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/*
 * 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.clerezza.utils;

import org.apache.clerezza.*;
import org.apache.clerezza.implementation.in_memory.SimpleGraph;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * Utility methods to manipulate Graphs
 *
 * @author reto
 */
public class GraphUtils {

    /**
     * Removes a subGraph from an Graph. The subGraph must match a subgraph of
     * Graph so that for every node in subGraph
     * each triple it appears in is also present in mGraph. Two
     * bnodes are considered equals if their contexts (as returned by
     * GraphNode.getNodeContext are equals.
     *
     * @param mGraph
     * @param subGraph
     * @throws org.apache.clerezza.rdf.utils.GraphUtils.NoSuchSubGraphException
     */
    public static void removeSubGraph(Graph mGraph, Graph subGraph)
            throws NoSuchSubGraphException {
        //point to triples of mGraph that are to be removed (if something is removed)
        final Set removingTriples = new HashSet();
        //we first check only the grounded triples and put the non-grounded in here:
        final Graph unGroundedTriples = new SimpleGraph();
        for (Triple triple : subGraph) {
            if (isGrounded(triple)) {
                if (!mGraph.contains(triple)) {
                    throw new NoSuchSubGraphException();
                }
                removingTriples.add(triple);
            } else {
                unGroundedTriples.add(triple);
            }
        }

        //we first remove the context of bnodes we find in object position
        OBJ_BNODE_LOOP:
        while (true) {
            final Triple triple = getTripleWithBlankNodeObject(unGroundedTriples);
            if (triple == null) {
                break;
            }
            final GraphNode objectGN = new GraphNode(triple.getObject(), unGroundedTriples);
            BlankNodeOrIRI subject = triple.getSubject();
            ImmutableGraph context = objectGN.getNodeContext();
            Iterator potentialIter = mGraph.filter(subject, triple.getPredicate(), null);
            while (potentialIter.hasNext()) {
                try {
                    final Triple potentialTriple = potentialIter.next();
                    BlankNode potentialMatch = (BlankNode) potentialTriple.getObject();
                    final ImmutableGraph potentialContext = new GraphNode(potentialMatch, mGraph).getNodeContext();
                    if (potentialContext.equals(context)) {
                        removingTriples.addAll(potentialContext);
                        unGroundedTriples.removeAll(context);
                        continue OBJ_BNODE_LOOP;
                    }
                } catch (ClassCastException e) {
                    continue;
                }
            }
            throw new NoSuchSubGraphException();
        }
        SUBJ_BNODE_LOOP:
        while (true) {
            final Triple triple = getTripleWithBlankNodeSubject(unGroundedTriples);
            if (triple == null) {
                break;
            }
            final GraphNode subjectGN = new GraphNode(triple.getSubject(), unGroundedTriples);
            RDFTerm object = triple.getObject();
            if (object instanceof BlankNode) {
                object = null;
            }
            ImmutableGraph context = subjectGN.getNodeContext();
            Iterator potentialIter = mGraph.filter(null, triple.getPredicate(), object);
            while (potentialIter.hasNext()) {
                try {
                    final Triple potentialTriple = potentialIter.next();
                    BlankNode potentialMatch = (BlankNode) potentialTriple.getSubject();
                    final ImmutableGraph potentialContext = new GraphNode(potentialMatch, mGraph).getNodeContext();
                    if (potentialContext.equals(context)) {
                        removingTriples.addAll(potentialContext);
                        unGroundedTriples.removeAll(context);
                        continue SUBJ_BNODE_LOOP;
                    }
                } catch (ClassCastException e) {
                    continue;
                }
            }
            throw new NoSuchSubGraphException();
        }
        mGraph.removeAll(removingTriples);
    }

    private static boolean isGrounded(Triple triple) {
        if (triple.getSubject() instanceof BlankNode) {
            return false;
        }
        if (triple.getObject() instanceof BlankNode) {
            return false;
        }
        return true;
    }

    /**
     * retrun triples with a bnode only at object position
     *
     * @param triples
     * @return
     */
    private static Triple getTripleWithBlankNodeObject(Graph triples) {
        for (Triple triple : triples) {
            if (triple.getSubject() instanceof BlankNode) {
                continue;
            }
            if (triple.getObject() instanceof BlankNode) {
                return triple;
            }
        }
        return null;
    }

    private static Triple getTripleWithBlankNodeSubject(Graph triples) {
        for (Triple triple : triples) {
            if (triple.getSubject() instanceof BlankNode) {
                return triple;
            }
        }
        return null;
    }

    public static class NoSuchSubGraphException extends Exception {
    }

}