/**************************************************************************
 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
 *                                                                        *
 * Author: The ALICE Off-line Project.                                    *
 * Contributors are mentioned in the code where appropriate.              *
 *                                                                        *
 * Permission to use, copy, modify and distribute this software and its   *
 * documentation strictly for non-commercial purposes is hereby granted   *
 * without fee, provided that the above copyright notice appears in all   *
 * copies and that both the copyright notice and this permission notice   *
 * appear in the supporting documentation. The authors make no claims     *
 * about the suitability of this software for any purpose. It is          *
 * provided "as is" without express or implied warranty.                  *
 **************************************************************************/

//-------------------------------------------------------------------------
//               Implementation of the V0 vertex class
//
//     Origin: Iouri Belikov, IReS, Strasbourg, Jouri.Belikov@cern.ch
//-------------------------------------------------------------------------
#include <TMath.h>

#include "AliV0vertex.h"
#include "AliITStrackV2.h"

ClassImp(AliV0vertex)

AliV0vertex::AliV0vertex(const AliITStrackV2 &n, const AliITStrackV2 &p) {
  //--------------------------------------------------------------------
  // Main constructor
  //--------------------------------------------------------------------
  for (Int_t i=0; i<6; i++) {
    fPosCov[i]= 0.;
    fNmomCov[i] = 0.;
    fPmomCov[i] = 0.;
  }
  fPdgCode=kK0Short;
  fNidx=n.GetLabel(); fPidx=p.GetLabel(); //indices in the array of ESD tracks

  //Trivial estimation of the vertex parameters
  Double_t pt, phi, x, par[5];
  Double_t alpha, cs, sn;

  n.GetExternalParameters(x,par); alpha=n.GetAlpha();
  pt=1./TMath::Abs(par[4]);
  phi=TMath::ASin(par[2]) + alpha;  
  Double_t px1=pt*TMath::Cos(phi), py1=pt*TMath::Sin(phi), pz1=pt*par[3];
  cs=TMath::Cos(alpha); sn=TMath::Sin(alpha);
  Double_t x1=x*cs - par[0]*sn;
  Double_t y1=x*sn + par[0]*cs;
  Double_t z1=par[1];
  Double_t sx1=sn*sn*n.GetSigmaY2(), sy1=cs*cs*n.GetSigmaY2(); 

  p.GetExternalParameters(x,par); alpha=p.GetAlpha();
  pt=1./TMath::Abs(par[4]);
  phi=TMath::ASin(par[2]) + alpha;  
  Double_t px2=pt*TMath::Cos(phi), py2=pt*TMath::Sin(phi), pz2=pt*par[3];
  cs=TMath::Cos(alpha); sn=TMath::Sin(alpha);
  Double_t x2=x*cs - par[0]*sn;
  Double_t y2=x*sn + par[0]*cs;
  Double_t z2=par[1];
  Double_t sx2=sn*sn*p.GetSigmaY2(), sy2=cs*cs*p.GetSigmaY2(); 
    
  Double_t sz1=n.GetSigmaZ2(), sz2=p.GetSigmaZ2();
  Double_t wx1=sx2/(sx1+sx2), wx2=1.- wx1;
  Double_t wy1=sy2/(sy1+sy2), wy2=1.- wy1;
  Double_t wz1=sz2/(sz1+sz2), wz2=1.- wz1;
  fPos[0]=wx1*x1 + wx2*x2; fPos[1]=wy1*y1 + wy2*y2; fPos[2]=wz1*z1 + wz2*z2;

  //fPos[0]=0.5*(x1+x2); fPos[1]=0.5*(y1+y2); fPos[2]=0.5*(z1+z2);
  fNmom[0]=px1; fNmom[1]=py1; fNmom[2]=pz1; 
  fPmom[0]=px2; fPmom[1]=py2; fPmom[2]=pz2;

  Double_t e1=TMath::Sqrt(0.13957*0.13957 + px1*px1 + py1*py1 + pz1*pz1);
  Double_t e2=TMath::Sqrt(0.13957*0.13957 + px2*px2 + py2*py2 + pz2*pz2);
  fEffMass=TMath::Sqrt((e1+e2)*(e1+e2)-
    (px1+px2)*(px1+px2)-(py1+py2)*(py1+py2)-(pz1+pz2)*(pz1+pz2));

  fChi2=7.;   
}