package tarau.jinni;

/**
 * A Fluent is a Jinni Object which has its own state, subject to changes over time.
 * 
 */
public class Fluent extends SystemObject {
  public Fluent(Prog p) {
    trailMe(p);
  }

  private boolean persistent=false;
  
  /**
   * Dynamically sets the persistence status of this Fluent.
   * A persistent Fluent will not have its stop
   * method outomatically called upon backtracking.
   * A typical example would be a file or socket handle
   * saved to the database to be reused after backtracking.
   */
  public void setPersistent(boolean persistent) {
    this.persistent=persistent;
  }
 
  /**
   *  returns true if this Fluent is persistent, false otherwise
   */
  public boolean getPersistent() {
    return this.persistent;
  }
   
  /**
   * Adds this Fluent to the parent Solver's trail, which
   * will eventually call the undo method of the Fluent on
   * backtracking.
   */
  protected void trailMe(Prog p) {
    if(null!=p) p.getTrail().push(this);
  }
  
  public void stop() {
  }

  /**
   * applies a non-persistent Fluent's stop() method on backtracking
   */
  protected void undo() {
    if(!persistent) stop();
  }
}