMode() const;

protected:

    /**

    Internal ScanDrive mode specific errors. In Rugged FAT mode (current implementatio) any type of error of this kind can occur only once and it will be fixed.

    Othersise the FS is considered to be corrupted

    */

    enum TDirError 

        {

        ENoDirError= 0,         ///< no errors found

        EScanMatchingEntry=1,   ///< Two entries pointing to the same cluster chain; Rugged FAT rename/replace artefact

        EScanPartEntry,         ///< Deleted DOS entry and orphaned VFAT ones from the same entryset; Rugged FAT 'file/dir delete' artefact

        };

    TPartVFatEntry          iPartEntry;         ///< Storage for a partial VFat entry set error, see EScanPartEntry

	TMatchingStartCluster   iMatching;          ///< Storage for Matching start cluster error, see EScanMatchingEntry

    TDirError               iDirError;          ///< Indicates the error tpye found also used to indicate if an error has occured

    TInt                    iDirsChecked;       ///< Count of the number of directories checked

    TUint                   iListArrayIndex;    ///< Current position into cluster list array

	TUint32                 iTruncationCluster; ///< Cluster at which cluster chain truncation should take place, used for truncation errors

	TUint32                 iMaxClusters;       ///< Max. amount of clusters on the volume

    RBitVector              iMediaFatBits;      ///< Storage for bit packed Fat read from media 

    RBitVector              iScanFatBits;       ///< Storage for bit packed Fat built up by the scan

    TGenericError           iGenericError;      ///< FS error that is discovered by scanning in any mode  

    TScanDriveMode          iScanDriveMode;     ///< mode of operation