/**
 * 
 */
package org.vamsas.client.simpleclient;

import java.io.File;

/**
 * @author jim
 * Watches a particular file for its creation, deletion, or modification.
 */
public class FileWatcher {
  private File subject=null;
  private long lastStat;
  boolean exists=false;
  /**
   * Make a watcher for a particular file.
   * If the file doesn't exist, the watcher will watch
   * for its creation (and indicate a change of state)
   * @param subject
   */
  private boolean check() {
    if (subject!=null) {
      if (!subject.exists()) {
        if (exists) {
        exists=false;
        return true;
      } 
      return false;
    } else {
      long newStat=subject.lastModified();
      if (exists && lastStat==newStat) {
        return false;
      }
      lastStat=newStat;
      exists=true;
      return true;
    }
  }
    return false;
  }
  
  
  public FileWatcher(File subject) {
    // TODO Auto-generated constructor stub
    this.subject = subject;
    check();
  }
  public boolean hasChanged() {
    return check();
  }
}