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/*! \libinternal \file
 * \brief
 * Declares gmx::IForceProvider and ForceProviders.
 *
 * See \ref page_mdmodules for an overview of this and associated interfaces.
 *
 * \author Teemu Murtola <teemu.murtola@gmail.com>
 * \author Carsten Kutzner <ckutzne@gwdg.de>
 * \inlibraryapi
 * \ingroup module_mdtypes
 */
#ifndef GMX_MDTYPES_IFORCEPROVIDER_H
#define GMX_MDTYPES_IFORCEPROVIDER_H

#include <memory>

#include "gromacs/math/vec.h"
#include "gromacs/utility/arrayref.h"
#include "gromacs/utility/gmxassert.h"

struct gmx_enerdata_t;
struct t_commrec;
struct t_forcerec;

namespace gmx
{

template<typename T>
class ArrayRef;
class ForceWithVirial;


/*! \libinternal \brief
 * Helper struct that bundles data for passing it over to the force providers
 *
 * This is a short-lived container that bundles up all necessary input data for the
 * force providers. Its only purpose is to allow calling forceProviders->calculateForces()
 * with just two arguments, one being the container for the input data,
 * the other the container for the output data.
 *
 * Both ForceProviderInput as well as ForceProviderOutput only package existing
 * data structs together for handing it over to calculateForces(). Apart from the
 * POD entries they own nothing.
 */
class ForceProviderInput
{
public:
    /*! \brief Constructor assembles all necessary force provider input data
     *
     * \param[in]  x        Atomic positions.
     * \param[in]  homenr   Number of atoms on the domain.
     * \param[in]  chargeA  Atomic charges for atoms on the domain.
     * \param[in]  massT    Atomic masses for atoms on the domain.
     * \param[in]  time     The current time in the simulation.
     * \param[in]  step     The current step in the simulation
     * \param[in]  box      The simulation box.
     * \param[in]  cr       Communication record structure.
     */
    ForceProviderInput(ArrayRef<const RVec> x,
                       int                  homenr,
                       ArrayRef<const real> chargeA,
                       ArrayRef<const real> massT,
                       double               time,
                       int64_t              step,
                       const matrix         box,
                       const t_commrec&     cr) :
        x_(x), homenr_(homenr), chargeA_(chargeA), massT_(massT), t_(time), step_(step), cr_(cr)
    {
        copy_mat(box, box_);
    }

    ArrayRef<const RVec> x_; //!< The atomic positions
    int                  homenr_;
    ArrayRef<const real> chargeA_;
    ArrayRef<const real> massT_;
    double               t_;    //!< The current time in the simulation
    int64_t              step_; //!< The current step in the simulation
    matrix               box_ = { { 0, 0, 0 }, { 0, 0, 0 }, { 0, 0, 0 } }; //!< The simulation box
    const t_commrec&     cr_; //!< Communication record structure
};

/*! \brief Take pointer, check if valid, return reference
 */
template<class T>
T& makeRefFromPointer(T* ptr)
{
    GMX_ASSERT(ptr != nullptr, "got null pointer");
    return *ptr;
}

/*! \libinternal \brief
 * Helper struct bundling the output data of a force provider
 *
 * Same as for the ForceProviderInput class, but these variables can be written as well.
 */
class ForceProviderOutput
{
public:
    /*! \brief Constructor assembles all necessary force provider output data
     *
     * \param[in,out]  forceWithVirial  Container for force and virial
     * \param[in,out]  enerd            Structure containing energy data
     */
    ForceProviderOutput(ForceWithVirial* forceWithVirial, gmx_enerdata_t* enerd) :
        forceWithVirial_(makeRefFromPointer(forceWithVirial)), enerd_(makeRefFromPointer(enerd))
    {
    }

    ForceWithVirial& forceWithVirial_; //!< Container for force and virial
    gmx_enerdata_t&  enerd_;           //!< Structure containing energy data
};


/*! \libinternal \brief
 * Interface for a component that provides forces during MD.
 *
 * Modules implementing IMDModule generally implement this internally, and use
 * IMDModule::initForceProviders() to register their implementation in
 * ForceProviders.
 *
 * The interface most likely requires additional generalization for use in
 * other modules than the current electric field implementation.
 *
 * The forces that are produced by force providers are not taken into account
 * in the calculation of the virial. When applicable, the provider should
 * compute its own virial contribution.
 *
 * \inlibraryapi
 * \ingroup module_mdtypes
 */
class IForceProvider
{
public:
    /*! \brief
     * Computes forces.
     *
     * \param[in]    forceProviderInput    struct that collects input data for the force providers
     * \param[in,out] forceProviderOutput   struct that collects output data of the force providers
     */
    virtual void calculateForces(const ForceProviderInput& forceProviderInput,
                                 ForceProviderOutput*      forceProviderOutput) = 0;

protected:
    ~IForceProvider() {}
};

/*! \libinternal \brief
 * Evaluates forces from a collection of gmx::IForceProvider.
 *
 * \inlibraryapi
 * \ingroup module_mdtypes
 */
class ForceProviders
{
public:
    ForceProviders();
    ~ForceProviders();

    /*! \brief
     * Adds a provider.
     */
    void addForceProvider(gmx::IForceProvider* provider);

    //! Whether there are modules added.
    bool hasForceProvider() const;

    //! Computes forces.
    void calculateForces(const gmx::ForceProviderInput& forceProviderInput,
                         gmx::ForceProviderOutput*      forceProviderOutput) const;

private:
    class Impl;

    std::unique_ptr<Impl> impl_;
};

} // namespace gmx

#endif
