/**
 * Copyright (c) 2002-2011 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.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 Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.index.impl.lucene;

import org.apache.lucene.index.IndexCommit;
import org.apache.lucene.index.KeepOnlyLastCommitDeletionPolicy;
import org.apache.lucene.index.SnapshotDeletionPolicy;

class MultipleBackupDeletionPolicy extends SnapshotDeletionPolicy
{
    private IndexCommit snapshot;
    private int snapshotUsers;

    MultipleBackupDeletionPolicy()
    {
        super( new KeepOnlyLastCommitDeletionPolicy() );
    }

    @Override
    public synchronized IndexCommit snapshot()
    {
        if ( (snapshotUsers++) == 0 )
        {
            snapshot = super.snapshot();
        }
        return snapshot;
    }

    @Override
    public synchronized void release()
    {
        if ( (--snapshotUsers) > 0 ) return;
        super.release();
        snapshot = null;
        if ( snapshotUsers < 0 )
        {
            snapshotUsers = 0;
            throw new IllegalStateException( "Cannot release snapshot, no snapshot held" );
        }
    }
}