/******************************************************************************
 * $Id: mbtilesdataset.cpp 35569 2016-09-30 19:39:05Z rouault $
 *
 * Project:  GDAL MBTiles driver
 * Purpose:  Implement GDAL MBTiles support using OGR SQLite driver
 * Author:   Even Rouault, Even Rouault <even.rouault at spatialys.com>
 *
 **********************************************************************
 * Copyright (c) 2012-2016, Even Rouault <even.rouault at spatialys.com>
 *
 * 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 "gdal_frmts.h"
#include "gdal_pam.h"
#include "ogr_api.h"
#include "cpl_vsil_curl_priv.h"
#include "gpkgmbtilescommon.h"
#include "gdalwarper.h"

#include "zlib.h"
#include "json.h"

#include <math.h>

CPL_CVSID("$Id: mbtilesdataset.cpp 35569 2016-09-30 19:39:05Z rouault $");

static const char * const apszAllowedDrivers[] = {"JPEG", "PNG", NULL};

#define SRS_EPSG_3857 "PROJCS[\"WGS 84 / Pseudo-Mercator\",GEOGCS[\"WGS 84\",DATUM[\"WGS_1984\",SPHEROID[\"WGS 84\",6378137,298.257223563,AUTHORITY[\"EPSG\",\"7030\"]],AUTHORITY[\"EPSG\",\"6326\"]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],UNIT[\"degree\",0.0174532925199433,AUTHORITY[\"EPSG\",\"9122\"]],AUTHORITY[\"EPSG\",\"4326\"]],PROJECTION[\"Mercator_1SP\"],PARAMETER[\"central_meridian\",0],PARAMETER[\"scale_factor\",1],PARAMETER[\"false_easting\",0],PARAMETER[\"false_northing\",0],UNIT[\"metre\",1,AUTHORITY[\"EPSG\",\"9001\"]],AXIS[\"X\",EAST],AXIS[\"Y\",NORTH],EXTENSION[\"PROJ4\",\"+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs\"],AUTHORITY[\"EPSG\",\"3857\"]]"

#define SPHERICAL_RADIUS        6378137.0
#define MAX_GM                  (SPHERICAL_RADIUS * M_PI)               // 20037508.342789244

// TileMatrixSet origin : caution this is in GeoPackage / WMTS convention ! That is upper-left corner
#define TMS_ORIGIN_X        -MAX_GM
#define TMS_ORIGIN_Y         MAX_GM

class MBTilesBand;

/************************************************************************/
/*                         MBTILESOpenSQLiteDB()                        */
/************************************************************************/

static OGRDataSourceH MBTILESOpenSQLiteDB(const char* pszFilename,
                                          GDALAccess eAccess)
{
    const char* l_apszAllowedDrivers[] = { "SQLITE", NULL };
    return (OGRDataSourceH)GDALOpenEx(pszFilename,
                                      GDAL_OF_VECTOR | GDAL_OF_INTERNAL |
                                      ((eAccess == GA_Update) ? GDAL_OF_UPDATE : 0),
                                      l_apszAllowedDrivers, NULL, NULL);
}

/************************************************************************/
/* ==================================================================== */
/*                              MBTilesDataset                          */
/* ==================================================================== */
/************************************************************************/

class MBTilesDataset : public GDALPamDataset, public GDALGPKGMBTilesLikePseudoDataset
{
    friend class MBTilesBand;

  public:
                 MBTilesDataset();

    virtual     ~MBTilesDataset();

    virtual CPLErr GetGeoTransform(double* padfGeoTransform);
    virtual CPLErr SetGeoTransform( double* padfGeoTransform );
    virtual const char* GetProjectionRef();
    virtual CPLErr SetProjection( const char* pszProjection );

    virtual char      **GetMetadataDomainList();
    virtual char      **GetMetadata( const char * pszDomain = "" );
    virtual const char *GetMetadataItem( const char* pszName, const char * pszDomain = "" );

    virtual CPLErr    IBuildOverviews(
                        const char * pszResampling,
                        int nOverviews, int * panOverviewList,
                        int nBandsIn, CPL_UNUSED int * panBandList,
                        GDALProgressFunc pfnProgress, void * pProgressData );

    static GDALDataset *Open( GDALOpenInfo * );
    static int          Identify( GDALOpenInfo * );
    static GDALDataset* Create( const char * pszFilename,
                                   int nXSize,
                                   int nYSize,
                                   int nBandsIn,
                                   GDALDataType eDT,
                                   char **papszOptions );
    static GDALDataset* CreateCopy( const char *pszFilename,
                                                GDALDataset *poSrcDS,
                                                int bStrict,
                                                char ** papszOptions,
                                                GDALProgressFunc pfnProgress,
                                                void * pProgressData );

    char*               FindKey(int iPixel, int iLine);

    bool                HasNonEmptyGrids();

  private:

    bool m_bWriteBounds;
    bool m_bWriteMinMaxZoom;
    MBTilesDataset* poMainDS;
    bool m_bGeoTransformValid;
    double m_adfGeoTransform[6];

    int m_nOverviewCount;
    MBTilesDataset** m_papoOverviewDS;

    OGRDataSourceH hDS;
    sqlite3* hDB;

#ifdef HAVE_SQLITE_VFS
    sqlite3_vfs*        pMyVFS;
#endif

    bool bFetchedMetadata;
    CPLStringList aosList;

    int nHasNonEmptyGrids;

    bool m_bInFlushCache;

    void ParseCompressionOptions(char** papszOptions);
    CPLErr FinalizeRasterRegistration();
    void ComputeTileAndPixelShifts();
    int InitRaster ( MBTilesDataset* poParentDS,
                     int nZoomLevel,
                     int nBandCount,
                     double dfGDALMinX,
                     double dfGDALMinY,
                     double dfGDALMaxX,
                     double dfGDALMaxY );

    bool CreateInternal( const char * pszFilename,
                         int nXSize,
                         int nYSize,
                         int nBandsIn,
                         GDALDataType eDT,
                         char **papszOptions );

    protected:
        // Coming from GDALGPKGMBTilesLikePseudoDataset

        virtual CPLErr                  IFlushCacheWithErrCode();
        virtual int                     IGetRasterCount() { return nBands; }
        virtual GDALRasterBand*         IGetRasterBand(int nBand) { return GetRasterBand(nBand); }
        virtual sqlite3                *IGetDB() { return hDB; }
        virtual bool                    IGetUpdate() { return eAccess == GA_Update; }
        virtual bool                    ICanIWriteBlock();
        virtual OGRErr                  IStartTransaction();
        virtual OGRErr                  ICommitTransaction();
        virtual const char             *IGetFilename() { return GetDescription(); }
        virtual int                     GetRowFromIntoTopConvention(int nRow);

};

/************************************************************************/
/* ==================================================================== */
/*                              MBTilesBand                             */
/* ==================================================================== */
/************************************************************************/

class MBTilesBand: public GDALGPKGMBTilesLikeRasterBand
{
    friend class MBTilesDataset;

    CPLString               osLocationInfo;

  public:
                            MBTilesBand( MBTilesDataset* poDS );

    virtual int             GetOverviewCount();
    virtual GDALRasterBand* GetOverview(int nLevel);

    virtual char      **GetMetadataDomainList();
    virtual const char *GetMetadataItem( const char * pszName,
                                         const char * pszDomain = "" );
};

/************************************************************************/
/*                            MBTilesBand()                             */
/************************************************************************/

MBTilesBand::MBTilesBand(MBTilesDataset* poDSIn) :
      GDALGPKGMBTilesLikeRasterBand(poDSIn, 256, 256)
{
}

/************************************************************************/
/*                           utf8decode()                               */
/************************************************************************/

static unsigned utf8decode(const char* p, const char* end, int* len)
{
  unsigned char c = *(unsigned char*)p;
  if (c < 0x80) {
    *len = 1;
    return c;
  } else if (c < 0xc2) {
    goto FAIL;
  }
  if (p+1 >= end || (p[1]&0xc0) != 0x80) goto FAIL;
  if (c < 0xe0) {
    *len = 2;
    return
      ((p[0] & 0x1f) << 6) +
      ((p[1] & 0x3f));
  } else if (c == 0xe0) {
    if (((unsigned char*)p)[1] < 0xa0) goto FAIL;
    goto UTF8_3;
  }
#if STRICT_RFC3629
  else if (c == 0xed) {
    // RFC 3629 says surrogate chars are illegal.
    if (((unsigned char*)p)[1] >= 0xa0) goto FAIL;
    goto UTF8_3;
  } else if (c == 0xef) {
    // 0xfffe and 0xffff are also illegal characters
    if (((unsigned char*)p)[1]==0xbf &&
    ((unsigned char*)p)[2]>=0xbe) goto FAIL;
    goto UTF8_3;
  }
#endif
  else if (c < 0xf0) {
  UTF8_3:
    if (p+2 >= end || (p[2]&0xc0) != 0x80) goto FAIL;
    *len = 3;
    return
      ((p[0] & 0x0f) << 12) +
      ((p[1] & 0x3f) << 6) +
      ((p[2] & 0x3f));
  } else if (c == 0xf0) {
    if (((unsigned char*)p)[1] < 0x90) goto FAIL;
    goto UTF8_4;
  } else if (c < 0xf4) {
  UTF8_4:
    if (p+3 >= end || (p[2]&0xc0) != 0x80 || (p[3]&0xc0) != 0x80) goto FAIL;
    *len = 4;
#if STRICT_RFC3629
    // RFC 3629 says all codes ending in fffe or ffff are illegal:
    if ((p[1]&0xf)==0xf &&
    ((unsigned char*)p)[2] == 0xbf &&
    ((unsigned char*)p)[3] >= 0xbe) goto FAIL;
#endif
    return
      ((p[0] & 0x07) << 18) +
      ((p[1] & 0x3f) << 12) +
      ((p[2] & 0x3f) << 6) +
      ((p[3] & 0x3f));
  } else if (c == 0xf4) {
    if (((unsigned char*)p)[1] > 0x8f) goto FAIL; // after 0x10ffff
    goto UTF8_4;
  } else {
  FAIL:
    *len = 1;
    return 0xfffd; // Unicode REPLACEMENT CHARACTER
  }
}

/************************************************************************/
/*                          HasNonEmptyGrids()                          */
/************************************************************************/

bool MBTilesDataset::HasNonEmptyGrids()
{
    OGRLayerH hSQLLyr;
    OGRFeatureH hFeat;
    const char* pszSQL;

    if (poMainDS)
        return poMainDS->HasNonEmptyGrids();

    if (nHasNonEmptyGrids >= 0)
        return nHasNonEmptyGrids != FALSE;

    nHasNonEmptyGrids = false;

    if (OGR_DS_GetLayerByName(hDS, "grids") == NULL)
        return false;

    pszSQL = "SELECT type FROM sqlite_master WHERE name = 'grids'";
    CPLDebug("MBTILES", "%s", pszSQL);
    hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
    if (hSQLLyr == NULL)
        return false;

    hFeat = OGR_L_GetNextFeature(hSQLLyr);
    if (hFeat == NULL || !OGR_F_IsFieldSet(hFeat, 0))
    {
        OGR_F_Destroy(hFeat);
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
        return false;
    }

    bool bGridsIsView = strcmp(OGR_F_GetFieldAsString(hFeat, 0), "view") == 0;

    OGR_F_Destroy(hFeat);
    OGR_DS_ReleaseResultSet(hDS, hSQLLyr);

    nHasNonEmptyGrids = TRUE;

    /* In the case 'grids' is a view (and a join between the 'map' and 'grid_utfgrid' layers */
    /* the cost of evaluating a join is very long, even if grid_utfgrid is empty */
    /* so check it is not empty */
    if (bGridsIsView)
    {
        OGRLayerH hGridUTFGridLyr;
        hGridUTFGridLyr = OGR_DS_GetLayerByName(hDS, "grid_utfgrid");
        if (hGridUTFGridLyr != NULL)
        {
            OGR_L_ResetReading(hGridUTFGridLyr);
            hFeat = OGR_L_GetNextFeature(hGridUTFGridLyr);
            OGR_F_Destroy(hFeat);

            nHasNonEmptyGrids = hFeat != NULL;
        }
    }

    return nHasNonEmptyGrids != FALSE;
}

/************************************************************************/
/*                             FindKey()                                */
/************************************************************************/

char* MBTilesDataset::FindKey(int iPixel, int iLine)
{
    const int nBlockXSize = 256, nBlockYSize = 256;

    // Compute shift between GDAL origin and TileMatrixSet origin
    // Caution this is in GeoPackage / WMTS convention ! That is upper-left corner
    const int nShiftXPixels = (int)floor(0.5 + (m_adfGeoTransform[0] - TMS_ORIGIN_X) /  m_adfGeoTransform[1]);
    const int nShiftYPixelsFromGPKGOrigin = (int)floor(0.5 + (m_adfGeoTransform[3] - TMS_ORIGIN_Y) /  m_adfGeoTransform[5]);

    const int iLineFromGPKGOrigin = iLine + nShiftYPixelsFromGPKGOrigin;
    const int iLineFromMBTilesOrigin = m_nTileMatrixHeight * nBlockYSize - 1 - iLineFromGPKGOrigin;
    const int iPixelFromMBTilesOrigin = iPixel + nShiftXPixels;

    const int nTileColumn = iPixelFromMBTilesOrigin / nBlockXSize;
    const int nTileRow = iLineFromMBTilesOrigin / nBlockYSize;
    int nColInTile = iPixelFromMBTilesOrigin % nBlockXSize;
    int nRowInTile = nBlockYSize - 1 - (iLineFromMBTilesOrigin % nBlockYSize);

    char* pszKey = NULL;

    OGRLayerH hSQLLyr;
    OGRFeatureH hFeat;
    const char* pszSQL;
    json_object* poGrid = NULL;
    int i;

    /* See https://github.com/mapbox/utfgrid-spec/blob/master/1.0/utfgrid.md */
    /* for the explanation of the following process */

    pszSQL = CPLSPrintf("SELECT grid FROM grids WHERE "
                        "zoom_level = %d AND tile_column = %d AND tile_row = %d",
                        m_nZoomLevel, nTileColumn, nTileRow);
    CPLDebug("MBTILES", "%s", pszSQL);
    hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
    if (hSQLLyr == NULL)
        return NULL;

    hFeat = OGR_L_GetNextFeature(hSQLLyr);
    if (hFeat == NULL || !OGR_F_IsFieldSet(hFeat, 0))
    {
        OGR_F_Destroy(hFeat);
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
        return NULL;
    }

    int nDataSize = 0;
    GByte* pabyData = OGR_F_GetFieldAsBinary(hFeat, 0, &nDataSize);

    int nUncompressedSize = 256*256;
    GByte* pabyUncompressed = (GByte*)VSIMalloc(nUncompressedSize + 1);
    if( pabyUncompressed == NULL )
    {
        OGR_F_Destroy(hFeat);
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
        return NULL;
    }

    z_stream sStream;
    memset(&sStream, 0, sizeof(sStream));
    inflateInit(&sStream);
    sStream.next_in   = pabyData;
    sStream.avail_in  = nDataSize;
    sStream.next_out  = pabyUncompressed;
    sStream.avail_out = nUncompressedSize;
    int nStatus = inflate(&sStream, Z_FINISH);
    inflateEnd(&sStream);
    if (nStatus != Z_OK && nStatus != Z_STREAM_END)
    {
        CPLDebug("MBTILES", "Error unzipping grid");
        nUncompressedSize = 0;
        pabyUncompressed[nUncompressedSize] = 0;
    }
    else
    {
        nUncompressedSize -= sStream.avail_out;
        pabyUncompressed[nUncompressedSize] = 0;
        //CPLDebug("MBTILES", "Grid size = %d", nUncompressedSize);
        //CPLDebug("MBTILES", "Grid value = %s", (const char*)pabyUncompressed);
    }

    struct json_tokener *jstok = NULL;
    json_object* jsobj = NULL;

    if (nUncompressedSize == 0)
    {
        goto end;
    }

    jstok = json_tokener_new();
    jsobj = json_tokener_parse_ex(jstok, (const char*)pabyUncompressed, -1);
    if( jstok->err != json_tokener_success)
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                    "JSON parsing error: %s (at offset %d)",
                    json_tokener_error_desc(jstok->err),
                    jstok->char_offset);
        json_tokener_free(jstok);

        goto end;
    }

    json_tokener_free(jstok);

    if (json_object_is_type(jsobj, json_type_object))
    {
        poGrid = json_object_object_get(jsobj, "grid");
    }
    if (poGrid != NULL && json_object_is_type(poGrid, json_type_array))
    {
        int nLines;
        int nFactor;
        json_object* poRow;
        char* pszRow = NULL;

        nLines = json_object_array_length(poGrid);
        if (nLines == 0)
            goto end;

        nFactor = 256 / nLines;
        nRowInTile /= nFactor;
        nColInTile /= nFactor;

        poRow = json_object_array_get_idx(poGrid, nRowInTile);

        /* Extract line of interest in grid */
        if (poRow != NULL && json_object_is_type(poRow, json_type_string))
        {
            pszRow = CPLStrdup(json_object_get_string(poRow));
        }

        if (pszRow == NULL)
            goto end;

        /* Unapply JSON encoding */
        for (i = 0; pszRow[i] != '\0'; i++)
        {
            unsigned char c = ((GByte*)pszRow)[i];
            if (c >= 93) c--;
            if (c >= 35) c--;
            if (c < 32)
            {
                CPLDebug("MBTILES", "Invalid character at byte %d", i);
                break;
            }
            c -= 32;
            ((GByte*)pszRow)[i] = c;
        }

        if (pszRow[i] == '\0')
        {
            char* pszEnd = pszRow + i;

            int iCol = 0;
            i = 0;
            int nKey = -1;
            while(pszRow + i < pszEnd)
            {
                int len = 0;
                unsigned int res = utf8decode(pszRow + i, pszEnd, &len);

                /* Invalid UTF8 ? */
                if (res > 127 && len == 1)
                    break;

                if (iCol == nColInTile)
                {
                    nKey = (int)res;
                    //CPLDebug("MBTILES", "Key index = %d", nKey);
                    break;
                }
                i += len;
                iCol ++;
            }

            /* Find key */
            json_object* poKeys = json_object_object_get(jsobj, "keys");
            if (nKey >= 0 && poKeys != NULL &&
                json_object_is_type(poKeys, json_type_array) &&
                nKey < json_object_array_length(poKeys))
            {
                json_object* poKey = json_object_array_get_idx(poKeys, nKey);
                if (poKey != NULL && json_object_is_type(poKey, json_type_string))
                {
                    pszKey = CPLStrdup(json_object_get_string(poKey));
                }
            }
        }

        CPLFree(pszRow);
    }

end:
    if (jsobj)
        json_object_put(jsobj);
    VSIFree(pabyUncompressed);
    if (hFeat)
        OGR_F_Destroy(hFeat);
    if (hSQLLyr)
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);

    return pszKey;
}

/************************************************************************/
/*                      GetMetadataDomainList()                         */
/************************************************************************/

char **MBTilesBand::GetMetadataDomainList()
{
    return CSLAddString(GDALPamRasterBand::GetMetadataDomainList(), "LocationInfo");
}

/************************************************************************/
/*                         GetMetadataItem()                            */
/************************************************************************/

const char *MBTilesBand::GetMetadataItem( const char * pszName,
                                          const char * pszDomain )
{
    MBTilesDataset* poGDS = (MBTilesDataset*) poDS;

/* ==================================================================== */
/*      LocationInfo handling.                                          */
/* ==================================================================== */
    if( pszDomain != NULL
        && EQUAL(pszDomain,"LocationInfo")
        && (STARTS_WITH_CI(pszName, "Pixel_") || STARTS_WITH_CI(pszName, "GeoPixel_")) )
    {
        int iPixel, iLine;

        if (!poGDS->HasNonEmptyGrids())
            return NULL;

/* -------------------------------------------------------------------- */
/*      What pixel are we aiming at?                                    */
/* -------------------------------------------------------------------- */
        if( STARTS_WITH_CI(pszName, "Pixel_") )
        {
            if( sscanf( pszName+6, "%d_%d", &iPixel, &iLine ) != 2 )
                return NULL;
        }
        else if( STARTS_WITH_CI(pszName, "GeoPixel_") )
        {
            double adfGeoTransform[6];
            double adfInvGeoTransform[6];
            double dfGeoX, dfGeoY;

            dfGeoX = CPLAtof(pszName + 9);
            const char* pszUnderscore = strchr(pszName + 9, '_');
            if( !pszUnderscore )
                return NULL;
            dfGeoY = CPLAtof(pszUnderscore + 1);

            if( GetDataset() == NULL )
                return NULL;

            if( GetDataset()->GetGeoTransform( adfGeoTransform ) != CE_None )
                return NULL;

            if( !GDALInvGeoTransform( adfGeoTransform, adfInvGeoTransform ) )
                return NULL;

            iPixel = (int) floor(
                adfInvGeoTransform[0]
                + adfInvGeoTransform[1] * dfGeoX
                + adfInvGeoTransform[2] * dfGeoY );
            iLine = (int) floor(
                adfInvGeoTransform[3]
                + adfInvGeoTransform[4] * dfGeoX
                + adfInvGeoTransform[5] * dfGeoY );
        }
        else
            return NULL;

        if( iPixel < 0 || iLine < 0
            || iPixel >= GetXSize()
            || iLine >= GetYSize() )
            return NULL;

        char* pszKey = poGDS->FindKey(iPixel, iLine);

        if (pszKey != NULL)
        {
            //CPLDebug("MBTILES", "Key = %s", pszKey);

            osLocationInfo = "<LocationInfo>";
            osLocationInfo += "<Key>";
            char* pszXMLEscaped = CPLEscapeString(pszKey, -1, CPLES_XML_BUT_QUOTES);
            osLocationInfo += pszXMLEscaped;
            CPLFree(pszXMLEscaped);
            osLocationInfo += "</Key>";

            if (OGR_DS_GetLayerByName(poGDS->hDS, "grid_data") != NULL &&
                strchr(pszKey, '\'') == NULL)
            {
                const char* pszSQL;
                OGRLayerH hSQLLyr;
                OGRFeatureH hFeat;

                pszSQL = CPLSPrintf("SELECT key_json FROM keymap WHERE "
                                    "key_name = '%s'",
                                    pszKey);
                CPLDebug("MBTILES", "%s", pszSQL);
                hSQLLyr = OGR_DS_ExecuteSQL(poGDS->hDS, pszSQL, NULL, NULL);
                if (hSQLLyr)
                {
                    hFeat = OGR_L_GetNextFeature(hSQLLyr);
                    if (hFeat != NULL && OGR_F_IsFieldSet(hFeat, 0))
                    {
                        const char* pszJSon = OGR_F_GetFieldAsString(hFeat, 0);
                        //CPLDebug("MBTILES", "JSon = %s", pszJSon);

                        osLocationInfo += "<JSon>";
#ifdef CPLES_XML_BUT_QUOTES
                        pszXMLEscaped = CPLEscapeString(pszJSon, -1, CPLES_XML_BUT_QUOTES);
#else
                        pszXMLEscaped = CPLEscapeString(pszJSon, -1, CPLES_XML);
#endif
                        osLocationInfo += pszXMLEscaped;
                        CPLFree(pszXMLEscaped);
                        osLocationInfo += "</JSon>";
                    }
                    OGR_F_Destroy(hFeat);
                }
                OGR_DS_ReleaseResultSet(poGDS->hDS, hSQLLyr);
            }

            osLocationInfo += "</LocationInfo>";

            CPLFree(pszKey);

            return osLocationInfo.c_str();
        }

        return NULL;
    }
    else
        return GDALPamRasterBand::GetMetadataItem(pszName, pszDomain);
}

/************************************************************************/
/*                         GetOverviewCount()                           */
/************************************************************************/

int MBTilesBand::GetOverviewCount()
{
    MBTilesDataset* poGDS = (MBTilesDataset*) poDS;

    if (poGDS->m_nOverviewCount >= 1)
        return poGDS->m_nOverviewCount;
    else
        return GDALPamRasterBand::GetOverviewCount();
}

/************************************************************************/
/*                              GetOverview()                           */
/************************************************************************/

GDALRasterBand* MBTilesBand::GetOverview(int nLevel)
{
    MBTilesDataset* poGDS = (MBTilesDataset*) poDS;

    if (poGDS->m_nOverviewCount == 0)
        return GDALPamRasterBand::GetOverview(nLevel);

    if (nLevel < 0 || nLevel >= poGDS->m_nOverviewCount)
        return NULL;

    GDALDataset* poOvrDS = poGDS->m_papoOverviewDS[nLevel];
    if (poOvrDS)
        return poOvrDS->GetRasterBand(nBand);
    else
        return NULL;
}

/************************************************************************/
/*                         MBTilesDataset()                          */
/************************************************************************/

MBTilesDataset::MBTilesDataset()
{
    m_bWriteBounds = true;
    m_bWriteMinMaxZoom = true;
    poMainDS = NULL;
    m_nOverviewCount = 0;
    hDS = NULL;
    m_papoOverviewDS = NULL;
    bFetchedMetadata = false;
    nHasNonEmptyGrids = -1;
    hDB = NULL;
#ifdef HAVE_SQLITE_VFS
    pMyVFS = NULL;
#endif
    m_bGeoTransformValid = false;
    m_adfGeoTransform[0] = 0.0;
    m_adfGeoTransform[1] = 1.0;
    m_adfGeoTransform[2] = 0.0;
    m_adfGeoTransform[3] = 0.0;
    m_adfGeoTransform[4] = 0.0;
    m_adfGeoTransform[5] = 1.0;
    m_bInFlushCache = false;

    m_osRasterTable = "tiles";
    m_eTF = GPKG_TF_PNG;
}

/************************************************************************/
/*                        ~MBTilesDataset()                             */
/************************************************************************/

MBTilesDataset::~MBTilesDataset()
{
    FlushCache();

    if (poMainDS == NULL)
    {
        if (m_papoOverviewDS)
        {
            for(int i=0;i<m_nOverviewCount;i++)
                delete m_papoOverviewDS[i];
            CPLFree(m_papoOverviewDS);
        }

        if (hDS != NULL)
        {
            OGRReleaseDataSource(hDS);
            hDB = NULL;
        }
        if( hDB != NULL )
        {
            sqlite3_close(hDB);

#ifdef HAVE_SQLITE_VFS
            if (pMyVFS)
            {
                sqlite3_vfs_unregister(pMyVFS);
                CPLFree(pMyVFS->pAppData);
                CPLFree(pMyVFS);
            }
#endif
        }
    }
}

/************************************************************************/
/*                         IStartTransaction()                          */
/************************************************************************/

OGRErr MBTilesDataset::IStartTransaction()
{
    char *pszErrMsg = NULL;
    const int rc = sqlite3_exec( hDB, "BEGIN", NULL, NULL, &pszErrMsg );
    if( rc != SQLITE_OK )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "%s transaction failed: %s",
                  "BEGIN", pszErrMsg );
        sqlite3_free( pszErrMsg );
        return OGRERR_FAILURE;
    }

    return OGRERR_NONE;
}

/************************************************************************/
/*                         ICommitTransaction()                         */
/************************************************************************/

OGRErr MBTilesDataset::ICommitTransaction()
{
    char *pszErrMsg = NULL;
    const int rc = sqlite3_exec( hDB, "COMMIT", NULL, NULL, &pszErrMsg );
    if( rc != SQLITE_OK )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "%s transaction failed: %s",
                  "COMMIT", pszErrMsg );
        sqlite3_free( pszErrMsg );
        return OGRERR_FAILURE;
    }

    return OGRERR_NONE;
}

/************************************************************************/
/*                         ICanIWriteBlock()                            */
/************************************************************************/

bool MBTilesDataset::ICanIWriteBlock()
{
    if( eAccess != GA_Update )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "IWriteBlock() not supported on dataset opened in read-only mode");
        return false;
    }

    if( !m_bGeoTransformValid )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "IWriteBlock() not supported if georeferencing not set");
        return false;
    }
    return true;
}

/************************************************************************/
/*                         IFlushCacheWithErrCode()                            */
/************************************************************************/

CPLErr MBTilesDataset::IFlushCacheWithErrCode()

{
    if( m_bInFlushCache )
        return CE_None;
    m_bInFlushCache = true;
    // Short circuit GDALPamDataset to avoid serialization to .aux.xml
    GDALDataset::FlushCache();

    CPLErr eErr = FlushTiles();

    m_bInFlushCache = false;
    return eErr;
}

/************************************************************************/
/*                         ICanIWriteBlock()                            */
/************************************************************************/

int MBTilesDataset::GetRowFromIntoTopConvention(int nRow)
{
    return m_nTileMatrixHeight - 1 - nRow;
}

/************************************************************************/
/*                          GetGeoTransform()                           */
/************************************************************************/

CPLErr MBTilesDataset::GetGeoTransform(double* padfGeoTransform)
{
    memcpy(padfGeoTransform, m_adfGeoTransform, 6 * sizeof(double));
    return ( m_bGeoTransformValid ) ? CE_None : CE_Failure;
}

/************************************************************************/
/*                     SphericalMercatorToLongLat()                     */
/************************************************************************/

static void SphericalMercatorToLongLat(double* x, double* y)
{
  double lng = *x / SPHERICAL_RADIUS / M_PI * 180;
  double lat = 2 * (atan(exp(*y / SPHERICAL_RADIUS)) - M_PI / 4) / M_PI * 180;
  *x = lng;
  *y = lat;
}

/************************************************************************/
/*                     LongLatToSphericalMercator()                     */
/************************************************************************/

static void LongLatToSphericalMercator(double* x, double* y)
{
  double X = SPHERICAL_RADIUS * (*x) / 180 * M_PI;
  double Y = SPHERICAL_RADIUS * log( tan(M_PI / 4 + 0.5 * (*y) / 180 * M_PI) );
  *x = X;
  *y = Y;
}

/************************************************************************/
/*                          SetGeoTransform()                           */
/************************************************************************/

CPLErr MBTilesDataset::SetGeoTransform( double* padfGeoTransform )
{
    if( eAccess != GA_Update )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "SetGeoTransform() not supported on read-only dataset");
        return CE_Failure;
    }
    if( m_bGeoTransformValid )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "Cannot modify geotransform once set");
        return CE_Failure;
    }
    if( padfGeoTransform[2] != 0.0 || padfGeoTransform[4] != 0 ||
        padfGeoTransform[5] > 0.0 )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "Only north-up non rotated geotransform supported");
        return CE_Failure;
    }

    if( m_bWriteBounds )
    {
        double minx = padfGeoTransform[0];
        double miny = padfGeoTransform[3] + nRasterYSize * padfGeoTransform[5];
        double maxx = padfGeoTransform[0] + nRasterXSize * padfGeoTransform[1];
        double maxy = padfGeoTransform[3];

        SphericalMercatorToLongLat(&minx, &miny);
        SphericalMercatorToLongLat(&maxx, &maxy);
        if( fabs(minx + 180) < 1e-7 && fabs(maxx - 180) < 1e-7 )
        {
            minx = -180.0;
            maxx = 180.0;
        }

        // Clamp latitude so that when transformed back to EPSG:3857, we don't
        // have too big northings
        double tmpx = 0, ok_maxy = MAX_GM;
        SphericalMercatorToLongLat(&tmpx, &ok_maxy);
        if( maxy > ok_maxy)
            maxy = ok_maxy;
        if( miny < -ok_maxy)
            miny = -ok_maxy;

        char* pszSQL = sqlite3_mprintf(
            "INSERT INTO metadata (name, value) VALUES ('bounds', '%.18g,%.18g,%.18g,%.18g')",
            minx, miny, maxx, maxy );
        sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
        sqlite3_free(pszSQL);
    }

    const double dfPixelXSizeZoomLevel0 = 2 * MAX_GM / 256;
    const double dfPixelYSizeZoomLevel0 = 2 * MAX_GM / 256;
    for( m_nZoomLevel = 0; m_nZoomLevel < 25; m_nZoomLevel++ )
    {
        double dfExpectedPixelXSize = dfPixelXSizeZoomLevel0 / (1 << m_nZoomLevel);
        double dfExpectedPixelYSize = dfPixelYSizeZoomLevel0 / (1 << m_nZoomLevel);
        if( fabs( padfGeoTransform[1] - dfExpectedPixelXSize ) < 1e-8 * dfExpectedPixelXSize &&
            fabs( fabs(padfGeoTransform[5]) - dfExpectedPixelYSize ) < 1e-8 * dfExpectedPixelYSize )
        {
            break;
        }
    }
    if( m_nZoomLevel == 25 )
    {
        m_nZoomLevel = -1;
        CPLError(CE_Failure, CPLE_NotSupported,
                  "Could not find an appropriate zoom level that matches raster pixel size");
        return CE_Failure;
    }

    memcpy(m_adfGeoTransform, padfGeoTransform, 6 * sizeof(double));
    m_bGeoTransformValid = true;

    return FinalizeRasterRegistration();
}

/************************************************************************/
/*                      ComputeTileAndPixelShifts()                     */
/************************************************************************/

void MBTilesDataset::ComputeTileAndPixelShifts()
{
    int nTileWidth, nTileHeight;
    GetRasterBand(1)->GetBlockSize(&nTileWidth, &nTileHeight);

    // Compute shift between GDAL origin and TileMatrixSet origin
    // Caution this is in GeoPackage / WMTS convention ! That is upper-left corner
    int nShiftXPixels = (int)floor(0.5 + (m_adfGeoTransform[0] - TMS_ORIGIN_X) /  m_adfGeoTransform[1]);
    m_nShiftXTiles = (int)floor(1.0 * nShiftXPixels / nTileWidth);
    m_nShiftXPixelsMod = ((nShiftXPixels % nTileWidth) + nTileWidth) % nTileWidth;
    int nShiftYPixels = (int)floor(0.5 + (m_adfGeoTransform[3] - TMS_ORIGIN_Y) /  m_adfGeoTransform[5]);
    m_nShiftYTiles = (int)floor(1.0 * nShiftYPixels / nTileHeight);
    m_nShiftYPixelsMod = ((nShiftYPixels % nTileHeight) + nTileHeight) % nTileHeight;

}

/************************************************************************/
/*                      FinalizeRasterRegistration()                    */
/************************************************************************/

CPLErr MBTilesDataset::FinalizeRasterRegistration()
{
    m_nTileMatrixWidth = (1 << m_nZoomLevel);
    m_nTileMatrixHeight = (1 << m_nZoomLevel);

    ComputeTileAndPixelShifts();

    double dfGDALMinX = m_adfGeoTransform[0];
    double dfGDALMinY = m_adfGeoTransform[3] + nRasterYSize * m_adfGeoTransform[5];
    double dfGDALMaxX = m_adfGeoTransform[0] + nRasterXSize * m_adfGeoTransform[1];
    double dfGDALMaxY = m_adfGeoTransform[3];

    m_nOverviewCount = m_nZoomLevel;
    m_papoOverviewDS = (MBTilesDataset**) CPLCalloc(sizeof(MBTilesDataset*),
                                                           m_nOverviewCount);

    if( m_bWriteMinMaxZoom )
    {
        char* pszSQL = sqlite3_mprintf(
            "INSERT INTO metadata (name, value) VALUES ('minzoom', '%d')", m_nZoomLevel );
        sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
        sqlite3_free(pszSQL);
        pszSQL = sqlite3_mprintf(
            "INSERT INTO metadata (name, value) VALUES ('maxzoom', '%d')", m_nZoomLevel );
        sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
        sqlite3_free(pszSQL);
    }

    for(int i=0; i<m_nOverviewCount; i++)
    {
        MBTilesDataset* poOvrDS = new MBTilesDataset();
        poOvrDS->InitRaster ( this, i, nBands,
                              dfGDALMinX, dfGDALMinY,
                              dfGDALMaxX, dfGDALMaxY );

        m_papoOverviewDS[m_nZoomLevel-1-i] = poOvrDS;
    }

    return CE_None;
}

/************************************************************************/
/*                         InitRaster()                                 */
/************************************************************************/

int MBTilesDataset::InitRaster ( MBTilesDataset* poParentDS,
                                 int nZoomLevel,
                                 int nBandCount,
                                 double dfGDALMinX,
                                 double dfGDALMinY,
                                 double dfGDALMaxX,
                                 double dfGDALMaxY )
{
    m_nZoomLevel = nZoomLevel;
    m_nTileMatrixWidth = 1 << nZoomLevel;
    m_nTileMatrixHeight = 1 << nZoomLevel;

    const int nTileWidth = 256;
    const int nTileHeight = 256;
    const double dfPixelXSize = 2 * MAX_GM / 256 / (1 << nZoomLevel);
    const double dfPixelYSize = dfPixelXSize;

    m_bGeoTransformValid = true;
    m_adfGeoTransform[0] = dfGDALMinX;
    m_adfGeoTransform[1] = dfPixelXSize;
    m_adfGeoTransform[3] = dfGDALMaxY;
    m_adfGeoTransform[5] = -dfPixelYSize;
    double dfRasterXSize = 0.5 + (dfGDALMaxX - dfGDALMinX) / dfPixelXSize;
    double dfRasterYSize = 0.5 + (dfGDALMaxY - dfGDALMinY) / dfPixelYSize;
    if( dfRasterXSize > INT_MAX || dfRasterYSize > INT_MAX )
        return FALSE;
    nRasterXSize = (int)dfRasterXSize;
    nRasterYSize = (int)dfRasterYSize;

    m_pabyCachedTiles = (GByte*) VSI_MALLOC3_VERBOSE(4 * 4, nTileWidth, nTileHeight);
    if( m_pabyCachedTiles == NULL )
    {
        return FALSE;
    }

    for(int i = 1; i <= nBandCount; i ++)
        SetBand( i, new MBTilesBand(this) );

    ComputeTileAndPixelShifts();

    GDALDataset::SetMetadataItem("INTERLEAVE", "PIXEL", "IMAGE_STRUCTURE");
    GDALDataset::SetMetadataItem("ZOOM_LEVEL", CPLSPrintf("%d", m_nZoomLevel));

    if( poParentDS )
    {
        m_poParentDS = poParentDS;
        poMainDS = poParentDS;
        eAccess = poParentDS->eAccess;
        hDS = poParentDS->hDS;
        hDB = poParentDS->hDB;
        m_eTF = poParentDS->m_eTF;
        m_nQuality = poParentDS->m_nQuality;
        m_nZLevel = poParentDS->m_nZLevel;
        m_bDither = poParentDS->m_bDither;
        m_osWHERE = poParentDS->m_osWHERE;
        SetDescription(CPLSPrintf("%s - zoom_level=%d",
                                  poParentDS->GetDescription(), m_nZoomLevel));
    }

    return TRUE;
}

/************************************************************************/
/*                         GetProjectionRef()                           */
/************************************************************************/

const char* MBTilesDataset::GetProjectionRef()
{
    return SRS_EPSG_3857;
}

/************************************************************************/
/*                           SetProjection()                            */
/************************************************************************/

CPLErr MBTilesDataset::SetProjection( const char* pszProjection )
{
    if( eAccess != GA_Update )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "SetProjection() not supported on read-only dataset");
        return CE_Failure;
    }

    OGRSpatialReference oSRS;
    if( oSRS.SetFromUserInput(pszProjection) != OGRERR_NONE )
        return CE_Failure;
    if( oSRS.GetAuthorityName(NULL) == NULL ||
        !EQUAL(oSRS.GetAuthorityName(NULL), "EPSG") ||
        oSRS.GetAuthorityCode(NULL) == NULL ||
        !EQUAL(oSRS.GetAuthorityCode(NULL), "3857") )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "Only EPSG:3857 supported on MBTiles dataset");
        return CE_Failure;
    }
    return CE_None;
}

/************************************************************************/
/*                      GetMetadataDomainList()                         */
/************************************************************************/

char **MBTilesDataset::GetMetadataDomainList()
{
    return BuildMetadataDomainList(GDALDataset::GetMetadataDomainList(),
                                   TRUE,
                                   "", NULL);
}

/************************************************************************/
/*                            GetMetadata()                             */
/************************************************************************/

char** MBTilesDataset::GetMetadata( const char * pszDomain )
{
    if (pszDomain != NULL && !EQUAL(pszDomain, ""))
        return GDALPamDataset::GetMetadata(pszDomain);

    if (bFetchedMetadata)
        return aosList.List();

    bFetchedMetadata = true;
    aosList = CPLStringList(GDALPamDataset::GetMetadata(), FALSE);

    OGRLayerH hSQLLyr = OGR_DS_ExecuteSQL(hDS,
            "SELECT name, value FROM metadata", NULL, NULL);
    if (hSQLLyr == NULL)
        return NULL;

    if (OGR_FD_GetFieldCount(OGR_L_GetLayerDefn(hSQLLyr)) != 2)
    {
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
        return NULL;
    }

    OGRFeatureH hFeat;
    while( (hFeat = OGR_L_GetNextFeature(hSQLLyr)) != NULL )
    {
        if (OGR_F_IsFieldSet(hFeat, 0) && OGR_F_IsFieldSet(hFeat, 1))
        {
            const char* pszName = OGR_F_GetFieldAsString(hFeat, 0);
            const char* pszValue = OGR_F_GetFieldAsString(hFeat, 1);
            if (pszValue[0] != '\0' &&
                !STARTS_WITH(pszValue, "function(") &&
                strstr(pszValue, "<img ") == NULL &&
                strstr(pszValue, "<p>") == NULL &&
                strstr(pszValue, "</p>") == NULL &&
                strstr(pszValue, "<div") == NULL)
            {
                aosList.AddNameValue(pszName, pszValue);
            }
        }
        OGR_F_Destroy(hFeat);
    }
    OGR_DS_ReleaseResultSet(hDS, hSQLLyr);

    return aosList.List();
}

/************************************************************************/
/*                         GetMetadataItem()                            */
/************************************************************************/

const char *MBTilesDataset::GetMetadataItem( const char* pszName, const char * pszDomain )
{
    if( pszDomain == NULL || EQUAL(pszDomain, "") )
    {
        const char* pszValue = CSLFetchNameValue( GetMetadata(), pszName );
        if( pszValue )
            return pszValue;
    }
    return GDALPamDataset::GetMetadataItem(pszName, pszDomain);
}

/************************************************************************/
/*                             Identify()                               */
/************************************************************************/

int MBTilesDataset::Identify(GDALOpenInfo* poOpenInfo)
{
    if ( (EQUAL(CPLGetExtension(poOpenInfo->pszFilename), "MBTILES") ||
      // Allow direct Amazon S3 signed URLs that contains .mbtiles in the middle of the URL
          strstr(poOpenInfo->pszFilename, ".mbtiles") != NULL) &&
        poOpenInfo->nHeaderBytes >= 1024 &&
        STARTS_WITH_CI((const char*)poOpenInfo->pabyHeader, "SQLite Format 3"))
    {
        return TRUE;
    }

    return FALSE;
}

/************************************************************************/
/*                        MBTilesGetMinMaxZoomLevel()                   */
/************************************************************************/

static
int MBTilesGetMinMaxZoomLevel(OGRDataSourceH hDS, int bHasMap,
                                int &nMinLevel, int &nMaxLevel)
{
    const char* pszSQL;
    OGRLayerH hSQLLyr;
    OGRFeatureH hFeat;
    int bHasMinMaxLevel = FALSE;

    pszSQL = "SELECT value FROM metadata WHERE name = 'minzoom' UNION ALL "
             "SELECT value FROM metadata WHERE name = 'maxzoom'";
    CPLDebug("MBTILES", "%s", pszSQL);
    hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
    if (hSQLLyr)
    {
        hFeat = OGR_L_GetNextFeature(hSQLLyr);
        if (hFeat)
        {
            int bHasMinLevel = FALSE;
            if (OGR_F_IsFieldSet(hFeat, 0))
            {
                nMinLevel = OGR_F_GetFieldAsInteger(hFeat, 0);
                bHasMinLevel = TRUE;
            }
            OGR_F_Destroy(hFeat);

            if (bHasMinLevel)
            {
                hFeat = OGR_L_GetNextFeature(hSQLLyr);
                if (hFeat)
                {
                    if (OGR_F_IsFieldSet(hFeat, 0))
                    {
                        nMaxLevel = OGR_F_GetFieldAsInteger(hFeat, 0);
                        bHasMinMaxLevel = TRUE;
                    }
                    OGR_F_Destroy(hFeat);
                }
            }
        }

        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
    }

    if( !bHasMinMaxLevel )
    {
#define OPTIMIZED_FOR_VSICURL
#ifdef  OPTIMIZED_FOR_VSICURL
        int iLevel;
        for(iLevel = 0; nMinLevel < 0 && iLevel <= 32; iLevel ++)
        {
            pszSQL = CPLSPrintf(
                "SELECT zoom_level FROM %s WHERE zoom_level = %d LIMIT 1",
                (bHasMap) ? "map" : "tiles", iLevel);
            CPLDebug("MBTILES", "%s", pszSQL);
            hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
            if (hSQLLyr)
            {
                hFeat = OGR_L_GetNextFeature(hSQLLyr);
                if (hFeat)
                {
                    nMinLevel = iLevel;
                    OGR_F_Destroy(hFeat);
                }
                OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
            }
        }

        if (nMinLevel < 0)
            return FALSE;

        for(iLevel = 32; nMaxLevel < 0 && iLevel >= nMinLevel; iLevel --)
        {
            pszSQL = CPLSPrintf(
                "SELECT zoom_level FROM %s WHERE zoom_level = %d LIMIT 1",
                (bHasMap) ? "map" : "tiles", iLevel);
            CPLDebug("MBTILES", "%s", pszSQL);
            hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
            if (hSQLLyr)
            {
                hFeat = OGR_L_GetNextFeature(hSQLLyr);
                if (hFeat)
                {
                    nMaxLevel = iLevel;
                    bHasMinMaxLevel = TRUE;
                    OGR_F_Destroy(hFeat);
                }
                OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
            }
        }
#else
        pszSQL = "SELECT min(zoom_level), max(zoom_level) FROM tiles";
        CPLDebug("MBTILES", "%s", pszSQL);
        hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
        if (hSQLLyr == NULL)
        {
            return FALSE;
        }

        hFeat = OGR_L_GetNextFeature(hSQLLyr);
        if (hFeat == NULL)
        {
            OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
            return FALSE;
        }

        if (OGR_F_IsFieldSet(hFeat, 0) && OGR_F_IsFieldSet(hFeat, 1))
        {
            nMinLevel = OGR_F_GetFieldAsInteger(hFeat, 0);
            nMaxLevel = OGR_F_GetFieldAsInteger(hFeat, 1);
            bHasMinMaxLevel = TRUE;
        }

        OGR_F_Destroy(hFeat);
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
#endif
    }

    return bHasMinMaxLevel;
}

/************************************************************************/
/*                   MBTilesTileCoordToWorldCoord()                     */
/************************************************************************/

static double MBTilesTileCoordToWorldCoord(double dfTileCoord, int nZoomLevel)
{
    return -MAX_GM + 2 * MAX_GM * (dfTileCoord / (1 << nZoomLevel));
}

/************************************************************************/
/*                   MBTilesWorldCoordToTileCoord()                     */
/************************************************************************/

static double MBTilesWorldCoordToTileCoord(double dfWorldCoord, int nZoomLevel)
{
    return (dfWorldCoord + MAX_GM) / (2 * MAX_GM) * (1 << nZoomLevel);
}

/************************************************************************/
/*                           MBTilesGetBounds()                         */
/************************************************************************/

static
bool MBTilesGetBounds(OGRDataSourceH hDS, bool bUseBounds,
                     int nMaxLevel,
                     double& minX, double& minY,
                     double& maxX, double& maxY)
{
    const char* pszSQL;
    bool bHasBounds = false;
    OGRLayerH hSQLLyr;
    OGRFeatureH hFeat;

    if( bUseBounds )
    {
        pszSQL = "SELECT value FROM metadata WHERE name = 'bounds'";
        CPLDebug("MBTILES", "%s", pszSQL);
        hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
        if (hSQLLyr)
        {
            hFeat = OGR_L_GetNextFeature(hSQLLyr);
            if (hFeat != NULL)
            {
                const char* pszBounds = OGR_F_GetFieldAsString(hFeat, 0);
                char** papszTokens = CSLTokenizeString2(pszBounds, ",", 0);
                if (CSLCount(papszTokens) != 4 ||
                    fabs(CPLAtof(papszTokens[0])) > 180 ||
                    fabs(CPLAtof(papszTokens[1])) >= 89.99 ||
                    fabs(CPLAtof(papszTokens[2])) > 180 ||
                    fabs(CPLAtof(papszTokens[3])) >= 89.99 ||
                    CPLAtof(papszTokens[0]) > CPLAtof(papszTokens[2]) ||
                    CPLAtof(papszTokens[1]) > CPLAtof(papszTokens[3]))
                {
                    CPLError(CE_Warning, CPLE_AppDefined, "Invalid value for 'bounds' metadata. Ignoring it and fall back to present tile extent");
                }
                else
                {
                    minX = CPLAtof(papszTokens[0]);
                    minY = CPLAtof(papszTokens[1]);
                    maxX = CPLAtof(papszTokens[2]);
                    maxY = CPLAtof(papszTokens[3]);
                    LongLatToSphericalMercator(&minX, &minY);
                    LongLatToSphericalMercator(&maxX, &maxY);

                    // Clamp northings
                    if( maxY > MAX_GM)
                        maxY = MAX_GM;
                    if( minY < -MAX_GM)
                        minY = -MAX_GM;

                    bHasBounds = true;
                }

                CSLDestroy(papszTokens);

                OGR_F_Destroy(hFeat);
            }
            OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
        }
    }

    if (!bHasBounds)
    {
        pszSQL = CPLSPrintf("SELECT min(tile_column), max(tile_column), "
                            "min(tile_row), max(tile_row) FROM tiles "
                            "WHERE zoom_level = %d", nMaxLevel);
        CPLDebug("MBTILES", "%s", pszSQL);
        hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
        if (hSQLLyr == NULL)
        {
            return false;
        }

        hFeat = OGR_L_GetNextFeature(hSQLLyr);
        if (hFeat == NULL)
        {
            OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
            return false;
        }

        if (OGR_F_IsFieldSet(hFeat, 0) &&
            OGR_F_IsFieldSet(hFeat, 1) &&
            OGR_F_IsFieldSet(hFeat, 2) &&
            OGR_F_IsFieldSet(hFeat, 3))
        {
            int nMinTileCol = OGR_F_GetFieldAsInteger(hFeat, 0);
            int nMaxTileCol = OGR_F_GetFieldAsInteger(hFeat, 1);
            int nMinTileRow = OGR_F_GetFieldAsInteger(hFeat, 2);
            int nMaxTileRow = OGR_F_GetFieldAsInteger(hFeat, 3);
            minX = MBTilesTileCoordToWorldCoord(nMinTileCol, nMaxLevel);
            minY = MBTilesTileCoordToWorldCoord(nMinTileRow, nMaxLevel);
            maxX = MBTilesTileCoordToWorldCoord(nMaxTileCol + 1, nMaxLevel);
            maxY = MBTilesTileCoordToWorldCoord(nMaxTileRow + 1, nMaxLevel);
            bHasBounds = true;
        }

        OGR_F_Destroy(hFeat);
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
    }

    return bHasBounds;
}

/************************************************************************/
/*                        MBTilesCurlReadCbk()                          */
/************************************************************************/

/* We spy the data received by CURL for the initial request where we try */
/* to get a first tile to see its characteristics. We just need the header */
/* to determine that, so let's make VSICurl stop reading after we have found it */

static int MBTilesCurlReadCbk(CPL_UNUSED VSILFILE* fp,
                              void *pabyBuffer, size_t nBufferSize,
                              void* pfnUserData)
{
    const GByte abyPNGSig[] = { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, /* PNG signature */
                                0x00, 0x00, 0x00, 0x0D, /* IHDR length */
                                0x49, 0x48, 0x44, 0x52  /* IHDR chunk */ };

    /* JPEG SOF0 (Start Of Frame 0) marker */
    const GByte abyJPEG1CompSig[] = { 0xFF, 0xC0, /* marker */
                                      0x00, 0x0B, /* data length = 8 + 1 * 3 */
                                      0x08,       /* depth : 8 bit */
                                      0x01, 0x00, /* width : 256 */
                                      0x01, 0x00, /* height : 256 */
                                      0x01        /* components : 1 */
                                    };
    const GByte abyJPEG3CompSig[] = { 0xFF, 0xC0, /* marker */
                                      0x00, 0x11, /* data length = 8 + 3 * 3 */
                                      0x08,       /* depth : 8 bit */
                                      0x01, 0x00, /* width : 256 */
                                      0x01, 0x00, /* width : 256 */
                                      0x03        /* components : 3 */
                                     };

    int i;
    for(i = 0; i < (int)nBufferSize - (int)sizeof(abyPNGSig); i++)
    {
        if (memcmp(((GByte*)pabyBuffer) + i, abyPNGSig, sizeof(abyPNGSig)) == 0 &&
            i + sizeof(abyPNGSig) + 4 + 4 + 1 + 1 < nBufferSize)
        {
            GByte* ptr = ((GByte*)(pabyBuffer)) + i + (int)sizeof(abyPNGSig);

            int nWidth;
            memcpy(&nWidth, ptr, 4);
            CPL_MSBPTR32(&nWidth);
            ptr += 4;

            int nHeight;
            memcpy(&nHeight, ptr, 4);
            CPL_MSBPTR32(&nHeight);
            ptr += 4;

            GByte nDepth = *ptr;
            ptr += 1;

            GByte nColorType = *ptr;
            CPLDebug("MBTILES", "PNG: nWidth=%d nHeight=%d depth=%d nColorType=%d",
                        nWidth, nHeight, nDepth, nColorType);

            int* pnBands = (int*) pfnUserData;
            *pnBands = -2;
            if (nWidth == 256 && nHeight == 256 && nDepth == 8)
            {
                if (nColorType == 0)
                    *pnBands = 1; /* Gray */
                else if (nColorType == 2)
                    *pnBands = 3; /* RGB */
                else if (nColorType == 3)
                {
                    /* This might also be a color table with transparency */
                    /* but we cannot tell ! */
                    *pnBands = -1;
                    return TRUE;
                }
                else if (nColorType == 4)
                    *pnBands = 2; /* Gray + alpha */
                else if (nColorType == 6)
                    *pnBands = 4; /* RGB + alpha */
            }

            return FALSE;
        }
    }

    for(i = 0; i < (int)nBufferSize - (int)sizeof(abyJPEG1CompSig); i++)
    {
        if (memcmp(((GByte*)pabyBuffer) + i, abyJPEG1CompSig, sizeof(abyJPEG1CompSig)) == 0)
        {
            CPLDebug("MBTILES", "JPEG: nWidth=%d nHeight=%d depth=%d nBands=%d",
                        256, 256, 8, 1);

            int* pnBands = (int*) pfnUserData;
            *pnBands = 1;

            return FALSE;
        }
        else if (memcmp(((GByte*)pabyBuffer) + i, abyJPEG3CompSig, sizeof(abyJPEG3CompSig)) == 0)
        {
            CPLDebug("MBTILES", "JPEG: nWidth=%d nHeight=%d depth=%d nBands=%d",
                        256, 256, 8, 3);

            int* pnBands = (int*) pfnUserData;
            *pnBands = 3;

            return FALSE;
        }
    }

    return TRUE;
}

/************************************************************************/
/*                        MBTilesGetBandCount()                         */
/************************************************************************/

static
int MBTilesGetBandCount(OGRDataSourceH &hDS,
                        int nMaxLevel,
                        int nMinTileRow, int nMaxTileRow,
                        int nMinTileCol, int nMaxTileCol)
{
    OGRLayerH hSQLLyr;
    OGRFeatureH hFeat;
    const char* pszSQL;
    VSILFILE* fpCURLOGR = NULL;
    int bFirstSelect = TRUE;

    int nBands = -1;

    /* Small trick to get the VSILFILE associated with the OGR SQLite */
    /* DB */
    CPLString osDSName(OGR_DS_GetName(hDS));
    if (STARTS_WITH(osDSName.c_str(), "/vsicurl/"))
    {
        CPLErrorReset();
        CPLPushErrorHandler(CPLQuietErrorHandler);
        hSQLLyr = OGR_DS_ExecuteSQL(hDS, "GetVSILFILE()", NULL, NULL);
        CPLPopErrorHandler();
        CPLErrorReset();
        if (hSQLLyr != NULL)
        {
            hFeat = OGR_L_GetNextFeature(hSQLLyr);
            if (hFeat)
            {
                if (OGR_F_IsFieldSet(hFeat, 0))
                {
                    const char* pszPointer = OGR_F_GetFieldAsString(hFeat, 0);
                    fpCURLOGR = (VSILFILE* )CPLScanPointer( pszPointer, static_cast<int>(strlen(pszPointer)) );
                }
                OGR_F_Destroy(hFeat);
            }
            OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
        }
    }

    pszSQL = CPLSPrintf("SELECT tile_data FROM tiles WHERE "
                            "tile_column = %d AND tile_row = %d AND zoom_level = %d",
                            (nMinTileCol  + nMaxTileCol) / 2,
                            (nMinTileRow  + nMaxTileRow) / 2,
                            nMaxLevel);
    CPLDebug("MBTILES", "%s", pszSQL);

    if (fpCURLOGR)
    {
        /* Install a spy on the file connection that will intercept */
        /* PNG or JPEG headers, to interrupt their downloading */
        /* once the header is found. Speeds up dataset opening. */
        CPLErrorReset();
        VSICurlInstallReadCbk(fpCURLOGR, MBTilesCurlReadCbk, &nBands, TRUE);

        CPLErrorReset();
        CPLPushErrorHandler(CPLQuietErrorHandler);
        hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
        CPLPopErrorHandler();

        VSICurlUninstallReadCbk(fpCURLOGR);

        /* Did the spy intercept something interesting ? */
        if (nBands != -1)
        {
            CPLErrorReset();

            OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
            hSQLLyr = NULL;

            // Re-open OGR SQLite DB, because with our spy we have simulated an
            // I/O error that SQLite will have difficulties to recover within
            // the existing connection.  This will be fast because
            // the /vsicurl/ cache has cached the already read blocks.
            OGRReleaseDataSource(hDS);
            hDS = MBTILESOpenSQLiteDB(osDSName.c_str(), GA_ReadOnly);
            if (hDS == NULL)
                return -1;

            /* Unrecognized form of PNG. Error out */
            if (nBands <= 0)
                return -1;

            return nBands;
        }
        else if (CPLGetLastErrorType() == CE_Failure)
        {
            CPLError(CE_Failure, CPLGetLastErrorNo(), "%s", CPLGetLastErrorMsg());
        }
    }
    else
    {
        hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
    }

    while( true )
    {
        if (hSQLLyr == NULL && bFirstSelect)
        {
            bFirstSelect = FALSE;
            pszSQL = CPLSPrintf("SELECT tile_data FROM tiles WHERE "
                                "zoom_level = %d LIMIT 1", nMaxLevel);
            CPLDebug("MBTILES", "%s", pszSQL);
            hSQLLyr = OGR_DS_ExecuteSQL(hDS, pszSQL, NULL, NULL);
            if (hSQLLyr == NULL)
                return -1;
        }

        hFeat = OGR_L_GetNextFeature(hSQLLyr);
        if (hFeat == NULL)
        {
            OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
            hSQLLyr = NULL;
            if( !bFirstSelect )
                return -1;
        }
        else
            break;
    }

    CPLString osMemFileName;
    osMemFileName.Printf("/vsimem/%p", hSQLLyr);

    int nDataSize = 0;
    GByte* pabyData = OGR_F_GetFieldAsBinary(hFeat, 0, &nDataSize);

    VSIFCloseL(VSIFileFromMemBuffer( osMemFileName.c_str(), pabyData,
                                    nDataSize, FALSE));

    GDALDatasetH hDSTile = GDALOpenEx(osMemFileName.c_str(), GDAL_OF_RASTER,
                                          apszAllowedDrivers, NULL, NULL);
    if (hDSTile == NULL)
    {
        VSIUnlink(osMemFileName.c_str());
        OGR_F_Destroy(hFeat);
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
        return -1;
    }

    nBands = GDALGetRasterCount(hDSTile);

    if ((nBands != 1 && nBands != 2 && nBands != 3 && nBands != 4) ||
        GDALGetRasterXSize(hDSTile) != 256 ||
        GDALGetRasterYSize(hDSTile) != 256 ||
        GDALGetRasterDataType(GDALGetRasterBand(hDSTile, 1)) != GDT_Byte)
    {
        CPLError(CE_Failure, CPLE_NotSupported, "Unsupported tile characteristics");
        GDALClose(hDSTile);
        VSIUnlink(osMemFileName.c_str());
        OGR_F_Destroy(hFeat);
        OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
        return -1;
    }

    GDALColorTableH hCT = GDALGetRasterColorTable(GDALGetRasterBand(hDSTile, 1));
    if (nBands == 1 && hCT != NULL)
    {
        nBands = 3;
        if( GDALGetColorEntryCount(hCT) > 0 )
        {
            /* Typical of paletted PNG with transparency */
            const GDALColorEntry* psEntry = GDALGetColorEntry( hCT, 0 );
            if( psEntry->c4 == 0 )
                nBands = 4;
        }
    }

    GDALClose(hDSTile);
    VSIUnlink(osMemFileName.c_str());
    OGR_F_Destroy(hFeat);
    OGR_DS_ReleaseResultSet(hDS, hSQLLyr);

    return nBands;
}

/************************************************************************/
/*                                Open()                                */
/************************************************************************/

GDALDataset* MBTilesDataset::Open(GDALOpenInfo* poOpenInfo)
{
    CPLString osFileName;
    CPLString osTableName;

    if (!Identify(poOpenInfo))
        return NULL;

    if (OGRGetDriverCount() == 0)
        OGRRegisterAll();

/* -------------------------------------------------------------------- */
/*      Open underlying OGR DB                                          */
/* -------------------------------------------------------------------- */

    OGRDataSourceH hDS = MBTILESOpenSQLiteDB(poOpenInfo->pszFilename,
                                             poOpenInfo->eAccess);

    MBTilesDataset* poDS = NULL;

    if (hDS == NULL)
        goto end;

/* -------------------------------------------------------------------- */
/*      Build dataset                                                   */
/* -------------------------------------------------------------------- */
    {
        CPLString osMetadataTableName, osRasterTableName;
        CPLString osSQL;
        OGRLayerH hMetadataLyr, hRasterLyr;
        OGRFeatureH hFeat;
        int nBands;
        OGRLayerH hSQLLyr = NULL;
        int nMinLevel = -1, nMaxLevel = -1;
        int bHasMinMaxLevel = FALSE;
        int bHasMap;

        osMetadataTableName = "metadata";

        hMetadataLyr = OGR_DS_GetLayerByName(hDS, osMetadataTableName.c_str());
        if (hMetadataLyr == NULL)
            goto end;

        osRasterTableName += "tiles";

        hRasterLyr = OGR_DS_GetLayerByName(hDS, osRasterTableName.c_str());
        if (hRasterLyr == NULL)
            goto end;

        bHasMap = OGR_DS_GetLayerByName(hDS, "map") != NULL;
        if (bHasMap)
        {
            bHasMap = FALSE;

            hSQLLyr = OGR_DS_ExecuteSQL(hDS, "SELECT type FROM sqlite_master WHERE name = 'tiles'", NULL, NULL);
            if (hSQLLyr != NULL)
            {
                hFeat = OGR_L_GetNextFeature(hSQLLyr);
                if (hFeat)
                {
                    if (OGR_F_IsFieldSet(hFeat, 0))
                    {
                        bHasMap = strcmp(OGR_F_GetFieldAsString(hFeat, 0),
                                         "view") == 0;
                        if (!bHasMap)
                        {
                            CPLDebug("MBTILES", "Weird! 'tiles' is not a view, but 'map' exists");
                        }
                    }
                    OGR_F_Destroy(hFeat);
                }
                OGR_DS_ReleaseResultSet(hDS, hSQLLyr);
            }
        }

/* -------------------------------------------------------------------- */
/*      Get minimum and maximum zoom levels                             */
/* -------------------------------------------------------------------- */

        bHasMinMaxLevel = MBTilesGetMinMaxZoomLevel(hDS, bHasMap,
                                                    nMinLevel, nMaxLevel);

        const char* pszZoomLevel = CSLFetchNameValue(poOpenInfo->papszOpenOptions, "ZOOM_LEVEL");
        if( pszZoomLevel != NULL )
            nMaxLevel = atoi(pszZoomLevel);

        if (bHasMinMaxLevel && (nMinLevel < 0 || nMinLevel > nMaxLevel))
        {
            CPLError(CE_Failure, CPLE_AppDefined,
                     "Inconsistent values : min(zoom_level) = %d, max(zoom_level) = %d",
                     nMinLevel, nMaxLevel);
            goto end;
        }

        if (bHasMinMaxLevel && nMaxLevel > 22)
        {
            CPLError(CE_Failure, CPLE_NotSupported,
                     "zoom_level > 22 not supported");
            goto end;
        }

        if (!bHasMinMaxLevel)
        {
            CPLError(CE_Failure, CPLE_AppDefined, "Cannot find min and max zoom_level");
            goto end;
        }

/* -------------------------------------------------------------------- */
/*      Get bounds                                                      */
/* -------------------------------------------------------------------- */
        double dfMinX = 0.0, dfMinY = 0.0, dfMaxX = 0.0, dfMaxY = 0.0;
        bool bUseBounds = CPLFetchBool(const_cast<const char**>(poOpenInfo->papszOpenOptions),
                                      "USE_BOUNDS", true);
        const char* pszMinX = CSLFetchNameValue(poOpenInfo->papszOpenOptions, "MINX");
        const char* pszMinY = CSLFetchNameValue(poOpenInfo->papszOpenOptions, "MINY");
        const char* pszMaxX = CSLFetchNameValue(poOpenInfo->papszOpenOptions, "MAXX");
        const char* pszMaxY = CSLFetchNameValue(poOpenInfo->papszOpenOptions, "MAXY");
        bool bHasBounds;
        if( pszMinX != NULL && pszMinY != NULL && pszMaxX != NULL && pszMaxY != NULL )
        {
            bHasBounds = true;
        }
        else
        {
            bHasBounds = MBTilesGetBounds(hDS, bUseBounds, nMaxLevel,
                                          dfMinX, dfMinY,
                                          dfMaxX, dfMaxY);
        }
        if (!bHasBounds)
        {
            CPLError(CE_Failure, CPLE_AppDefined, "Cannot find min and max tile numbers");
            goto end;
        }
        if( pszMinX != NULL ) dfMinX = CPLAtof(pszMinX);
        if( pszMinY != NULL ) dfMinY = CPLAtof(pszMinY);
        if( pszMaxX != NULL ) dfMaxX = CPLAtof(pszMaxX);
        if( pszMaxY != NULL ) dfMaxY = CPLAtof(pszMaxY);

/* -------------------------------------------------------------------- */
/*      Get number of bands                                             */
/* -------------------------------------------------------------------- */
        const char* pszBandCount = CSLFetchNameValueDef(
            poOpenInfo->papszOpenOptions, "BAND_COUNT",
            CPLGetConfigOption("MBTILES_BAND_COUNT", "-1"));
        nBands = atoi(pszBandCount);

        if( ! (nBands == 1 || nBands == 2 || nBands == 3 || nBands == 4) )
        {
            int nMinTileCol = static_cast<int>(MBTilesWorldCoordToTileCoord( dfMinX, nMaxLevel ));
            int nMinTileRow = static_cast<int>(MBTilesWorldCoordToTileCoord( dfMinY, nMaxLevel ));
            int nMaxTileCol = static_cast<int>(MBTilesWorldCoordToTileCoord( dfMaxX, nMaxLevel ));
            int nMaxTileRow = static_cast<int>(MBTilesWorldCoordToTileCoord( dfMaxY, nMaxLevel ));
            nBands = MBTilesGetBandCount(hDS, nMaxLevel,
                                         nMinTileRow, nMaxTileRow,
                                         nMinTileCol, nMaxTileCol);
            if (nBands < 0)
                nBands = 4;
        }

/* -------------------------------------------------------------------- */
/*      Set dataset attributes                                          */
/* -------------------------------------------------------------------- */

        poDS = new MBTilesDataset();
        poDS->eAccess = poOpenInfo->eAccess;
        poDS->hDS = hDS;
        poDS->hDB = (sqlite3*) GDALGetInternalHandle( (GDALDatasetH)hDS, "SQLITE_HANDLE" );
        CPLAssert(poDS->hDB != NULL);

        /* poDS will release it from now */
        hDS = NULL;

        poDS->InitRaster ( NULL, nMaxLevel, nBands,
                           dfMinX, dfMinY, dfMaxX, dfMaxY );

        if( poDS->eAccess == GA_Update )
        {
            // So that we can edit all potential overviews
            nMinLevel = 0;

            const char* pszFormat = poDS->GetMetadataItem("format");
            if( pszFormat != NULL && (EQUAL(pszFormat, "jpg") || EQUAL(pszFormat, "jpeg")) )
            {
                poDS->m_eTF = GPKG_TF_JPEG;
            }

            const char* pszTF = CSLFetchNameValue(poOpenInfo->papszOpenOptions, "TILE_FORMAT");
            if( pszTF )
            {
                poDS->m_eTF = GDALGPKGMBTilesGetTileFormat(pszTF);
                if( (pszFormat != NULL && (EQUAL(pszFormat, "jpg") || EQUAL(pszFormat, "jpeg")) &&
                     poDS->m_eTF != GPKG_TF_JPEG) ||
                    (pszFormat != NULL && EQUAL(pszFormat, "png") && poDS->m_eTF == GPKG_TF_JPEG) )
                {
                    CPLError(CE_Warning, CPLE_AppDefined,
                             "Format metadata = '%s', but TILE_FORMAT='%s'",
                             pszFormat, pszTF);
                }
            }

            poDS->ParseCompressionOptions(poOpenInfo->papszOpenOptions);
        }

/* -------------------------------------------------------------------- */
/*      Add overview levels as internal datasets                        */
/* -------------------------------------------------------------------- */
        for( int iLevel = nMaxLevel - 1; iLevel >= nMinLevel; iLevel-- )
        {
            MBTilesDataset* poOvrDS = new MBTilesDataset();
            poOvrDS->InitRaster ( poDS, iLevel, nBands, dfMinX, dfMinY, dfMaxX, dfMaxY );

            poDS->m_papoOverviewDS = (MBTilesDataset**) CPLRealloc(poDS->m_papoOverviewDS,
                            sizeof(MBTilesDataset*) * (poDS->m_nOverviewCount+1));
            poDS->m_papoOverviewDS[poDS->m_nOverviewCount ++] = poOvrDS;

            if( poOvrDS->GetRasterXSize() < 256 &&
                poOvrDS->GetRasterYSize() < 256 )
            {
                break;
            }
        }

/* -------------------------------------------------------------------- */
/*      Initialize any PAM information.                                 */
/* -------------------------------------------------------------------- */
        poDS->SetDescription( poOpenInfo->pszFilename );

        if ( !STARTS_WITH_CI(poOpenInfo->pszFilename, "/vsicurl/") )
            poDS->TryLoadXML();
        else
        {
            poDS->SetPamFlags(poDS->GetPamFlags() & ~GPF_DIRTY);
        }
    }

end:
    if (hDS)
        OGRReleaseDataSource(hDS);

    return poDS;
}

/************************************************************************/
/*                                Create()                              */
/************************************************************************/

GDALDataset* MBTilesDataset::Create( const char * pszFilename,
                                   int nXSize,
                                   int nYSize,
                                   int nBandsIn,
                                   GDALDataType eDT,
                                   char **papszOptions )
{
    MBTilesDataset* poDS = new MBTilesDataset();
    if( !poDS->CreateInternal(pszFilename, nXSize, nYSize, nBandsIn, eDT, papszOptions) )
    {
        delete poDS;
        poDS = NULL;
    }
    return poDS;
}

/************************************************************************/
/*                            CreateInternal()                          */
/************************************************************************/

bool MBTilesDataset::CreateInternal( const char * pszFilename,
                                   int nXSize,
                                   int nYSize,
                                   int nBandsIn,
                                   GDALDataType eDT,
                                   char **papszOptions )
{
    if( eDT != GDT_Byte )
    {
        CPLError(CE_Failure, CPLE_NotSupported, "Only Byte supported");
        return false;
    }
    if( nBandsIn != 1 && nBandsIn != 2 && nBandsIn != 3 && nBandsIn != 4 )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                  "Only 1 (Grey/ColorTable), 2 (Grey+Alpha), 3 (RGB) or 4 (RGBA) band dataset supported");
        return false;
    }

    // for test/debug purposes only. true is the nominal value
    m_bPNGSupports2Bands = CPLTestBool(CPLGetConfigOption("MBTILES_PNG_SUPPORTS_2BANDS", "TRUE"));
    m_bPNGSupportsCT = CPLTestBool(CPLGetConfigOption("MBTILES_PNG_SUPPORTS_CT", "TRUE"));
    m_bWriteBounds = CPLFetchBool(const_cast<const char**>(papszOptions), "WRITE_BOUNDS", true);
    m_bWriteMinMaxZoom = CPLFetchBool(const_cast<const char**>(papszOptions), "WRITE_MINMAXZOOM", true);

    VSIUnlink( pszFilename );
    SetDescription( pszFilename );

    int rc;
#ifdef HAVE_SQLITE_VFS
    if (STARTS_WITH(pszFilename, "/vsi"))
    {
        pMyVFS = OGRSQLiteCreateVFS(NULL, NULL);
        sqlite3_vfs_register(pMyVFS, 0);
        rc = sqlite3_open_v2( pszFilename, &hDB, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, pMyVFS->zName );
    }
    else
#endif
    {
        rc = sqlite3_open( pszFilename, &hDB );
    }

    if( rc != SQLITE_OK )
    {
        CPLError(CE_Failure, CPLE_FileIO, "Cannot create %s", pszFilename);
        return false;
    }

    sqlite3_exec( hDB, "PRAGMA synchronous = OFF", NULL, NULL, NULL );

    rc = sqlite3_exec( hDB, "CREATE TABLE tiles ("
          "zoom_level INTEGER NOT NULL,"
          "tile_column INTEGER NOT NULL,"
          "tile_row INTEGER NOT NULL,"
          "tile_data BLOB NOT NULL,"
          "UNIQUE (zoom_level, tile_column, tile_row) )", NULL, NULL, NULL );
    if( rc != SQLITE_OK )
    {
        CPLError(CE_Failure, CPLE_FileIO, "Cannot create tiles table");
        return false;
    }

    rc = sqlite3_exec( hDB, "CREATE TABLE metadata (name TEXT, value TEXT)", NULL, NULL, NULL );
    if( rc != SQLITE_OK )
    {
        CPLError(CE_Failure, CPLE_FileIO, "Cannot create metadata table");
        return false;
    }

    char* pszSQL;

    const char* pszName = CSLFetchNameValueDef(papszOptions, "NAME",
                                               CPLGetBasename(pszFilename));
    pszSQL = sqlite3_mprintf(
        "INSERT INTO metadata (name, value) VALUES ('name', '%q')", pszName );
    sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
    sqlite3_free(pszSQL);

    const char* pszType = CSLFetchNameValueDef(papszOptions, "TYPE",
                                               "overlay");
    pszSQL = sqlite3_mprintf(
        "INSERT INTO metadata (name, value) VALUES ('type', '%q')", pszType );
    sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
    sqlite3_free(pszSQL);

    const char* pszDescription = CSLFetchNameValueDef(papszOptions, "DESCRIPTION",
                                               CPLGetBasename(pszFilename));
    pszSQL = sqlite3_mprintf(
        "INSERT INTO metadata (name, value) VALUES ('description', '%q')", pszDescription );
    sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
    sqlite3_free(pszSQL);

    const char* pszVersion = CSLFetchNameValueDef(papszOptions, "VERSION", "1.1");
    pszSQL = sqlite3_mprintf(
        "INSERT INTO metadata (name, value) VALUES ('version', '%q')", pszVersion );
    sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
    sqlite3_free(pszSQL);

    const char* pszTF = CSLFetchNameValue(papszOptions, "TILE_FORMAT");
    if( pszTF )
        m_eTF = GDALGPKGMBTilesGetTileFormat(pszTF);

    const char* pszFormat = CSLFetchNameValueDef(papszOptions, "FORMAT",
                                        (m_eTF == GPKG_TF_JPEG) ? "jpg" : "png" );
    pszSQL = sqlite3_mprintf(
        "INSERT INTO metadata (name, value) VALUES ('format', '%q')", pszFormat );
    sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
    sqlite3_free(pszSQL);

    m_bNew = true;
    eAccess = GA_Update;
    nRasterXSize = nXSize;
    nRasterYSize = nYSize;

    m_pabyCachedTiles = (GByte*) VSI_MALLOC3_VERBOSE(4 * 4, 256, 256);
    if( m_pabyCachedTiles == NULL )
    {
        return false;
    }

    for(int i = 1; i <= nBandsIn; i ++)
        SetBand( i, new MBTilesBand(this) );

    ParseCompressionOptions(papszOptions);

    return true;
}

/************************************************************************/
/*                            CreateCopy()                              */
/************************************************************************/

typedef struct
{
    const char*         pszName;
    GDALResampleAlg     eResampleAlg;
} WarpResamplingAlg;

static const WarpResamplingAlg asResamplingAlg[] =
{
    { "NEAREST", GRA_NearestNeighbour },
    { "BILINEAR", GRA_Bilinear },
    { "CUBIC", GRA_Cubic },
    { "CUBICSPLINE", GRA_CubicSpline },
    { "LANCZOS", GRA_Lanczos },
    { "MODE", GRA_Mode },
    { "AVERAGE", GRA_Average },
};

GDALDataset* MBTilesDataset::CreateCopy( const char *pszFilename,
                                         GDALDataset *poSrcDS,
                                         int /*bStrict*/,
                                         char ** papszOptions,
                                         GDALProgressFunc pfnProgress,
                                         void * pProgressData )
{

    int nBands = poSrcDS->GetRasterCount();
    if( nBands != 1 && nBands != 2 && nBands != 3 && nBands != 4 )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                    "Only 1 (Grey/ColorTable), 2 (Grey+Alpha), 3 (RGB) or 4 (RGBA) band dataset supported");
        return NULL;
    }

    char** papszTO = CSLSetNameValue( NULL, "DST_SRS", SRS_EPSG_3857 );
    void* hTransformArg =
            GDALCreateGenImgProjTransformer2( poSrcDS, NULL, papszTO );
    if( hTransformArg == NULL )
    {
        CSLDestroy(papszTO);
        return NULL;
    }

    GDALTransformerInfo* psInfo = (GDALTransformerInfo*)hTransformArg;
    double adfGeoTransform[6];
    double adfExtent[4];
    int    nXSize, nYSize;

    if ( GDALSuggestedWarpOutput2( poSrcDS,
                                  psInfo->pfnTransform, hTransformArg,
                                  adfGeoTransform,
                                  &nXSize, &nYSize,
                                  adfExtent, 0 ) != CE_None )
    {
        CSLDestroy(papszTO);
        GDALDestroyGenImgProjTransformer( hTransformArg );
        return NULL;
    }

    GDALDestroyGenImgProjTransformer( hTransformArg );
    hTransformArg = NULL;

    // Hack to compensate for  GDALSuggestedWarpOutput2() failure when 
    // reprojection latitude = +/- 90 to EPSG:3857
    double adfSrcGeoTransform[6];
    if( poSrcDS->GetGeoTransform(adfSrcGeoTransform) == CE_None )
    {
        const char* pszSrcWKT = poSrcDS->GetProjectionRef();
        if( pszSrcWKT != NULL && pszSrcWKT[0] != '\0' )
        {
            OGRSpatialReference oSRS;
            if( oSRS.SetFromUserInput( pszSrcWKT ) == OGRERR_NONE &&
                oSRS.IsGeographic() )
            {
                double minLat = MIN( adfSrcGeoTransform[3], adfSrcGeoTransform[3] + poSrcDS->GetRasterYSize() * adfSrcGeoTransform[5] );
                double maxLat = MAX( adfSrcGeoTransform[3], adfSrcGeoTransform[3] + poSrcDS->GetRasterYSize() * adfSrcGeoTransform[5] );
                double maxNorthing = adfGeoTransform[3];
                double minNorthing = adfGeoTransform[3] + adfGeoTransform[5] * nYSize;
                bool bChanged = false;
                if( maxLat > 89.9999999 )
                {
                    bChanged = true;
                    maxNorthing = MAX_GM;
                }
                if( minLat <= -89.9999999 )
                {
                    bChanged = true;
                    minNorthing = -MAX_GM;
                }
                if( bChanged )
                {
                    adfGeoTransform[3] = maxNorthing;
                    nYSize = int((maxNorthing - minNorthing) / (-adfGeoTransform[5]) + 0.5);
                    adfExtent[1] = maxNorthing + nYSize * adfGeoTransform[5];
                    adfExtent[3] = maxNorthing;
                }
            }
        }
    }

    int nZoomLevel;
    double dfComputedRes = adfGeoTransform[1];
    double dfPrevRes = 0, dfRes = 0;
    const double dfPixelXSizeZoomLevel0 = 2 * MAX_GM / 256;
    for(nZoomLevel = 0; nZoomLevel < 25; nZoomLevel++)
    {
        dfRes = dfPixelXSizeZoomLevel0 / (1 << nZoomLevel);
        if( dfComputedRes > dfRes )
            break;
        dfPrevRes = dfRes;
    }
    if( nZoomLevel == 25 )
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "Could not find an appropriate zoom level");
        CSLDestroy(papszTO);
        return NULL;
    }

    const char* pszZoomLevelStrategy = CSLFetchNameValueDef(papszOptions,
                                                            "ZOOM_LEVEL_STRATEGY",
                                                            "AUTO");
    if( fabs( dfComputedRes - dfRes ) / dfRes > 1e-8 )
    {
        if( EQUAL(pszZoomLevelStrategy, "LOWER") )
        {
            if( nZoomLevel > 0 )
                nZoomLevel --;
        }
        else if( EQUAL(pszZoomLevelStrategy, "UPPER") )
        {
            /* do nothing */
        }
        else if( nZoomLevel > 0 )
        {
            if( dfPrevRes / dfComputedRes < dfComputedRes / dfRes )
                nZoomLevel --;
        }
    }

    dfRes = dfPixelXSizeZoomLevel0 / (1 << nZoomLevel);

    double dfMinX = adfExtent[0];
    double dfMinY = adfExtent[1];
    double dfMaxX = adfExtent[2];
    double dfMaxY = adfExtent[3];

    nXSize = (int) ( 0.5 + ( dfMaxX - dfMinX ) / dfRes );
    nYSize = (int) ( 0.5 + ( dfMaxY - dfMinY ) / dfRes );
    adfGeoTransform[1] = dfRes;
    adfGeoTransform[5] = -dfRes;

    int nTargetBands = nBands;
    /* For grey level or RGB, if there's reprojection involved, add an alpha */
    /* channel */
    if( (nBands == 1 && poSrcDS->GetRasterBand(1)->GetColorTable() == NULL) ||
        nBands == 3 )
    {
        OGRSpatialReference oSrcSRS;
        oSrcSRS.SetFromUserInput(poSrcDS->GetProjectionRef());
        oSrcSRS.AutoIdentifyEPSG();
        if( oSrcSRS.GetAuthorityCode(NULL) == NULL ||
            atoi(oSrcSRS.GetAuthorityCode(NULL)) != 3857 )
        {
            nTargetBands ++;
        }
    }

    GDALResampleAlg eResampleAlg = GRA_Bilinear;
    const char* pszResampling = CSLFetchNameValue(papszOptions, "RESAMPLING");
    if( pszResampling )
    {
        for(size_t iAlg = 0; iAlg < sizeof(asResamplingAlg)/sizeof(asResamplingAlg[0]); iAlg ++)
        {
            if( EQUAL(pszResampling, asResamplingAlg[iAlg].pszName) )
            {
                eResampleAlg = asResamplingAlg[iAlg].eResampleAlg;
                break;
            }
        }
    }

    if( nBands == 1 && poSrcDS->GetRasterBand(1)->GetColorTable() != NULL &&
        eResampleAlg != GRA_NearestNeighbour && eResampleAlg != GRA_Mode )
    {
        CPLError(CE_Warning, CPLE_AppDefined,
                 "Input dataset has a color table, which will likely lead to "
                 "bad results when using a resampling method other than "
                 "nearest neighbour or mode. Converting the dataset to 24/32 bit "
                 "(e.g. with gdal_translate -expand rgb/rgba) is advised.");
    }

    GDALDataset* poDS = Create( pszFilename, nXSize, nYSize, nTargetBands, GDT_Byte,
                                   papszOptions );
    if( poDS == NULL )
    {
        CSLDestroy(papszTO);
        return NULL;
    }
    poDS->SetGeoTransform(adfGeoTransform);
    if( nTargetBands == 1 && nBands == 1 && poSrcDS->GetRasterBand(1)->GetColorTable() != NULL )
    {
        poDS->GetRasterBand(1)->SetColorTable( poSrcDS->GetRasterBand(1)->GetColorTable() );
    }

    hTransformArg =
        GDALCreateGenImgProjTransformer2( poSrcDS, poDS, papszTO );
    CSLDestroy(papszTO);
    if( hTransformArg == NULL )
    {
        CPLError(CE_Failure, CPLE_AppDefined, "GDALCreateGenImgProjTransformer2 failed");
        delete poDS;
        return NULL;
    }

/* -------------------------------------------------------------------- */
/*      Warp the transformer with a linear approximator                 */
/* -------------------------------------------------------------------- */
    hTransformArg =
        GDALCreateApproxTransformer( GDALGenImgProjTransform,
                                     hTransformArg, 0.125 );
    GDALApproxTransformerOwnsSubtransformer(hTransformArg, TRUE);

/* -------------------------------------------------------------------- */
/*      Setup warp options.                                             */
/* -------------------------------------------------------------------- */
    GDALWarpOptions *psWO = GDALCreateWarpOptions();

    psWO->papszWarpOptions = CSLSetNameValue(NULL, "OPTIMIZE_SIZE", "YES");
    psWO->eWorkingDataType = GDT_Byte;

    psWO->eResampleAlg = eResampleAlg;

    psWO->hSrcDS = poSrcDS;
    psWO->hDstDS = poDS;

    psWO->pfnTransformer = GDALApproxTransform;
    psWO->pTransformerArg = hTransformArg;

    psWO->pfnProgress = pfnProgress;
    psWO->pProgressArg = pProgressData;

/* -------------------------------------------------------------------- */
/*      Setup band mapping.                                             */
/* -------------------------------------------------------------------- */

    if( nBands == 2 || nBands == 4 )
        psWO->nBandCount = nBands - 1;
    else
        psWO->nBandCount = nBands;

    psWO->panSrcBands = (int *) CPLMalloc(psWO->nBandCount*sizeof(int));
    psWO->panDstBands = (int *) CPLMalloc(psWO->nBandCount*sizeof(int));

    for( int i = 0; i < psWO->nBandCount; i++ )
    {
        psWO->panSrcBands[i] = i+1;
        psWO->panDstBands[i] = i+1;
    }

    if( nBands == 2 || nBands == 4 )
    {
        psWO->nSrcAlphaBand = nBands;
    }
    if( nTargetBands == 2 || nTargetBands == 4 )
    {
        psWO->nDstAlphaBand = nTargetBands;
    }

/* -------------------------------------------------------------------- */
/*      Initialize and execute the warp.                                */
/* -------------------------------------------------------------------- */
    GDALWarpOperation oWO;

    CPLErr eErr = oWO.Initialize( psWO );
    if( eErr == CE_None )
    {
        /*if( bMulti )
            eErr = oWO.ChunkAndWarpMulti( 0, 0, nXSize, nYSize );
        else*/
        eErr = oWO.ChunkAndWarpImage( 0, 0, nXSize, nYSize );
    }
    if (eErr != CE_None)
    {
        delete poDS;
        poDS = NULL;
    }

    GDALDestroyTransformer( hTransformArg );
    GDALDestroyWarpOptions( psWO );

    return poDS;
}

/************************************************************************/
/*                        ParseCompressionOptions()                     */
/************************************************************************/

void MBTilesDataset::ParseCompressionOptions(char** papszOptions)
{
    const char* pszZLevel = CSLFetchNameValue(papszOptions, "ZLEVEL");
    if( pszZLevel )
        m_nZLevel = atoi(pszZLevel);

    const char* pszQuality = CSLFetchNameValue(papszOptions, "QUALITY");
    if( pszQuality )
        m_nQuality = atoi(pszQuality);

    const char* pszDither = CSLFetchNameValue(papszOptions, "DITHER");
    if( pszDither )
        m_bDither = CPLTestBool(pszDither);
}

/************************************************************************/
/*                          IBuildOverviews()                           */
/************************************************************************/

static int GetFloorPowerOfTwo(int n)
{
    int p2 = 1;
    while( (n = n >> 1) > 0 )
    {
        p2 <<= 1;
    }
    return p2;
}

CPLErr MBTilesDataset::IBuildOverviews(
                        const char * pszResampling,
                        int nOverviews, int * panOverviewList,
                        int nBandsIn, int * /*panBandList*/,
                        GDALProgressFunc pfnProgress, void * pProgressData )
{
    if( GetAccess() != GA_Update )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "Overview building not supported on a database opened in read-only mode");
        return CE_Failure;
    }
    if( m_poParentDS != NULL )
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "Overview building not supported on overview dataset");
        return CE_Failure;
    }

    if( nOverviews == 0 )
    {
        for(int i=0;i<m_nOverviewCount;i++)
            m_papoOverviewDS[i]->FlushCache();
        char* pszSQL = sqlite3_mprintf("DELETE FROM 'tiles' WHERE zoom_level < %d",
                                       m_nZoomLevel);
        char* pszErrMsg = NULL;
        int ret = sqlite3_exec(hDB, pszSQL, NULL, NULL, &pszErrMsg);
        sqlite3_free(pszSQL);
        if( ret != SQLITE_OK )
        {
            CPLError(CE_Failure, CPLE_AppDefined, "Failure: %s",
                     pszErrMsg ? pszErrMsg : "");
            sqlite3_free(pszErrMsg);
            return CE_Failure;
        }

        int nRows = 0, nCols = 0;
        char** papszResult = NULL;
        sqlite3_get_table(hDB, "SELECT * FROM metadata WHERE name = 'minzoom'", &papszResult, &nRows, &nCols, NULL);
        sqlite3_free_table(papszResult);
        if( nRows == 1 )
        {
            sqlite3_exec(hDB, "DELETE FROM metadata WHERE name = 'minzoom'", NULL, NULL, NULL);
            pszSQL = sqlite3_mprintf(
                "INSERT INTO metadata (name, value) VALUES ('minzoom', '%d')", m_nZoomLevel );
            sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
            sqlite3_free(pszSQL);
        }

        return CE_None;
    }

    if( nBandsIn != nBands )
    {
        CPLError( CE_Failure, CPLE_NotSupported,
                  "Generation of overviews only"
                  "supported when operating on all bands." );
        return CE_Failure;
    }

    if( m_nOverviewCount == 0 )
    {
        CPLError(CE_Failure, CPLE_AppDefined, "Image too small to support overviews");
        return CE_Failure;
    }

    FlushCache();
    for(int i=0;i<nOverviews;i++)
    {
        if( panOverviewList[i] < 2 )
        {
            CPLError(CE_Failure, CPLE_IllegalArg, "Overview factor '%d' must be >= 2",
                     panOverviewList[i]);
            return CE_Failure;
        }

        if( GetFloorPowerOfTwo( panOverviewList[i] ) != panOverviewList[i] )
        {
            CPLError(CE_Failure, CPLE_IllegalArg, "Overview factor '%d' is not a power of 2",
                     panOverviewList[i]);
            return CE_Failure;
        }
    }

    GDALRasterBand*** papapoOverviewBands = (GDALRasterBand ***) CPLCalloc(sizeof(void*),nBands);
    int iCurOverview = 0;
    int nMinZoom = m_nZoomLevel;
    for( int iBand = 0; iBand < nBands; iBand++ )
    {
        papapoOverviewBands[iBand] = (GDALRasterBand **) CPLCalloc(sizeof(void*),nOverviews);
        iCurOverview = 0;
        for(int i=0;i<nOverviews;i++)
        {
            int nVal = panOverviewList[i];
            int iOvr = -1;
            while( nVal > 1 )
            {
                nVal >>= 1;
                iOvr ++;
            }
            if( iOvr >= m_nOverviewCount )
            {
                continue;
            }
            MBTilesDataset* poODS = m_papoOverviewDS[iOvr];
            if( poODS->m_nZoomLevel < nMinZoom )
                nMinZoom = poODS->m_nZoomLevel;
            papapoOverviewBands[iBand][iCurOverview] = poODS->GetRasterBand(iBand+1);
            iCurOverview++ ;
        }
    }

    CPLErr eErr = GDALRegenerateOverviewsMultiBand(nBands, papoBands,
                                     iCurOverview, papapoOverviewBands,
                                     pszResampling, pfnProgress, pProgressData );

    for( int iBand = 0; iBand < nBands; iBand++ )
    {
        CPLFree(papapoOverviewBands[iBand]);
    }
    CPLFree(papapoOverviewBands);

    if( eErr == CE_None )
    {
        int nRows = 0, nCols = 0;
        char** papszResult = NULL;
        sqlite3_get_table(hDB, "SELECT * FROM metadata WHERE name = 'minzoom'", &papszResult, &nRows, &nCols, NULL);
        sqlite3_free_table(papszResult);
        if( nRows == 1 )
        {
            sqlite3_exec(hDB, "DELETE FROM metadata WHERE name = 'minzoom'", NULL, NULL, NULL);
            char* pszSQL = sqlite3_mprintf(
                "INSERT INTO metadata (name, value) VALUES ('minzoom', '%d')", nMinZoom );
            sqlite3_exec( hDB, pszSQL, NULL, NULL, NULL );
            sqlite3_free(pszSQL);
        }
    }

    return eErr;
}

/************************************************************************/
/*                       GDALRegister_MBTiles()                         */
/************************************************************************/

void GDALRegister_MBTiles()

{
    if( !GDAL_CHECK_VERSION( "MBTiles driver" ) )
        return;

    if( GDALGetDriverByName( "MBTiles" ) != NULL )
        return;

    GDALDriver *poDriver = new GDALDriver();

    poDriver->SetDescription( "MBTiles" );
    poDriver->SetMetadataItem( GDAL_DCAP_RASTER, "YES" );
    poDriver->SetMetadataItem( GDAL_DMD_LONGNAME, "MBTiles" );
    poDriver->SetMetadataItem( GDAL_DMD_HELPTOPIC, "frmt_mbtiles.html" );
    poDriver->SetMetadataItem( GDAL_DMD_EXTENSION, "mbtiles" );
    poDriver->SetMetadataItem( GDAL_DMD_CREATIONDATATYPES, "Byte" );

#define COMPRESSION_OPTIONS \
"  <Option name='TILE_FORMAT' type='string-select' description='Format to use to create tiles' default='PNG'>" \
"    <Value>PNG</Value>" \
"    <Value>PNG8</Value>" \
"    <Value>JPEG</Value>" \
"  </Option>" \
"  <Option name='QUALITY' type='int' min='1' max='100' description='Quality for JPEG tiles' default='75'/>" \
"  <Option name='ZLEVEL' type='int' min='1' max='9' description='DEFLATE compression level for PNG tiles' default='6'/>" \
"  <Option name='DITHER' type='boolean' description='Whether to apply Floyd-Steinberg dithering (for TILE_FORMAT=PNG8)' default='NO'/>" \

    poDriver->SetMetadataItem( GDAL_DMD_OPENOPTIONLIST, "<OpenOptionList>"
"  <Option name='ZOOM_LEVEL' type='integer' description='Zoom level of full resolution. If not specified, maximum non-empty zoom level'/>"
"  <Option name='BAND_COUNT' type='string-select' description='Number of raster bands' default='AUTO'>"
"    <Value>AUTO</Value>"
"    <Value>1</Value>"
"    <Value>2</Value>"
"    <Value>3</Value>"
"    <Value>4</Value>"
"  </Option>"
"  <Option name='MINX' type='float' description='Minimum X of area of interest'/>"
"  <Option name='MINY' type='float' description='Minimum Y of area of interest'/>"
"  <Option name='MAXX' type='float' description='Maximum X of area of interest'/>"
"  <Option name='MAXY' type='float' description='Maximum Y of area of interest'/>"
"  <Option name='USE_BOUNDS' type='boolean' description='Whether to use the bounds metadata, when available, to determine the AOI' default='YES'/>"
COMPRESSION_OPTIONS
"</OpenOptionList>");

    poDriver->SetMetadataItem( GDAL_DMD_CREATIONOPTIONLIST, "<CreationOptionList>"
"  <Option name='NAME' type='string' description='Tileset name'/>"
"  <Option name='DESCRIPTION' type='string' description='A description of the layer'/>"
"  <Option name='TYPE' type='string-select' description='Layer type' default='overlay'>"
"    <Value>overlay</Value>"
"    <Value>baselayer</Value>"
"  </Option>"
"  <Option name='VERSION' type='string' description='The version of the tileset, as a plain number' default='1.1'/>"
COMPRESSION_OPTIONS
"  <Option name='ZOOM_LEVEL_STRATEGY' type='string-select' description='Strategy to determine zoom level.' default='AUTO'>"
"    <Value>AUTO</Value>"
"    <Value>LOWER</Value>"
"    <Value>UPPER</Value>"
"  </Option>"
"  <Option name='RESAMPLING' type='string-select' description='Resampling algorithm.' default='BILINEAR'>"
"    <Value>NEAREST</Value>"
"    <Value>BILINEAR</Value>"
"    <Value>CUBIC</Value>"
"    <Value>CUBICSPLINE</Value>"
"    <Value>LANCZOS</Value>"
"    <Value>MODE</Value>"
"    <Value>AVERAGE</Value>"
"  </Option>"
"  <Option name='WRITE_BOUNDS' type='boolean' description='Whether to write the bounds metadata' default='YES'/>"
"  <Option name='WRITE_MINMAXZOOM' type='boolean' description='Whether to write the minzoom and maxzoom metadata' default='YES'/>"
"</CreationOptionList>");
    poDriver->SetMetadataItem( GDAL_DCAP_VIRTUALIO, "YES" );

    poDriver->pfnOpen = MBTilesDataset::Open;
    poDriver->pfnIdentify = MBTilesDataset::Identify;
    poDriver->pfnCreateCopy = MBTilesDataset::CreateCopy;
    poDriver->pfnCreate = MBTilesDataset::Create;

    GetGDALDriverManager()->RegisterDriver( poDriver );
}
