import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 *
 * <pre>
 *  Copyright (C): 2012
 *
 *  Description:
 *   仿oracle的sequence的调用接口
 *
 *  Revision History:
 *  2012-10-23 		initial version.
 *
 * </pre>
 */
public class SequenceUtil
{
	private Map<String,ISequence> keyMap = new ConcurrentHashMap<String, ISequence>();

	private static SequenceUtil _instance = new SequenceUtil();

	private SequenceUtil(){};

	public static SequenceUtil getInstance(){
		return _instance;
	}

	/**
	 * getSequence
	 * @param sequenceName
	 * @return
	 */
	private ISequence getSequence(String sequenceName){
	//	return new SequenceImpl();
		return new AtomicLongSequence(sequenceName);
	}

	/**
	 * 重置序列,其实就是从数据最目前为至最大的序列
	 * @param sequenceName 序列名称
	 */
	public void resetSequence(String sequenceName){
		if(keyMap.containsKey(sequenceName)){
			ISequence sequence = keyMap.get(sequenceName);
			keyMap.remove(sequenceName);
			sequence = null;
		}
	}

	/**
	 * 取得下一个序列
	 * @param sequenceName 序列名称
	 * @return
	 */
	public long getNextVal(String sequenceName){
		ISequence sequence = null;

		if(keyMap.containsKey(sequenceName)){
			sequence = keyMap.get(sequenceName);
		}
		else{
			sequence = getSequence(sequenceName);
			keyMap.put(sequenceName, sequence);
		}

		return sequence.getNextVal();

	}


}