/*

  * Licensed to the Apache Software Foundation (ASF) under one or more

  * contributor license agreements.  See the NOTICE file distributed with

  * this work for additional information regarding copyright ownership.

  * The ASF licenses this file to You under the Apache License, Version 2.0

  * (the "License"); you may not use this file except in compliance with

  * the License.  You may obtain a copy of the License at

  *

  *  http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.apache.any23.io.nquads;

 import org.openrdf.model.BNode;

 import org.openrdf.model.Literal;

 import org.openrdf.model.Resource;

 import org.openrdf.model.Statement;

 import org.openrdf.model.URI;

 import org.openrdf.model.Value;

 import org.openrdf.rio.RDFFormat;

 import org.openrdf.rio.RDFHandlerException;

 import org.openrdf.rio.RDFWriter;

 import org.openrdf.rio.ntriples.NTriplesUtil;

 import java.io.IOException;

 import java.io.OutputStream;

 import java.io.OutputStreamWriter;

 import java.io.Writer;

 import java.util.HashMap;

 import java.util.Map;

 /**

  * <i>N-Quads</i> implementation of an {@link org.openrdf.rio.RDFWriter}.

  * See the format specification <a href="http://sw.deri.org/2008/07/n-quads/">here</a>.

  *

  * @author Michele Mostarda (mostarda@fbk.eu)

  */

 public class NQuadsWriter implements RDFWriter {

     /**

      * The table maintaining namespaces.

      */

     private Map<String,String> namespaceTable;

     /**

      * The output writer.

      */

     private Writer writer;

     /**

      * Maintain the started status.

      */

     private boolean started = false;

     public NQuadsWriter(OutputStream os) {

         this( new OutputStreamWriter(os) );

     }

     public NQuadsWriter(Writer w) {

         if(w == null) {

             throw new NullPointerException("the writer cannot be null.");

         }

         writer = w;

     }

     public RDFFormat getRDFFormat() {

         return NQuads.FORMAT;

     }

     public void startRDF() throws RDFHandlerException {

         if(started) {

             throw new IllegalStateException("Parsing already started.");

         }

         started = true;

     }

     public void endRDF() throws RDFHandlerException {

         if(!started) {

             throw new IllegalStateException("Parsing never started.");

         }

         try {

             writer.flush();

         } catch (IOException ioe) {

             throw new RDFHandlerException("Error while flushing writer.", ioe);

         } finally {

             started = false;

             if(namespaceTable != null) {

                 namespaceTable.clear();

             }

         }

     }

     public void handleNamespace(String ns, String uri) throws RDFHandlerException {

         if(!started) {

             throw new IllegalStateException("Parsing never started.");

         }

         if(namespaceTable == null) {

             namespaceTable = new HashMap<String, String>();

         }

         namespaceTable.put(ns, NTriplesUtil.escapeString(uri) );

     }

     public void handleStatement(Statement statement) throws RDFHandlerException {

         if(!started) {

             throw new IllegalStateException("Cannot handle statement without start parsing first.");

         }

         try {

             printSubject(statement);

             printSpace();

             printPredicate(statement);

             printSpace();

             printObject(statement);

             printSpace();

             printGraph(statement);

             printCloseStatement();

         } catch (IOException ioe) {

             throw new RDFHandlerException("An error occurred while printing statement.", ioe);

         }

     }

     public void handleComment(String comment) throws RDFHandlerException {

         try {

             writer.write("# ");

             writer.write(comment);

             writer.append('\n');

         } catch (IOException ioe) {

             throw new RDFHandlerException("An error occurred while printing comment.", ioe);

         }

     }

     /**

      * Prints out a space.

      *

      * @throws IOException

      */

     private void printSpace() throws IOException {

         writer.append(' ');

     }

     /**

      * Prints out the close statement.

      * 

      * @throws IOException

      */

     private void printCloseStatement() throws IOException {

         writer.append(" .\n");

     }

     /**

      * Prints out a URI string, replacing the existing prefix if found.

      * 

      * @param uri the URI to print.

      * @throws IOException

      */

     private void printURI(URI uri) throws IOException {

         final String uriString = uri.stringValue();

         int splitIdx = 0;

         String namespace = null;

         if(namespaceTable != null) {

             splitIdx = uriString.indexOf(':');

             if (splitIdx > 0) {

                 String prefix = uriString.substring(0, splitIdx);

                 namespace = namespaceTable.get(prefix);

             }

         }

         if (namespace != null) {

             writer.append('<');

             writer.append(namespace);

             writer.append( NTriplesUtil.escapeString(uriString.substring(splitIdx)) );

             writer.append('>');

         } else {

             writer.append('<');

             writer.append( NTriplesUtil.escapeString(uriString) );

             writer.append('>');

         }

     }

     /**

      * Prints out the bnode.

      *

      * @param b bnode value.

      * @throws IOException

      */

     private void printBNode(BNode b) throws IOException {

         writer.append( NTriplesUtil.toNTriplesString(b) );

     }

     /**

      * Prints out the resource.

      *

      * @param r resource value.

      * @throws java.io.IOException

      */

     private void printResource(Resource r) throws IOException {

         if(r instanceof BNode) {

             printBNode((BNode) r);

         } else if(r instanceof URI) {

             printURI((URI) r);

         } else {

             throw new IllegalStateException();

         }

     }

     /**

      * Prints out a literal value.

      *

      * @param l literal value.

      * @throws java.io.IOException

      */

     private void printLiteral(Literal l) throws IOException {

         writer.append( NTriplesUtil.toNTriplesString(l) );

     }

     /**

      * Prints out the subject.

      * 

      * @param s

      * @throws IOException

      */

     private void printSubject(Statement s) throws IOException {

         printResource( s.getSubject() );

     }

     /**

      * Prints out the predicate.

      *

      * @param s

      * @throws IOException

      */

     private void printPredicate(Statement s) throws IOException {

         printURI( s.getPredicate() );

     }

     /**

      * Prints out the object, handling all the logic to manage

      * the literal data type / language attribute.

      *

      * @param s

      * @throws IOException

      */

     private void printObject(Statement s) throws IOException {

         Value v = s.getObject();

         if(v instanceof Resource) {

             printResource((Resource) v);

             return;

         }

         printLiteral( (Literal) v );

     }

     /**

      * Prints out the graph.

      *

      * @param s

      * @throws IOException

      */

     private void printGraph(Statement s) throws IOException {

         Resource graph = s.getContext();

         if(graph != null) {

             printResource( s.getContext() );

         }

     }

 }