/**
 * 
 */
package uk.ac.vamsas.client.utils;

import java.io.IOException;
import java.io.Reader;

/**
 * @author JimP
 * Simple wrapper for reader to keep track of position in stream.
 * This is used in the document unmarshalling mechanism to compute
 * a simple hash based on the distance between the read blocks containing
 * the start and end tags of the XML.
 */
public class ChecksummedReader extends Reader {
  private Reader myReader=null;
  private long count=0;
  public ChecksummedReader(Reader myReader) {
    super();
    this.myReader = myReader;
    count=0;
  }

  /* (non-Javadoc)
   * @see java.io.Reader#close()
   */
  public void close() throws IOException {
    if (myReader!=null)
      myReader.close();
    else
      throw new IOException("Close called on un-inited ChecksummedReader");
  }

  /* (non-Javadoc)
   * @see java.io.Reader#read(char[], int, int)
   */
  public int read(char[] cbuf, int off, int len) throws IOException {
    int rlen = myReader.read(cbuf, off, len);
    if (rlen>0)
      count+=cbuf.hashCode();
    return rlen;
  }
  /**
   * Return current checksum of read bytes.
   * @return stream checksum
   */
  public long getChecksum() {
    return count;
  }
  /**
   * Return existing checksum value and reset
   * @return old count
   */
  public long getAndResetChecksum() {
    long cnt=count;
    count=0;
    return cnt;
  }
}