#ifndef OPENMM_DRUDELANGEVININTEGRATOR_H_
#define OPENMM_DRUDELANGEVININTEGRATOR_H_

/* -------------------------------------------------------------------------- *
 *                                   OpenMM                                   *
 * -------------------------------------------------------------------------- *
 * This is part of the OpenMM molecular simulation toolkit.                   *
 * See https://openmm.org/development.                                        *
 *                                                                            *
 * Portions copyright (c) 2008-2022 Stanford University and the Authors.      *
 * Authors: Peter Eastman                                                     *
 * Contributors:                                                              *
 *                                                                            *
 * Permission is hereby granted, free of charge, to any person obtaining a    *
 * copy of this software and associated documentation files (the "Software"), *
 * to deal in the Software without restriction, including without limitation  *
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,   *
 * and/or sell copies of the Software, and to permit persons to whom the      *
 * Software is furnished to do so, subject to the following conditions:       *
 *                                                                            *
 * The above copyright notice and this permission notice shall be included in *
 * all copies or substantial portions of the Software.                        *
 *                                                                            *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,   *
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL    *
 * THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,    *
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 * -------------------------------------------------------------------------- */

#include "openmm/DrudeIntegrator.h"
#include "openmm/Kernel.h"
#include "openmm/internal/windowsExportDrude.h"

namespace OpenMM {

/**
 * This Integrator simulates systems that include Drude particles.  It applies two different Langevin
 * thermostats to different parts of the system.  The first is applied to ordinary particles (ones that
 * are not part of a Drude particle pair), as well as to the center of mass of each Drude particle pair.
 * A second thermostat, typically with a much lower temperature, is applied to the relative internal
 * displacement of each pair.
 *
 * This integrator can optionally set an upper limit on how far any Drude particle is ever allowed to
 * get from its parent particle.  This can sometimes help to improve stability.  The limit is enforced
 * with a hard wall constraint.  By default the limit is set to 0.02 nm.
 * 
 * This Integrator requires the System to include a DrudeForce, which it uses to identify the Drude
 * particles.
 */

class OPENMM_EXPORT_DRUDE DrudeLangevinIntegrator : public DrudeIntegrator {
public:
    /**
     * Create a DrudeLangevinIntegrator.
     *
     * @param temperature    the temperature of the main heat bath (in Kelvin)
     * @param frictionCoeff  the friction coefficient which couples the system to the main heat bath (in inverse picoseconds)
     * @param drudeTemperature    the temperature of the heat bath applied to internal coordinates of Drude particles (in Kelvin)
     * @param drudeFrictionCoeff  the friction coefficient which couples the system to the heat bath applied to internal coordinates of Drude particles (in inverse picoseconds)
     * @param stepSize       the step size with which to integrator the system (in picoseconds)
     */
    DrudeLangevinIntegrator(double temperature, double frictionCoeff, double drudeTemperature, double drudeFrictionCoeff, double stepSize);
    /**
     * Get the temperature of the main heat bath (in Kelvin).
     *
     * @return the temperature of the heat bath, measured in Kelvin
     */
    double getTemperature() const {
        return temperature;
    }
    /**
     * Set the temperature of the main heat bath (in Kelvin).
     *
     * @param temp    the temperature of the heat bath, measured in Kelvin
     */
    void setTemperature(double temp);
    /**
     * Get the friction coefficient which determines how strongly the system is coupled to
     * the main heat bath (in inverse ps).
     *
     * @return the friction coefficient, measured in 1/ps
     */
    double getFriction() const {
        return friction;
    }
    /**
     * Set the friction coefficient which determines how strongly the system is coupled to
     * the main heat bath (in inverse ps).
     *
     * @param coeff    the friction coefficient, measured in 1/ps
     */
    void setFriction(double coeff);
    /**
     * Get the friction coefficient which determines how strongly the internal coordinates of Drude particles
     * are coupled to the heat bath (in inverse ps).
     *
     * @return the friction coefficient, measured in 1/ps
     */
    double getDrudeFriction() const {
        return drudeFriction;
    }
    /**
     * Set the friction coefficient which determines how strongly the internal coordinates of Drude particles
     * are coupled to the heat bath (in inverse ps).
     *
     * @param coeff    the friction coefficient, measured in 1/ps
     */
    void setDrudeFriction(double coeff);
    /**
     * Advance a simulation through time by taking a series of time steps.
     *
     * @param steps   the number of time steps to take
     */
    void step(int steps) override;
    /**
     * Compute the instantaneous temperature of the System, measured in Kelvin.
     * This is calculated based on the kinetic energy of the ordinary particles (ones
     * not attached to a Drude particle), as well as the center of mass motion of the
     * Drude particle pairs.  It does not include the internal motion of the pairs.
     * On average, this should be approximately equal to the value returned by
     * getTemperature().
     */
    double computeSystemTemperature();
    /**
     * Compute the instantaneous temperature of the Drude system, measured in Kelvin.
     * This is calculated based on the kinetic energy of the internal motion of Drude pairs
     * and should remain close to the prescribed Drude temperature.
     */
    double computeDrudeTemperature();
protected:
    /**
     * This will be called by the Context when it is created.  It informs the Integrator
     * of what context it will be integrating, and gives it a chance to do any necessary initialization.
     * It will also get called again if the application calls reinitialize() on the Context.
     */
    void initialize(ContextImpl& context) override;
    /**
     * This will be called by the Context when it is destroyed to let the Integrator do any necessary
     * cleanup.  It will also get called again if the application calls reinitialize() on the Context.
     */
    void cleanup() override;
    /**
     * Get the names of all Kernels used by this Integrator.
     */
    std::vector<std::string> getKernelNames() override;
    /**
     * Compute the kinetic energy of the system at the current time.
     */
    double computeKineticEnergy() override;
private:
    double temperature, friction, drudeFriction;
    Kernel kernel;
};

} // namespace OpenMM

#endif /*OPENMM_DRUDELANGEVININTEGRATOR_H_*/
