package org.autoplot.pds;

import com.opencsv.exceptions.CsvValidationException;
import gov.nasa.pds.label.Label;
import gov.nasa.pds.label.object.ArrayObject;
import gov.nasa.pds.label.object.FieldDescription;
import gov.nasa.pds.label.object.TableObject;
import gov.nasa.pds.label.object.TableRecord;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URL;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.autoplot.datasource.AbstractDataSource;
import org.autoplot.datasource.DataSetURI;
import org.autoplot.datasource.URISplit;
import org.autoplot.metatree.MetadataUtil;
import org.das2.datum.DatumRangeUtil;
import org.das2.datum.DatumUtil;
import org.das2.datum.NumberUnits;
import org.das2.datum.TimeUtil;
import org.das2.datum.Units;
import org.das2.datum.UnitsUtil;
import org.das2.qds.ArrayDataSet;
import org.das2.qds.DDataSet;
import org.das2.qds.MutablePropertyDataSet;
import org.das2.qds.QDataSet;
import org.das2.qds.ops.Ops;
import org.das2.qds.util.DataSetBuilder;
import org.das2.util.monitor.NullProgressMonitor;
import org.das2.util.monitor.ProgressMonitor;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * PDS4 file source.  This is pointed at PDS4 xml files and will return data
 * they describe.
 * @author jbf
 */
public class PdsDataSource extends AbstractDataSource {

    public PdsDataSource(URI uri) {
        super(uri);
    }

    /**
     * new version of PDS library now throws CsvValidationException, catch this and
     * wrap it to look like IOException for now.
     * TODO: review this.
     * @param t the table
     * @return the TableRecord
     * @throws Exception 
     */
    private static TableRecord readNextTableRecord(TableObject t ) throws Exception {
        try {
            return t.readNext();
        } catch ( CsvValidationException ex ) {
            throw new IOException(ex);
        }
    }
    
    
    /**
     * bootstrap routine for getting data from fields of a TableObject.  TODO: rewrite so that
     * multiple fields are read at once.
     * @param t
     * @param columnName
     * @return
     * @throws IOException 
     */
    private QDataSet getFromTable( TableObject t, String[] columnNames ) throws Exception {
        
        int ncols= columnNames.length;
        int[] icols= new int[ncols];
        
        DataSetBuilder dsb= new DataSetBuilder(2,100,ncols);
        
        for ( int i=0; i<ncols; i++ ) {
            int icol= -1;
            FieldDescription[] fields= t.getFields();
            for ( int j=0; j<fields.length; j++ ) {
                if ( fields[j].getName().equals(columnNames[i]) ) {
                    icol= j;
                    break;
                }
            }
            //TODO: what is returned when column isn't found?
            icols[i]= icol;
            FieldDescription fieldDescription= t.getFields()[icol];
            dsb.setName( i, fieldDescription.getName() );
            dsb.setLabel( i, fieldDescription.getName() );
            //TODO: Larry has nice descriptions.  How to get at those? https://space.physics.uiowa.edu/pds/cassini-rpws-electron_density/data/2006/rpws_fpe_2006-141_v1.xml
            //TODO: also https://pds-ppi.igpp.ucla.edu/data/cassini-caps-fitted-parameters/Data/CAS_CAPS_FITTED_PARAMETERS_WILSON_V01.xml?Sc_lat&X=Utc
            switch (fieldDescription.getType()) {
                case ASCII_DATE:
                case ASCII_DATE_DOY:
                case ASCII_DATE_TIME_DOY_UTC:
                case ASCII_DATE_TIME_UTC:
                case ASCII_DATE_TIME_DOY:
                case ASCII_DATE_TIME_YMD:
                case ASCII_DATE_TIME_YMD_UTC:
                    dsb.setUnits(i, Units.us2000);
                    break;
                    //TODO: create timeparser 
                case ASCII_STRING:
                    dsb.setUnits(i, Units.nominal(fieldDescription.getName()) );
                default:
                    dsb.setUnits(i, Units.dimensionless ); // TODO: how to get "unit" from label
            }
        }
        
        boolean doTimeCheck= true; // allow ASCII_STRING to contain times, flipping from nominal units to time location units.
        
        TableRecord r;
        while ( ( r= readNextTableRecord(t) )!=null ) {
            for ( int i=0; i<ncols; i++ ) {
                try {
                    if ( doTimeCheck ) {
                        String s= r.getString(icols[i]+1);
                        if ( DatumRangeUtil.parseISO8601(s)!=null && !( dsb.getUnits(i) instanceof NumberUnits ) ) {
                            dsb.setUnits( i, Units.us2000 );
                        }
                    }
                    dsb.putValue( -1, i, r.getString(icols[i]+1) );
                } catch (ParseException ex) {
                    dsb.putValue( -1, i, dsb.getUnits(i).getFillDatum() );
                }
            }
            doTimeCheck= false;
            dsb.nextRecord();
        }
        
        return dsb.getDataSet();
    }
    
    private double[] flatten( double[][] dd ) {
        double[] rank1= new double[dd.length*dd[0].length];
        int nj= dd[0].length;
        int kk= 0;
        for ( int i=0; i<dd.length; i++ ) {
            double[] d= dd[i];
            for ( int j=0; j<nj; j++ ) {
                rank1[kk++]= d[j];
            }
        }
        return rank1;
    }
    
    private double[] flatten3d( double[][][] dd ) {
        double[] rank1= new double[dd.length*dd[0].length*dd[0][0].length];
        int kk= 0;
        int[] qube= new int[] { dd.length, dd[0].length, dd[0][0].length };
        for ( int i0=0; i0<qube[0]; i0++ ) {
            for ( int i1=0; i1<qube[1]; i1++ ) {
                double[] d1= dd[i0][i1];
                for ( int i2=0; i2<qube[2]; i2++ ) {
                    rank1[kk++]= d1[i2];
                }
            }
        }
        return rank1;
    }
    /**
     * Read the XML file into a document.
     * @param f the file
     * @return the document object
     * @throws IOException
     * @throws SAXException
     */
    public static Document readXML( File f ) throws IOException, SAXException {
        DocumentBuilder builder= null;
        try {
            builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
        } catch (ParserConfigurationException ex) {
            throw new RuntimeException(ex);
        }

        Document document;
        
        try (InputStream in = new FileInputStream(f)) {
            InputSource source = new InputSource( in );
            document = builder.parse(source);
        }     
        
        return document;
    }
    
    private static void addAxisArray( Node n,  Map<Integer,String> axisNames ) throws XPathExpressionException {
        XPathFactory factory= XPathFactory.newInstance();
        XPath xpath= factory.newXPath();
        String name =   (String)xpath.evaluate( "axis_name", n, XPathConstants.STRING );
        Double sequence_number = (Double)xpath.evaluate( "sequence_number", n, XPathConstants.NUMBER );
        axisNames.put( sequence_number.intValue(), name );
    }
    
    /**
     * return the name of the independent parameter that works in this axis.
     * This currently assumes the first node with this axisName is the 
     * independent axis.
     * 
     * For example, with https://space.physics.uiowa.edu/voyager/data/voyager-2-pws-wf/data/1987/vg2_pws_wf_1987-04-21T17_v1.0.xml,
     * if axisName=='time' then the result will be "Epoch"
     * 
     * This shows where this logic fails:
     * https://pds-ppi.igpp.ucla.edu/data/maven-swea-calibrated/data/arc_pad/2016/03/mvn_swe_l2_arcpad_20160316_v04_r01.xml
     * For this file, I had to kludge in a test for the pitch angles.
     * 
     * @param doc the xml document
     * @param axisName the axis name
     * @return null or the independent variable for the axis.
     * @throws javax.xml.xpath.XPathExpressionException
     */
    public static String resolveIndependentAxis( Document doc, String axisName ) throws XPathExpressionException {
            
        XPathFactory factory= XPathFactory.newInstance();
        XPath xpath= factory.newXPath();

        String s=  "Product_Observational/File_Area_Observational/Array[Axis_Array/axis_name='"+axisName +"']";
        NodeList oo=   (NodeList) xpath.evaluate( s, doc, XPathConstants.NODESET );

        // jbf: I don't see how one can resolve the independent parameter properly.
        // I'll go through and find the lowest rank data with the axis.
        // "pitch angle" -> "pa"
        if ( oo.getLength()>0 ) {
            int best=0;
            for ( int i=0; i<oo.getLength(); i++ ) {
                Node o = oo.item(i);
                String name = (String)xpath.evaluate( "name", o, XPathConstants.STRING );
                if ( axisName.equals("pitch angle") && name.equals("pa") ) {  //kludge for mvn_swe_l2_arcpad_20160316_v04_r01.xml
                    best= i;
                }
            }
            Node o=  oo.item(best);

            String axes= (String)xpath.evaluate( "axes", o, XPathConstants.STRING );
            
            if ( Integer.parseInt(axes)==1 ) {
                String name = (String)xpath.evaluate( "name", o, XPathConstants.STRING );
                return name;
            } else {
                return null;
            }
            
        }
        
        return null;
    }
    
    /**
     * look through the PDS label document to see if dependencies can be 
     * identified.  Presently, this is simply one other dataset with the 
     * same axis (as in sample_offset) or the same axis name as something
     * that has a time unit (Epoch).  
     * @see https://space.physics.uiowa.edu/voyager/data/voyager-2-pws-wf/data/1987/vg2_pws_wf_1987-04-21T17_v0.9.xml
     * @param doc the parsed document for the label XML
     * @param depend the name of the data for the dependent variable, e.g. Waveform
     * @return ( Epoch, sample_offset, Waveform ) 
     * @throws javax.xml.xpath.XPathExpressionException
     */
    public static List<String> seekDependencies( Document doc, List<String> depend ) throws XPathExpressionException {
        if ( depend.size()==1 ) { // always will have one element.
        
            XPathFactory factory= XPathFactory.newInstance();
            XPath xpath= factory.newXPath();
        
            String name= depend.get(0);
            
            Map<Integer,String> axisNames= new LinkedHashMap<>();
            
            NodeList oo= (NodeList) xpath.evaluate( "//Product_Observational/File_Area_Observational/Array[name='"+name+"']/Axis_Array", doc, XPathConstants.NODESET );
            
            for ( int i=0; i<oo.getLength(); i++ ) {
                Node n = oo.item(i);
                addAxisArray( n, axisNames );
            }
            
            if ( axisNames.get(4)!=null ) {
                String n1= resolveIndependentAxis( doc, axisNames.get(1) );
                String n2= resolveIndependentAxis( doc, axisNames.get(2) );
                String n3= resolveIndependentAxis( doc, axisNames.get(3) );
                String n4= resolveIndependentAxis( doc, axisNames.get(4) );
                depend= new LinkedList<>(depend);
                depend.add(0,n1);
                depend.add(1,n2);
                depend.add(2,n3);
                if ( n4!=null && !n4.equals(name) ) {
                    depend.add(3,n4);
                }                
            } else if ( axisNames.get(3)!=null ) {
                String n1= resolveIndependentAxis( doc, axisNames.get(1) );
                String n2= resolveIndependentAxis( doc, axisNames.get(2) );
                String n3= resolveIndependentAxis( doc, axisNames.get(3) );
                depend= new LinkedList<>(depend);
                depend.add(0,n1);
                depend.add(1,n2);
                if ( n3!=null && !n3.equals(name) ) {
                    depend.add(2,n3);
                }                
            } else if ( axisNames.get(2)!=null ) {
                String n1= resolveIndependentAxis( doc, axisNames.get(1) );
                String n2= resolveIndependentAxis( doc, axisNames.get(2) );
                depend= new LinkedList<>(depend);
                depend.add(0,n1);
                if ( n2!=null && !n2.equals(name) ) {
                    depend.add(1,n2);
                }
            } else if ( axisNames.get(1)!=null ) {
                String n1= resolveIndependentAxis( doc, axisNames.get(1) );
                depend= new LinkedList<>(depend);
                if ( !n1.equals(name) ) {
                    depend.add(0,n1);
                }
            }
            
        }
        
        return depend;
    }
     
    /**
     * given the bundle, figure out which files should be loaded to implement the time range.  This will call recursively
     * into this code for each item.  This unimplemented stub returns an empty dataset.
     * //TODO: implement me
     * @param doc the xml document
     * @param mon progress monitor
     * @return rank 0 stub
     * @throws Exception 
     */
    public org.das2.qds.QDataSet getDataSetFromBundle(Document doc,ProgressMonitor mon) throws Exception {
        
        XPathExpression xp= XPathFactory.newInstance().newXPath().compile(
                "//Product_Bundle/Bundle_Member_Entry/lidvid_reference/text()");
        String lidvid= (String)xp.evaluate( doc, XPathConstants.STRING );
        
        if ( lidvid.trim().length()==0 ) {
            throw new IllegalArgumentException("lidvid is empty or not found at "+
                    "//Product_Bundle/Bundle_Member_Entry/lidvid_reference/text()");
        }
        
        return Ops.dataset(lidvid,Units.nominal());
    }
    
    /**
     * given the collection, figure out which files should be loaded to implement the time range.  This will call recursively
     * into this code for each item.  This unimplemented stub returns an empty dataset.
     * //TODO: implement me
     * @param doc the xml document
     * @param mon progress monitor
     * @return rank 0 stub
     * @throws Exception 
     */
    public org.das2.qds.QDataSet getDataSetFromCollection(Document doc,ProgressMonitor mon) throws Exception {
        
        XPathExpression xp= XPathFactory.newInstance().newXPath().compile(
                "//Product_Collection/File_Area_Inventory/File/file_name/text()");
        String csvfile= (String)xp.evaluate( doc, XPathConstants.STRING );
        
        if ( csvfile.trim().length()==0 ) {
            throw new IllegalArgumentException("file name is empty or not found at "+
                "//Product_Collection/File_Area_Inventory/File/file_name/text()");
        }
        
        return Ops.dataset(csvfile,Units.nominal());
    }
    
    
    @Override
    public org.das2.qds.QDataSet getDataSet(ProgressMonitor mon) throws Exception {
        String name= getParam("arg_0","");
        
        URISplit split= URISplit.parse( getURI() );
            
        File xmlfile = DataSetURI.getFile( split.resourceUri.toURL() ,new NullProgressMonitor());
        Document doc= readXML(xmlfile);
        
        if ( doc.getDocumentElement().getNodeName().equals("Product_Bundle") ) {
            return getDataSetFromBundle(doc,mon);
        }
        
        if ( doc.getDocumentElement().getNodeName().equals("Product_Collection")) {
            return getDataSetFromCollection(doc,mon);
        }
        
        URL fileUrl= PdsDataSourceFactory.getFileResource( split.resourceUri.toURL(), mon );
        DataSetURI.getFile(fileUrl,mon );
                    
        Label label = Label.open( xmlfile.toURI().toURL() ); 
                
        List<String> names= new ArrayList<>();
        String X= getParam("X","");
        if ( !X.equals("") ) {
            names.add(X);
        }
        String Y= getParam("Y","");
        if ( !Y.equals("") ) {
            names.add(Y);
        }
        
        String Z= getParam("Z","");
        if ( !Z.equals("") ) {
            names.add(Z);
        }

        if ( !name.equals("") ) {
            names.add(name);
        }

        List<String> names1= seekDependencies(doc, names );
        boolean okay= true;
        for ( int i=0; i<names1.size(); i++ ) {
            if ( names1.get(i)==null ) okay=false;
        }
        if ( okay ) {
            names= names1;
        }
            
        QDataSet result=null;
        QDataSet[] results= new QDataSet[names.size()];
        
        // see which parameters will come from tables.
        for ( TableObject t : label.getObjects( TableObject.class) ) {
            List<String> tableColumnNames= new ArrayList<>();
            List<Integer> datasetColumnIndexes= new ArrayList<>();
            
            for ( int i=0; i<names.size(); i++ ) {
                name= names.get(i);
                if ( name==null ) {
                    
                } else {
                    for ( FieldDescription fd: t.getFields() ) {
                        if ( name.equals( fd.getName() ) ) { 
                            tableColumnNames.add( fd.getName() );
                            datasetColumnIndexes.add(i);
                        }
                    }
                }
            }
            if ( tableColumnNames.size()>0 ) {
                QDataSet bresults= getFromTable( t, tableColumnNames.toArray(new String[tableColumnNames.size()]) );
                for ( int iii=0; iii<datasetColumnIndexes.size(); iii++ ) {
                    int i= datasetColumnIndexes.get(iii);
                    name= tableColumnNames.get(iii);
                    ArrayDataSet result1= DDataSet.copy( Ops.unbundle( bresults, i ) );
                    
                    results[i]= result1;
                    Units units= (Units) result1.property(QDataSet.UNITS);
                    if ( doc!=null ) {
                        XPathFactory factory= XPathFactory.newInstance();
                        XPath xpath= factory.newXPath();

                        String sunits= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Table_Character/Record_Character/Field_Character[name='"+name+"']/unit/text()", doc );
                        sunits= sunits.trim();
                        if ( sunits.length()>0 ) {
                            result1.putProperty( QDataSet.UNITS, Units.lookupUnits(sunits) );
                        }
                        if ( units==null || !UnitsUtil.isTimeLocation(units) ) {
                            String labl= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Table_Character/Record_Character/Field_Character[name='"+name+"']/name/text()", doc ); // TODO: Stupid, isn't this?
                            if ( labl.length()==0 ) labl= name;
                            ((MutablePropertyDataSet)results[i]).putProperty( QDataSet.LABEL, labl );
                            String title= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Table_Character/Record_Character/Field_Character[name='"+name+"']/description/text()", doc );
                            if ( title.length()>0 ) {
                                result1.putProperty( QDataSet.TITLE, title.trim() );
                            }
                        
                            String sfillValue= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Table_Character/Record_Character/Field_Character[name='"+name+"']/Special_Constants/invalid_constant/text()", doc );
                            if ( sfillValue.length()==0 ) 
                                sfillValue= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Table_Character/Record_Character/Field_Character[name='"+name+"']/Special_Constants/missing_constant/text()", doc );
                            String svalidMax= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Table_Character/Record_Character/Field_Character[name='"+name+"']/Special_Constants/valid_maximum/text()", doc );
                            String svalidMin= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Table_Character/Record_Character/Field_Character[name='"+name+"']/Special_Constants/valid_minimum/text()", doc );
                            if ( sfillValue.trim().length()>0 ) {
                                double fillValue= Double.parseDouble(sfillValue);
                                result1.putProperty( QDataSet.FILL_VALUE, fillValue );
                            }
                            if ( svalidMax.trim().length()>0 ) {
                                double validMax= Double.parseDouble(svalidMax);
                                result1.putProperty( QDataSet.VALID_MAX, validMax );
                            }
                            if ( svalidMin.trim().length()>0 ) {
                                double validMin= Double.parseDouble(svalidMin);
                                result1.putProperty( QDataSet.VALID_MIN, validMin );
                            }
                        }
                    }
                }
            }
        }

        for ( int i=0; i<names.size(); i++ ) {
            if ( results[i]!=null ) continue;
            name= names.get(i);            
            for ( ArrayObject a: label.getObjects(ArrayObject.class) ) {
                Units units=null;
                if ( a.getName().equals(name) ) {
                    MutablePropertyDataSet result1;
                    switch (a.getAxes()) {
                        case 1:    {
                                double[] dd= a.getElements1D();
                                int[] qube= new int[] { dd.length };
                                DDataSet ddresult= DDataSet.wrap( dd, qube );
                                if ( name.equals("Epoch") ) {
                                    logger.info("Epoch kludge results in CDF_TT2000 units");
                                    units= Units.cdfTT2000;
                                    ddresult.putProperty( QDataSet.UNITS, units );
                                }       
                                results[i]= ddresult;
                                result1= ddresult;
                                break;
                            }
                        case 2:    {
                                double[][] dd= a.getElements2D();
                                double[] rank1= flatten(dd);
                                int[] qube= new int[] { dd.length, dd[0].length };
                                DDataSet ddresult= DDataSet.wrap( rank1, qube );
                                results[i]= ddresult;
                                result1= ddresult;
                                break;
                            }
                        case 3:    {
                                double[][][] dd= a.getElements3D();
                                double[] rank1= flatten3d(dd);
                                int[] qube= new int[] { dd.length, dd[0].length, dd[0][0].length };
                                DDataSet ddresult= DDataSet.wrap( rank1, qube );
                                results[i]= ddresult;
                                result1= ddresult;
                                break;
                            }
                        default:
                            logger.warning("Unsupported number of axes, only one, two, or three.");
                            results[i]= null;
                            continue;
                    }
                    
                    if ( result1!=null && doc!=null ) {
                        XPathFactory factory= XPathFactory.newInstance();
                        XPath xpath= factory.newXPath();

                        String sunits= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Array[name='"+name+"']/Element_Array/unit/text()", doc );
                        sunits= sunits.trim();
                        if ( sunits.length()>0 && units==null ) {
                            result1.putProperty( QDataSet.UNITS, Units.lookupUnits(sunits) );
                        }
                        if ( units==null || !UnitsUtil.isTimeLocation(units) ) {
                            String labl= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Array[name='"+name+"']/name/text()", doc );
                            if ( labl.length()==0 ) labl= name;
                            ((MutablePropertyDataSet)results[i]).putProperty( QDataSet.LABEL, labl );
                            String title= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Array[name='"+name+"']/description/text()", doc );
                            if ( title.length()>0 ) {
                                result1.putProperty( QDataSet.TITLE, title.trim() );
                            }
                        }
                        
                        String sfillValue= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Array[name='"+name+"']/Special_Constants/invalid_constant/text()", doc );
                        if ( sfillValue.length()==0 ) 
                            sfillValue= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Array[name='"+name+"']/Special_Constants/missing_constant/text()", doc );
                        String svalidMax= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Array[name='"+name+"']/Special_Constants/valid_maximum/text()", doc );
                        String svalidMin= (String) xpath.evaluate( "//Product_Observational/File_Area_Observational/Array[name='"+name+"']/Special_Constants/valid_minimum/text()", doc );
                        if ( sfillValue.trim().length()>0 ) {
                            double fillValue= Double.parseDouble(sfillValue);
                            result1.putProperty( QDataSet.FILL_VALUE, fillValue );
                        }
                        if ( svalidMax.trim().length()>0 ) {
                            double validMax= Double.parseDouble(svalidMax);
                            result1.putProperty( QDataSet.VALID_MAX, validMax );
                        }
                        if ( svalidMin.trim().length()>0 ) {
                            double validMin= Double.parseDouble(svalidMin);
                            result1.putProperty( QDataSet.VALID_MIN, validMin );
                        }
                    }
                }
            }
        }
        
        if ( result==null ) {
            switch (results.length) {
                case 1:
                    result= results[0];
                    break;
                case 2:
                    result= Ops.link( results[0], results[1] );
                    break;
                case 3:
                    try {
                        result= Ops.link( results[0], results[1], results[2] );
                    } catch ( Exception ex ) {
                        ((MutablePropertyDataSet)results[2]).putProperty(QDataSet.DEPEND_1,null);
                        result= results[2];
                    }
                    break;
                case 4:
                    try {
                        result= Ops.link( results[0], results[1], results[2], results[3] );
                    } catch ( Exception ex ) {
                        ((MutablePropertyDataSet)results[3]).putProperty(QDataSet.DEPEND_1,null);
                        ((MutablePropertyDataSet)results[3]).putProperty(QDataSet.DEPEND_2,null);
                        result= results[3];
                    }
                    break;
                default:
                    break;
            }
        }
        
        if ( result instanceof MutablePropertyDataSet ) {
            ((MutablePropertyDataSet)result).makeImmutable();
        }
        
        return result;
    }
    
    protected static boolean isLeaf( Node node ) {
        return node.getChildNodes().getLength()==1 && node.getFirstChild().getNodeType()==Node.TEXT_NODE;
    }
    
    protected static Map<String, Object> convertDocumentToMap( Node root ) {
        Map<String, Object> resultMap = new HashMap<>();
        NodeList nodeList = root.getChildNodes();

        for (int i = 0; i < nodeList.getLength(); i++) {
            Node node = nodeList.item(i);
            String key = node.getNodeName();
            if ( isLeaf(node) ) {
                Object value = node.getTextContent(); // or another method to extract the value
                resultMap.put(key, value);
            } else if ( node.getNodeType() == Node.ELEMENT_NODE ) {
                Map<String,Object> subNode= convertDocumentToMap( node );
                resultMap.put(key, subNode);
            }
        }

        return resultMap;
    }
    
    @Override
    public Map<String, Object> getMetadata(ProgressMonitor mon) throws Exception {
        URISplit split= URISplit.parse( getURI() );
            
        File xmlfile = DataSetURI.getFile( split.resourceUri.toURL() , mon );
        Document doc= readXML(xmlfile);
        return convertDocumentToMap(doc);
        
    }
    
    
    
}