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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.util.diffsets;

import java.util.Collections;
import java.util.Iterator;
import java.util.Set;
import java.util.function.Predicate;

import org.neo4j.collection.trackable.HeapTrackingCollections;
import org.neo4j.internal.helpers.collection.Iterables;
import org.neo4j.internal.helpers.collection.Iterators;
import org.neo4j.memory.EmptyMemoryTracker;
import org.neo4j.memory.MemoryTracker;

import static java.lang.String.format;

public class MutableDiffSetsImpl implements MutableDiffSets
{
    private final MemoryTracker memoryTracker;
    private Set addedElements;
    private Set removedElements;
    private Predicate filter;

    private MutableDiffSetsImpl( Set addedElements, Set removedElements, MemoryTracker memoryTracker )
    {
        this.addedElements = addedElements;
        this.removedElements = removedElements;
        this.memoryTracker = memoryTracker;
    }

    public static  MutableDiffSets newMutableDiffSets( MemoryTracker memoryTracker )
    {
        return new MutableDiffSetsImpl<>( null, null, memoryTracker );
    }

    @Override
    public boolean add( T elem )
    {
        boolean wasRemoved = removed( false ).remove( elem );
        // Add to the addedElements only if it was not removed from the removedElements
        return wasRemoved || added( true ).add( elem );
    }

    @Override
    public boolean remove( T elem )
    {
        boolean removedFromAddedElements = added( false ).remove( elem );
        // Add to the removedElements only if it was not removed from the addedElements.
        return removedFromAddedElements || removed( true ).add( elem );
    }

    @Override
    public boolean unRemove( T item )
    {
        return removed( false ).remove( item );
    }

    @Override
    public String toString()
    {
        return format( "{+%s, -%s}", added( false ), removed( false ) );
    }

    @Override
    public boolean isAdded( T elem )
    {
        return added( false ).contains( elem );
    }

    @Override
    public boolean isRemoved( T elem )
    {
        return removed( false ).contains( elem );
    }

    @Override
    public Set getAdded()
    {
        return resultSet( addedElements );
    }

    @Override
    public Set getRemoved()
    {
        return resultSet( removedElements );
    }

    @Override
    public boolean isEmpty()
    {
        return added( false ).isEmpty() && removed( false ).isEmpty();
    }

    @SuppressWarnings( "unchecked" )
    @Override
    public Iterator apply( Iterator source )
    {
        Iterator result = (Iterator) source;
        if ( (removedElements != null && !removedElements.isEmpty()) ||
                (addedElements != null && !addedElements.isEmpty()) )
        {
            if ( filter == null )
            {
                filter = item -> !removed( false ).contains( item ) && !added( false ).contains( item );
            }
            result = Iterators.filter( filter, result );
        }
        if ( addedElements != null && !addedElements.isEmpty() )
        {
            result = Iterators.concat( result, addedElements.iterator() );
        }
        return result;
    }

    @Override
    public MutableDiffSetsImpl filterAdded( Predicate addedFilter )
    {
        return new MutableDiffSetsImpl<>(
                Iterables.asSet( Iterables.filter( addedFilter, added( false ) ) ),
                Iterables.asSet( removed( false ) ), EmptyMemoryTracker.INSTANCE ); // no tracker, hopefully a temporary copy
    }

    private Set added( boolean create )
    {
        if ( addedElements == null )
        {
            if ( !create )
            {
                return Collections.emptySet();
            }
            addedElements = HeapTrackingCollections.newSet( memoryTracker );
        }
        return addedElements;
    }

    private Set removed( boolean create )
    {
        if ( removedElements == null )
        {
            if ( !create )
            {
                return Collections.emptySet();
            }
            removedElements = HeapTrackingCollections.newSet( memoryTracker );
        }
        return removedElements;
    }

    private Set resultSet( Set coll )
    {
        return coll == null ? Collections.emptySet() : Collections.unmodifiableSet( coll );
    }
}