/*
 * 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.sparql.core;

import java.util.HashMap ;
import java.util.Map ;

import org.apache.jena.atlas.logging.Log ;
import org.apache.jena.graph.Graph ;
import org.apache.jena.graph.Node ;
import org.apache.jena.query.ReadWrite ;
import org.apache.jena.sparql.graph.GraphReadOnly ;

/** Read-only view of a DatasetGraph.  Assumes the dataset underneath isn't changing.
 */
public class DatasetGraphReadOnly extends DatasetGraphWrapper
{
    public DatasetGraphReadOnly(DatasetGraph dsg) { super(dsg) ; }
    
    private Graph dftGraph = null ;
    
    @Override
    public Graph getDefaultGraph()
    {
        if ( dftGraph == null )
            dftGraph = new GraphReadOnly(super.getDefaultGraph()) ;
        return dftGraph ;
    }

    @Override public void begin(ReadWrite mode)         {
        if ( mode == ReadWrite.WRITE )
            //throw new JenaTransactionException("read-only dataset : no write transactions") ;
            Log.warn(this,  "Write transaction on a read-only dataset") ;
        get().begin(mode) ; 
    }
    
    private Map<Node, Graph> namedGraphs = new HashMap<>() ;

    @Override
    public Graph getGraph(Node graphNode) {
        if ( namedGraphs.containsKey(graphNode) ) {
            if ( !super.containsGraph(graphNode) ) {
                namedGraphs.remove(graphNode) ;
                return null ;
            }
            return namedGraphs.get(graphNode) ;
        }

        Graph g = super.getGraph(graphNode) ;
        if ( g == null )
            return null ;
        g = new GraphReadOnly(g) ;
        namedGraphs.put(graphNode, g) ;
        return g ;
    }

    @Override
    public void setDefaultGraph(Graph g)
    { throw new UnsupportedOperationException("read-only dataset") ; }

    @Override
    public void addGraph(Node graphName, Graph graph)
    { throw new UnsupportedOperationException("read-only dataset") ; }

    @Override
    public void removeGraph(Node graphName)
    { throw new UnsupportedOperationException("read-only dataset") ; }

    /** For operations that write the DatasetGraph. */
    @Override
    protected DatasetGraph getW()
    { throw new UnsupportedOperationException("read-only dataset") ; }
    
    @Override
    public void close()
    { get().close() ; }
}

@@ -855,20 +855,16 @@
 va.util.
-Hash
 Map ;%0Aim
@@ -878,20 +878,44 @@
 va.util.
+concurrent.ConcurrentHash
 Map
- 
 ;%0A%0Aimpor
@@ -1273,16 +1273,106 @@
 apper%0A%7B%0A
+    // Add a read-only wrapper any graphs returned.%0A    // Block write access at getW().%0A%0A
     publ
@@ -2018,16 +2018,26 @@
 s = new 
+Concurrent
 HashMap%3C
@@ -2097,24 +2097,158 @@
 raphNode) %7B%0A
+        // Cache GraphReadOnly wrappers. This also makes == work (a nicety)%0A        // if the underlying DatasetGraph isn't changing.%0A
         if (
@@ -2693,405 +2693,8 @@
  %7D%0A%0A
-    @Override%0A    public void setDefaultGraph(Graph g)%0A    %7B throw new UnsupportedOperationException(%22read-only dataset%22) ; %7D%0A%0A    @Override%0A    public void addGraph(Node graphName, Graph graph)%0A    %7B throw new UnsupportedOperationException(%22read-only dataset%22) ; %7D%0A%0A    @Override%0A    public void removeGraph(Node graphName)%0A    %7B throw new UnsupportedOperationException(%22read-only dataset%22) ; %7D%0A%0A
     

Use only getW() for the denying write operations.