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SPL(Structured Process Language) A programming language specially for structured data computing.
There is a newer version: 20241126
package com.scudata.dm.cursor;

import java.util.ArrayList;

import com.scudata.dm.Sequence;
import com.scudata.dm.op.Operation;

/**
 * ???ڴ????й????α?
 * A.cursor() A.cursor(k:n)
 * @author RunQian
 *
 */
public class MemoryCursor extends ICursor {
	private Sequence data; // ????
	private int startSeq; // ??ʼλ?ã?????
	private int endSeq; // ????λ?ã?????
	private int next = 1; // ??һ????¼?????
	
	/**
	 * ?????ڴ??α?
	 * @param seq Դ????
	 */
	public MemoryCursor(Sequence seq) {
		if (seq != null) {
			if (seq.length() > 0) {
				data = seq;
				next = 1;
				startSeq = 1;
				endSeq = seq.length();
			} else {
				setDataStruct(seq.dataStruct());
			}
		}
	}

	/**
	 * ??ָ?????乹???ڴ??α?
	 * @param seq Դ????
	 * @param start ??ʼλ?ã?????
	 * @param end ????λ?ã???????
	 */
	public MemoryCursor(Sequence seq, int start, int end) {
		if (seq != null) {
			if (seq.length() > 0 && start < end) {
				int len = seq.length();
				if (start <= len) {
					data = seq;
					next = start;
					startSeq = start;
					
					if (end > len) {
						endSeq = len;
					} else {
						endSeq = end - 1;
					}
				}
			} else {
				setDataStruct(seq.dataStruct());
			}
		}
	}

	/**
	 * ??ȡָ???????????ݷ???
	 * @param n ????
	 * @return Sequence
	 */
	protected Sequence get(int n) {
		int rest = endSeq - next + 1;
		if (rest < 1 || n < 1) {
			return null;
		}
		
		Sequence data = this.data;
		if (rest >= n) {
			int end = next + n;
			Sequence table = new Sequence(n);
			for (int i = next; i < end; ++i) {
				table.add(data.getMem(i));
			}

			this.next = end;
			return table;
		} else {
			if (next == 1 && endSeq == data.length()) {
				next = endSeq + 1;
				//return data;
				
				// ??????ܻ??޸?data????????Ҫ?????¶???
				return new Sequence(data);
			}
			
			Sequence table = new Sequence(rest);
			for (int i = next, end = endSeq; i <= end; ++i) {
				table.add(data.getMem(i));
			}

			next = endSeq + 1;
			return table;
		}
	}

	/**
	 * ????ָ????????????
	 * @param n ????
	 * @return long ʵ????????????
	 */
	protected long skipOver(long n) {
		int rest = endSeq - next + 1;
		if (rest < 1 || n < 1) {
			return 0;
		}

		if (rest > n) {
			this.next += n;
			return n;
		} else {
			next = endSeq + 1;
			return rest;
		}
	}

	/**
	 * ?ر??α?
	 */
	public synchronized void close() {
		super.close();
		next = endSeq + 1;
	}
	
	/**
	 * ?????α?
	 * @return ?????Ƿ?ɹ???true???α???Դ?ͷ????ȡ????false???????Դ?ͷ????ȡ??
	 */
	public boolean reset() {
		close();
		
		next = startSeq;
		return true;
	}
	
	//public Sequence fuzzyFetch(int n) {
	//	return fetch();
	//}

	/**
	 * ????ʣ??ļ?¼???ر??α?
	 * @return Sequence
	 */
	public Sequence fetch() {
		int rest = endSeq - next + 1;
		if (rest < 1) {
			Sequence result = cache;
			close();
			return result;
		}
		
		Sequence result;
		if (next == 1 && endSeq == data.length()) {
			result = data;
		} else {
			result = new Sequence(rest);
			for (int i = next, end = endSeq; i <= end; ++i) {
				result.add(data.getMem(i));
			}
		}
				
		ArrayList opList = this.opList;
		if (opList != null) {
			result = doOperation(result, opList, ctx);
			Sequence tmp = finish(opList, ctx);
			if (tmp != null) {
				if (result == null) {
					result = tmp;
				} else {
					result = append(result, tmp);
				}
			}
		}
		
		if (cache != null) {
			result = append(cache, result);
		}
		
		close();
		return result;
	}
}