/**
    * 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.commons.rdf.simple;
  
  import java.util.Optional;
  import java.util.stream.Stream;
  
  import org.apache.commons.rdf.api.BlankNode;
  import org.apache.commons.rdf.api.BlankNodeOrIRI;
  import org.apache.commons.rdf.api.Dataset;
  import org.apache.commons.rdf.api.Graph;
  import org.apache.commons.rdf.api.IRI;
  import org.apache.commons.rdf.api.Quad;
  import org.apache.commons.rdf.api.RDFTerm;
  import org.apache.commons.rdf.api.Triple;
  
  /**
   * A {@link Graph} view on a {@link Dataset}.
   * <p>
   * This view is backed by a {@link Dataset}, and can be constructed in two ways:
   * 
   * <dl>
   * <dt>{@link #DatasetGraphView(Dataset)}</dt>
   * <dd>Expose a <em>union graph</em> view of the Dataset, where all the
   * {@link Quad}s of the Dataset is represented as a {@link Triple}. Adding
   * triples will add them to the <em>default graph</em>, while removing triples
   * will remove from all graphs.</dd>
   * 
   * <dt>{@link #DatasetGraphView(Dataset, BlankNodeOrIRI)}</dt>
   * <dd>Expose a particular graph of the Dataset, either named by an {@link IRI},
   * a {@link BlankNode}, or <code>null</code> for the <em>default
   * graph</em>.</dd>
   * </dl>
   * <p>
   * Changes in the Graph are reflected directly in the Dataset and vice versa.
   * This class is thread-safe is the underlying Dataset is thread-safe.
   */
  public class DatasetGraphView implements Graph {
  
      private final boolean unionGraph;
      private final BlankNodeOrIRI namedGraph;
      private final Dataset dataset;
  
      public DatasetGraphView(final Dataset dataset) {
          this.dataset = dataset;
          this.namedGraph = null;
          this.unionGraph = true;
      }
  
      public DatasetGraphView(final Dataset dataset, final BlankNodeOrIRI namedGraph) {
          this.dataset = dataset;
          this.namedGraph = namedGraph;
          this.unionGraph = false;
      }
  
      @Override
      public void close() throws Exception {
          dataset.close();
  
      }
  
      @Override
      public void add(final Triple triple) {
          dataset.add(namedGraph, triple.getSubject(), triple.getPredicate(), triple.getObject());
      }
  
      @Override
      public void add(final BlankNodeOrIRI subject, final IRI predicate, final RDFTerm object) {
          dataset.add(namedGraph, subject, predicate, object);
      }
  
      @Override
      public boolean contains(final Triple triple) {
          return dataset.contains(unionOrNamedGraph(), triple.getSubject(), triple.getPredicate(), triple.getObject());
      }
  
      private Optional<BlankNodeOrIRI> unionOrNamedGraph() {
          if (unionGraph) {
              return null;
          }
          return Optional.ofNullable(namedGraph);
      }
  
      @Override
     public boolean contains(final BlankNodeOrIRI subject, final IRI predicate, final RDFTerm object) {
         return dataset.contains(unionOrNamedGraph(), subject, predicate, object);
     }
 
     @Override
     public void remove(final Triple triple) {
         dataset.remove(unionOrNamedGraph(), triple.getSubject(), triple.getPredicate(), triple.getObject());
     }
 
     @Override
     public void remove(final BlankNodeOrIRI subject, final IRI predicate, final RDFTerm object) {
         dataset.remove(unionOrNamedGraph(), subject, predicate, object);
     }
 
     @Override
     public void clear() {
         dataset.remove(unionOrNamedGraph(), null, null, null);
     }
 
     @Override
     public long size() {
         return stream().count();
     }
 
     @Override
     public Stream<? extends Triple> stream() {
         return stream(null, null, null);
     }
 
     @Override
     public Stream<? extends Triple> stream(final BlankNodeOrIRI subject, final IRI predicate, final RDFTerm object) {
         final Stream<Triple> stream = dataset.stream(unionOrNamedGraph(), subject, predicate, object).map(Quad::asTriple);
         if (unionGraph) {
             // remove duplicates
             return stream.distinct();
         }
         return stream;
     }
 
 }