jena-arq/src/main/java/org/apache/jena/riot/writer/WriterStreamRDFBase.java

/**
 * 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.jena.riot.writer;
import static org.apache.jena.riot.writer.WriterConst.rdfNS;
import java.io.BufferedWriter;
import java.io.OutputStream;
import java.io.Writer;

import org.apache.jena.atlas.io.IndentedWriter;
import org.apache.jena.graph.Node;
import org.apache.jena.graph.Triple;
import org.apache.jena.riot.RIOT;
import org.apache.jena.riot.out.NodeFormatterTTL;
import org.apache.jena.riot.out.NodeToLabel;
import org.apache.jena.riot.system.PrefixMap;
import org.apache.jena.riot.system.PrefixMapFactory;
import org.apache.jena.riot.system.RiotLib;
import org.apache.jena.riot.system.StreamRDF;
import org.apache.jena.sparql.core.Quad;
import org.apache.jena.sparql.util.Context;

/**
 * Core engine for output of triples / quads that is streaming. It covers Turtle and
 * TriG "{@link WriterStreamRDFFlat flat}" and "{@link WriterStreamRDFBlocks blocks}"
 * variants.
 * <p>
 * It handles prefixes and base and node formats which is controlled by a {@link NodeFormatterTTL}.
 * <p>
 * The output is valid TriG.<br/>
 * If fed only triples, the output is valid Turtle.
 * <p>
 * For N-Quads and N-triples use {@link WriterStreamRDFPlain}.
 */
public abstract class WriterStreamRDFBase implements StreamRDF
{
    // What did we do last?
    protected boolean activeTripleData  = false;
    protected boolean activeQuadData    = false;
    protected boolean lastWasDirective  = false;

    protected final PrefixMap pMap;
    protected String baseURI = null;
    protected final NodeToLabel nodeToLabel;

    protected NodeFormatterTTL fmt;
    protected final IndentedWriter out;
    protected final DirectiveStyle directiveStyle;
    // Allows for ability to write RDF without writing the base URI.
    protected final boolean printBase;
    // Is there an active prefix mapping for the RDF namespace.
    protected int countPrefixesForRDF = 0;

    protected WriterStreamRDFBase(OutputStream output, Context context) {
        this(new IndentedWriter(output), context);
    }

    protected WriterStreamRDFBase(Writer output, Context context) {
        this(wrap(output), context);
    }

    protected WriterStreamRDFBase(IndentedWriter output, Context context) {
        this(output,
             NodeToLabel.createScopeByDocument(),
             WriterLib.directiveStyle(context),
             context.isFalseOrUndef(RIOT.symTurtleOmitBase));
    }

    protected WriterStreamRDFBase(IndentedWriter output,
                                  NodeToLabel nodeToLabel,
                                  DirectiveStyle directiveStyle,
                                  boolean printBase) {
        // Stream writing does not take an external base URI from the API "write"
        // call. The base URI is output if StreamRDF.base() called, which means BASE
        // was in the data stream.
        this.out = output;
        this.baseURI = null;
        this.pMap = PrefixMapFactory.create();
        this.nodeToLabel = nodeToLabel;
        this.directiveStyle = directiveStyle;
        this.printBase = printBase;
        setFormatter();
    }

    // Set and reset the formatter. It needs resetting if BASE is encountered.
    private void setFormatter() {
        fmt = new NodeFormatterTTL(baseURI, pMap, nodeToLabel);
    }

    private static IndentedWriter wrap(Writer output) {
        if ( !(output instanceof BufferedWriter) )
            output = new BufferedWriter(output, 32 * 1024);
        return RiotLib.create(output);
    }

    private void reset$() {
        activeTripleData = false;
        activeQuadData = false;
        lastWasDirective = false;
    }

    @Override
    public final void start() {
        reset$();
        startData();
    }

    @Override
    public final void finish() {
        endData();
        out.flush();
    }

    @Override
    public final void triple(Triple triple) {
        print(triple);
        activeTripleData = true;
    }

    @Override
    public final void quad(Quad quad) {
        print(quad);
        activeQuadData = true;
    }

    @Override
    public final void base(String base) {
        baseURI = base;
        lastWasDirective = true;
        setFormatter();
        if ( printBase )
            RiotLib.writeBase(out, base, directiveStyle);
    }

    @Override
    public final void prefix(String prefix, String iri) {
        endData();
        prefixSetup(prefix, iri);
        lastWasDirective = true;
        if ( pMap.containsPrefix(prefix) ) {
            // Overwrite?
            // Update for PrefixMap.get
            String old = pMap.getMapping().get(prefix);
            if ( rdfNS.equals(old) ) {
                countPrefixesForRDF--;
            }
        }
        if ( rdfNS.equals(iri) ) {
            countPrefixesForRDF++;
        }

        pMap.add(prefix, iri);
        RiotLib.writePrefix(out, prefix, iri, directiveStyle);
    }

    protected void prefixSetup(String prefix, String iri) {}

    protected void outputNode(Node n) {
        fmt.format(out, n);
    }

    /**
     * Helper for formats that wish to print 'a' or 'rdf:type' based
     * on whether a prefix definition is in-scope.
     */
    protected void printProperty(Node p) {
        if ( countPrefixesForRDF <= 0 && WriterConst.RDF_type.equals(p) )
            out.print('a');
        else
            outputNode(p);
    }

    // Subclass contract

    protected abstract void startData();

    protected abstract void endData();

    protected abstract void print(Quad quad);

    protected abstract void print(Triple triple);

    protected abstract void reset();
}