#ifndef TRACK_FITTER_KALMAN_H
#define TRACK_FITTER_KALMAN_H

#include <string>
#include <marlin/StringParameters.h>
#include <EVENT/LCRunHeader.h>
#include <EVENT/Track.h>
#include <IMPL/TrackImpl.h>
#include <EVENT/TrackerHit.h>
#include "TrackFitterBase.h"

class EXTPCKalDetector;

namespace gear {
    class TPCParameters;
    class PadRowLayout2D;
} //namespace gear

namespace marlintpc {
  /** Kalman filter track fitter
   *
   *  (to be filled)
   */

  class TrackFitterKalman : public TrackFitterBase {

  private:

    /** The constructor needs nothing for pad geometry information.
     *  Kalman filter implementation is independent of pad geometry.
     *
     *  TrackFitterKalman class is a singleton.
     */
    TrackFitterKalman();

  public:

    virtual ~TrackFitterKalman();

    /// Well defined interface to create a new instance of the track fitter
    static TrackFitterBase * getInstance(LCParameters const * parameters);

    virtual std::string getRevision();

    /// Information what fitter implementation this is.
    virtual unsigned char getFitterType() const;

#if 0
    /** Return the distance of the hit \c testHitNumber of the testTrack 
     *  to the point of closest approach on the referenceTrack wrt.\ the 
     *  hit.
     *  If no referenceTrack is given the
     *  distance to the testTrack is returned.
     * 
     *  Throws EVENT::DataNotAvailableException in case there is no hit number 
     *  "testHitNumber" on testHit.
     *
     *  Calls  calculateResidual(EVENT::TrackerHit *testHit, EVENT::Track *trackWithoutTestHit)
     *  in this implementation.
     */

    virtual DoubleVec calculateResiduals(EVENT::Track *testTrack,
					 unsigned int testHitNumber,
					 EVENT::Track *referenceTrack = NULL);

    /** Return the distance of the given hit to the test track 
     *  where this hit has been removed.
     *  The residual is calculated as the distance 
     *  along the pad row.
     *  
     */
    virtual DoubleVec calculateResiduals(EVENT::TrackerHit *testHit,
                                         EVENT::Track *trackWithoutTestHit);
#endif

    /** Perform the actual fitting. Uses TrackFitterSimpleChiSquare::fitTrack, using the residuals
     *  from this class, and then setting the correct fitter type.
     */
    virtual IMPL::TrackImpl *fitTrack(EVENT::Track const * seedTrack);


  private:

    /// Calculate the angular distance on a circle.
    /// The maximum can be \f$\pi\f$.
    double distanceOnCircle(double phi1, double phi2);

  private:

    /// A pointer to the GEAR TPC parameters
    gear::TPCParameters const * _TPCParameters;

    /// A pointer to the GEAR pad layout
    gear::PadRowLayout2D const * _padLayout;

    /// A pinter to the EXTPCKalDetector
    static EXTPCKalDetector * _kaldetPtr;

    /// The type of pad layout (PadRowLayout2D::CARTESIAN or PadRowLayout2D::POLAR)
    int _padLayoutType;

    /// The private variable pointintg to the instance you get using getInstance function.
    /// This class is not explicitly a singleton, but if you use getInstance it behaves like one
    /// to avoid overhead by allocating and deallocating memory.
    static TrackFitterKalman * _theKalmanFilterFitter;

    /// temporary data members
#if 1
    static bool fgIsUpperHit;
    static bool fgIsLowerHit;
    static bool fgIsMidHit;
#endif
  };

} // namespace marlintpc

#endif // TRACK_FITTER_KALMAN_H