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Java 8 RDF support for the Inrupt Java Client Libraries.
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/*
 * Copyright Inrupt Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
 * Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
package com.inrupt.client.rdf.legacy;

import com.inrupt.client.spi.RdfService;
import com.inrupt.commons.rdf4j.RDF4J;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.stream.Stream;

import org.apache.commons.rdf.api.Dataset;
import org.apache.commons.rdf.api.Graph;
import org.apache.commons.rdf.api.RDFSyntax;
import org.eclipse.rdf4j.model.Model;
import org.eclipse.rdf4j.model.Statement;
import org.eclipse.rdf4j.repository.Repository;
import org.eclipse.rdf4j.repository.RepositoryConnection;
import org.eclipse.rdf4j.repository.sail.SailRepository;
import org.eclipse.rdf4j.rio.RDFFormat;
import org.eclipse.rdf4j.rio.RDFWriter;
import org.eclipse.rdf4j.rio.Rio;
import org.eclipse.rdf4j.sail.memory.MemoryStore;

/**
 * An {@link RdfService} that uses a Java 8-compatible version of the RDF4J library.
 */
public class RDFLegacyService implements RdfService {

    private static final Map SYNTAX_TO_FORMAT = buildSyntaxMapping();
    private static final RDF4J rdf = new RDF4J();

    @Override
    public void fromDataset(final Dataset dataset, final RDFSyntax syntax, final OutputStream output)
            throws IOException {
        final RDFFormat format = Objects.requireNonNull(SYNTAX_TO_FORMAT.get(syntax));
        final RDFWriter writer = Rio.createWriter(format, output);
        try {
            writer.startRDF();
            try (final Stream statements = dataset.stream().map(rdf::asStatement)) {
                statements.sequential().forEach(writer::handleStatement);
            }
            writer.endRDF();
        } catch (final org.eclipse.rdf4j.RDF4JException ex) {
            throw new IOException("Error serializing dataset", ex);
        }
    }

    @Override
    public void fromGraph(final Graph graph, final RDFSyntax syntax, final OutputStream output) throws IOException {
        final RDFFormat format = Objects.requireNonNull(SYNTAX_TO_FORMAT.get(syntax));
        final RDFWriter writer = Rio.createWriter(format, output);
        try {
            writer.startRDF();
            try (final Stream statements = graph.stream().map(rdf::asStatement)) {
                statements.sequential().forEach(writer::handleStatement);
            }
            writer.endRDF();
        } catch (final org.eclipse.rdf4j.RDF4JException ex) {
            throw new IOException("Error serializing graph", ex);
        }
    }

    @Override
    public Dataset toDataset(final RDFSyntax syntax, final InputStream input, final String baseUri) throws IOException {
        final RDFFormat format = Objects.requireNonNull(SYNTAX_TO_FORMAT.get(syntax));
        final Repository repository = new SailRepository(new MemoryStore());
        try {
            try (final RepositoryConnection conn = repository.getConnection()) {
                conn.add(input, baseUri, format);
            }
            return rdf.asDataset(repository);
        } catch (final org.eclipse.rdf4j.RDF4JException ex) {
            throw new IOException("Error parsing dataset", ex);
        }
    }

    @Override
    public Graph toGraph(final RDFSyntax syntax, final InputStream input, final String baseUri) throws IOException {
        final RDFFormat format = Objects.requireNonNull(SYNTAX_TO_FORMAT.get(syntax));

        try {
            final Model model = Rio.parse(input, baseUri, format);
            return rdf.asGraph(model);
        } catch (final org.eclipse.rdf4j.RDF4JException ex) {
            throw new IOException("Error parsing graph", ex);
        }
    }

    static Map buildSyntaxMapping() {
        final Map mapping = new HashMap<>();
        mapping.put(RDFSyntax.TURTLE, RDFFormat.TURTLE);
        mapping.put(RDFSyntax.TRIG, RDFFormat.TRIG);
        mapping.put(RDFSyntax.JSONLD, RDFFormat.JSONLD);
        mapping.put(RDFSyntax.NTRIPLES, RDFFormat.NTRIPLES);
        mapping.put(RDFSyntax.NQUADS, RDFFormat.NQUADS);
        return Collections.unmodifiableMap(mapping);
    }
}