package uk.ac.vamsas.client.simpleclient;

import java.io.File;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * methods for setting and checking 
 * binary flags in a vamsas session directory.
 * all methods apart from the constructor will 
 * throw a fatal error if the flagFile is not
 * a valid java.io.File object.
 * LATER: extract SessionFlag interface for generalizing the vamsas session code 
 * @author jimp
 *
 */
public class SessionFlagFile {
  private static Log log = LogFactory.getLog(SessionFlagFile.class);
  protected File flagFile=null;
  private void checkFlagFile() {
    if (flagFile==null) {
      log.fatal("Implementation error - uninitialized SessionFlagFile", 
          new Error("Implementation error - uninitialized SessionFlagFile"));
    }
  }
  /**
   * will log a warning if exceptions occur during flag creation.
   * @return true if flag was set successfully
   */
  public boolean setFlag() {
    checkFlagFile();
    try {
      if (flagFile.createNewFile()) {
        log.debug("Set session flag "+flagFile);
      } else {
        log.debug("Session flag already set "+flagFile);
      }
      return true;
    }
    catch (Exception e) {
      log.warn("Couldn't set session flag "+flagFile, e);
    }
    return false;
  }
  /**
   * 
   * @return true if flag was cleared successfully
   */
  public boolean clearFlag() {
    checkFlagFile();
    if (flagFile.exists()) {
      log.debug("clearing session flag "+flagFile);
      if (!flagFile.delete()) {
        log.warn("failed to clear session flag "+flagFile);
        return false;
      }
    } else {
      log.debug("clearFlag called for already cleared flag "+flagFile);
    }
    return true;
  }
    /**
     * 
     * @return state of session flag
     */
  public boolean checkFlag() {
    checkFlagFile();
    if (flagFile.exists()) {
      if (log.isDebugEnabled())
        log.debug("Flag '"+flagFile+"' is set.");
      return true;
    }
    if (log.isDebugEnabled())
      log.debug("Flag '"+flagFile+"' is not set.");    
    return false;
  }
    /**
     * @param flagFile
     */
    public SessionFlagFile(File flagFile) {
      super();
      this.flagFile = flagFile;
    };
}