using System;
using System.Diagnostics;
using System.Text;

using i64 = System.Int64;
using u8 = System.Byte;
using u32 = System.UInt32;

using Pgno = System.UInt32;


namespace Community.CsharpSqlite
{
  using sqlite3_int64 = System.Int64;
  using DbPage = Sqlite3.PgHdr;
  public partial class Sqlite3
  {
/*
** 2009 January 28
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the implementation of the sqlite3_backup_XXX()
** API functions and the related features.
*************************************************************************
**  Included in SQLite3 port to C#-SQLite;  2008 Noah B Hart
**  C#-SQLite is an independent reimplementation of the SQLite software library
**
**  SQLITE_SOURCE_ID: 2011-05-19 13:26:54 ed1da510a239ea767a01dc332b667119fa3c908e
**
*************************************************************************
*/
//#include "sqliteInt.h"
//#include "btreeInt.h"

/* Macro to find the minimum of two numeric values.
*/
#if !MIN
//# define MIN(x,y) ((x)<(y)?(x):(y))
#endif

/*
** Structure allocated for each backup operation.
*/
public class sqlite3_backup
{
  public sqlite3 pDestDb;         /* Destination database handle */
  public Btree pDest;             /* Destination b-tree file */
  public u32 iDestSchema;         /* Original schema cookie in destination */
  public int bDestLocked;         /* True once a write-transaction is open on pDest */

  public Pgno iNext;              /* Page number of the next source page to copy */
  public sqlite3 pSrcDb;          /* Source database handle */
  public Btree pSrc;              /* Source b-tree file */

  public int rc;                  /* Backup process error code */

  /* These two variables are set by every call to backup_step(). They are
  ** read by calls to backup_remaining() and backup_pagecount().
  */
  public Pgno nRemaining;         /* Number of pages left to copy */
  public Pgno nPagecount;         /* Total number of pages to copy */

  public int isAttached;          /* True once backup has been registered with pager */
  public sqlite3_backup pNext;    /* Next backup associated with source pager */
};

/*
** THREAD SAFETY NOTES:
**
**   Once it has been created using backup_init(), a single sqlite3_backup
**   structure may be accessed via two groups of thread-safe entry points:
**
**     * Via the sqlite3_backup_XXX() API function backup_step() and
**       backup_finish(). Both these functions obtain the source database
**       handle mutex and the mutex associated with the source BtShared
**       structure, in that order.
**
**     * Via the BackupUpdate() and BackupRestart() functions, which are
**       invoked by the pager layer to report various state changes in
**       the page cache associated with the source database. The mutex
**       associated with the source database BtShared structure will always
**       be held when either of these functions are invoked.
**
**   The other sqlite3_backup_XXX() API functions, backup_remaining() and
**   backup_pagecount() are not thread-safe functions. If they are called
**   while some other thread is calling backup_step() or backup_finish(),
**   the values returned may be invalid. There is no way for a call to
**   BackupUpdate() or BackupRestart() to interfere with backup_remaining()
**   or backup_pagecount().
**
**   Depending on the SQLite configuration, the database handles and/or
**   the Btree objects may have their own mutexes that require locking.
**   Non-sharable Btrees (in-memory databases for example), do not have
**   associated mutexes.
*/

/*
** Return a pointer corresponding to database zDb (i.e. "main", "temp")
** in connection handle pDb. If such a database cannot be found, return
** a NULL pointer and write an error message to pErrorDb.
**
** If the "temp" database is requested, it may need to be opened by this
** function. If an error occurs while doing so, return 0 and write an
** error message to pErrorDb.
*/
static Btree findBtree( sqlite3 pErrorDb, sqlite3 pDb, string zDb )
{
  int i = sqlite3FindDbName( pDb, zDb );

  if ( i == 1 )
  {
    Parse pParse;
    int rc = 0;
    pParse = new Parse();//sqlite3StackAllocZero(pErrorDb, sizeof(*pParse));
    if ( pParse == null )
    {
      sqlite3Error( pErrorDb, SQLITE_NOMEM, "out of memory" );
      rc = SQLITE_NOMEM;
    }
    else
    {
      pParse.db = pDb;
      if ( sqlite3OpenTempDatabase( pParse ) != 0 )
      {
        sqlite3Error( pErrorDb, pParse.rc, "%s", pParse.zErrMsg );
        rc = SQLITE_ERROR;
      }
      sqlite3DbFree( pErrorDb, ref pParse.zErrMsg );
      //sqlite3StackFree( pErrorDb, pParse );
    }
    if ( rc != 0 )
    {
      return null;
    }
  }

  if ( i < 0 )
  {
    sqlite3Error( pErrorDb, SQLITE_ERROR, "unknown database %s", zDb );
    return null;
  }

  return pDb.aDb[i].pBt;
}

/*
** Attempt to set the page size of the destination to match the page size
** of the source.
*/
static int setDestPgsz( sqlite3_backup p )
{
  int rc;
  rc = sqlite3BtreeSetPageSize( p.pDest, sqlite3BtreeGetPageSize( p.pSrc ), -1, 0 );
  return rc;
}

/*
** Create an sqlite3_backup process to copy the contents of zSrcDb from
** connection handle pSrcDb to zDestDb in pDestDb. If successful, return
** a pointer to the new sqlite3_backup object.
**
** If an error occurs, NULL is returned and an error code and error message
** stored in database handle pDestDb.
*/
static public sqlite3_backup sqlite3_backup_init(
sqlite3 pDestDb,                 /* Database to write to */
string zDestDb,                  /* Name of database within pDestDb */
sqlite3 pSrcDb,                  /* Database connection to read from */
string zSrcDb                    /* Name of database within pSrcDb */
)
{
  sqlite3_backup p;                    /* Value to return */

  /* Lock the source database handle. The destination database
  ** handle is not locked in this routine, but it is locked in
  ** sqlite3_backup_step(). The user is required to ensure that no
  ** other thread accesses the destination handle for the duration
  ** of the backup operation.  Any attempt to use the destination
  ** database connection while a backup is in progress may cause
  ** a malfunction or a deadlock.
  */
  sqlite3_mutex_enter( pSrcDb.mutex );
  sqlite3_mutex_enter( pDestDb.mutex );

  if ( pSrcDb == pDestDb )
  {
    sqlite3Error(
    pDestDb, SQLITE_ERROR, "source and destination must be distinct"
    );
    p = null;
  }
  else
  {
    /* Allocate space for a new sqlite3_backup object...
    ** EVIDENCE-OF: R-64852-21591 The sqlite3_backup object is created by a
    ** call to sqlite3_backup_init() and is destroyed by a call to
    ** sqlite3_backup_finish(). */
    p = new sqlite3_backup();// (sqlite3_backup)sqlite3_malloc( sizeof( sqlite3_backup ) );
    //if ( null == p )
    //{
    //  sqlite3Error( pDestDb, SQLITE_NOMEM, 0 );
    //}
  }

  /* If the allocation succeeded, populate the new object. */
  if ( p != null )
  {
    // memset( p, 0, sizeof( sqlite3_backup ) );
    p.pSrc = findBtree( pDestDb, pSrcDb, zSrcDb );
    p.pDest = findBtree( pDestDb, pDestDb, zDestDb );
    p.pDestDb = pDestDb;
    p.pSrcDb = pSrcDb;
    p.iNext = 1;
    p.isAttached = 0;

    if ( null == p.pSrc || null == p.pDest || setDestPgsz( p ) == SQLITE_NOMEM )
    {
      /* One (or both) of the named databases did not exist or an OOM
      ** error was hit.  The error has already been written into the
      ** pDestDb handle.  All that is left to do here is free the
      ** sqlite3_backup structure.
      */
      //sqlite3_free( ref p );
      p = null;
    }
  }

  if ( p != null )
  {
    p.pSrc.nBackup++;
  }

  sqlite3_mutex_leave( pDestDb.mutex );
  sqlite3_mutex_leave( pSrcDb.mutex );
  return p;
}

/*
** Argument rc is an SQLite error code. Return true if this error is
** considered fatal if encountered during a backup operation. All errors
** are considered fatal except for SQLITE_BUSY and SQLITE_LOCKED.
*/
static bool isFatalError( int rc )
{
  return ( rc != SQLITE_OK && rc != SQLITE_BUSY && ALWAYS( rc != SQLITE_LOCKED ) );
}

/*
** Parameter zSrcData points to a buffer containing the data for
** page iSrcPg from the source database. Copy this data into the
** destination database.
*/
static int backupOnePage( sqlite3_backup p, Pgno iSrcPg, byte[] zSrcData )
{
  Pager pDestPager = sqlite3BtreePager( p.pDest );
  int nSrcPgsz = sqlite3BtreeGetPageSize( p.pSrc );
  int nDestPgsz = sqlite3BtreeGetPageSize( p.pDest );
  int nCopy = MIN( nSrcPgsz, nDestPgsz );
  i64 iEnd = (i64)iSrcPg * (i64)nSrcPgsz;
#if SQLITE_HAS_CODEC
  int nSrcReserve = sqlite3BtreeGetReserve(p.pSrc);
  int nDestReserve = sqlite3BtreeGetReserve(p.pDest);
#endif

  int rc = SQLITE_OK;
  i64 iOff;

  Debug.Assert( p.bDestLocked != 0 );
  Debug.Assert( !isFatalError( p.rc ) );
  Debug.Assert( iSrcPg != PENDING_BYTE_PAGE( p.pSrc.pBt ) );
  Debug.Assert( zSrcData != null );

  /* Catch the case where the destination is an in-memory database and the
  ** page sizes of the source and destination differ.
  */
  if ( nSrcPgsz != nDestPgsz && sqlite3PagerIsMemdb( pDestPager ) )
  {
    rc = SQLITE_READONLY;
  }

#if SQLITE_HAS_CODEC
  /* Backup is not possible if the page size of the destination is changing
  ** and a codec is in use.
  */
  if ( nSrcPgsz != nDestPgsz && sqlite3PagerGetCodec( pDestPager ) != null )
  {
    rc = SQLITE_READONLY;
  }

  /* Backup is not possible if the number of bytes of reserve space differ
  ** between source and destination.  If there is a difference, try to
  ** fix the destination to agree with the source.  If that is not possible,
  ** then the backup cannot proceed.
  */
  if ( nSrcReserve != nDestReserve )
  {
    u32 newPgsz = (u32)nSrcPgsz;
    rc = sqlite3PagerSetPagesize( pDestPager, ref newPgsz, nSrcReserve );
    if ( rc == SQLITE_OK && newPgsz != nSrcPgsz )
      rc = SQLITE_READONLY;
  }
#endif

  /* This loop runs once for each destination page spanned by the source
  ** page. For each iteration, variable iOff is set to the byte offset
  ** of the destination page.
  */
  for ( iOff = iEnd - (i64)nSrcPgsz; rc == SQLITE_OK && iOff < iEnd; iOff += nDestPgsz )
  {
    DbPage pDestPg = null;
    u32 iDest = (u32)( iOff / nDestPgsz ) + 1;
    if ( iDest == PENDING_BYTE_PAGE( p.pDest.pBt ) )
      continue;
    if ( SQLITE_OK == ( rc = sqlite3PagerGet( pDestPager, iDest, ref pDestPg ) )
    && SQLITE_OK == ( rc = sqlite3PagerWrite( pDestPg ) )
    )
    {
      //string zIn = &zSrcData[iOff%nSrcPgsz];
      byte[] zDestData = sqlite3PagerGetData( pDestPg );
      //string zOut = &zDestData[iOff % nDestPgsz];

      /* Copy the data from the source page into the destination page.
      ** Then clear the Btree layer MemPage.isInit flag. Both this module
      ** and the pager code use this trick (clearing the first byte
      ** of the page 'extra' space to invalidate the Btree layers
      ** cached parse of the page). MemPage.isInit is marked
      ** "MUST BE FIRST" for this purpose.
      */
      Buffer.BlockCopy( zSrcData, (int)( iOff % nSrcPgsz ), zDestData, (int)( iOff % nDestPgsz ), nCopy );// memcpy( zOut, zIn, nCopy );
      sqlite3PagerGetExtra( pDestPg ).isInit = 0;// ( sqlite3PagerGetExtra( pDestPg ) )[0] = 0;
    }
    sqlite3PagerUnref( pDestPg );
  }

  return rc;
}

/*
** If pFile is currently larger than iSize bytes, then truncate it to
** exactly iSize bytes. If pFile is not larger than iSize bytes, then
** this function is a no-op.
**
** Return SQLITE_OK if everything is successful, or an SQLite error
** code if an error occurs.
*/
static int backupTruncateFile( sqlite3_file pFile, int iSize )
{
  long iCurrent = 0;
  int rc = sqlite3OsFileSize( pFile, ref iCurrent );
  if ( rc == SQLITE_OK && iCurrent > iSize )
  {
    rc = sqlite3OsTruncate( pFile, iSize );
  }
  return rc;
}

/*
** Register this backup object with the associated source pager for
** callbacks when pages are changed or the cache invalidated.
*/
static void attachBackupObject( sqlite3_backup p )
{
  sqlite3_backup pp;
  Debug.Assert( sqlite3BtreeHoldsMutex( p.pSrc ) );
  pp = sqlite3PagerBackupPtr( sqlite3BtreePager( p.pSrc ) );
  p.pNext = pp;
  sqlite3BtreePager( p.pSrc ).pBackup = p; //*pp = p;
  p.isAttached = 1;
}

/*
** Copy nPage pages from the source b-tree to the destination.
*/
static public int sqlite3_backup_step( sqlite3_backup p, int nPage )
{
  int rc;
  int destMode;       /* Destination journal mode */
  int pgszSrc = 0;    /* Source page size */
  int pgszDest = 0;   /* Destination page size */

  sqlite3_mutex_enter( p.pSrcDb.mutex );
  sqlite3BtreeEnter( p.pSrc );
  if ( p.pDestDb != null )
  {
    sqlite3_mutex_enter( p.pDestDb.mutex );
  }

  rc = p.rc;
  if ( !isFatalError( rc ) )
  {
    Pager pSrcPager = sqlite3BtreePager( p.pSrc );    /* Source pager */
    Pager pDestPager = sqlite3BtreePager( p.pDest );   /* Dest pager */
    int ii;                            /* Iterator variable */
    Pgno nSrcPage = 0;                 /* Size of source db in pages */
    int bCloseTrans = 0;               /* True if src db requires unlocking */

    /* If the source pager is currently in a write-transaction, return
    ** SQLITE_BUSY immediately.
    */
    if ( p.pDestDb != null && p.pSrc.pBt.inTransaction == TRANS_WRITE )
    {
      rc = SQLITE_BUSY;
    }
    else
    {
      rc = SQLITE_OK;
    }

    /* Lock the destination database, if it is not locked already. */
    if ( SQLITE_OK == rc && p.bDestLocked == 0
    && SQLITE_OK == ( rc = sqlite3BtreeBeginTrans( p.pDest, 2 ) )
    )
    {
      p.bDestLocked = 1;
      sqlite3BtreeGetMeta( p.pDest, BTREE_SCHEMA_VERSION, ref p.iDestSchema );
    }

    /* If there is no open read-transaction on the source database, open
    ** one now. If a transaction is opened here, then it will be closed
    ** before this function exits.
    */
    if ( rc == SQLITE_OK && !sqlite3BtreeIsInReadTrans( p.pSrc ) )
    {
      rc = sqlite3BtreeBeginTrans( p.pSrc, 0 );
      bCloseTrans = 1;
    }

    /* Do not allow backup if the destination database is in WAL mode
    ** and the page sizes are different between source and destination */
    pgszSrc = sqlite3BtreeGetPageSize( p.pSrc );
    pgszDest = sqlite3BtreeGetPageSize( p.pDest );
    destMode = sqlite3PagerGetJournalMode( sqlite3BtreePager( p.pDest ) );
    if ( SQLITE_OK == rc && destMode == PAGER_JOURNALMODE_WAL && pgszSrc != pgszDest )
    {
      rc = SQLITE_READONLY;
    }

    /* Now that there is a read-lock on the source database, query the
    ** source pager for the number of pages in the database.
    */
    nSrcPage = sqlite3BtreeLastPage( p.pSrc );
    Debug.Assert( nSrcPage >= 0 );

    for ( ii = 0; ( nPage < 0 || ii < nPage ) && p.iNext <= nSrcPage && 0 == rc; ii++ )
    {
      Pgno iSrcPg = p.iNext;                 /* Source page number */
      if ( iSrcPg != PENDING_BYTE_PAGE( p.pSrc.pBt ) )
      {
        DbPage pSrcPg = null;                             /* Source page object */
        rc = sqlite3PagerGet( pSrcPager, (u32)iSrcPg, ref pSrcPg );
        if ( rc == SQLITE_OK )
        {
          rc = backupOnePage( p, iSrcPg, sqlite3PagerGetData( pSrcPg ) );
          sqlite3PagerUnref( pSrcPg );
        }
      }
      p.iNext++;
    }
    if ( rc == SQLITE_OK )
    {
      p.nPagecount = nSrcPage;
      p.nRemaining = ( nSrcPage + 1 - p.iNext );
      if ( p.iNext > nSrcPage )
      {
        rc = SQLITE_DONE;
      }
      else if ( 0 == p.isAttached )
      {
        attachBackupObject( p );
      }
    }


    /* Update the schema version field in the destination database. This
    ** is to make sure that the schema-version really does change in
    ** the case where the source and destination databases have the
    ** same schema version.
    */
    if ( rc == SQLITE_DONE
    && ( rc = sqlite3BtreeUpdateMeta( p.pDest, 1, p.iDestSchema + 1 ) ) == SQLITE_OK
    )
    {
      Pgno nDestTruncate;
      if ( p.pDestDb != null )
      {
        sqlite3ResetInternalSchema( p.pDestDb, -1 );
      }

      /* Set nDestTruncate to the final number of pages in the destination
      ** database. The complication here is that the destination page
      ** size may be different to the source page size.
      **
      ** If the source page size is smaller than the destination page size,
      ** round up. In this case the call to sqlite3OsTruncate() below will
      ** fix the size of the file. However it is important to call
      ** sqlite3PagerTruncateImage() here so that any pages in the
      ** destination file that lie beyond the nDestTruncate page mark are
      ** journalled by PagerCommitPhaseOne() before they are destroyed
      ** by the file truncation.
      */
      Debug.Assert( pgszSrc == sqlite3BtreeGetPageSize( p.pSrc ) );
      Debug.Assert( pgszDest == sqlite3BtreeGetPageSize( p.pDest ) );
      if ( pgszSrc < pgszDest )
      {
        int ratio = pgszDest / pgszSrc;
        nDestTruncate = (Pgno)( ( nSrcPage + ratio - 1 ) / ratio );
        if ( nDestTruncate == (int)PENDING_BYTE_PAGE( p.pDest.pBt ) )
        {
          nDestTruncate--;
        }
      }
      else
      {
        nDestTruncate = (Pgno)( nSrcPage * ( pgszSrc / pgszDest ) );
      }
      sqlite3PagerTruncateImage( pDestPager, nDestTruncate );

      if ( pgszSrc < pgszDest )
      {
        /* If the source page-size is smaller than the destination page-size,
        ** two extra things may need to happen:
        **
        **   * The destination may need to be truncated, and
        **
        **   * Data stored on the pages immediately following the
        **     pending-byte page in the source database may need to be
        **     copied into the destination database.
        */
        int iSize = (int)( pgszSrc * nSrcPage );
        sqlite3_file pFile = sqlite3PagerFile( pDestPager );
        i64 iOff;
        i64 iEnd;

        Debug.Assert( pFile != null );
        Debug.Assert( (i64)nDestTruncate * (i64)pgszDest >= iSize || (
        nDestTruncate == (int)( PENDING_BYTE_PAGE( p.pDest.pBt ) - 1 )
        && iSize >= PENDING_BYTE && iSize <= PENDING_BYTE + pgszDest
        ) );

        /* This call ensures that all data required to recreate the original
        ** database has been stored in the journal for pDestPager and the
        ** journal synced to disk. So at this point we may safely modify
        ** the database file in any way, knowing that if a power failure
        ** occurs, the original database will be reconstructed from the 
        ** journal file.  */
        rc = sqlite3PagerCommitPhaseOne( pDestPager, null, true );

        /* Write the extra pages and truncate the database file as required. */
        iEnd = MIN( PENDING_BYTE + pgszDest, iSize );
        for (
        iOff = PENDING_BYTE + pgszSrc;
        rc == SQLITE_OK && iOff < iEnd;
        iOff += pgszSrc
        )
        {
          PgHdr pSrcPg = null;
          u32 iSrcPg = (u32)( ( iOff / pgszSrc ) + 1 );
          rc = sqlite3PagerGet( pSrcPager, iSrcPg, ref pSrcPg );
          if ( rc == SQLITE_OK )
          {
            byte[] zData = sqlite3PagerGetData( pSrcPg );
            rc = sqlite3OsWrite( pFile, zData, pgszSrc, iOff );
          }
          sqlite3PagerUnref( pSrcPg );
        }
        if ( rc == SQLITE_OK )
        {
          rc = backupTruncateFile( pFile, (int)iSize );
        }

        /* Sync the database file to disk. */
        if ( rc == SQLITE_OK )
        {
          rc = sqlite3PagerSync( pDestPager );
        }
      }
      else
      {
        rc = sqlite3PagerCommitPhaseOne( pDestPager, null, false );
      }

      /* Finish committing the transaction to the destination database. */
      if ( SQLITE_OK == rc
      && SQLITE_OK == ( rc = sqlite3BtreeCommitPhaseTwo( p.pDest, 0 ) )
      )
      {
        rc = SQLITE_DONE;
      }
    }

    /* If bCloseTrans is true, then this function opened a read transaction
    ** on the source database. Close the read transaction here. There is
    ** no need to check the return values of the btree methods here, as
    ** "committing" a read-only transaction cannot fail.
    */
    if ( bCloseTrans != 0 )
    {
#if !NDEBUG || SQLITE_COVERAGE_TEST
      //TESTONLY( int rc2 );
      //TESTONLY( rc2  = ) sqlite3BtreeCommitPhaseOne(p.pSrc, 0);
      //TESTONLY( rc2 |= ) sqlite3BtreeCommitPhaseTwo(p.pSrc);
      int rc2;
      rc2 = sqlite3BtreeCommitPhaseOne( p.pSrc, string.Empty );
      rc2 |= sqlite3BtreeCommitPhaseTwo( p.pSrc, 0 );
      Debug.Assert( rc2 == SQLITE_OK );
#else
sqlite3BtreeCommitPhaseOne(p.pSrc, null);
sqlite3BtreeCommitPhaseTwo(p.pSrc, 0);
#endif
    }

    if ( rc == SQLITE_IOERR_NOMEM )
    {
      rc = SQLITE_NOMEM;
    }
    p.rc = rc;
  }
  if ( p.pDestDb != null )
  {
    sqlite3_mutex_leave( p.pDestDb.mutex );
  }
  sqlite3BtreeLeave( p.pSrc );
  sqlite3_mutex_leave( p.pSrcDb.mutex );
  return rc;
}

/*
** Release all resources associated with an sqlite3_backup* handle.
*/
static public int sqlite3_backup_finish( sqlite3_backup p )
{
  sqlite3_backup pp;                 /* Ptr to head of pagers backup list */
  sqlite3_mutex mutex;               /* Mutex to protect source database */
  int rc;                            /* Value to return */

  /* Enter the mutexes */
  if ( p == null )
    return SQLITE_OK;
  sqlite3_mutex_enter( p.pSrcDb.mutex );
  sqlite3BtreeEnter( p.pSrc );
  mutex = p.pSrcDb.mutex;
  if ( p.pDestDb != null )
  {
    sqlite3_mutex_enter( p.pDestDb.mutex );
  }

  /* Detach this backup from the source pager. */
  if ( p.pDestDb != null )
  {
    p.pSrc.nBackup--;
  }
  if ( p.isAttached != 0 )
  {
    pp = sqlite3PagerBackupPtr( sqlite3BtreePager( p.pSrc ) );
    while ( pp != p )
    {
      pp = ( pp ).pNext;
    }
    sqlite3BtreePager( p.pSrc ).pBackup = p.pNext;
  }

  /* If a transaction is still open on the Btree, roll it back. */
  sqlite3BtreeRollback( p.pDest );

  /* Set the error code of the destination database handle. */
  rc = ( p.rc == SQLITE_DONE ) ? SQLITE_OK : p.rc;
  sqlite3Error( p.pDestDb, rc, 0 );

  /* Exit the mutexes and free the backup context structure. */
  if ( p.pDestDb != null )
  {
    sqlite3_mutex_leave( p.pDestDb.mutex );
  }
  sqlite3BtreeLeave( p.pSrc );
  if ( p.pDestDb != null )
  {
    /* EVIDENCE-OF: R-64852-21591 The sqlite3_backup object is created by a
    ** call to sqlite3_backup_init() and is destroyed by a call to
    ** sqlite3_backup_finish(). */
    //sqlite3_free( ref p );
  }
  sqlite3_mutex_leave( mutex );
  return rc;
}

/*
** Return the number of pages still to be backed up as of the most recent
** call to sqlite3_backup_step().
*/
static int sqlite3_backup_remaining( sqlite3_backup p )
{
  return (int)p.nRemaining;
}

/*
** Return the total number of pages in the source database as of the most
** recent call to sqlite3_backup_step().
*/
static int sqlite3_backup_pagecount( sqlite3_backup p )
{
  return (int)p.nPagecount;
}

/*
** This function is called after the contents of page iPage of the
** source database have been modified. If page iPage has already been
** copied into the destination database, then the data written to the
** destination is now invalidated. The destination copy of iPage needs
** to be updated with the new data before the backup operation is
** complete.
**
** It is assumed that the mutex associated with the BtShared object
** corresponding to the source database is held when this function is
** called.
*/
static void sqlite3BackupUpdate( sqlite3_backup pBackup, Pgno iPage, byte[] aData )
{
  sqlite3_backup p;                   /* Iterator variable */
  for ( p = pBackup; p != null; p = p.pNext )
  {
    Debug.Assert( sqlite3_mutex_held( p.pSrc.pBt.mutex ) );
    if ( !isFatalError( p.rc ) && iPage < p.iNext )
    {
      /* The backup process p has already copied page iPage. But now it
      ** has been modified by a transaction on the source pager. Copy
      ** the new data into the backup.
      */
      int rc;
      Debug.Assert( p.pDestDb != null );
      sqlite3_mutex_enter( p.pDestDb.mutex );
      rc = backupOnePage( p, iPage, aData );
      sqlite3_mutex_leave( p.pDestDb.mutex );
      Debug.Assert( rc != SQLITE_BUSY && rc != SQLITE_LOCKED );
      if ( rc != SQLITE_OK )
      {
        p.rc = rc;
      }
    }
  }
}

/*
** Restart the backup process. This is called when the pager layer
** detects that the database has been modified by an external database
** connection. In this case there is no way of knowing which of the
** pages that have been copied into the destination database are still
** valid and which are not, so the entire process needs to be restarted.
**
** It is assumed that the mutex associated with the BtShared object
** corresponding to the source database is held when this function is
** called.
*/
static void sqlite3BackupRestart( sqlite3_backup pBackup )
{
  sqlite3_backup p;                   /* Iterator variable */
  for ( p = pBackup; p != null; p = p.pNext )
  {
    Debug.Assert( sqlite3_mutex_held( p.pSrc.pBt.mutex ) );
    p.iNext = 1;
  }
}

#if !SQLITE_OMIT_VACUUM
/*
** Copy the complete content of pBtFrom into pBtTo.  A transaction
** must be active for both files.
**
** The size of file pTo may be reduced by this operation. If anything
** goes wrong, the transaction on pTo is rolled back. If successful, the
** transaction is committed before returning.
*/
static int sqlite3BtreeCopyFile( Btree pTo, Btree pFrom )
{
  int rc;
  sqlite3_backup b;
  sqlite3BtreeEnter( pTo );
  sqlite3BtreeEnter( pFrom );

  /* Set up an sqlite3_backup object. sqlite3_backup.pDestDb must be set
  ** to 0. This is used by the implementations of sqlite3_backup_step()
  ** and sqlite3_backup_finish() to detect that they are being called
  ** from this function, not directly by the user.
  */
  b = new sqlite3_backup();// memset( &b, 0, sizeof( b ) );
  b.pSrcDb = pFrom.db;
  b.pSrc = pFrom;
  b.pDest = pTo;
  b.iNext = 1;

  /* 0x7FFFFFFF is the hard limit for the number of pages in a database
  ** file. By passing this as the number of pages to copy to
  ** sqlite3_backup_step(), we can guarantee that the copy finishes
  ** within a single call (unless an error occurs). The Debug.Assert() statement
  ** checks this assumption - (p.rc) should be set to either SQLITE_DONE
  ** or an error code.
  */
  sqlite3_backup_step( b, 0x7FFFFFFF );
  Debug.Assert( b.rc != SQLITE_OK );
  rc = sqlite3_backup_finish( b );
  if ( rc == SQLITE_OK )
  {
    pTo.pBt.pageSizeFixed = false;
  }

  sqlite3BtreeLeave( pFrom );
  sqlite3BtreeLeave( pTo );
  return rc;
}
#endif //* SQLITE_OMIT_VACUUM */
  }
}