package  org.lcsim.recon.tracking.trfzp;
   
   // Generator for ClusZPlane2 objects.
   
   import org.lcsim.recon.tracking.trfutil.Assert;
   
   import org.lcsim.recon.tracking.trfbase.HitGenerator;
   import org.lcsim.recon.tracking.trfbase.VTrack;
   import org.lcsim.recon.tracking.trfbase.Surface;
  import org.lcsim.recon.tracking.trfbase.Cluster;
  import org.lcsim.recon.tracking.trfbase.HitError;
  /**
   * Generates two dimensional (x,y) hits on a z plane with a gaussian spread
   * in the measurements correlated according to
   * the covariance matrix.
   *
   *
   *@author Norman A. Graf
   *@version 1.0
   *
   */
  public class HitZPlane2Generator extends HitGenerator
  {
      
      // attributes
      private static final int IX = ClusZPlane2.IX;
      private static final int IY = ClusZPlane2.IY;
      
      // the surface
      private SurfZPlane _szp;
      
      // the error matrix for the measurement (x,y)
      private HitError _dhm;
      
      
      
      //
      
      /**
       *Construct an instance  from the z plane position and measurement 
       * position uncertainty.
       *
       * @param   zpos The z position of the plane.
       * @param   dhm  The hit error covariance matrix.
       */
      public HitZPlane2Generator(double zpos, HitError dhm)
      {
          super();
          _szp = new SurfZPlane(zpos);
          _dhm = dhm;
          Assert.assertTrue( _dhm.get(IX,IX) >= 0.0 && _dhm.get(IY,IY) >= 0.0);
          
          // check that determinant of _dhm is positive
          Assert.assertTrue( _dhm.get(IX,IX)*_dhm.get(IY,IY) - _dhm.get(IX,IY)*_dhm.get(IX,IY) >= 0.0);
          
          Assert.assertTrue( _dhm.size() == 2);
      }
      
      //
      
      /**
       *Construct an instance from the z plane position the measurement position uncertainty
       * and random number seed.
       *
       * @param   zpos The z position of the plane.
       * @param   dhm  The hit error covariance matrix.
       * @param   iseed The seed for the random number used by the HitGenerator.
       */
      public HitZPlane2Generator(double zpos, HitError dhm, long iseed)
      {
          super(iseed);
          _szp = new SurfZPlane(zpos);
          _dhm = dhm;
          Assert.assertTrue( _dhm.get(IX,IX) >= 0.0 && _dhm.get(IY,IY) >= 0.0);
          
          // check that determinant of _dhm is positive
          Assert.assertTrue( _dhm.get(IX,IX)*_dhm.get(IY,IY) - _dhm.get(IX,IY)*_dhm.get(IX,IY) >= 0.0);
          
          Assert.assertTrue( _dhm.size() == 2);  }
      
      //
      
     /**
       *Construct an instance replicating the HitZPlane2Generator ( copy constructor ).
       *
       * @param  gen The HitZPlane2Generator to replicate.
       */
      public HitZPlane2Generator( HitZPlane2Generator gen)
      {
          super(gen);
          _szp = new SurfZPlane(gen._szp);
          _dhm = (gen._dhm);
          Assert.assertTrue( _dhm.get(IX,IX) >= 0.0 && _dhm.get(IY,IY) >= 0.0 );
          
          // check that determinant of _dhm is positive
          Assert.assertTrue( _dhm.get(IX,IX)*_dhm.get(IY,IY) - _dhm.get(IX,IY)*_dhm.get(IX,IY) >= 0.0);
          
          Assert.assertTrue( _dhm.size() == 2 );
      }
     
     //
     
     /**
      *Return the surface associated with this HitZPlane2Generator.
      *
      * @return The surface associated with this HitZPlane2Generator.
      */
     public  Surface surface()
     { return _szp; }
     
     //
     
     /**
      *Generate a new cluster.
      * Return null for failure.
      *
      * @param   trv The VTrack for which to generate a cluster at this surface.
      * @return   The cluster for this track at this surface, null for failure.
      */
     public Cluster newCluster( VTrack trv )
     {
         return newCluster(trv, 0);
     }
     
     /**
      *Generate a new cluster with the specified Monte Carlo track ID.
      * Return null for failure.
      *
     * @param   trv The VTrack for which to generate a cluster at this surface.
      * @param   mcid The MC ID to associate with this cluster.
      * @return   The cluster for this track at this surface, null for failure.
      */
     public Cluster newCluster( VTrack trv, int mcid)
     {
         // Check track has been propagated to the surface.
         Assert.assertTrue( _szp.pureEqual( trv.surface() ) );
         if ( ! _szp.pureEqual( trv.surface() ) ) return null;
         
         // calculate axy.
         double x_track = trv.vector().get(SurfZPlane.IX);
         double y_track = trv.vector().get(SurfZPlane.IY);
         double a1  = _dhm.get(IX,IX);
         double a2  = _dhm.get(IY,IY);
         double a12 = _dhm.get(IX,IY);
         double phi;
         if(a12 == 0.)
         {
             phi = 0.;
         }
         else
         {
             if(a1 == a2 )
             {
                 phi = Math.PI/4.;
             }
             else
             {
                 phi = 0.5*Math.atan(2*a12/(a1-a2));
             }
         }
         double cphi= Math.cos(phi);
         double sphi= Math.sin(phi);
         double xx = cphi*cphi*a1 + sphi*sphi*a2 + 2*cphi*sphi*a12;
         double yy = cphi*cphi*a2 + sphi*sphi*a1 - 2*cphi*sphi*a12;
         
         // simple check. To be removed later
         
         Assert.assertTrue( Math.abs(cphi*cphi*a12 - sphi*sphi*a12 + cphi*sphi*(a2-a1)) < 1.e-10);
         Assert.assertTrue( Math.abs(xx*yy - (a1*a2 - a12*a12)) < 1.e-10 );
         
         // Very important test
         
         Assert.assertTrue( xx > 0.);
         Assert.assertTrue( yy > 0.);
         
         double dxx = gauss()/Math.sqrt(xx);
         double dyy = gauss()/Math.sqrt(yy);
         double b1 = cphi*dxx - sphi*dyy;
         double b2 = cphi*dyy + sphi*dxx;
         
         double ax  = x_track + (a1*b1+a12*b2);
         double ay  = y_track + (a2*b2+a12*b1);
         
         // construct cluster
         double zpos = _szp.parameter(SurfZPlane.ZPOS);
         return new ClusZPlane2(zpos,ax,ay,_dhm.get(IX,IX), _dhm.get(IY,IY), _dhm.get(IX,IY), mcid );
     }
     
     
     /**
      *output stream
      *
      * @return A String representation of this instance.
      */
     public String toString()
     {
         return  "Surface: " + _szp
         + "\n Measurement error (dhm): " + _dhm ;
     }
 }