package org.lcsim.recon.tracking.trffit;
   import java.util.List;
   import java.util.ArrayList;
   import java.util.Iterator;
   
   import org.lcsim.recon.tracking.trfutil.RandomGenerator;
   
   import org.lcsim.recon.tracking.trfbase.Surface;
   import org.lcsim.recon.tracking.trfbase.Cluster;
  import org.lcsim.recon.tracking.trfbase.Hit;
  import org.lcsim.recon.tracking.trfbase.Propagator;
  import org.lcsim.recon.tracking.trfbase.PropStat;
  import org.lcsim.recon.tracking.trfbase.TrackVector;
  import org.lcsim.recon.tracking.trfbase.HitGenerator;
  import org.lcsim.recon.tracking.trfbase.VTrack;
  import org.lcsim.recon.tracking.trfbase.ETrack;
  import org.lcsim.recon.tracking.trfbase.TrackError;
  
  /**
   * Generates an HTrack from a VTrack using its track error matrix
   * and a list of hit generators.  The VTrack is propagated to each
   * of the hit generator surfaces and used to generate a cluster which
   * is in turn used to generate a hit.  This is repeated until a hit is
   * succesfully produced at each surface.  The first hit from each
   * surface is assigned to the HTrack.
   *
   *@author Norman A. Graf
   *@version 1.0
   *
   */
  
  
  public class HTrackGenerator extends RandomGenerator
  {
      
      // The Hit generators.
      private List _hgens;
      
      // The starting surface.
      private Surface _srf;
      
      // The track error matrix.
      private TrackError _terr;
      
      // Propagator.
      private Propagator _prop;
      
      /**
       *Construct an instance from a list of HitGenerators, a Propagator,
       * a starting Surface and a track error.
       *
       * @param   hgens The list of HitGenerators.
       * @param   prop  The Propagator for propagating the track.
       * @param   srf   The Surface at which to start the track.
       * @param   terr  The starting TrackError.
       */
      public HTrackGenerator(  List hgens,   Propagator prop,
              Surface srf,   TrackError terr)
      {
          _hgens = hgens;
          _terr = new TrackError(terr);
          _prop = prop.newPropagator();
          _srf = srf.newPureSurface();
      }
      
      //
      
      /**
       *Return a new HTrack.
       * Return null for failure.
       *
       * @param   trv The starting VTrack.
       * @return  The HTrack containing hits.
       */
      public HTrack newTrack(  VTrack trv)
      {
          HTrack trh = null;
          VTrack newtrv = new VTrack(trv);
          // Create new list of hits.
          List track_hits = new ArrayList();
          // Loop over hit surfaces.
          
          for ( Iterator ihgen=_hgens.iterator(); ihgen.hasNext(); )
          {
              HitGenerator hgen = (HitGenerator) ihgen.next();
              // Propagate to the surface.
              PropStat pstat = _prop.vecProp(newtrv,hgen.surface());
              if ( ! pstat.success() ) break;
              // Generate a cluster.
              Cluster clu = hgen.newCluster(newtrv,0);
              if ( clu == null ) break;
              // Generate a hit.
              List hits = clu.predict( new ETrack(newtrv,_terr), clu );
              if ( hits.size() == 0 ) break;
              track_hits.add( hits.get(0) );
          }
          // If the number of assigned does not equal the number of hit
          // generators, all hits were not found.  Exit with error.
          if ( track_hits.size() != _hgens.size() ) return trh;
         // Propagate to the surface.
         VTrack starttrv = new VTrack(trv);
         PropStat pstat = _prop.vecProp(starttrv,_srf);
         if ( ! pstat.success() ) return trh;
         ETrack tre = new ETrack(starttrv,_terr);
         trh = new HTrack(tre);
         
         for ( Iterator ihit=track_hits.iterator(); ihit.hasNext(); )
             trh.addHit((Hit) ihit.next());
         return trh;
     }
     
     
     /**
      * Output stream
      *
      * @return String representation of the class
      */
     public String toString()
     {
         return getClass().getName();
     }
     
 }