#ifndef AliRICHHelix_h
#define AliRICHHelix_h

#include <TObject.h>
#include <TVector3.h>
#include "AliRICHParam.h"
#include "AliRICHChamber.h"

class AliRICHHelix: public TObject
{
public:
  AliRICHHelix():TObject()                                                                                                          {;}
  AliRICHHelix(const TVector3 &x0,const TVector3 &p0,Int_t q=1,Double_t b=0.2):TObject(),fX0(x0),fP0(p0),fX(x0),fP(p0),
                                                                                         fLen(0),fQ(q),fBz(b)                       {;}
  virtual ~AliRICHHelix()                                                                                                           {;}        
           
  inline void     Propagate(Double_t len);                                          //propogate helix by length len along it
  inline Int_t    RichIntersect(AliRICHParam *pParam);                              //search intersection with any RICH chamber 
  inline Bool_t   Intersection(TVector3 planePnt,TVector3 planeNorm);               //intersection with plane given by point and normal vector
         Bool_t   Intersection(TVector3 pl)    {return Intersection(pl,pl.Unit());} // special plane given by point only
         TVector2 PosRad()                const{return fPosRad;}          //returns position of intersection with radiator (local system)
         TVector2 PosAnod()               const{return fPosAnod;}         //returns position of intersection with anod wires plane (local system)
         TVector2 PosPc()                 const{return fPosPc;}           //returns position of intersection with PC (local system)
         TVector3 Ploc()                  const{return fPloc;}            //returns momentum at the position of intersection with radiator   
         Double_t Length()                const{return fLen;}             //returns length of the track from initial point to RICH
         void     Print(Option_t *sOption)const; //virtual interface from TObject
protected:
  TVector3 fX0;            //helix position in parametrised point, cm    in MRS
  TVector3 fP0;            //helix momentum in parametrised point, GeV/c in MRS
  TVector3 fX;             //helix position in point of interest,  cm    in MRS
  TVector3 fP;             //helix momentum in point of interest,  GeV/c in MRS
  Double_t fLen;           //helix length in point of interest    
  Int_t    fQ;             //sign of track charge (value not provided by current ESD)  
  Double_t fBz;            //magnetic field along z value in Tesla under assumption of uniformity 
  TVector2 fPosRad;        //track intersection with radiator (local system)
  TVector2 fPosAnod;       //track intersection with anod wires plane (local system)
  TVector2 fPosPc;         //track intersection with PC (local system)
  TVector3 fPloc;          //momentum in local system
  ClassDef(AliRICHHelix,0) //General helix
};//class AliRICHHelix
//__________________________________________________________________________________________________
void AliRICHHelix::Propagate(Double_t len)
{
// Propogates the helix to the position of interest defined by helix length s  
// Assumes uniform magnetic field along z direction.  
  const Double_t c = 0.00299792458;//this value provides that coordinates are in cm momentum in GeV/c
  Double_t a = -c*fBz*fQ;
 
  Double_t rho = a/fP0.Mag();
  fX.SetX( fX0.X()+fP0.X()*TMath::Sin(rho*len)/a-fP0.Y()*(1-TMath::Cos(rho*len))/a  );
  fX.SetY( fX0.Y()+fP0.Y()*TMath::Sin(rho*len)/a+fP0.X()*(1-TMath::Cos(rho*len))/a  ); 
  fX.SetZ( fX0.Z()+fP0.Z()*len/fP0.Mag()                                            );
  fP.SetX( fP0.X()*TMath::Cos(rho*len)-fP0.Y()*TMath::Sin(rho*len)                  );
  fP.SetY( fP0.Y()*TMath::Cos(rho*len)+fP0.X()*TMath::Sin(rho*len)                  );
  fP.SetZ( fP0.Z()                                                                  );
  fLen=len;
}
//__________________________________________________________________________________________________
Bool_t AliRICHHelix::Intersection(TVector3 planePoint,TVector3 planeNorm)
{
// Finds point of intersection (if exists) of the helix to the plane given by point and normal vector.
// Returns kTrue if helix intersects the plane, kFALSE otherwise.
// Stores result in current helix fields fX and fP.   
  
  Double_t s=(planePoint-fX0)*planeNorm,dist=99999,distPrev=dist;//estimates initial distance to plane

  while(TMath::Abs(dist)>0.00001){
    Propagate(s);                        //calculates helix at the distance s from x0 ALONG the helix
    dist=(fX-planePoint)*planeNorm;      //distance between current helix position and plane
    if(TMath::Abs(dist) >= TMath::Abs(distPrev)) { return kFALSE;}
    distPrev=dist;
    s-=dist;
  }
  return kTRUE;
}
//__________________________________________________________________________________________________
Int_t AliRICHHelix::RichIntersect(AliRICHParam *pParam)
{
// Searchs for intersection of this helix with all RICH chambers, returns chamber number or 0 if no intersection
// On exit fPosRad contain position of intersection in Local System with radiator     
//         fPosPc  contains the same for photocathode  
  for(Int_t iChamberN=1;iChamberN<=kNchambers;iChamberN++){//chamber loop
    if(Intersection(pParam->C(iChamberN)->Rad())){//there is intersection with radiator plane
      fPosRad=pParam->C(iChamberN)->Mrs2Rad(fX);//position on radiator plane
      if(pParam->IsAccepted(fPosRad)){//intersection within radiator (even if in dead zone)
        
        if(Intersection(pParam->C(iChamberN)->Pc())){//there is intersection with photocathode
          fPosPc=pParam->C(iChamberN)->Mrs2Pc(fX);//position on photcathode plane
          if(pParam->IsAccepted(fPosPc)){//intersection within pc (even if in dead zone)
            
            Intersection(pParam->C(iChamberN)->Anod()); //search for anod intersection position
            fPosAnod=pParam->C(iChamberN)->Mrs2Anod(fX);
            
            fPloc=pParam->C(iChamberN)->PMrs2Loc(fP);//trasform p to local system
            return iChamberN;
          }//if inside PC
        }//if intersects PC
        
      }//if inside radiator
    }//if for radiator       
  }//chamber loop
  return 0;
}
//__________________________________________________________________________________________________    
#endif