/******************************************************************************
 *
 * Purpose:  Implementation of the CPCIDSKFile class.
 *
 ******************************************************************************
 * Copyright (c) 2009
 * PCI Geomatics, 90 Allstate Parkway, Markham, Ontario, Canada.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 ****************************************************************************/
#include "pcidsk_file.h"
#include "pcidsk_exception.h"
#include "pcidsk_channel.h"
#include "pcidsk_segment.h"
#include "core/mutexholder.h"
#include "core/pcidsk_utils.h"
#include "core/cpcidskfile.h"
#include "core/cpcidskblockfile.h"

// Channel types
#include "channel/cbandinterleavedchannel.h"
#include "channel/cpixelinterleavedchannel.h"
#include "channel/ctiledchannel.h"
#include "channel/cexternalchannel.h"

// Segment types
#include "segment/cpcidskgeoref.h"
#include "segment/cpcidskpct.h"
#include "segment/cpcidskbpct.h"
#include "segment/cpcidsklut.h"
#include "segment/cpcidskblut.h"
#include "segment/cpcidskvectorsegment.h"
#include "segment/metadatasegment.h"
#include "segment/systiledir.h"
#include "segment/cpcidskrpcmodel.h"
#include "segment/cpcidskgcp2segment.h"
#include "segment/cpcidskbitmap.h"
#include "segment/cpcidsk_tex.h"
#include "segment/cpcidsk_array.h"
#include "segment/cpcidsktoutinmodel.h"
#include "segment/cpcidskpolymodel.h"
#include "segment/cpcidskbinarysegment.h"
#include "core/clinksegment.h"

#ifdef PCIDSK_IMP_PARAM_SUPPORT
#define __INT16DEF__
#define __INT32DEF__
#define __INT64DEF__

#define __CINT16TDEF__
#define __CINT32TDEF__
#define __CINT64TDEF__
#define __CFLOAT32TDEF__
#define __CFLOAT64TDEF__

#define __CINT16DEF__
#define __CINT32DEF__
#define __CINT64DEF__
#define __CFLOAT32DEF__
#define __CFLOAT64DEF__

#include "core/impparam/impparam.h"
#endif

#include <cassert>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <limits>
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <algorithm>

using namespace PCIDSK;

/************************************************************************/
/*                             CPCIDSKFile()                             */
/************************************************************************/

CPCIDSKFile::CPCIDSKFile( const std::string& filename )

{
    io_handle = nullptr;
    io_mutex = nullptr;
    updatable = false;
    base_filename = filename;
    width = 0;
    height = 0;
    channel_count = 0;
    segment_count = 0;
    segment_pointers_offset = 0;
    block_size = 0;
    pixel_group_size = 0;
    segment_count = 0;
    segment_pointers_offset = 0;
    block_size = 0;
    pixel_group_size = 0;
    first_line_offset = 0;
    last_block_index = 0;
    last_block_dirty = false;
    last_block_xoff = 0;
    last_block_xsize = 0;
    last_block_data = nullptr;
    last_block_mutex = nullptr;
    file_size = 0;

    file_list.reserve(1024);

/* -------------------------------------------------------------------- */
/*      Initialize the metadata object, but do not try to load till     */
/*      needed.                                                         */
/* -------------------------------------------------------------------- */
    metadata.Initialize( this, "FIL", 0 );
}

/************************************************************************/
/*                            ~CPCIDSKFile()                             */
/************************************************************************/

CPCIDSKFile::~CPCIDSKFile()

{
    try
    {
        Synchronize();
    }
    catch( const PCIDSKException& e )
    {
        fprintf(stderr, "Exception in ~CPCIDSKFile(): %s", e.what()); // ok
    }

/* -------------------------------------------------------------------- */
/*      Cleanup last block buffer.                                      */
/* -------------------------------------------------------------------- */
    if( last_block_data != nullptr )
    {
        last_block_index = -1;
        free( last_block_data );
        last_block_data = nullptr;
        delete last_block_mutex;
    }

/* -------------------------------------------------------------------- */
/*      Cleanup channels and segments.                                  */
/* -------------------------------------------------------------------- */
    size_t i;
    for( i = 0; i < channels.size(); i++ )
    {
        delete channels[i];
        channels[i] = nullptr;
    }

    for( i = 0; i < segments.size(); i++ )
    {
        delete segments[i];
        segments[i] = nullptr;
    }

/* -------------------------------------------------------------------- */
/*      Close and cleanup IO stuff.                                     */
/* -------------------------------------------------------------------- */
    {
        MutexHolder oHolder( io_mutex );

        if( io_handle )
        {
            interfaces.io->Close( io_handle );
            io_handle = nullptr;
        }
    }

    size_t i_file;

    for( i_file=0; i_file < file_list.size(); i_file++ )
    {
        delete file_list[i_file].io_mutex;
        file_list[i_file].io_mutex = nullptr;

        interfaces.io->Close( file_list[i_file].io_handle );
        file_list[i_file].io_handle = nullptr;
    }

    for( i_file=0; i_file < edb_file_list.size(); i_file++ )
    {
        delete edb_file_list[i_file].io_mutex;
        edb_file_list[i_file].io_mutex = nullptr;

        delete edb_file_list[i_file].file;
        edb_file_list[i_file].file = nullptr;
    }

    delete io_mutex;
}

/************************************************************************/
/*                            Synchronize()                             */
/************************************************************************/

void CPCIDSKFile::Synchronize()

{
    if( !GetUpdatable() )
        return;

/* -------------------------------------------------------------------- */
/*      Flush out last line caching stuff for pixel interleaved data.   */
/* -------------------------------------------------------------------- */
    FlushBlock();

/* -------------------------------------------------------------------- */
/*      Synchronize all channels.                                       */
/* -------------------------------------------------------------------- */
    size_t i;
    for( i = 0; i < channels.size(); i++ )
        channels[i]->Synchronize();

/* -------------------------------------------------------------------- */
/*      Synchronize all segments we have instantiated.                  */
/* -------------------------------------------------------------------- */
    for( i = 0; i < segments.size(); i++ )
    {
        if( segments[i] != nullptr )
            segments[i]->Synchronize();
    }

/* -------------------------------------------------------------------- */
/*      Ensure the file is synchronized to disk.                        */
/* -------------------------------------------------------------------- */
    MutexHolder oHolder( io_mutex );

    interfaces.io->Flush( io_handle );
}

/************************************************************************/
/*                             GetChannel()                             */
/************************************************************************/

PCIDSKChannel *CPCIDSKFile::GetChannel( int band )

{
    if( band < 1 || band > channel_count )
        return (PCIDSKChannel*)ThrowPCIDSKExceptionPtr( "Out of range band (%d) requested.",
                              band );

    return channels[band-1];
}

/************************************************************************/
/*                             GetSegment()                             */
/************************************************************************/

PCIDSK::PCIDSKSegment *CPCIDSKFile::GetSegment( int segment )

{
/* -------------------------------------------------------------------- */
/*      Is this a valid segment?                                        */
/* -------------------------------------------------------------------- */
    if( segment < 1 || segment > segment_count )
        return nullptr;

    const char *segment_pointer = segment_pointers.buffer + (segment-1) * 32;
    if( segment_pointer[0] != 'A' && segment_pointer[0] != 'L' )
        return nullptr;

/* -------------------------------------------------------------------- */
/*      Do we already have a corresponding object?                      */
/* -------------------------------------------------------------------- */
    if( segments[segment] != nullptr )
        return segments[segment];

/* -------------------------------------------------------------------- */
/*      Instantiate per the type.                                       */
/* -------------------------------------------------------------------- */
    int segment_type = segment_pointers.GetInt((segment-1)*32+1,3);
    PCIDSKSegment *segobj = nullptr;

    switch( segment_type )
    {
      case SEG_GEO:
        segobj = new CPCIDSKGeoref( this, segment, segment_pointer );
        break;

      case SEG_PCT:
        segobj = new CPCIDSK_PCT( this, segment, segment_pointer );
        break;

      case SEG_BPCT:
        segobj = new CPCIDSK_BPCT( this, segment, segment_pointer );
        break;

      case SEG_LUT:
        segobj = new CPCIDSK_LUT( this, segment, segment_pointer );
        break;

      case SEG_BLUT:
        segobj = new CPCIDSK_BLUT( this, segment, segment_pointer );
        break;

      case SEG_VEC:
        segobj = new CPCIDSKVectorSegment( this, segment, segment_pointer );
        break;

      case SEG_BIT:
        segobj = new CPCIDSKBitmap( this, segment, segment_pointer );
        break;

      case SEG_TEX:
        segobj = new CPCIDSK_TEX( this, segment, segment_pointer );
        break;

      case SEG_SYS:
        if (STARTS_WITH(segment_pointer + 4, "SysBMDir") ||
            STARTS_WITH(segment_pointer + 4, "TileDir"))
        {
            segobj = new SysTileDir( this, segment, segment_pointer );
        }
        else if( STARTS_WITH(segment_pointer + 4, "METADATA") )
            segobj = new MetadataSegment( this, segment, segment_pointer );
        else if (STARTS_WITH(segment_pointer + 4, "Link    ") )
            segobj = new CLinkSegment(this, segment, segment_pointer);
        else
            segobj = new CPCIDSKSegment( this, segment, segment_pointer );

        break;

      case SEG_GCP2:
        segobj = new CPCIDSKGCP2Segment(this, segment, segment_pointer);
        break;

      case SEG_ORB:
        segobj = new CPCIDSKEphemerisSegment(this, segment, segment_pointer);
        break;

      case SEG_ARR:
        segobj = new CPCIDSK_ARRAY(this, segment, segment_pointer);
        break;

      case SEG_BIN:
        if (STARTS_WITH(segment_pointer + 4, "RFMODEL "))
        {
            segobj = new CPCIDSKRPCModelSegment( this, segment, segment_pointer );
        }
        else if (STARTS_WITH(segment_pointer + 4, "APMODEL "))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "POLYMDL "))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "TPSMODEL"))
        {
            segobj = new CPCIDSKGCP2Segment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "RTCSMDL "))
        {
            segobj = new CPCIDSKGCP2Segment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "MMRTCS  "))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "MODEL   "))
        {
            segobj = new CPCIDSKToutinModelSegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "MMSPB   "))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "MMADS   "))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "MMSRS   "))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "MMSGS   "))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "LRSMODEL"))
        {
            segobj = new CPCIDSKGCP2Segment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "MMLRS   "))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        else if (STARTS_WITH(segment_pointer + 4, "EPIPOLAR"))
        {
            segobj = new CPCIDSKBinarySegment(this, segment, segment_pointer);
        }
        break;
    }

    if (segobj == nullptr)
        segobj = new CPCIDSKSegment( this, segment, segment_pointer );

    segments[segment] = segobj;

    return segobj;
}

/************************************************************************/
/*                             GetSegment()                             */
/*                                                                      */
/*      Find segment by type/name.                                      */
/************************************************************************/

PCIDSK::PCIDSKSegment *CPCIDSKFile::GetSegment( int type, const std::string & name,
                                                int previous)
{
    int  i;
    char type_str[16];

    //we want the 3 less significant digit only in case type is too big
    // Note : that happen with SEG_VEC_TABLE that is equal to 65652 in GDB.
    //see function BuildChildrenLayer in jtfile.cpp, the call on GDBSegNext
    //in the loop on gasTypeTable can create issue in PCIDSKSegNext
    //(in pcic/gdbfrtms/pcidskopen.cpp)
    CPLsnprintf( type_str, sizeof(type_str), "%03d", (type % 1000) );
    for( i = previous; i < segment_count; i++ )
    {
        if( type != SEG_UNKNOWN
            && strncmp(segment_pointers.buffer+i*32+1,type_str,3) != 0 )
            continue;

        auto pszName = segment_pointers.buffer + i*32 + 4;
        if(!CheckSegNamesEqual(pszName, 8, name.data(), (unsigned)name.size()))
            continue;

        // Ignore deleted segments.
        if (*(segment_pointers.buffer + i * 32 + 0) == 'D') continue;

        return GetSegment(i+1);
    }

    return nullptr;
}

unsigned int CPCIDSKFile::GetSegmentID(int type, const std::string &name,
                                       unsigned previous) const
{
    //we want the 3 less significant digit only in case type is too big
    // Note : that happen with SEG_VEC_TABLE that is equal to 65652 in GDB.
    //see function BuildChildrenLayer in jtfile.cpp, the call on GDBSegNext
    //in the loop on gasTypeTable can create issue in PCIDSKSegNext
    //(in pcic/gdbfrtms/pcidskopen.cpp)
    char type_str[16];
    CPLsnprintf(type_str, sizeof(type_str), "%03d", (type % 1000) );

    for(int i = previous; i < segment_count; i++ )
    {
        if( type != SEG_UNKNOWN
            && strncmp(segment_pointers.buffer+i*32+1,type_str,3) != 0 )
            continue;

        auto pszName = segment_pointers.buffer + i*32 + 4;
        if(!CheckSegNamesEqual(pszName, 8, name.data(), (unsigned)name.size()))
            continue;

        // Ignore deleted segments.
        if (*(segment_pointers.buffer + i * 32 + 0) == 'D') continue;

        return i+1;
    }
    return 0;
}

std::vector<unsigned> CPCIDSKFile::GetSegmentIDs(int type,
           const std::function<bool(const char *,unsigned)> & oFilter) const
{
    std::vector<unsigned> vnSegments;
    char type_str[16];
    CPLsnprintf(type_str, sizeof(type_str), "%03d", (type % 1000) );

    for(int i = 0; i < segment_count; i++)
    {
        if( type != SEG_UNKNOWN
            && strncmp(segment_pointers.buffer+i*32+1,type_str,3) != 0 )
            continue;

        auto pszName = segment_pointers.buffer + i*32 + 4;
        if(!oFilter(pszName, 8))
            continue;

        // Ignore deleted segments.
        if (*(segment_pointers.buffer + i * 32 + 0) == 'D') continue;

        vnSegments.push_back(i + 1);
    }
    return vnSegments;
}

/************************************************************************/
/*                        InitializeFromHeader()                        */
/************************************************************************/

void CPCIDSKFile::InitializeFromHeader(int max_channel_count_allowed)

{
/* -------------------------------------------------------------------- */
/*      Process the file header.                                        */
/* -------------------------------------------------------------------- */
    PCIDSKBuffer fh(512);

    ReadFromFile( fh.buffer, 0, 512 );

    width = atoi(fh.Get(384,8));
    height = atoi(fh.Get(392,8));
    channel_count = atoi(fh.Get(376,8));
    if( width < 0 || height < 0 || channel_count < 0 )
    {
        return ThrowPCIDSKException(
            "Invalid width, height and/or channel_count" );
    }
    if( max_channel_count_allowed >= 0 && channel_count > max_channel_count_allowed )
    {
        return ThrowPCIDSKException(
            "channel_count = %d exceeds max_channel_count_allowed = %d",
            channel_count,
            max_channel_count_allowed );
    }
    file_size = fh.GetUInt64(16,16);

    if (file_size > std::numeric_limits<uint64>::max() / 512)
    {
        return ThrowPCIDSKException("Invalid file_size: " PCIDSK_FRMT_UINT64,
                                    file_size);
    }

    uint64 ih_start_block = atouint64(fh.Get(336,16));
    uint64 image_start_block = atouint64(fh.Get(304,16));
    fh.Get(360,8,interleaving);

    if( image_start_block == 0 ||
        image_start_block-1 > std::numeric_limits<uint64>::max() / 512 )
    {
        return ThrowPCIDSKException(
            "Invalid image_start_block: " PCIDSK_FRMT_UINT64, image_start_block );
    }
    uint64 image_offset = (image_start_block-1) * 512;

    block_size = 0;
    last_block_index = -1;
    last_block_dirty = false;
    last_block_data = nullptr;
    last_block_mutex = nullptr;

/* -------------------------------------------------------------------- */
/*      Load the segment pointers into a PCIDSKBuffer.  For now we      */
/*      try to avoid doing too much other processing on them.           */
/* -------------------------------------------------------------------- */
    int segment_block_count = atoi(fh.Get(456,8));
    if( segment_block_count < 0 ||
        segment_block_count > std::numeric_limits<int>::max() / 512 )
        return ThrowPCIDSKException( "Invalid segment_block_count: %d",
                                     segment_block_count );

    segment_pointers_offset = atouint64(fh.Get(440,16));
    if( segment_pointers_offset == 0 ||
        segment_pointers_offset-1 > file_size )
    {
        return ThrowPCIDSKException(
            "Invalid segment_pointers_offset: " PCIDSK_FRMT_UINT64, segment_pointers_offset );
    }
    segment_pointers_offset = segment_pointers_offset * 512 - 512;

    // Sanity check to avoid allocating too much memory
    if( segment_block_count * 512 > 100 * 1024 * 1024 )
    {
        MutexHolder oHolder( io_mutex );

        interfaces.io->Seek( io_handle, 0, SEEK_END );
        const auto nRealFileSize = interfaces.io->Tell( io_handle );
        if( segment_pointers_offset > nRealFileSize )
        {
            return ThrowPCIDSKException(
                "Invalid segment_pointers_offset: " PCIDSK_FRMT_UINT64, segment_pointers_offset );
        }
        if( static_cast<unsigned>(segment_block_count * 512) > nRealFileSize - segment_pointers_offset )
        {
            // I guess we could also decide to error out
            segment_block_count = static_cast<int>((nRealFileSize - segment_pointers_offset) / 512);
        }
    }

    segment_count = (segment_block_count * 512) / 32;
    segment_pointers.SetSize( segment_block_count * 512 );

    ReadFromFile( segment_pointers.buffer, segment_pointers_offset,
                  segment_block_count * 512 );

    segments.resize( segment_count + 1 );

/* -------------------------------------------------------------------- */
/*      Get the number of each channel type - only used for some        */
/*      interleaving cases.                                             */
/* -------------------------------------------------------------------- */
    int count_8u = 0;
    int count_16s = 0;
    int count_16u = 0;
    int count_32r = 0;
    int count_c16u = 0;
    int count_c16s = 0;
    int count_c32r = 0;

    int16 count_32s = 0;
    int16 count_32u = 0;
    int16 count_64s = 0;
    int16 count_64u = 0;
    int16 count_64r = 0;
    int16 count_c32s = 0;
    int16 count_c32u = 0;

    if (strcmp(fh.Get(464,4), "    ") == 0)
    {
        count_8u = channel_count;
    }
    else
    {
        count_8u = atoi(fh.Get(464,4));
        count_16s = atoi(fh.Get(468,4));
        count_16u = atoi(fh.Get(472,4));
        count_32r = atoi(fh.Get(476,4));
        count_c16u = atoi(fh.Get(480,4));
        count_c16s = atoi(fh.Get(484,4));
        count_c32r = atoi(fh.Get(488,4));

        count_32s = *(int16 *) fh.Get(492,2);
        count_32u = *(int16 *) fh.Get(494,2);
        count_64s = *(int16 *) fh.Get(496,2);
        count_64u = *(int16 *) fh.Get(498,2);
        count_64r = *(int16 *) fh.Get(500,2);
        count_c32s = *(int16 *) fh.Get(502,2);
        count_c32u = *(int16 *) fh.Get(504,2);

        if (!BigEndianSystem())
        {
            SwapData(&count_32s, 2, 1);
            SwapData(&count_32u, 2, 1);
            SwapData(&count_64s, 2, 1);
            SwapData(&count_64u, 2, 1);
            SwapData(&count_64r, 2, 1);
            SwapData(&count_c32s, 2, 1);
            SwapData(&count_c32u, 2, 1);
        }

        // 8224 is two space characters.
        if (count_32s == 8224)
            count_32s = 0;
        if (count_32u == 8224)
            count_32u = 0;
        if (count_64s == 8224)
            count_64s = 0;
        if (count_64u == 8224)
            count_64u = 0;
        if (count_64r == 8224)
            count_64r = 0;
        if (count_c32s == 8224)
            count_c32s = 0;
        if (count_c32u == 8224)
            count_c32u = 0;
    }

    if (channel_count !=
        count_8u +
        count_16s +
        count_16u +
        count_32s +
        count_32u +
        count_32r +
        count_64s +
        count_64u +
        count_64r +
        count_c16s +
        count_c16u +
        count_c32s +
        count_c32u +
        count_c32r)
    {
        return ThrowPCIDSKException("The file seems to contain an unsupported data type.");
    }

/* -------------------------------------------------------------------- */
/*      for pixel interleaved files we need to compute the length of    */
/*      a scanline padded out to a 512 byte boundary.                   */
/* -------------------------------------------------------------------- */
    if( interleaving == "PIXEL" )
    {
        first_line_offset = image_offset;
        pixel_group_size =
            count_8u +
            count_16s*2 +
            count_16u*2 +
            count_32s*4 +
            count_32u*4 +
            count_32r*4 +
            count_64s*8 +
            count_64u*8 +
            count_64r*8 +
            count_c16u*4 +
            count_c16s*4 +
            count_c32u*8 +
            count_c32s*8 +
            count_c32r*8;

        block_size = static_cast<PCIDSK::uint64>(pixel_group_size) * width;
        if( block_size % 512 != 0 )
            block_size += 512 - (block_size % 512);
        if( block_size != static_cast<size_t>(block_size) )
        {
             return ThrowPCIDSKException(
                "Allocating " PCIDSK_FRMT_UINT64 " bytes for scanline "
                "buffer failed.", block_size );
        }

        last_block_data = calloc(1, static_cast<size_t>(block_size));
        if( last_block_data == nullptr )
        {
             return ThrowPCIDSKException(
                "Allocating " PCIDSK_FRMT_UINT64 " bytes for scanline "
                "buffer failed.", block_size );
        }

        last_block_mutex = interfaces.CreateMutex();
        image_offset = 0;
    }

/* -------------------------------------------------------------------- */
/*      Initialize the list of channels.                                */
/* -------------------------------------------------------------------- */
    int channelnum;

    for( channelnum = 1; channelnum <= channel_count; channelnum++ )
    {
        PCIDSKBuffer ih(1024);
        PCIDSKChannel *channel = nullptr;
        if( ih_start_block == 0 ||
            ih_start_block-1 > std::numeric_limits<uint64>::max() / 512 ||
            (ih_start_block-1)*512 > std::numeric_limits<uint64>::max() - (channelnum-1)*1024 )
        {
            return ThrowPCIDSKException( "Integer overflow when computing ih_offset");
        }
        uint64  ih_offset = (ih_start_block-1)*512 + (channelnum-1)*1024;

        ReadFromFile( ih.buffer, ih_offset, 1024 );

        // fetch the filename, if there is one.
        std::string filename;
        ih.Get(64,64,filename);
        filename.resize(strlen(filename.c_str()));

        // Check for an extended link file
        bool bLinked = false;
        if (STARTS_WITH(filename.c_str(), "LNK"))
        {
            std::string seg_str(filename, 4, 4);
            unsigned int seg_num = std::atoi(seg_str.c_str());

            if (seg_num == 0)
            {
                throw PCIDSKException("Unable to find link segment. Link name:%s",
                                      filename.c_str());
            }

            CLinkSegment* link_seg =
                dynamic_cast<CLinkSegment*>(GetSegment(seg_num));
            if (link_seg == nullptr)
            {
                throw PCIDSKException("Failed to get Link Information Segment.");
            }

            filename = link_seg->GetPath();
            bLinked = true;
        }
        else if (!filename.empty() &&
                 filename != "<uninitialized>" &&
                 filename.substr(0,5) != "/SIS=")
        {
            // adjust it relative to the path of the pcidsk file.
            std::string oTmp = interfaces.MergeRelativePath(interfaces.io,base_filename,filename);

            if(std::ifstream( filename.c_str() ).is_open() ||
               std::ifstream( oTmp.c_str() ).is_open() )
            {
                bLinked = true;
            }

            try
            {
                PCIDSK::EDBFile* poEDBFile = interfaces.OpenEDB(oTmp.c_str(),"r");
                delete poEDBFile;
                bLinked = true;
            }
            catch(...)
            {
                bLinked = false;
            }
        }
        if (bLinked)
        {
            // adjust it relative to the path of the pcidsk file.
            filename = interfaces.MergeRelativePath(interfaces.io,base_filename,filename);
        }
        // work out channel type from header
        eChanType pixel_type;
        const char *pixel_type_string = ih.Get( 160, 8 );

        pixel_type = GetDataTypeFromName(pixel_type_string);

        // For file interleaved channels, we expect a valid channel type.
        if (interleaving == "FILE" && pixel_type == CHN_UNKNOWN)
        {
            return ThrowPCIDSKException("Invalid or unsupported channel type: %s",
                                        pixel_type_string);
        }

        // if we didn't get channel type in header, work out from counts (old).
        // Check this only if we don't have complex channels:

        if (STARTS_WITH(pixel_type_string,"        "))
        {
            if( !( count_c32r == 0 && count_c16u == 0 && count_c16s == 0 ) )
                return ThrowPCIDSKException("Assertion 'count_c32r == 0 && count_c16u == 0 && count_c16s == 0' failed");

            if( channelnum <= count_8u )
                pixel_type = CHN_8U;
            else if( channelnum <= count_8u + count_16s )
                pixel_type = CHN_16S;
            else if( channelnum <= count_8u + count_16s + count_16u )
                pixel_type = CHN_16U;
            else
                pixel_type = CHN_32R;
        }

        if( interleaving == "BAND"  )
        {
            channel = new CBandInterleavedChannel( ih, ih_offset, fh,
                                                   channelnum, this,
                                                   image_offset, pixel_type );


            image_offset += (int64)DataTypeSize(channel->GetType())
                * (int64)width * (int64)height;
        }

        else if( interleaving == "PIXEL" )
        {
            channel = new CPixelInterleavedChannel( ih, ih_offset, fh,
                                                    channelnum, this,
                                                    (int) image_offset,
                                                    pixel_type );
            image_offset += DataTypeSize(pixel_type);
        }

        else if( interleaving == "FILE"
                 && STARTS_WITH(filename.c_str(), "/SIS=") )
        {
            channel = new CTiledChannel( ih, ih_offset, fh,
                                         channelnum, this, pixel_type );
        }

        else if( bLinked ||
                 (interleaving == "FILE"
                 && filename != ""
                 && !STARTS_WITH(((const char*)ih.buffer)+282, "        ")) )
        {
            channel = new CExternalChannel( ih, ih_offset, fh, filename,
                                            channelnum, this, pixel_type );
        }

        else if( interleaving == "FILE" )
        {
            channel = new CBandInterleavedChannel( ih, ih_offset, fh,
                                                   channelnum, this,
                                                   0, pixel_type );
        }

        else
            return ThrowPCIDSKException( "Unsupported interleaving:%s",
                                       interleaving.c_str() );

        channels.push_back( channel );
    }
}

/************************************************************************/
/*                            ReadFromFile()                            */
/************************************************************************/

void CPCIDSKFile::ReadFromFile( void *buffer, uint64 offset, uint64 size )

{
    MutexHolder oHolder( io_mutex );

    interfaces.io->Seek( io_handle, offset, SEEK_SET );

    uint64 nReadSize = interfaces.io->Read(buffer, 1, size, io_handle);

    if (nReadSize != size)
    {
        // Only throw an exception if the sum of the offset and size is
        // greater than the internal file size.
        if (offset + size > file_size * 512)
        {
            std::stringstream oOffsetStream;
            std::stringstream oSizeStream;

            oOffsetStream << offset;
            oSizeStream << size;

            return ThrowPCIDSKException("Failed to read %s bytes at offset %s in file: %s",
                           oSizeStream.str().c_str(),
                           oOffsetStream.str().c_str(),
                           base_filename.c_str());
        }

        // If we were not able to read the requested size, initialize
        // the remaining bytes to 0.
        std::memset((char *) buffer + nReadSize, 0,
                    static_cast<size_t>(size - nReadSize));
    }
}

/************************************************************************/
/*                            WriteToFile()                             */
/************************************************************************/

void CPCIDSKFile::WriteToFile( const void *buffer, uint64 offset, uint64 size )

{
    if( !GetUpdatable() )
        throw PCIDSKException( "File not open for update in WriteToFile()" );

    MutexHolder oHolder( io_mutex );

    interfaces.io->Seek( io_handle, offset, SEEK_SET );

    uint64 nWriteSize = interfaces.io->Write(buffer, 1, size, io_handle);

    if (nWriteSize != size)
    {
        std::stringstream oOffsetStream;
        std::stringstream oSizeStream;

        oOffsetStream << offset;
        oSizeStream << size;

        ThrowPCIDSKException("Failed to write %s bytes at offset %s in file: %s",
                       oSizeStream.str().c_str(),
                       oOffsetStream.str().c_str(),
                       base_filename.c_str());
    }
}

/************************************************************************/
/*                          ReadAndLockBlock()                          */
/************************************************************************/

void *CPCIDSKFile::ReadAndLockBlock( int block_index,
                                     int win_xoff, int win_xsize )

{
    if( last_block_data == nullptr )
        return ThrowPCIDSKExceptionPtr( "ReadAndLockBlock() called on a file that is not pixel interleaved." );

/* -------------------------------------------------------------------- */
/*      Default, and validate windowing.                                */
/* -------------------------------------------------------------------- */
    if( win_xoff == -1 && win_xsize == -1 )
    {
        win_xoff = 0;
        win_xsize = GetWidth();
    }

    if( win_xoff < 0 || win_xoff+win_xsize > GetWidth() )
    {
        return ThrowPCIDSKExceptionPtr( "CPCIDSKFile::ReadAndLockBlock(): Illegal window - xoff=%d, xsize=%d",
                                   win_xoff, win_xsize );
    }

    if( block_index == last_block_index
        && win_xoff == last_block_xoff
        && win_xsize == last_block_xsize )
    {
        last_block_mutex->Acquire();
        return last_block_data;
    }

/* -------------------------------------------------------------------- */
/*      Flush any dirty writable data.                                  */
/* -------------------------------------------------------------------- */
    // We cannot use FlushBlock() because this method needs to acquire the
    // last_block_mutex but we must do everything at once with last_block_data
    // to prevent race conditions.
    //
    // --------------------------------------------------------------------
    // Process 1                             Process 2
    // FlushBlock()
    //                                       FlushBlock()
    // last_block_mutex->Acquire();
    // ReadFromFile(last_block_data);
    // last_block_mutex->Release();
    //                                       last_block_mutex->Acquire();
    //                                       ReadFromFile(last_block_data);
    //                                       last_block_mutex->Release();
    // --------------------------------------------------------------------
    //
    // Now the data in last_block_data set by process 1 will never be flushed
    // because process 2 overwrites it without calling FlushBlock.

    last_block_mutex->Acquire();

    if( last_block_dirty )
    {
        WriteBlock( last_block_index, last_block_data );
        last_block_dirty = 0;
    }
/* -------------------------------------------------------------------- */
/*      Read the requested window.                                      */
/* -------------------------------------------------------------------- */

    ReadFromFile( last_block_data,
                  first_line_offset + block_index*block_size
                  + static_cast<uint64_t>(win_xoff) * pixel_group_size,
                  static_cast<uint64_t>(pixel_group_size) * win_xsize );
    last_block_index = block_index;
    last_block_xoff = win_xoff;
    last_block_xsize = win_xsize;

    return last_block_data;
}

/************************************************************************/
/*                            UnlockBlock()                             */
/************************************************************************/

void CPCIDSKFile::UnlockBlock( bool mark_dirty )

{
    if( last_block_mutex == nullptr )
        return;

    last_block_dirty |= mark_dirty;
    last_block_mutex->Release();
}

/************************************************************************/
/*                             WriteBlock()                             */
/************************************************************************/

void CPCIDSKFile::WriteBlock( int block_index, void *buffer )

{
    if( !GetUpdatable() )
        return ThrowPCIDSKException( "File not open for update in WriteBlock()" );

    if( last_block_data == nullptr )
        return ThrowPCIDSKException( "WriteBlock() called on a file that is not pixel interleaved." );

    WriteToFile( buffer,
                 first_line_offset + block_index*block_size,
                 block_size );
}

/************************************************************************/
/*                             FlushBlock()                             */
/************************************************************************/

void CPCIDSKFile::FlushBlock()

{
    if( last_block_dirty )
    {
        last_block_mutex->Acquire();
        if( last_block_dirty ) // is it still dirty?
        {
            WriteBlock( last_block_index, last_block_data );
            last_block_dirty = false;
        }
        last_block_mutex->Release();
    }
}

/************************************************************************/
/*                         GetEDBFileDetails()                          */
/************************************************************************/

bool CPCIDSKFile::GetEDBFileDetails( EDBFile** file_p,
                                     Mutex **io_mutex_p,
                                     const std::string& filename )

{
    *file_p = nullptr;
    *io_mutex_p = nullptr;

/* -------------------------------------------------------------------- */
/*      Does the file exist already in our file list?                   */
/* -------------------------------------------------------------------- */
    unsigned int i;

    for( i = 0; i < edb_file_list.size(); i++ )
    {
        if( edb_file_list[i].filename == filename )
        {
            *file_p = edb_file_list[i].file;
            *io_mutex_p = edb_file_list[i].io_mutex;
            return edb_file_list[i].writable;
        }
    }

/* -------------------------------------------------------------------- */
/*      If not, we need to try and open the file.  Eventually we        */
/*      will need better rules about read or update access.             */
/* -------------------------------------------------------------------- */
    ProtectedEDBFile new_file;

    new_file.file = nullptr;
    new_file.writable = false;

    if( GetUpdatable() )
    {
        try
        {
            new_file.file = interfaces.OpenEDB( filename, "r+" );
            new_file.writable = true;
        }
        catch (PCIDSK::PCIDSKException &)
        {
        }
        catch (std::exception &)
        {
        }
    }

    if( new_file.file == nullptr )
        new_file.file = interfaces.OpenEDB( filename, "r" );

    if( new_file.file == nullptr )
        return ThrowPCIDSKException( 0, "Unable to open file '%s'.",
                              filename.c_str() ) != 0;

/* -------------------------------------------------------------------- */
/*      Push the new file into the list of files managed for this       */
/*      PCIDSK file.                                                    */
/* -------------------------------------------------------------------- */
    new_file.io_mutex = interfaces.CreateMutex();
    new_file.filename = filename;

    edb_file_list.push_back( new_file );

    *file_p = edb_file_list.back().file;
    *io_mutex_p  = edb_file_list.back().io_mutex;

    return new_file.writable;
}

/************************************************************************/
/*                            GetUniqueEDBFilename()                    */
/************************************************************************/
/**
 * If the PIX file is a link pix where all channels are linked
 * to the same file, then this filename is given to be able to
 * access it directly without going through PCIDSK code.
 */
std::string CPCIDSKFile::GetUniqueEDBFilename()
{
    bool bAllSameFile = true;
    bool bAllExternal = true;

    std::string oEDBName;

    for(int iChan=1 ; iChan <= this->GetChannels() ; iChan++)
    {
        PCIDSK::PCIDSKChannel* poChannel = this->GetChannel(iChan);

        PCIDSK::CExternalChannel* poExt =
            dynamic_cast<PCIDSK::CExternalChannel*>(poChannel);

        if(!poExt)
        {
            bAllExternal = false;
            break;
        }

        //trigger call to AccessDB()
        poChannel->GetBlockWidth();

        const std::string oFilename = poExt->GetExternalFilename();

        if(oEDBName.size() == 0)
        {
            oEDBName = oFilename;
        }
        else if(oEDBName != oFilename)
        {
            bAllSameFile = false;
            break;
        }
    }

    if(bAllExternal && bAllSameFile)
    {
        return oEDBName;
    }
    return "";
}

/************************************************************************/
/*                              GetEDBChannelMap()                      */
/************************************************************************/
/**
 * Gets the mapping between channels in this CPCIDSKFile and the channels
 * they are linked to in the external file.
 *
 * Current File         External File
 * 2 -----------------> 1
 * 3 -----------------> 3
 * 4 -----------------> 6
 *
 * This would return this map:
 * (2,1), (3,3), (4,6)
 *
 * @param oExtFilename  The external file we want a mapping for
 *
 * @return A map with the mapping between the channels in the current file
 *         and the channels the refer to in the external file.
 */
std::map<int,int> CPCIDSKFile::GetEDBChannelMap(std::string oExtFilename)
{
    std::map<int,int> vnChanMap;

    for(int iChan=1 ; iChan <= this->GetChannels() ; iChan++)
    {
        PCIDSK::PCIDSKChannel* poChannel = this->GetChannel(iChan);

        PCIDSK::CExternalChannel* poExt =
            dynamic_cast<PCIDSK::CExternalChannel*>(poChannel);

        if(poExt)
        {
            std::string oFilename = poExt->GetExternalFilename();

            if(oExtFilename == oFilename)
                vnChanMap[iChan] = poExt->GetExternalChanNum();
        }
    }

    return vnChanMap;
}

/************************************************************************/
/*                            GetIODetails()                            */
/************************************************************************/

void CPCIDSKFile::GetIODetails( void ***io_handle_pp,
                                Mutex ***io_mutex_pp,
                                const std::string& filename,
                                bool writable )

{
    *io_handle_pp = nullptr;
    *io_mutex_pp = nullptr;

/* -------------------------------------------------------------------- */
/*      Does this reference the PCIDSK file itself?                     */
/* -------------------------------------------------------------------- */
    if( filename.empty() )
    {
        *io_handle_pp = &io_handle;
        *io_mutex_pp = &io_mutex;
        return;
    }

/* -------------------------------------------------------------------- */
/*      Does the file exist already in our file list?                   */
/* -------------------------------------------------------------------- */
    unsigned int i;

    for( i = 0; i < file_list.size(); i++ )
    {
        if( file_list[i].filename == filename
            && (!writable || file_list[i].writable) )
        {
            *io_handle_pp = &(file_list[i].io_handle);
            *io_mutex_pp = &(file_list[i].io_mutex);
            return;
        }
    }

/* -------------------------------------------------------------------- */
/*      If not, we need to try and open the file.  Eventually we        */
/*      will need better rules about read or update access.             */
/* -------------------------------------------------------------------- */
    ProtectedFile new_file;

    if( writable )
        new_file.io_handle = interfaces.io->Open( filename, "r+" );
    else
        new_file.io_handle = interfaces.io->Open( filename, "r" );

    if( new_file.io_handle == nullptr )
        return ThrowPCIDSKException( "Unable to open file '%s'.",
                              filename.c_str() );

/* -------------------------------------------------------------------- */
/*      Push the new file into the list of files managed for this       */
/*      PCIDSK file.                                                    */
/* -------------------------------------------------------------------- */
    new_file.io_mutex = interfaces.CreateMutex();
    new_file.filename = filename;
    new_file.writable = writable;

    file_list.push_back( new_file );

    *io_handle_pp = &(file_list.back().io_handle);
    *io_mutex_pp  = &(file_list.back().io_mutex);
}

/************************************************************************/
/*                           DeleteSegment()                            */
/************************************************************************/

void CPCIDSKFile::DeleteSegment( int segment )

{
/* -------------------------------------------------------------------- */
/*      Is this an existing segment?                                    */
/* -------------------------------------------------------------------- */
    PCIDSKSegment *poSeg = GetSegment( segment );

    if( poSeg == nullptr )
        return ThrowPCIDSKException( "DeleteSegment(%d) failed, segment does not exist.", segment );

/* -------------------------------------------------------------------- */
/*      Wipe associated metadata.                                       */
/* -------------------------------------------------------------------- */
    std::vector<std::string> md_keys = poSeg->GetMetadataKeys();
    unsigned int i;

    for( i = 0; i < md_keys.size(); i++ )
        poSeg->SetMetadataValue( md_keys[i], "" );

/* -------------------------------------------------------------------- */
/*      Remove the segment object from the segment object cache.  I     */
/*      hope the application is not retaining any references to this    */
/*      segment!                                                        */
/* -------------------------------------------------------------------- */
    segments[segment] = nullptr;
    delete poSeg;

/* -------------------------------------------------------------------- */
/*      Mark the segment pointer as deleted.                            */
/* -------------------------------------------------------------------- */
    segment_pointers.buffer[(segment-1)*32] = 'D';

    // write the updated segment pointer back to the file.
    WriteToFile( segment_pointers.buffer + (segment-1)*32,
                 segment_pointers_offset + (segment-1)*32,
                 32 );
}

/************************************************************************/
/*                           CreateSegment()                            */
/************************************************************************/

int CPCIDSKFile::CreateSegment( std::string name, std::string description,
                                eSegType seg_type, int data_blocks )

{
/* -------------------------------------------------------------------- */
/*      Set the size of fixed length segments.                          */
/* -------------------------------------------------------------------- */
    int expected_data_blocks = 0;
    bool prezero = false;

    switch( seg_type )
    {
      case SEG_PCT:
        expected_data_blocks = 6;
        break;

      case SEG_BPCT:
        expected_data_blocks = 12;
        break;

      case SEG_LUT:
        expected_data_blocks = 2;
        break;

      case SEG_BLUT:
        expected_data_blocks = 6;
        break;

      case SEG_SIG:
        expected_data_blocks = 12;
        break;

      case SEG_GCP2:
        // expected_data_blocks = 67;
        // Change seg type to new GCP segment type
        expected_data_blocks = 129;
        break;

      case SEG_GEO:
        expected_data_blocks = 6;
        break;

      case SEG_TEX:
        expected_data_blocks = 64;
        prezero = true;
        break;

      case SEG_BIT:
      {
          uint64 bytes = ((width * (uint64) height) + 7) / 8;
          expected_data_blocks = (int) ((bytes + 511) / 512);
          prezero = true;
      }
      break;

      default:
        break;
    }

    if( data_blocks == 0 && expected_data_blocks != 0 )
        data_blocks = expected_data_blocks;

/* -------------------------------------------------------------------- */
/*      Find an empty Segment Pointer.  For System segments we start    */
/*      at the end, instead of the beginning to avoid using up          */
/*      segment numbers that the user would notice.                     */
/* -------------------------------------------------------------------- */
    int segment = 1;
    int64 seg_start = -1;
    PCIDSKBuffer segptr( 32 );

    if( seg_type == SEG_SYS )
    {
        for( segment=segment_count; segment >= 1; segment-- )
        {
            memcpy( segptr.buffer, segment_pointers.buffer+(segment-1)*32, 32);

            uint64 this_seg_size = segptr.GetUInt64(23,9);
            char flag = (char) segptr.buffer[0];

            if( flag == 'D'
                && (uint64) data_blocks+2 == this_seg_size
                && this_seg_size > 0 )
                seg_start = segptr.GetUInt64(12,11) - 1;
            else if( flag == ' ' )
                seg_start = 0;
            else if( flag && this_seg_size == 0 )
                seg_start = 0;

            if( seg_start != -1 )
                break;
        }
    }
    else
    {
        for( segment=1; segment <= segment_count; segment++ )
        {
            memcpy( segptr.buffer, segment_pointers.buffer+(segment-1)*32, 32);

            uint64 this_seg_size = segptr.GetUInt64(23,9);
            char flag = (char) segptr.buffer[0];

            if( flag == 'D'
                && (uint64) data_blocks+2 == this_seg_size
                && this_seg_size > 0 )
                seg_start = segptr.GetUInt64(12,11) - 1;
            else if( flag == ' ' )
                seg_start = 0;
            else if( flag && this_seg_size == 0 )
                seg_start = 0;

            if( seg_start != -1 )
                break;
        }
    }

    if( segment <= 0 || segment > segment_count )
        return ThrowPCIDSKException(0, "All %d segment pointers in use.", segment_count);

/* -------------------------------------------------------------------- */
/*      If the segment does not have a data area already, identify      */
/*      its location at the end of the file, and extend the file to     */
/*      the desired length.                                             */
/* -------------------------------------------------------------------- */
    if( seg_start == 0 )
    {
        seg_start = GetFileSize();
        ExtendFile( data_blocks + 2, prezero );
    }
    else
    {
        std::vector<uint8> zeros;
        uint64 blocks_to_zero = data_blocks + 2;
        uint64 segiter = seg_start;

        zeros.resize( 512 * 32 );

        while( blocks_to_zero > 0 )
        {
            uint64 this_time = blocks_to_zero;
            if( this_time > 32 )
                this_time = 32;

            WriteToFile( &(zeros[0]), segiter * 512, this_time*512 );
            blocks_to_zero -= this_time;
            segiter += this_time;
        }
    }

/* -------------------------------------------------------------------- */
/*      Update the segment pointer information.                         */
/* -------------------------------------------------------------------- */
    // SP1.1 - Flag
    segptr.Put( "A", 0, 1 );

    // SP1.2 - Type
    segptr.Put( (int) seg_type, 1, 3 );

    // SP1.3 - Name
    segptr.Put( name.c_str(), 4, 8 );

    // SP1.4 - start block
    segptr.Put( (uint64) (seg_start + 1), 12, 11 );

    // SP1.5 - data blocks.
    segptr.Put( data_blocks+2, 23, 9 );

    // Update in memory copy of segment pointers.
    memcpy( segment_pointers.buffer+(segment-1)*32, segptr.buffer, 32);

    // Update on disk.
    WriteToFile( segptr.buffer,
                 segment_pointers_offset + (segment-1)*32, 32 );

/* -------------------------------------------------------------------- */
/*      Prepare segment header.                                         */
/* -------------------------------------------------------------------- */
    PCIDSKBuffer sh(1024);

    char current_time[17];

    GetCurrentDateTime( current_time );

    sh.Put( " ", 0, 1024 );

    // SH1 - segment content description
    sh.Put( description.c_str(), 0, 64 );

    // SH3 - Creation time/date
    sh.Put( current_time, 128, 16 );

    // SH4 - Last Update time/date
    sh.Put( current_time, 144, 16 );

/* -------------------------------------------------------------------- */
/*      Write segment header.                                           */
/* -------------------------------------------------------------------- */
    WriteToFile( sh.buffer, seg_start * 512, 1024 );

/* -------------------------------------------------------------------- */
/*      Initialize the newly created segment.                           */
/* -------------------------------------------------------------------- */
    PCIDSKSegment *seg_obj = GetSegment( segment );

    seg_obj->Initialize();

#ifdef PCIDSK_IMP_PARAM_SUPPORT
    // Update the Last Segment Number Created parameter.
    if (seg_type != SEG_SYS)
    {
        float fLASC = (float) segment;
        IMPPutReal("LASC;", &fLASC, 1);
    }
#endif

    return segment;
}// CreateSegment

/************************************************************************/
/*                             ExtendFile()                             */
/************************************************************************/

void CPCIDSKFile::ExtendFile( uint64 blocks_requested,
                              bool prezero, bool writedata )

{
    if( prezero )
    {
        const int nBufferSize = 64 * 1024 * 1024;
        const int nBufferBlocks = nBufferSize / 512;

        PCIDSKBuffer oZero(nBufferSize);

        std::memset(oZero.buffer, 0, nBufferSize);

        uint64 nBlockCount = blocks_requested;

        while (nBlockCount > 0)
        {
            uint64 nCurrentBlocks = nBlockCount;
            if (nCurrentBlocks > nBufferBlocks)
                nCurrentBlocks = nBufferBlocks;

            WriteToFile(oZero.buffer, file_size * 512, nCurrentBlocks * 512);

            nBlockCount -= nCurrentBlocks;

            file_size += nCurrentBlocks;
        }
    }
    else
    {
        if ( writedata )
            WriteToFile( "\0", (file_size + blocks_requested) * 512 - 1, 1 );

        file_size += blocks_requested;
    }

    PCIDSKBuffer fh3( 16 );
    fh3.Put( file_size, 0, 16 );
    WriteToFile( fh3.buffer, 16, 16 );
}

/************************************************************************/
/*                           ExtendSegment()                            */
/************************************************************************/

void CPCIDSKFile::ExtendSegment( int segment, uint64 blocks_requested,
                                 bool prezero, bool writedata )

{
    PCIDSKSegment * poSegment = GetSegment(segment);

    if (!poSegment)
    {
        return ThrowPCIDSKException("ExtendSegment(%d) failed, "
                                    "segment does not exist.", segment);
    }

    // Move the segment at the end of file if necessary.
    if (!poSegment->IsAtEOF())
        MoveSegmentToEOF(segment);

    // Extend the file.
    ExtendFile( blocks_requested, prezero, writedata );

    // Update the segment pointer in memory and on disk.
    int segptr_off = (segment - 1) * 32;

    segment_pointers.Put(
        segment_pointers.GetUInt64(segptr_off+23,9) + blocks_requested,
        segptr_off+23, 9 );

    WriteToFile( segment_pointers.buffer + segptr_off,
                 segment_pointers_offset + segptr_off,
                 32 );

    // Update the segment information.
    poSegment->LoadSegmentPointer(segment_pointers.buffer + segptr_off);
}

/************************************************************************/
/*                          MoveSegmentToEOF()                          */
/************************************************************************/

void CPCIDSKFile::MoveSegmentToEOF( int segment )

{
    PCIDSKSegment * poSegment = GetSegment(segment);

    if (!poSegment)
    {
        return ThrowPCIDSKException("MoveSegmentToEOF(%d) failed, "
                                    "segment does not exist.", segment);
    }

    int segptr_off = (segment - 1) * 32;
    uint64 seg_start, seg_size;
    uint64 new_seg_start;

    seg_start = segment_pointers.GetUInt64( segptr_off + 12, 11 );
    seg_size = segment_pointers.GetUInt64( segptr_off + 23, 9 );

    // Are we already at the end of the file?
    if( (seg_start + seg_size - 1) == file_size )
        return;

    new_seg_start = file_size + 1;

    // Grow the file to hold the segment at the end.
    ExtendFile( seg_size, false, false );

    // Move the segment data to the new location.
    uint8 copy_buf[16384];
    uint64 srcoff, dstoff, bytes_to_go;

    bytes_to_go = seg_size * 512;
    srcoff = (seg_start - 1) * 512;
    dstoff = (new_seg_start - 1) * 512;

    while( bytes_to_go > 0 )
    {
        uint64 bytes_this_chunk = sizeof(copy_buf);
        if( bytes_to_go < bytes_this_chunk )
            bytes_this_chunk = bytes_to_go;

        ReadFromFile( copy_buf, srcoff, bytes_this_chunk );
        WriteToFile( copy_buf, dstoff, bytes_this_chunk );

        srcoff += bytes_this_chunk;
        dstoff += bytes_this_chunk;
        bytes_to_go -= bytes_this_chunk;
    }

    // Update the segment pointer in memory and on disk.
    segment_pointers.Put( new_seg_start, segptr_off + 12, 11 );

    WriteToFile( segment_pointers.buffer + segptr_off,
                 segment_pointers_offset + segptr_off,
                 32 );

    // Update the segment information.
    poSegment->LoadSegmentPointer(segment_pointers.buffer + segptr_off);
}

/************************************************************************/
/*                          CreateOverviews()                           */
/************************************************************************/
/*
 const char *pszResampling;
             Can be "NEAREST" for Nearest Neighbour resampling (the fastest),
             "AVERAGE" for block averaging or "MODE" for block mode.  This
             establishing the type of resampling to be applied when preparing
             the decimated overviews. Other methods can be set as well, but
             not all applications might support a given overview generation
             method.
*/

void CPCIDSKFile::CreateOverviews( int chan_count, const int *chan_list,
                                   int factor, std::string resampling )

{
    std::vector<int> default_chan_list;

/* -------------------------------------------------------------------- */
/*      Default to processing all bands.                                */
/* -------------------------------------------------------------------- */
    if( chan_count == 0 )
    {
        chan_count = channel_count;
        default_chan_list.resize( chan_count );

        for( int i = 0; i < chan_count; i++ )
            default_chan_list[i] = i+1;

        chan_list = &(default_chan_list[0]);
    }

/* -------------------------------------------------------------------- */
/*      Work out the creation options that should apply for the         */
/*      overview.                                                       */
/* -------------------------------------------------------------------- */
    std::string layout = GetMetadataValue( "_DBLayout" );
    int         tilesize = PCIDSK_DEFAULT_TILE_SIZE;
    std::string compression = "NONE";

    if( STARTS_WITH( layout.c_str(), "TILED") )
    {
        ParseTileFormat(layout, tilesize, compression);
    }

/* -------------------------------------------------------------------- */
/*      Make sure we have a block tile directory for managing the       */
/*      tile layers.                                                    */
/* -------------------------------------------------------------------- */
    CPCIDSKBlockFile oBlockFile(this);

    SysTileDir * poTileDir = oBlockFile.GetTileDir();

    if (!poTileDir)
        poTileDir = oBlockFile.CreateTileDir();

/* ==================================================================== */
/*      Loop over the channels.                                         */
/* ==================================================================== */
    for( int chan_index = 0; chan_index < chan_count; chan_index++ )
    {
        int channel_number = chan_list[chan_index];
        PCIDSKChannel *channel = GetChannel( channel_number );

/* -------------------------------------------------------------------- */
/*      Figure out if the given overview level already exists           */
/*      for a given channel; if it does, skip creating it.              */
/* -------------------------------------------------------------------- */
        bool overview_exists = false;
        for( int i = channel->GetOverviewCount()-1; i >= 0; i-- )
        {
            PCIDSKChannel *overview = channel->GetOverview( i );

            if( overview->GetWidth() == channel->GetWidth() / factor
                && overview->GetHeight() == channel->GetHeight() / factor )
            {
                overview_exists = true;
            }
        }

        if (overview_exists == false && poTileDir != nullptr)
        {
/* -------------------------------------------------------------------- */
/*      Create the overview as a tiled image layer.                     */
/* -------------------------------------------------------------------- */
            int virtual_image =
                poTileDir->CreateTileLayer(channel->GetWidth() / factor,
                                           channel->GetHeight() / factor,
                                           tilesize, tilesize,
                                           channel->GetType(),
                                           compression);

/* -------------------------------------------------------------------- */
/*      Attach reference to this overview as metadata.                  */
/* -------------------------------------------------------------------- */
            char overview_md_key[128];
            char overview_md_value[128];

            snprintf( overview_md_key, sizeof(overview_md_key),  "_Overview_%d", factor );
            snprintf( overview_md_value, sizeof(overview_md_value), "%d 0 %s",virtual_image,resampling.c_str());

            channel->SetMetadataValue( overview_md_key, overview_md_value );

/* -------------------------------------------------------------------- */
/*      Update the internal overview lists                              */
/* -------------------------------------------------------------------- */
            CPCIDSKChannel* cpcidskchannel = dynamic_cast<CPCIDSKChannel *>(channel);
            if( cpcidskchannel )
                cpcidskchannel->UpdateOverviewInfo(overview_md_value, factor);
        }
    }
}

