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//--------------------------------------------------------------------------
// File and Version Information:
//      $Id: Trajectory.h,v 1.3 2010/03/25 09:54:17 zhangy Exp $
// 
// Description:
//  Abstract base class to describe 3-dimensional trajectories in space. 
//  Defines an interface, and provides one data member -- the pathlength 
//  range for which a trejectory object is valid (infinite by default).  
//  In all cases, "flightlength" = 3-d pathlength along traj.
//
//      Software developed for the BaBar Detector at the SLAC B-Factory.
//
// Author(s): Dave Brown, Steve Schaffner
//
//------------------------------------------------------------------------
#ifndef TRAJECTORY_H
#define TRAJECTORY_H

//----------------
//-- header --
//----------------
#include <iosfwd>
#include "CLHEP/Matrix/Vector.h"
#include "CLHEP/Vector/ThreeVector.h"

#include "CLHEP/Geometry/Point3D.h"
#ifndef ENABLE_BACKWARDS_COMPATIBILITY
typedef HepGeom::Point3D<double> HepPoint3D;
#endif


using namespace CLHEP;


class Trajectory{

  public:
    //*******************
    // Constructors, etc.
    //*******************
    //       By default, the valid flight distance range is really big
    Trajectory(double lowlim, double hilim);
    virtual ~Trajectory();

    //**********
    //  Access 
    //**********
    // As a function of the flight distance
    virtual HepPoint3D   position( double )  const = 0;
    virtual Hep3Vector direction( double ) const = 0;
    virtual Hep3Vector delDirect( double ) const = 0; // 2nd deriv. WRT pathlen
    virtual double     curvature( double ) const = 0; // = |delDirect|
    // For more efficient calling:
    virtual void  getInfo(double fltLen, HepPoint3D& pos, Hep3Vector& direction) const = 0;
    virtual void  getInfo(double fltLen, HepPoint3D& pos, Hep3Vector& direction,
        Hep3Vector& delDirect) const = 0;

    // How far can you go using given approximation in direction (+/- 1) pathDir 
    //      before error > tolerance?  Only the sign of pathDir matters; magnitude
    //      must be 1.  Returned distance is >= 0.
    double distTo0thError(double s, double tol, int pathDir) const;
    virtual double distTo1stError(double s, double tol, int pathDir) const = 0;
    virtual double distTo2ndError(double s, double tol, int pathDir) const = 0;

    //  CopyOf function 
    virtual Trajectory* clone() const = 0;

    // Range of valid flight distances:
    bool validFlightDistance(double f,double tolerance=0.0) const;
    virtual void setFlightRange(double newrange[2]);
    double lowRange() const;
    double hiRange() const;
    double range() const;
    //  Print functions

    virtual void print(std::ostream& os) const;
    virtual void printAll(std::ostream& os) const;
    //**************
    // End interface
    //**************
  protected:
    Trajectory& operator=(const Trajectory&);
    double flightrange[2]; // validity range for the flight distance parameter
};

// inline functions

inline bool Trajectory::validFlightDistance(double f,double tol) const {
  return f >= flightrange[0]-tol && f <= flightrange[1]+tol; 
}
inline double Trajectory::lowRange() const {return flightrange[0];}
inline double Trajectory::hiRange() const {return flightrange[1];}
inline double Trajectory::range() const  { return hiRange()-lowRange(); }
#endif

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