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SPL(Structured Process Language) A programming language specially for structured data computing.

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package com.scudata.dm.cursor;

import com.scudata.dm.Context;
import com.scudata.dm.Sequence;
import com.scudata.expression.Expression;

/**
 * ???????α꣬???α????ݽ????????飬Ȼ?????α귽ʽ????
 * ???ڹ?ϣ??ʵ???????麯??cs.groupx()?Ķ??η??飬???????ѷ????ֶι?ϣֵ??ͬ????д??ͬһ????ʱ?ļ???
 * Ȼ??ÿ????ʱ?ļ?????һ?????α꣬Ҫȡ???α?????ʱ?????ж?????????
 * @author RunQian
 *
 */
public class GroupxCursor extends ICursor {
	private ICursor src; // ?α?
	private Expression[] exps; // ???????ʽ
	private String []names; // ?????ֶ???
	private Expression[] calcExps; // ???ܱ???ʽ
	private String []calcNames; // ?????ֶ???
	private String opt; // ѡ??
	private int capacity; // ?ڴ??б??????????????
	
	private ICursor result; // ??????α?

	/**
	 * ???????????α?
	 * @param cursor Դ?????α?
	 * @param exps ???????ʽ????
	 * @param names	?????ֶ???????
	 * @param calcExps ???ܱ???ʽ	????
	 * @param calcNames	?????ֶ???????
	 * @param opt ѡ??
	 * @param ctx ??????????
	 * @param capacity	?ڴ??б??????????????
	 */
	public GroupxCursor(ICursor cursor, Expression[] exps, String []names, 
			Expression[] calcExps, String []calcNames, String opt, Context ctx, int capacity) {
		this.src = cursor;
		this.exps = exps;
		this.names = names;
		this.calcExps = calcExps;
		this.calcNames = calcNames;
		this.opt = opt;
		this.ctx = ctx;
		this.capacity = capacity;
	}
	
	// ???м???ʱ??Ҫ?ı???????
	// ?̳???????õ??˱???ʽ????Ҫ?????????????½???????ʽ
	public void resetContext(Context ctx) {
		if (this.ctx != ctx) {
			src.resetContext(ctx);
			super.resetContext(ctx);
		}
	}

	/**
	 * ??ȡָ???????????ݷ???
	 * @param n ????
	 * @return Sequence
	 */
	protected Sequence get(int n) {
		if (result == null) {
			if (src == null) {
				return null;
			}
			
			result = src.groupx(exps, names, calcExps, calcNames, opt, ctx, capacity);
		}
		
		return result.fetch(n);
	}

	/**
	 * ????ָ????????????
	 * @param n ????
	 * @return long ʵ????????????
	 */
	protected long skipOver(long n) {
		if (result == null) {
			if (src == null) {
				return 0;
			}
			
			result = src.groupx(exps, names, calcExps, calcNames, opt, ctx, capacity);
		}
		
		return result.skipOver(n);
	}

	/**
	 * ?ر??α?
	 */
	public synchronized void close() {
		super.close();
		if (src != null) {
			src.close();
			src = null;
			
			if (result != null) {
				result.close();
				result = null;
			}
		}
	}
}