#ifndef TG4HitGas_hxx_seen
#define TG4HitGas_hxx_seen

#include "IG4VHit.hxx"
#include <TVector3.h>

namespace COMET { 
    class IG4HitGas; 
}

/**
 * @brief Hit class used to save gas-detector hits into a root output file.
 * In one event, one HitGas is kept for each track entering a cell.
 *
 * If a track enters a cell more than once, more than one instance of
 * HitGas are created by the COMETGasSD, one for every entry.
 * 
 */
class COMET::IG4HitGas: public IG4VHit {
public:
    IG4HitGas();
    virtual ~IG4HitGas();

    /// @name Position at the point of closest approach
    /// For gaseous hits, the position is defined as the
    /// position of closest approach of a track onto the
    /// associated wire.
    /// @{
    double GetPosX() const;
    double GetPosY() const;
    double GetPosZ() const;
    double GetPosT() const;
    const TVector3& GetPosition() const;
    /// @}

    /// @name Momentum at the point of closest approach
    /// @{
    double GetMomX() const;
    double GetMomY() const;
    double GetMomZ() const;
    double GetMomentumMag() const;
    const TVector3& GetMomentum() const;
    /// @}

    /// @name Position, time and momentum when the track enters the cell
    /// @{
    const TVector3& GetFirstPosition() const;
    double GetFirstTime() const;
    const TVector3& GetFirstMomentum() const;
    /// @}

    /// @name Position, time and momentum when the track exits the cell
    /// @{
    const TVector3& GetLastPosition() const;
    double GetLastTime() const;
    const TVector3& GetLastMomentum() const;
    /// @}

    /// Energy deposit is defined as the energy deposited by a
    /// track by continuous processes, i.e. without the production
    /// of secondaries or delta rays.
    double GetEnergyDeposit() const { return fEnergyDeposit; }

    int GetPDGEncoding() const { return fPDGEncoding; }

    /// Distance of closest approach from the track to the wire
    double GetDOCA() const;
    /// Point of closest approach from the track to the wire
    const TVector3& GetPOCA() const;

    /// Point on the wire that was closest to the track
    const TVector3& GetPOCAOnWire() const;

    /// Total distance travelled by particle inside cell
    double GetLength() const;

    /// Print the hit information.
    virtual void ls(Option_t* = "") const;
    virtual void Print(Option_t* = "") const;

    /// Auxiliary point containing position, time and energy deposited
    /// information about the track which produced the hit. This additional
    /// info will be stored if the DetailedCDCSD is enabled.
    struct Auxiliary {
        TVector3 fPosition;
        double fTime;
        double fEnergyDeposit;
    };

    const std::vector<Auxiliary>& GetAuxiliaryPoints() const;

protected:

    /// @name Track position and momentum
    /// Triad of position, time and momentum for the entry point, exit point
    /// and point of closest approach of the track to the wire of the CDC cell.
    /// @{
    /// Point of closest approach of the track to the wire.
    TVector3 fPOCA;
    /// Point on the wire that was closest to the track
    TVector3 fPOCAOnWire;
    /// Time at the point of closest approach of the track to the wire.
    double fTime;
    /// Momentum at the point of closest approach of the track to the wire.
    TVector3 fMomentum;

    /// Position of the track as it enters (or is born inside) the cell.
    TVector3 fFirstPosition;
    /// Time as the track enters (or is born inside) the cell.
    double fFirstTime;
    /// Momentum of the track as it enters (or is born inside) the cell.
    TVector3 fFirstMomentum;

    /// Position of the track as it exits (or dies inside) the cell.
    TVector3 fLastPosition;
    /// Time as the track exits (or dies inside) the cell.
    double fLastTime;
    /// Momentum of the track as it exits (or dies inside) the cell.
    TVector3 fLastMomentum;
    /// @}

    /// Total distance travelled by particle inside cell.
    double fLength;
    /// Energy deposited by this track in the cell through continuous processes.
    /// This energy is lost to the medium and is the quantity of interest for
    /// reconstruction.
    double fEnergyDeposit;

    /// Particle ID
    int fPDGEncoding;

    /// Vector of auxiliary points containing additional
    /// position, time and energy deposit information about the track which
    /// produced the hit. This vector is filled by the DetailedCDCSD if enabled.
    std::vector<Auxiliary> fAuxiliaryPoints;

    ClassDef(IG4HitGas,2);
};

#endif