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// G4EqGravityField
//
// Class description:
//
// This is the right-hand side of equation of motion in a gravity field.

// Author: Peter Gumplinger (TRIUMF), 14.06.11 - Adopted from G4EqMagElectricField
//         Thanks to P.Fierlinger (PSI) and A.Capra and A.Fontana (INFN Pavia)
// -------------------------------------------------------------------
#ifndef G4EQGRAVITYFIELD_HH
#define G4EQGRAVITYFIELD_HH

#include "G4ChargeState.hh"
#include "G4EquationOfMotion.hh"
#include "G4UniformGravityField.hh"

/**
 * @brief G4EqGravityField implements the right-hand side of equation
 * of motion in a gravity field.
 */

class G4EqGravityField : public G4EquationOfMotion
{
  public:

    /**
     * Constructor for G4EqGravityField.
     *  @param[in] gField Pointer to the uniform gravity field.
     */
    G4EqGravityField(G4UniformGravityField* gField);

    /**
     * Default Destructor.
     */
    ~G4EqGravityField() override = default;

    /**
     * Sets the charge, momentum and mass of the current particle.
     * Used to set the equation's coefficients.
     *  @param[in] particleCharge Magnetic charge and moments in e+ units.
     *  @param[in] MomentumXc Particle momentum.
     *  @param[in] mass Particle mass.
     */
    void SetChargeMomentumMass(G4ChargeState particleCharge, // in e+ units
                               G4double MomentumXc,
                               G4double mass) override;

    /**
     * Calculates the value of the derivative, given the value of the
     * electromagnetic field.
     *  @param[in] y Coefficients array.
     *  @param[in] Field Field value.
     *  @param[out] dydx Derivatives array.
     */
    void EvaluateRhsGivenB( const G4double y[],
                            const G4double Field[],
                                  G4double dydx[] ) const override;

    /**
     * Returns the equation type-ID, "kEqGravity".
     */
    inline G4EquationType GetEquationType() const override { return kEqGravity; }

  private:

    G4double fMass = 0.0;
};

#endif