/*
 *  ReadOnceStrategy.java
 *  Copyright (C) 2006 Amin Ahmad           
 *
 *  This program 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 2 of the License, or
 *  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, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
package org.ahmadsoft.postal;

import java.io.File;
import java.io.RandomAccessFile;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * A retrieval strategy that looks up from disk the first time
 * and subsequently reads from cache. The Read-Once strategy
 * is quite acceptable for day to day usage, its main problem
 * being that memory usage limits cannot be enforced.
 * 
 * @author Amin Ahmad
 */
public class ReadOnceStrategy implements PostalRetrievalStrategy {
	
	private RandomAccessFile dataFile;
	private RandomAccessFile indexFile;

	private static Map cache = Collections.synchronizedMap(new HashMap());

	/**
	 * @inheritDoc
	 */
	public void initialize(File _indexFile, File _dataFile) throws Exception {
		dataFile = new RandomAccessFile(_dataFile, "r");
		indexFile = new RandomAccessFile(_indexFile, "r");
	}

	private synchronized List diskLookup(int postalCode) {
		List result = new ArrayList();

		try {
			indexFile.seek((postalCode-1) * 8);
			indexFile.readInt();
			int loc = indexFile.readInt();
			
			dataFile.seek(loc);
			short type=0;
			while (0 != (type=dataFile.readShort())) {
				String state = dataFile.readUTF();
				String city = dataFile.readUTF();
				
				result.add(new PostalCodeEntry(postalCode,city,state,type));
			}
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
		
		return result;
	}

	/**
	 * @inheritDoc
	 */
	public List getCandidates(int postalCode) {
		if (postalCode < 1 || postalCode > 99999) {
			return new ArrayList();
		}
		
		List candidates = null;
		if (!cache.containsKey(new Integer(postalCode))) {
			candidates = Collections.unmodifiableList(diskLookup(postalCode));
			cache.put(new Integer(postalCode), candidates);
		} else {
			candidates = (List) cache.get(new Integer(postalCode));
		}
		
		return candidates;
	}

	/**
	 * @inheritDoc
	 */
	public void dispose() throws Exception {
		dataFile.close();
		indexFile.close();
		cache = null;
	}

}