package tarau.jinni;
import java.util.Enumeration;
import java.util.Vector;

/**
  An Infinite Source.
  If based on a finite Source, it moves to its the first element after reaching its last element.
  A SourceLoop returns 'no' if the original Source is empty. 
  In case the original Source is infinite, a SourceLoop will 
  return the same elements as the original Source. 
  (In particular, this happens if the original Source is also a Source loop).
*/
class SourceLoop extends Source {
  private Vector v;
  Source s;
  private int i;

  SourceLoop(Source s,Prog p) {
    super(p);
    this.s=s;
    this.v=new Vector();
    this.i=0;
  }
    
  private final Term getMemoized() {
    if(null==v || v.size()<=0) return null;
    Term T=(Term)v.elementAt(i);
    i= (i+1) % v.size();
    return T;
  }
  
  public Term getElement() {
    Term T=null;
    if(null!=s) { //s is alive
      T=s.getElement();
      if(null!=T)
        v.addElement(T);
      else {
        s=null;
      }
    }
    if(null==s) 
      T=getMemoized();
    return T;
  }

  public void stop() {
    v=null;
    s=null;
  }
}