/************************************************************************/
/*                         getNormalizedValue()                         */
/*                                                                      */
/*      Parse a node to get it's numerical value, and then normalize    */
/*      into meters of degrees depending on the measure type.           */
/************************************************************************/

static double getNormalizedValue( CPLXMLNode *psNode, const char *pszPath,
                                  const char * /*pszMeasure*/, 
                                  double dfDefault )

{
    CPLXMLNode *psTargetNode;
    CPLXMLNode *psValueNode;

    if( pszPath == NULL || strlen(pszPath) == 0 )
        psTargetNode = psNode;
    else
        psTargetNode = CPLGetXMLNode( psNode, pszPath );
    
    if( psTargetNode == NULL )
        return dfDefault;

    for( psValueNode = psTargetNode->psChild; 
         psValueNode != NULL && psValueNode->eType != CXT_Text;
         psValueNode = psValueNode->psNext ) {}

    if( psValueNode == NULL )
        return dfDefault;
    
    // Add normalization later.

    return atof(psValueNode->pszValue);
}

/************************************************************************/
/*                        importGeogCSFromXML()                         */
/************************************************************************/

static OGRErr importGeogCSFromXML( OGRSpatialReference *poSRS, 
                                   CPLXMLNode *psCRS )

{
    const char     *pszGeogName, *pszDatumName, *pszEllipsoidName, *pszPMName;
    double         dfSemiMajor, dfInvFlattening, dfPMOffset = 0.0;

/* -------------------------------------------------------------------- */
/*      Set the GEOGCS name from the srsName.                           */
/* -------------------------------------------------------------------- */
    pszGeogName = 
        CPLGetXMLValue( psCRS, "srsName", "Unnamed GeogCS" );

/* -------------------------------------------------------------------- */
/*      If we don't seem to have a detailed coordinate system           */
/*      definition, check if we can define based on an EPSG code.       */
/* -------------------------------------------------------------------- */
    CPLXMLNode     *psDatum;

    psDatum = CPLGetXMLNode( psCRS, "usesGeodeticDatum.GeodeticDatum" );

    if( psDatum == NULL )
    {
        OGRSpatialReference oIdSRS;

        oIdSRS.SetLocalCS( "dummy" );
        importXMLAuthority( psCRS, &oIdSRS, "srsID", "LOCAL_CS" );

        if( oIdSRS.GetAuthorityCode( "LOCAL_CS" ) != NULL
            && oIdSRS.GetAuthorityName( "LOCAL_CS" ) != NULL
            && EQUAL(oIdSRS.GetAuthorityName("LOCAL_CS"),"EPSG") )
        {
            return poSRS->importFromEPSG( 
                atoi(oIdSRS.GetAuthorityCode("LOCAL_CS")) );
        }
    }

/* -------------------------------------------------------------------- */
/*      Get datum name.                                                 */
/* -------------------------------------------------------------------- */
    pszDatumName = 
        CPLGetXMLValue( psDatum, "datumName", "Unnamed Datum" );

/* -------------------------------------------------------------------- */
/*      Get ellipsoid information.                                      */
/* -------------------------------------------------------------------- */
    CPLXMLNode *psE;

    psE = CPLGetXMLNode( psDatum, "usesEllipsoid.Ellipsoid" );
    pszEllipsoidName = 
        CPLGetXMLValue( psE, "ellipsoidName", "Unnamed Ellipsoid" );

    dfSemiMajor = getNormalizedValue( psE, "semiMajorAxis", "Linear", 
                                      SRS_WGS84_SEMIMAJOR );

    dfInvFlattening = 
        getNormalizedValue( psE, "secondDefiningParameter.inverseFlattening", 
                            "Unitless", 0.0 );

    if( dfInvFlattening == 0.0 )
    {
        CPLError( CE_Failure, CPLE_AppDefined, 
                  "Ellipsoid inverseFlattening corrupt or missing." );
        return OGRERR_CORRUPT_DATA;
    }

/* -------------------------------------------------------------------- */
/*      Get the prime meridian.                                         */
/* -------------------------------------------------------------------- */
    CPLXMLNode *psPM;

    psPM = CPLGetXMLNode( psDatum, "usesPrimeMeridian.PrimeMeridian" );
    if( psPM == NULL )
    {
        pszPMName = "Greenwich";
        dfPMOffset = 0.0;
    }
    else
    {
        pszPMName = CPLGetXMLValue( psPM, "meridianName", 
                                    "Unnamed Prime Meridian");
        dfPMOffset = 
            getNormalizedValue( psPM, "greenwichLongitude.angle",
                                "Angular", 0.0 );
    }

/* -------------------------------------------------------------------- */
/*      Set the geographic definition.                                  */
/* -------------------------------------------------------------------- */
    poSRS->SetGeogCS( pszGeogName, pszDatumName, 
                      pszEllipsoidName, dfSemiMajor, dfInvFlattening, 
                      pszPMName, dfPMOffset );

/* -------------------------------------------------------------------- */
/*      Look for angular units.  We don't check that all axes match     */
/*      at this time.                                                   */
/* -------------------------------------------------------------------- */
#ifdef notdef
    CPLXMLNode *psAxis;

    psAxis = CPLGetXMLNode( psGeo2DCRS, 
                            "EllipsoidalCoordinateSystem.CoordinateAxis" );
    importXMLUnits( psAxis, "AngularUnit", poSRS, "GEOGCS" );
#endif

/* -------------------------------------------------------------------- */
/*      Can we set authorities for any of the levels?                   */
/* -------------------------------------------------------------------- */
    importXMLAuthority( psCRS, poSRS, "srsID", "GEOGCS" );
    importXMLAuthority( psDatum, poSRS, "datumID", "GEOGCS|DATUM" );
    importXMLAuthority( psE, poSRS, "ellipsoidID", 
                        "GEOGCS|DATUM|SPHEROID" );
    importXMLAuthority( psDatum, poSRS, 
                        "usesPrimeMeridian.PrimeMeridian.meridianID",
                        "GEOGCS|PRIMEM" );

    poSRS->Fixup();
    
    return OGRERR_NONE;
}

/************************************************************************/
/*                        importProjCSFromXML()                         */
/************************************************************************/

static OGRErr importProjCSFromXML( OGRSpatialReference *poSRS, 
                                   CPLXMLNode *psCRS )

{
    CPLXMLNode *psSubXML;
    OGRErr eErr;

/* -------------------------------------------------------------------- */
/*      Setup the PROJCS node with a name.                              */
/* -------------------------------------------------------------------- */
    poSRS->SetProjCS( CPLGetXMLValue( psCRS, "srsName", "Unnamed" ) );

/* -------------------------------------------------------------------- */
/*      Get authority information if available.  If we got it, and      */
/*      we seem to be lacking inline definition values, try and         */
/*      define according to the EPSG code for the PCS.                  */
/* -------------------------------------------------------------------- */
    importXMLAuthority( psCRS, poSRS, "srsID", "PROJCS" );

    if( poSRS->GetAuthorityCode( "PROJCS" ) != NULL
        && poSRS->GetAuthorityName( "PROJCS" ) != NULL
        && EQUAL(poSRS->GetAuthorityName("PROJCS"),"EPSG")
        && (CPLGetXMLNode( psCRS, "definedByConversion.Conversion" ) == NULL
            || CPLGetXMLNode( psCRS, "baseCRS.GeographicCRS" ) == NULL) )
    {
        return poSRS->importFromEPSG( atoi(poSRS->GetAuthorityCode("PROJCS")) );
    }

/* -------------------------------------------------------------------- */
/*      Try to set the GEOGCS info.                                     */
/* -------------------------------------------------------------------- */
    
    psSubXML = CPLGetXMLNode( psCRS, "baseCRS.GeographicCRS" );
    if( psSubXML != NULL )
    {
        eErr = importGeogCSFromXML( poSRS, psSubXML );
        if( eErr != OGRERR_NONE )
            return eErr;
    }

/* -------------------------------------------------------------------- */
/*      Get the conversion node.  It should be the only child of the    */
/*      definedByConversion node.                                       */
/* -------------------------------------------------------------------- */
    CPLXMLNode *psConv = NULL;

    psConv = CPLGetXMLNode( psCRS, "definedByConversion.Conversion" );
    if( psConv == NULL || psConv->eType != CXT_Element )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "Unable to find a conversion node under the definedByConversion\n"
                  "node of the ProjectedCRS." );
        return OGRERR_CORRUPT_DATA;
    }

/* -------------------------------------------------------------------- */
/*      Determine the conversion method in effect.                      */
/* -------------------------------------------------------------------- */
    int nMethod = getEPSGObjectCodeValue( CPLGetXMLNode( psConv, "usesMethod"),
                                          "method", 0 );
    
/* -------------------------------------------------------------------- */
/*      Transverse Mercator.                                            */
/* -------------------------------------------------------------------- */
    if( nMethod == 9807 ) 
    {
        poSRS->SetTM( 
            getProjectionParm( psConv, 8801, "Angular", 0.0 ), 
            getProjectionParm( psConv, 8802, "Angular", 0.0 ), 
            getProjectionParm( psConv, 8805, "Unitless", 1.0 ), 
            getProjectionParm( psConv, 8806, "Linear", 0.0 ),
            getProjectionParm( psConv, 8807, "Linear", 0.0 ) );
    }

/* -------------------------------------------------------------------- */
/*      Didn't recognise?                                               */
/* -------------------------------------------------------------------- */
    else
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "Conversion method %d not recognised.", 
                  nMethod );
        return OGRERR_CORRUPT_DATA;
    }


/* -------------------------------------------------------------------- */
/*      Cleanup and return.                                             */
/* -------------------------------------------------------------------- */
    poSRS->Fixup();

    // Need to get linear units here!

    return OGRERR_NONE;
}

/************************************************************************/
/*                           importFromXML()                            */
/************************************************************************/

OGRErr OGRSpatialReference::importFromXML( const char *pszXML )

{
    CPLXMLNode *psTree;
    OGRErr  eErr = OGRERR_UNSUPPORTED_SRS;

    this->Clear();
        
/* -------------------------------------------------------------------- */
/*      Parse the XML.                                                  */
/* -------------------------------------------------------------------- */
    psTree = CPLParseXMLString( pszXML );
    
    if( psTree == NULL )
        return OGRERR_CORRUPT_DATA;

    CPLStripXMLNamespace( psTree, "gml", TRUE );

/* -------------------------------------------------------------------- */
/*      Import according to the root node type.  We walk through        */
/*      root elements as there is sometimes prefix stuff like           */
/*      <?xml>.                                                         */
/* -------------------------------------------------------------------- */
    CPLXMLNode *psNode = psTree;

    for( psNode = psTree; psNode != NULL; psNode = psNode->psNext )
    {
        if( EQUAL(psNode->pszValue,"GeographicCRS") )
        {
            eErr = importGeogCSFromXML( this, psNode );
            break;
        }
        
        else if( EQUAL(psNode->pszValue,"ProjectedCRS") )
        {
            eErr = importProjCSFromXML( this, psNode );
            break;
        }
    }

    CPLDestroyXMLNode( psTree );

    return eErr;
}

/************************************************************************/
/*                          OSRImportFromXML()                          */
/************************************************************************/

OGRErr OSRImportFromXML( OGRSpatialReferenceH hSRS, const char *pszXML )

{
    return ((OGRSpatialReference *) hSRS)->importFromXML( pszXML );
}