/*
 *                    BioJava development code
 *
 * This code may be freely distributed and modified under the
 * terms of the GNU Lesser General Public Licence.  This should
 * be distributed with the code.  If you do not have a copy,
 * see:
 *
 *      http://www.gnu.org/copyleft/lesser.html
 *
 * Copyright for this code is held jointly by the individual
 * authors.  These should be listed in @author doc comments.
 *
 * For more information on the BioJava project and its aims,
 * or to join the biojava-l mailing list, visit the home page
 * at:
 *
 *      http://www.biojava.org/
 *
 * Created on 01-21-2010
 *
 * @auther Scooter Willis
 *
 */
package org.biojava.nbio.core.sequence.loader;

import org.biojava.nbio.core.exceptions.CompoundNotFoundException;
import org.biojava.nbio.core.sequence.AccessionID;
import org.biojava.nbio.core.sequence.DataSource;
import org.biojava.nbio.core.sequence.ProteinSequence;
import org.biojava.nbio.core.sequence.Strand;
import org.biojava.nbio.core.sequence.compound.AminoAcidCompound;
import org.biojava.nbio.core.sequence.compound.AminoAcidCompoundSet;
import org.biojava.nbio.core.sequence.features.DBReferenceInfo;
import org.biojava.nbio.core.sequence.features.DatabaseReferenceInterface;
import org.biojava.nbio.core.sequence.features.FeaturesKeyWordInterface;
import org.biojava.nbio.core.sequence.storage.SequenceAsStringHelper;
import org.biojava.nbio.core.sequence.template.*;
import org.biojava.nbio.core.util.Equals;
import org.biojava.nbio.core.util.XMLHelper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.xml.sax.SAXException;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPathExpressionException;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.rmi.RemoteException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.regex.Pattern;

/**
 *
 * Pass in a Uniprot ID and this ProxySequenceReader when passed to a ProteinSequence will get the sequence data and other data elements
 * associated with the ProteinSequence by Uniprot. This is an example of how to map external databases of proteins and features to the BioJava3
 * ProteinSequence.
 * Important to call @see setUniprotDirectoryCache to allow caching of XML files so they don't need to be reloaded each time. Does
 * not manage cache.
 * @param <C>
 */
public class UniprotProxySequenceReader<C extends Compound> implements ProxySequenceReader<C>, FeaturesKeyWordInterface, DatabaseReferenceInterface {

        private final static Logger logger = LoggerFactory.getLogger(UniprotProxySequenceReader.class);

        /*
         * Taken from http://www.uniprot.org/help/accession_numbers
         */
        private static final String SPID_PATTERN = "[OPQ][0-9][A-Z0-9]{3}[0-9]";
        private static final String TREMBLID_PATTERN = "[A-NR-Z][0-9]([A-Z][A-Z0-9]{2}[0-9]){1,2}";
        public static final Pattern UP_AC_PATTERN = Pattern.compile("(" + SPID_PATTERN + "|" + TREMBLID_PATTERN + ")");

        public static final String DEFAULT_UNIPROT_BASE_URL = "https://www.uniprot.org";

        private static String uniprotbaseURL = DEFAULT_UNIPROT_BASE_URL;
        private static String uniprotDirectoryCache = null;
        private String sequence;
        private CompoundSet<C> compoundSet;
        private List<C> parsedCompounds = new ArrayList<C>();
        Document uniprotDoc;

        /**
         * The UniProt id is used to retrieve the UniProt XML which is then parsed as a DOM object
         * so we know everything about the protein. If an error occurs throw an exception. We could
         * have a bad uniprot id or network error
         * @param accession
         * @param compoundSet
         * @throws CompoundNotFoundException
         * @throws IOException if problems while reading the UniProt XML
         */
        public UniprotProxySequenceReader(String accession, CompoundSet<C> compoundSet) throws CompoundNotFoundException, IOException {
                if (!UP_AC_PATTERN.matcher(accession.toUpperCase()).matches()) {
                        throw new IllegalArgumentException("Accession provided " + accession + " doesn't comply with the uniprot acession pattern.");
                }
                setCompoundSet(compoundSet);
                uniprotDoc = this.getUniprotXML(accession);
                String seq = this.getSequence(uniprotDoc);
                setContents(seq);
        }

        /**
         * The xml is passed in as a DOM object so we know everything about the protein.
         *  If an error occurs throw an exception. We could have a bad uniprot id
         * @param document
         * @param compoundSet
         * @throws CompoundNotFoundException
         */
        public UniprotProxySequenceReader(Document document, CompoundSet<C> compoundSet) throws CompoundNotFoundException {
                setCompoundSet(compoundSet);
                uniprotDoc = document;
                String seq = this.getSequence(uniprotDoc);
                setContents(seq);
        }
        /**
         * The passed in xml is parsed as a DOM object so we know everything about the protein.
         *  If an error occurs throw an exception. We could have a bad uniprot id
         * @param xml
         * @param compoundSet
         * @return UniprotProxySequenceReader
         * @throws Exception
         */
        public static <C extends Compound> UniprotProxySequenceReader<C> parseUniprotXMLString(String xml, CompoundSet<C> compoundSet) {
                try {
                        Document document = XMLHelper.inputStreamToDocument(new ByteArrayInputStream(xml.getBytes()));
                        return new UniprotProxySequenceReader<C>(document, compoundSet);
                } catch (Exception e) {
                        logger.error("Exception on xml parse of: {}", xml);
                }
                return null;
        }

        @Override
        public void setCompoundSet(CompoundSet<C> compoundSet) {
                this.compoundSet = compoundSet;
        }

        /**
         * Once the sequence is retrieved set the contents and make sure everything this is valid
         * @param sequence
         * @throws CompoundNotFoundException
         */
        @Override
        public void setContents(String sequence) throws CompoundNotFoundException {
                // Horrendously inefficient - pretty much the way the old BJ did things.
                // TODO Should be optimised.
                this.sequence = sequence;
                this.parsedCompounds.clear();
                for (int i = 0; i < sequence.length();) {
                        String compoundStr = null;
                        C compound = null;
                        for (int compoundStrLength = 1; compound == null && compoundStrLength <= compoundSet.getMaxSingleCompoundStringLength(); compoundStrLength++) {
                                compoundStr = sequence.substring(i, i + compoundStrLength);
                                compound = compoundSet.getCompoundForString(compoundStr);
                        }
                        if (compound == null) {
                                throw new CompoundNotFoundException("Compound "+compoundStr+" not found");
                        } else {
                                i += compoundStr.length();
                        }
                        this.parsedCompounds.add(compound);
                }
        }

        /**
         * The sequence length
         * @return
         */
        @Override
        public int getLength() {
                return this.parsedCompounds.size();
        }

        /**
         *
         * @param position
         * @return
         */
        @Override
        public C getCompoundAt(int position) {
                return this.parsedCompounds.get(position - 1);
        }

        /**
         *
         * @param compound
         * @return
         */
        @Override
        public int getIndexOf(C compound) {
                return this.parsedCompounds.indexOf(compound) + 1;
        }

        /**
         *
         * @param compound
         * @return
         */
        @Override
        public int getLastIndexOf(C compound) {
                return this.parsedCompounds.lastIndexOf(compound) + 1;
        }

        /**
         *
         * @return
         */
        @Override
        public String toString() {
                return getSequenceAsString();
        }

        /**
         *
         * @return
         */
        @Override
        public String getSequenceAsString() {
                return sequence;
        }

        /**
         *
         * @return
         */
        @Override
        public List<C> getAsList() {
                return this.parsedCompounds;
        }

        @Override
        public boolean equals(Object o){

                if(! Equals.classEqual(this, o)) {
                        return false;
                }

                Sequence<C> other = (Sequence<C>)o;
                if ( other.getCompoundSet() != getCompoundSet())
                        return false;

                List<C> rawCompounds = getAsList();
                List<C> otherCompounds = other.getAsList();

                if ( rawCompounds.size() != otherCompounds.size())
                        return false;

                for (int i = 0 ; i < rawCompounds.size() ; i++){
                        Compound myCompound = rawCompounds.get(i);
                        Compound otherCompound = otherCompounds.get(i);
                        if ( ! myCompound.equalsIgnoreCase(otherCompound))
                                return false;
                }
                return true;
        }

        @Override
        public int hashCode(){
                String s = getSequenceAsString();
                return s.hashCode();
        }

        /**
         *
         * @return
         */
        @Override
        public SequenceView<C> getInverse() {
                return SequenceMixin.inverse(this);
        }

        /**
         *
         * @param bioBegin
         * @param bioEnd
         * @param strand
         * @return
         */
        public String getSequenceAsString(Integer bioBegin, Integer bioEnd, Strand strand) {
                SequenceAsStringHelper<C> sequenceAsStringHelper = new SequenceAsStringHelper<C>();
                return sequenceAsStringHelper.getSequenceAsString(this.parsedCompounds, compoundSet, bioBegin, bioEnd, strand);
        }

        /**
         *
         * @param bioBegin
         * @param bioEnd
         * @return
         */
        @Override
        public SequenceView<C> getSubSequence(final Integer bioBegin, final Integer bioEnd) {
                return new SequenceProxyView<C>(UniprotProxySequenceReader.this, bioBegin, bioEnd);
        }

        /**
         *
         * @return
         */
        @Override
        public Iterator<C> iterator() {
                return this.parsedCompounds.iterator();
        }

        /**
         *
         * @return
         */
        @Override
        public CompoundSet<C> getCompoundSet() {
                return compoundSet;
        }

        /**
         *
         * @return
         */
        @Override
        public AccessionID getAccession() {
                AccessionID accessionID = new AccessionID();
                if (uniprotDoc == null) {
                        return accessionID;
                }
                try {
                        Element uniprotElement = uniprotDoc.getDocumentElement();
                        Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                        Element nameElement = XMLHelper.selectSingleElement(entryElement, "name");
                        accessionID = new AccessionID(nameElement.getTextContent(), DataSource.UNIPROT);
                } catch (XPathExpressionException e) {
                        logger.error("Exception: ", e);
                }
                return accessionID;
        }

        /**
         * Pull uniprot accessions associated with this sequence
         * @return
         * @throws XPathExpressionException
         */
        public ArrayList<AccessionID> getAccessions() throws XPathExpressionException {
                ArrayList<AccessionID> accessionList = new ArrayList<AccessionID>();
                if (uniprotDoc == null) {
                        return accessionList;
                }
                Element uniprotElement = uniprotDoc.getDocumentElement();
                Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                ArrayList<Element> keyWordElementList = XMLHelper.selectElements(entryElement, "accession");
                for (Element element : keyWordElementList) {
                        AccessionID accessionID = new AccessionID(element.getTextContent(), DataSource.UNIPROT);
                        accessionList.add(accessionID);
                }

                return accessionList;
        }

        /**
         * Pull uniprot protein aliases associated with this sequence
         * Provided for backwards compatibility now that we support both
         * gene and protein aliases via separate methods.
         * @return
         * @throws XPathExpressionException
         */
        public ArrayList<String> getAliases() throws XPathExpressionException {

                return getProteinAliases();
        }
        /**
         * Pull uniprot protein aliases associated with this sequence
         * @return
         * @throws XPathExpressionException
         */
        public ArrayList<String> getProteinAliases() throws XPathExpressionException {
                ArrayList<String> aliasList = new ArrayList<String>();
                if (uniprotDoc == null) {
                        return aliasList;
                }
                Element uniprotElement = uniprotDoc.getDocumentElement();
                Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                Element proteinElement = XMLHelper.selectSingleElement(entryElement, "protein");
                ArrayList<Element> keyWordElementList = XMLHelper.selectElements(proteinElement, "alternativeName");
                for (Element element : keyWordElementList) {
                        Element fullNameElement = XMLHelper.selectSingleElement(element, "fullName");
                        aliasList.add(fullNameElement.getTextContent());
                        Element shortNameElement = XMLHelper.selectSingleElement(element, "shortName");
                        if(null != shortNameElement) {
                                String shortName = shortNameElement.getTextContent();
                                if(null != shortName && !shortName.trim().isEmpty()) {
                                        aliasList.add(shortName);
                                }
                        }
                }
                keyWordElementList = XMLHelper.selectElements(proteinElement, "recommendedName");
                for (Element element : keyWordElementList) {
                        Element fullNameElement = XMLHelper.selectSingleElement(element, "fullName");
                        aliasList.add(fullNameElement.getTextContent());
                        Element shortNameElement = XMLHelper.selectSingleElement(element, "shortName");
                        if(null != shortNameElement) {
                                String shortName = shortNameElement.getTextContent();
                                if(null != shortName && !shortName.trim().isEmpty()) {
                                        aliasList.add(shortName);
                                }
                        }
                }
                Element cdAntigen = XMLHelper.selectSingleElement(proteinElement, "cdAntigenName");
                if(null != cdAntigen) {
                        String cdAntigenName = cdAntigen.getTextContent();
                        if(null != cdAntigenName && !cdAntigenName.trim().isEmpty()) {
                                aliasList.add(cdAntigenName);
                        }
                }

                return aliasList;
        }

        /**
         * Pull uniprot gene aliases associated with this sequence
         * @return
         * @throws XPathExpressionException
         */
        public ArrayList<String> getGeneAliases() throws XPathExpressionException {
                ArrayList<String> aliasList = new ArrayList<String>();
                if (uniprotDoc == null) {
                        return aliasList;
                }
                Element uniprotElement = uniprotDoc.getDocumentElement();
                Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                ArrayList<Element> proteinElements = XMLHelper.selectElements(entryElement, "gene");
                for(Element proteinElement : proteinElements) {
                        ArrayList<Element> keyWordElementList = XMLHelper.selectElements(proteinElement, "name");
                        for (Element element : keyWordElementList) {
                                aliasList.add(element.getTextContent());
                        }
                }
                return aliasList;
        }

        /**
         *
         * @param compounds
         * @return
         */
        @Override
        public int countCompounds(C... compounds) {
                throw new UnsupportedOperationException("Not supported yet.");
        }

        /**
         *
         * @param accession
         * @return
         * @throws IOException
         */
        private Document getUniprotXML(String accession) throws IOException, CompoundNotFoundException {
                StringBuilder sb = new StringBuilder();
                // try in cache
                if (uniprotDirectoryCache != null && uniprotDirectoryCache.length() > 0) {
                        sb = fetchFromCache(accession);
                }

                // http://www.uniprot.org/uniprot/?query=SORBIDRAFT_03g027040&format=xml
                if (sb.length() == 0) {
                        String uniprotURL = getUniprotbaseURL() + "/uniprot/" + accession.toUpperCase() + ".xml";
                        logger.info("Loading: {}", uniprotURL);
                        sb = fetchUniprotXML(uniprotURL);

                        int index = sb.indexOf("xmlns="); //strip out name space stuff to make it easier on xpath
                        if (index != -1) {
                                int lastIndex = sb.indexOf(">", index);
                                sb.replace(index, lastIndex, "");
                        }
                        if (uniprotDirectoryCache != null && uniprotDirectoryCache.length() > 0)
                                writeCache(sb,accession);
                }

                logger.info("Load complete");
                try {
                        //       logger.debug(sb.toString());
                        Document document = XMLHelper.inputStreamToDocument(new ByteArrayInputStream(sb.toString().getBytes()));
                        return document;
                } catch (SAXException e) {
                        logger.error("Exception on xml parse of: {}", sb.toString());
                } catch (ParserConfigurationException e) {
                        logger.error("Exception on xml parse of: {}", sb.toString());
                }
                return null;
        }

        private void writeCache(StringBuilder sb, String accession) throws IOException {
                File f = new File(uniprotDirectoryCache + File.separatorChar + accession + ".xml");
                FileWriter fw = new FileWriter(f);
                fw.write(sb.toString());
                fw.close();
        }

        /**
         * Open a URL connection.
         *
         * Follows redirects.
         * @param url
         * @throws IOException
         */
        private static HttpURLConnection openURLConnection(URL url) throws IOException {
                // This method should be moved to a utility class in BioJava 5.0

                final int timeout = 5000;
                final String useragent = "BioJava";

                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestProperty("User-Agent", useragent);
                conn.setInstanceFollowRedirects(true);
                conn.setConnectTimeout(timeout);
                conn.setReadTimeout(timeout);

                int status = conn.getResponseCode();
                while (status == HttpURLConnection.HTTP_MOVED_TEMP
                                || status == HttpURLConnection.HTTP_MOVED_PERM
                                || status == HttpURLConnection.HTTP_SEE_OTHER) {
                        // Redirect!
                        String newUrl = conn.getHeaderField("Location");

                        if(newUrl.equals(url.toString())) {
                                throw new IOException("Cyclic redirect detected at "+newUrl);
                        }

                        // Preserve cookies
                        String cookies = conn.getHeaderField("Set-Cookie");

                        // open the new connection again
                        url = new URL(newUrl);
                        conn.disconnect();
                        conn = (HttpURLConnection) url.openConnection();
                        if(cookies != null) {
                                conn.setRequestProperty("Cookie", cookies);
                        }
                        conn.addRequestProperty("User-Agent", useragent);
                        conn.setInstanceFollowRedirects(true);
                        conn.setConnectTimeout(timeout);
                        conn.setReadTimeout(timeout);
                        conn.connect();

                        status = conn.getResponseCode();

                        logger.info("Redirecting from {} to {}", url, newUrl);
                }
                conn.connect();

                return conn;
        }

        private StringBuilder fetchUniprotXML(String uniprotURL)
                        throws IOException, CompoundNotFoundException {

                StringBuilder sb = new StringBuilder();
                URL uniprot = new URL(uniprotURL);
                int attempt = 5;
                List<String> errorCodes = new ArrayList<String>();
                while(attempt > 0) {
                        HttpURLConnection uniprotConnection = openURLConnection(uniprot);
                        int statusCode = uniprotConnection.getResponseCode();
                        if (statusCode == HttpURLConnection.HTTP_OK) {
                                BufferedReader in = new BufferedReader(
                                                new InputStreamReader(
                                                uniprotConnection.getInputStream()));
                                String inputLine;

                                while ((inputLine = in.readLine()) != null) {
                                        sb.append(inputLine);
                                }
                                in.close();
                                return sb;
                        }
                        attempt--;
                        errorCodes.add(String.valueOf(statusCode));
                }
                throw new RemoteException("Couldn't fetch accession from the url " + uniprotURL + " error codes on 5 attempts are " + errorCodes.toString());
        }

        /**
         * @param key
         * @return A string containing the contents of entry specified by key and if not found returns an empty string
         * @throws FileNotFoundException
         * @throws IOException
         */
        private StringBuilder fetchFromCache(String key)
                        throws FileNotFoundException, IOException {
                int index;
                File f = new File(uniprotDirectoryCache + File.separatorChar + key + ".xml");
                StringBuilder sb = new StringBuilder();
                if (f.exists()) {
                        FileReader fr = new FileReader(f);
                        int size = (int) f.length();
                        char[] data = new char[size];
                        fr.read(data);
                        fr.close();
                        sb.append(data);
                        index = sb.indexOf("xmlns="); //strip out name space stuff to make it easier on xpath
                        if (index != -1) {
                                int lastIndex = sb.indexOf(">", index);
                                sb.replace(index, lastIndex, "");
                        }
                }
                return sb;
        }

        /**
         *
         * @param uniprotDoc
         * @return
         */
        private String getSequence(Document uniprotDoc)  {

                try {
                        Element uniprotElement = uniprotDoc.getDocumentElement();
                        Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                        Element sequenceElement = XMLHelper.selectSingleElement(entryElement, "sequence");

                        String seqdata = sequenceElement.getTextContent();

                        return seqdata;
                } catch (XPathExpressionException e) {
                        logger.error("Problems while parsing sequence in UniProt XML: {}. Sequence will be blank.", e.getMessage());
                        return "";
                }
        }

        /**
         * The current UniProt URL to deal with caching issues. www.uniprot.org is load balanced
         * but you can access pir.uniprot.org directly.
         * @return the uniprotbaseURL
         */
        public static String getUniprotbaseURL() {
                return uniprotbaseURL;
        }

        /**
         * @param aUniprotbaseURL the uniprotbaseURL to set
         */
        public static void setUniprotbaseURL(String aUniprotbaseURL) {
                uniprotbaseURL = aUniprotbaseURL;
        }

        /**
         * Local directory cache of XML that can be downloaded
         * @return the uniprotDirectoryCache
         */
        public static String getUniprotDirectoryCache() {
                return uniprotDirectoryCache;
        }

        /**
         * @param aUniprotDirectoryCache the uniprotDirectoryCache to set
         */
        public static void setUniprotDirectoryCache(String aUniprotDirectoryCache) {
                File f = new File(aUniprotDirectoryCache);
                if (!f.exists()) {
                        f.mkdirs();
                }
                uniprotDirectoryCache = aUniprotDirectoryCache;
        }

        public static void main(String[] args) {

                try {
                        UniprotProxySequenceReader<AminoAcidCompound> uniprotSequence = new UniprotProxySequenceReader<AminoAcidCompound>("YA745_GIBZE", AminoAcidCompoundSet.getAminoAcidCompoundSet());
                        ProteinSequence proteinSequence = new ProteinSequence(uniprotSequence);
                        logger.info("Accession: {}", proteinSequence.getAccession().getID());
                        logger.info("Sequence: {}", proteinSequence.getSequenceAsString());
                } catch (Exception e) {
                        logger.error("Exception: ", e);
                }

        }

        /**
         * Get the gene name associated with this sequence.
         * @return
         */
        public String getGeneName() {
                if (uniprotDoc == null) {
                        return "";
                }
                try {
                        Element uniprotElement = uniprotDoc.getDocumentElement();
                        Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                        Element geneElement = XMLHelper.selectSingleElement(entryElement, "gene");
                        if (geneElement == null) {
                                return "";
                        }
                        Element nameElement = XMLHelper.selectSingleElement(geneElement, "name");
                        if (nameElement == null) {
                                return "";
                        }
                        return nameElement.getTextContent();
                } catch (XPathExpressionException e) {
                        logger.error("Problems while parsing gene name in UniProt XML: {}. Gene name will be blank.",e.getMessage());
                        return "";
                }
        }

        /**
         * Get the organism name assigned to this sequence
         * @return
         */
        public String getOrganismName() {
                if (uniprotDoc == null) {
                        return "";
                }
                try {
                        Element uniprotElement = uniprotDoc.getDocumentElement();
                        Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                        Element organismElement = XMLHelper.selectSingleElement(entryElement, "organism");
                        if (organismElement == null) {
                                return "";
                        }
                        Element nameElement = XMLHelper.selectSingleElement(organismElement, "name");
                        if (nameElement == null) {
                                return "";
                        }
                        return nameElement.getTextContent();
                } catch (XPathExpressionException e) {
                        logger.error("Problems while parsing organism name in UniProt XML: {}. Organism name will be blank.",e.getMessage());
                        return "";
                }

        }

        /**
         * Pull UniProt key words which is a mixed bag of words associated with this sequence
         * @return
         */
        @Override
        public ArrayList<String> getKeyWords() {
                ArrayList<String> keyWordsList = new ArrayList<String>();
                if (uniprotDoc == null) {
                        return keyWordsList;
                }
                try {
                        Element uniprotElement = uniprotDoc.getDocumentElement();

                        Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                        ArrayList<Element> keyWordElementList = XMLHelper.selectElements(entryElement, "keyword");
                        for (Element element : keyWordElementList) {
                                keyWordsList.add(element.getTextContent());
                        }
                } catch (XPathExpressionException e) {
                        logger.error("Problems while parsing keywords in UniProt XML: {}. No keywords will be available.",e.getMessage());
                        return new ArrayList<String>();
                }

                return keyWordsList;
        }

        /**
         * The Uniprot mappings to other database identifiers for this sequence
         * @return
         */
        @Override
        public LinkedHashMap<String, ArrayList<DBReferenceInfo>> getDatabaseReferences()  {
                LinkedHashMap<String, ArrayList<DBReferenceInfo>> databaseReferencesHashMap = new LinkedHashMap<String, ArrayList<DBReferenceInfo>>();
                if (uniprotDoc == null) {
                        return databaseReferencesHashMap;
                }

                try {
                        Element uniprotElement = uniprotDoc.getDocumentElement();
                        Element entryElement = XMLHelper.selectSingleElement(uniprotElement, "entry");
                        ArrayList<Element> dbreferenceElementList = XMLHelper.selectElements(entryElement, "dbReference");
                        for (Element element : dbreferenceElementList) {
                                String type = element.getAttribute("type");
                                String id = element.getAttribute("id");
                                ArrayList<DBReferenceInfo> idlist = databaseReferencesHashMap.get(type);
                                if (idlist == null) {
                                        idlist = new ArrayList<DBReferenceInfo>();
                                        databaseReferencesHashMap.put(type, idlist);
                                }
                                DBReferenceInfo dbreferenceInfo = new DBReferenceInfo(type, id);
                                ArrayList<Element> propertyElementList = XMLHelper.selectElements(element, "property");
                                for (Element propertyElement : propertyElementList) {
                                        String propertyType = propertyElement.getAttribute("type");
                                        String propertyValue = propertyElement.getAttribute("value");
                                        dbreferenceInfo.addProperty(propertyType, propertyValue);
                                }

                                idlist.add(dbreferenceInfo);
                        }
                } catch (XPathExpressionException e) {
                        logger.error("Problems while parsing db references in UniProt XML: {}. No db references will be available.",e.getMessage());
                        return new LinkedHashMap<String, ArrayList<DBReferenceInfo>>();
                }

                return databaseReferencesHashMap;
        }
}