package inputSystem;

import java.io.*;

/**
 * @author Cherry
 * @date 2022年1月19日
 * @time 16:18
 * @brief 从磁盘文件中读入缓冲区
 */

public class DiskFileHandler implements FileHandler {

 private String filename;
 //接收所有输入的字符串,将所有语句连成一行字符串
 public StringBuilder input_buffer = new StringBuilder();
 //input_buffer当前指针位置
 private int curPos = 0;

 FileInputStream fs = null;
 BufferedReader br = null;

 DiskFileHandler(String filename) {
 this.filename = filename;
 }

 @Override
 public void Open() throws IOException {
 String line = "";
 br = new BufferedReader(new FileReader(filename));
 while ((line = br.readLine()) != null) {
 input_buffer.append(line);
 input_buffer.append('\n');
 }
 }

 @Override
 public int Close() {
 return 0;
 }

 /**
 * 从 input_buffer 中读数据到缓冲区
 * @param buf 缓冲区 Start_buf
 * @param begin 缓冲区写入的起始地址
 * @param len 缓冲区要写入字符的长度
 * @return 返回实际上写入的字符数量
 */
 @Override
 public int Read(byte[] buf, int begin, int len) {
 int readCnt = 0; //实际上读取的字符数量
 if (curPos >= input_buffer.length()) {
 return 0;
 }
 byte[] inputBuf = input_buffer.toString().getBytes();
 //当已经读取的字符串长度小于要求读取的长度 且 已经读取的长度小于输入流中剩余的长度
 while (readCnt < len && curPos + readCnt < input_buffer.length()) {
 buf[begin + readCnt] = inputBuf[curPos + readCnt];
 readCnt++;
 }
 curPos = curPos + readCnt;
 return readCnt;
 }
}