/*
 * 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.graph.impl;

import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;

import org.apache.jena.graph.* ;
import org.apache.jena.mem.TrackingTripleIterator ;
import org.apache.jena.util.IteratorCollection ;
import org.apache.jena.util.iterator.ExtendedIterator ;

/**
    Simple implementation of GraphEventManager for GraphBase to use.
    The listeners are held as an [Array]List.
<p>
    This class also holds the utility method notifyingRemove, which wraps 
    iterators so that their .remove() operation notifies the specified graph of
    the removal.    
*/

public class SimpleEventManager implements GraphEventManager
{
    /* Implementation note:
     * 
     * Use of CopyOnWriteArray is unnecessarily inefficient, in that
     * a copy is only needed when the register or unregister
     * is concurrent with an iteration over the list.
     * Since this list is not public we can either make it private
     * or provide methods for iterating, so that we know when
     * it is necessary to copy the array of listeners and when it 
     * isn't.
     * This is a fair bit of code, and would need either a lock or
     * an atomic integer or something from the concurrent package.
     * Until and unless the high cost of registering and unregistering
     * is an issue I think the current code is elegant and clean.
     * In practice, most graphs have no more than 10 listeners
     * so the 10 registrations take 55 word copy operations - nothing
     * to get upset about.
     */
    
    /** @deprecated Use the graph passed in in notify operations. */
    @Deprecated
    protected Graph graph;
    protected List<GraphListener>  listeners;
    
    /** The graph object for the notification is passed
     *  @deprecated Use the no argument constructor.    
     */
    @Deprecated
    public SimpleEventManager( Graph graph )
    { 
        this();
        this.graph = graph;
    }
    
    public SimpleEventManager() {
        this.graph = null ;
        this.listeners = new CopyOnWriteArrayList<>();
    }
    
    @Override
    public GraphEventManager register( GraphListener listener ) { 
        listeners.add( listener );
        return this; 
        }

    @Override
    public GraphEventManager unregister(GraphListener listener) {
        listeners.remove(listener) ;
        return this ;
    }

    @Override
    public boolean listening() {
        return listeners.size() > 0 ;
    }

    @Override
    public void notifyAddTriple(Graph g, Triple t) {
        for ( GraphListener l : listeners )
            l.notifyAddTriple(g, t) ;
    }

    @Override
    public void notifyAddArray(Graph g, Triple[] ts) {
        for ( GraphListener l : listeners )
            l.notifyAddArray(g, ts) ;
    }

    @Override
    public void notifyAddList(Graph g, List<Triple> L) {
        for ( GraphListener l : listeners )
            l.notifyAddList(g, L) ;
    }

    @Override
    public void notifyAddIterator(Graph g, List<Triple> it) {
        for ( GraphListener l : listeners )
            l.notifyAddIterator(g, it.iterator()) ;
    }

    @Override
    public void notifyAddIterator(Graph g, Iterator<Triple> it) {
        notifyAddIterator(g, IteratorCollection.iteratorToList(it)) ;
    }

    @Override
    public void notifyAddGraph(Graph g, Graph added) {
        for ( GraphListener l : listeners )
            l.notifyAddGraph(g, added) ;
    }

    @Override
    public void notifyDeleteTriple(Graph g, Triple t) {
        for ( GraphListener l : listeners )
            l.notifyDeleteTriple(g, t) ;
    }

    @Override
    public void notifyDeleteArray(Graph g, Triple[] ts) {
        for ( GraphListener l : listeners )
            l.notifyDeleteArray(g, ts) ;
    }

    @Override
    public void notifyDeleteList(Graph g, List<Triple> L) {
        for ( GraphListener l : listeners )
            l.notifyDeleteList(g, L) ;
    }

    @Override
    public void notifyDeleteIterator(Graph g, List<Triple> L) {
        for ( GraphListener l : listeners )
            l.notifyDeleteIterator(g, L.iterator()) ;
    }

    @Override
    public void notifyDeleteIterator(Graph g, Iterator<Triple> it) {
        notifyDeleteIterator(g, IteratorCollection.iteratorToList(it)) ;
    }

    @Override
    public void notifyDeleteGraph(Graph g, Graph removed) {
        for ( GraphListener l : listeners )
            l.notifyDeleteGraph(g, removed) ;
    }

    @Override
    public void notifyEvent(Graph source, Object event) {
        for ( GraphListener l : listeners )
            l.notifyEvent(source, event) ;
    }

    /**
     * Answer an iterator which wraps <code>i</code> to ensure that if a
     * .remove() is executed on it, the graph <code>g</code> will be notified.
     */
    public static ExtendedIterator<Triple> notifyingRemove(final Graph g, Iterator<Triple> i) {
        return new TrackingTripleIterator(i) {
            protected final GraphEventManager gem = g.getEventManager() ;

            @Override
            public void remove() {
                super.remove() ;
                gem.notifyDeleteTriple(g, current) ;
            }
        } ;
    }

}