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#include "gmxpre.h"

#include "enerdata_utils.h"

#include <cmath>
#include <cstdio>

#include <algorithm>
#include <array>
#include <utility>
#include <vector>

#include "gromacs/gmxlib/network.h"
#include "gromacs/mdtypes/enerdata.h"
#include "gromacs/mdtypes/inputrec.h"
#include "gromacs/mdtypes/md_enums.h"
#include "gromacs/topology/ifunc.h"
#include "gromacs/utility/basedefinitions.h"
#include "gromacs/utility/enumerationhelpers.h"
#include "gromacs/utility/fatalerror.h"
#include "gromacs/utility/gmxassert.h"
#include "gromacs/utility/mpicomm.h"

ForeignLambdaTerms::ForeignLambdaTerms(
        const gmx::EnumerationArray<FreeEnergyPerturbationCouplingType, std::vector<double>>* allLambdas) :
    numLambdas_(allLambdas ? gmx::ssize((*allLambdas)[FreeEnergyPerturbationCouplingType::Fep]) : 0),
    allLambdas_(allLambdas),
    energies_(1 + numLambdas_),
    dhdl_(1 + numLambdas_)
{
    if (allLambdas_)
    {
        for (const auto& foreignLambdas : *allLambdas_)
        {
            GMX_RELEASE_ASSERT(gmx::ssize(foreignLambdas) == numLambdas_,
                               "All coupling types should have the same lambda count");
        }
    }
}

/*! \brief Composes dH/dlambda for the given lambda point \p lambdaIndex
 *
 * Different lambda components can be changed during different legs
 * of the complete lambda path. Thus dH/dlambda should only contain
 * contributions from components that are actually changed. Also when
 * a component in opposite direction, the sign of the contribution changes.
 *
 * \param[in] lambdaIndex  The lambda point index
 * \param[in] allLambdas   The lambda values for all points for all components
 * \param[in] dhdl         The current dH/dlambda values for \p lambdaIndex
 * \returns the composed dH/dlambda value
 */
static double
composeDhdl(const int lambdaIndex,
            const gmx::EnumerationArray<FreeEnergyPerturbationCouplingType, std::vector<double>>& allLambdas,
            const gmx::EnumerationArray<FreeEnergyPerturbationCouplingType, double>& dhdl)
{
    const int numLambdaPoints = gmx::ssize(allLambdas[FreeEnergyPerturbationCouplingType::Fep]);

    const bool isFirstLambdaIndex = (lambdaIndex == 0);
    const bool isLastLambdaIndex  = (lambdaIndex == numLambdaPoints - 1);

    // Loop over all lambda components and conditionally add their dhdl contributions
    double dhdlSum = 0;
    for (auto component : gmx::EnumerationWrapper<FreeEnergyPerturbationCouplingType>())
    {
        gmx::ArrayRef<const double> compLambdas = allLambdas[component];

        // When this lambda changes from the previous and/or next point,
        // we add dH/dlambda multiplied by a half for each side.
        // We also change sign when lambda decreases with increasing index.
        double fac = 0;
        if (!isFirstLambdaIndex)
        {
            double diff = compLambdas[lambdaIndex] - compLambdas[lambdaIndex - 1];
            if (diff != 0)
            {
                fac += std::copysign(isLastLambdaIndex ? 1.0 : 0.5, diff);
            }
        }
        if (!isLastLambdaIndex)
        {
            double diff = compLambdas[lambdaIndex + 1] - compLambdas[lambdaIndex];
            if (diff != 0)
            {
                fac += std::copysign(isFirstLambdaIndex ? 1.0 : 0.5, diff);
            }
        }
        dhdlSum += fac * dhdl[component];
    }

    return dhdlSum;
}

std::pair<std::vector<double>, std::vector<double>> ForeignLambdaTerms::getTerms(const gmx::MpiComm& mpiComm) const
{
    GMX_RELEASE_ASSERT(finalizedPotentialContributions_,
                       "The object needs to be finalized before calling getTerms");

    std::vector<double> data(2 * numLambdas_);
    for (int i = 0; i < numLambdas_; i++)
    {
        data[i]               = energies_[1 + i] - energies_[0];
        data[numLambdas_ + i] = composeDhdl(i, *allLambdas_, dhdl_[1 + i]);
    }
    if (mpiComm.isParallel())
    {
        mpiComm.sumReduce(data);
    }
    auto dataMid = data.begin() + numLambdas_;

    return { { data.begin(), dataMid }, { dataMid, data.end() } };
}

void ForeignLambdaTerms::zeroAllTerms()
{
    std::fill(energies_.begin(), energies_.end(), 0.0);
    for (auto& dhdl : dhdl_)
    {
        std::fill(dhdl.begin(), dhdl.end(), 0.0);
    }
    finalizedPotentialContributions_ = false;
}

gmx_enerdata_t::gmx_enerdata_t(
        int numEnergyGroups,
        const gmx::EnumerationArray<FreeEnergyPerturbationCouplingType, std::vector<double>>* allLambdas) :
    grpp(numEnergyGroups), foreignLambdaTerms(allLambdas)
{
}

static real sum_v(int n, gmx::ArrayRef<const real> v)
{
    real t;
    int  i;

    t = 0.0;
    for (i = 0; (i < n); i++)
    {
        t = t + v[i];
    }

    return t;
}

void sum_epot(const gmx_grppairener_t& grpp, gmx::EnumerationArray<InteractionFunction, real>& epot)
{
    int i;

    /* Accumulate energies */
    epot[InteractionFunction::CoulombShortRange] =
            sum_v(grpp.nener, grpp.energyGroupPairTerms[NonBondedEnergyTerms::CoulombSR]);
    epot[InteractionFunction::LennardJonesShortRange] =
            sum_v(grpp.nener, grpp.energyGroupPairTerms[NonBondedEnergyTerms::LJSR]);
    epot[InteractionFunction::LennardJones14] =
            sum_v(grpp.nener, grpp.energyGroupPairTerms[NonBondedEnergyTerms::LJ14]);
    epot[InteractionFunction::Coulomb14] =
            sum_v(grpp.nener, grpp.energyGroupPairTerms[NonBondedEnergyTerms::Coulomb14]);

    /* lattice part of LR doesnt belong to any group
     * and has been added earlier
     */
    epot[InteractionFunction::BuckinghamShortRange] =
            sum_v(grpp.nener, grpp.energyGroupPairTerms[NonBondedEnergyTerms::BuckinghamSR]);

    epot[InteractionFunction::PotentialEnergy] = 0;
    for (i = static_cast<int>(InteractionFunction::Bonds);
         (i < static_cast<int>(InteractionFunction::PotentialEnergy));
         i++)
    {
        if (i != static_cast<int>(InteractionFunction::DistanceRestraintViolations)
            && i != static_cast<int>(InteractionFunction::OrientationRestraintDeviations))
        {
            epot[InteractionFunction::PotentialEnergy] += epot[i];
        }
    }
}

// Adds computed dH/dlambda contribution i to the requested output
static void set_dhdl_output(gmx_enerdata_t* enerd, FreeEnergyPerturbationCouplingType i, const t_lambda& fepvals)
{
    if (fepvals.separate_dvdl[i])
    {
        /* Translate free-energy term indices to idef term indices.
         * Could this be done more readably/compactly?
         */
        InteractionFunction index;
        switch (i)
        {
            case (FreeEnergyPerturbationCouplingType::Mass):
                index = InteractionFunction::dEkineticdLambda;
                break;
            case (FreeEnergyPerturbationCouplingType::Coul):
                index = InteractionFunction::dVCoulombdLambda;
                break;
            case (FreeEnergyPerturbationCouplingType::Vdw):
                index = InteractionFunction::dVvanderWaalsdLambda;
                break;
            case (FreeEnergyPerturbationCouplingType::Bonded):
                index = InteractionFunction::dVbondeddLambda;
                break;
            case (FreeEnergyPerturbationCouplingType::Restraint):
                index = InteractionFunction::dVrestraintdLambda;
                break;
            default: index = InteractionFunction::dVremainingdLambda; break;
        }
        enerd->term[static_cast<int>(index)] = enerd->dvdl_lin[i] + enerd->dvdl_nonlin[i];
        if (debug)
        {
            fprintf(debug,
                    "dvdl-%s[%2d]: %f: non-linear %f + linear %f\n",
                    enumValueToString(i),
                    static_cast<int>(i),
                    enerd->term[static_cast<int>(index)],
                    enerd->dvdl_nonlin[i],
                    enerd->dvdl_lin[i]);
        }
    }
    else
    {
        enerd->term[InteractionFunction::dVremainingdLambda] +=
                enerd->dvdl_lin[i] + enerd->dvdl_nonlin[i];
        if (debug)
        {
            fprintf(debug,
                    "dvd-%sl[%2d]: %f: non-linear %f + linear %f\n",
                    enumValueToString(FreeEnergyPerturbationCouplingType::Fep),
                    static_cast<int>(i),
                    enerd->term[InteractionFunction::dVremainingdLambda],
                    enerd->dvdl_nonlin[i],
                    enerd->dvdl_lin[i]);
        }
    }
}

void ForeignLambdaTerms::addConstantDhdl(FreeEnergyPerturbationCouplingType couplingType, double dhdl)
{
    for (auto& foreignDhdl : dhdl_)
    {
        foreignDhdl[couplingType] += dhdl;
    }
}

void ForeignLambdaTerms::finalizePotentialContributions(
        const gmx::EnumerationArray<FreeEnergyPerturbationCouplingType, double>& dvdlLinear,
        gmx::ArrayRef<const real>                                                lambda,
        const t_lambda&                                                          fepvals)
{
    if (finalizedPotentialContributions_)
    {
        return;
    }

    for (auto i : gmx::EnumerationWrapper<FreeEnergyPerturbationCouplingType>{})
    {
        addConstantDhdl(i, dvdlLinear[i]);
    }

    /* Sum the foreign lambda energy difference contributions.
     * Note that here we only add the potential energy components.
     * The constraint and kinetic energy components are add after integration
     * by sum_dhdl().
     */
    for (int i = 0; i < fepvals.n_lambda; i++)
    {
        /* note we are iterating over fepvals here!
           For the current lam, dlam = 0 automatically,
           so we don't need to add anything to the
           enerd->enerpart_lambda[0] */

        /* we don't need to worry about dvdl_lin contributions to dE at
           current lambda, because the contributions to the current
           lambda are automatically zeroed */

        double enerpart_lambda = 0;
        for (gmx::Index j = 0; j < lambda.ssize(); j++)
        {
            /* Note that this loop is over all dhdl components, not just the separated ones */
            const double dlam = fepvals.all_lambda[j][i] - lambda[j];

            enerpart_lambda += dlam * dvdlLinear[j];
        }
        accumulate(1 + i, enerpart_lambda, gmx::EnumerationArray<FreeEnergyPerturbationCouplingType, real>());
    }

    finalizedPotentialContributions_ = true;
}

void accumulatePotentialEnergies(gmx_enerdata_t* enerd, gmx::ArrayRef<const real> lambda, const t_lambda* fepvals)
{
    sum_epot(enerd->grpp, enerd->term);

    if (fepvals)
    {
        enerd->term[InteractionFunction::dVremainingdLambda] = 0.0;
        for (auto i : gmx::EnumerationWrapper<FreeEnergyPerturbationCouplingType>{})
        {
            // Skip kinetic terms here, as those are not available here yet
            if (i != FreeEnergyPerturbationCouplingType::Mass)
            {
                set_dhdl_output(enerd, i, *fepvals);
            }
        }

        enerd->foreignLambdaTerms.finalizePotentialContributions(enerd->dvdl_lin, lambda, *fepvals);
    }
}

void ForeignLambdaTerms::accumulateKinetic(int listIndex, double energy, double dhdl)
{
    energies_[listIndex] += energy;
    dhdl_[listIndex][FreeEnergyPerturbationCouplingType::Mass] += dhdl;
}

void ForeignLambdaTerms::finalizeKineticContributions(const gmx::EnumerationArray<InteractionFunction, real>& energyTerms,
                                                      const double              dhdlMass,
                                                      gmx::ArrayRef<const real> lambda,
                                                      const t_lambda&           fepvals)
{
    // Add perturbed mass contributions
    addConstantDhdl(FreeEnergyPerturbationCouplingType::Mass, dhdlMass);

    // Treat current lambda, the deltaH contribution is 0 as delta-lambda=0 for the current lambda
    accumulateKinetic(0, 0.0, energyTerms[InteractionFunction::dHdLambdaConstraint]);
    accumulateKinetic(0, 0.0, dhdlMass);

    for (int i = 0; i < fepvals.n_lambda; i++)
    {
        /* Note that potential energy terms have been added by sum_epot() -> sum_dvdl() */

        /* Constraints can not be evaluated at foreign lambdas, so we add
         * a linear extrapolation. This is an approximation, but usually
         * quite accurate since constraints change little between lambdas.
         */
        const FreeEnergyPerturbationCouplingType lambdaIndex =
                (fepvals.separate_dvdl[FreeEnergyPerturbationCouplingType::Bonded]
                         ? FreeEnergyPerturbationCouplingType::Bonded
                         : FreeEnergyPerturbationCouplingType::Fep);
        const double dlam = fepvals.all_lambda[lambdaIndex][i] - lambda[static_cast<int>(lambdaIndex)];
        accumulateKinetic(1 + i,
                          dlam * energyTerms[InteractionFunction::dHdLambdaConstraint],
                          energyTerms[InteractionFunction::dHdLambdaConstraint]);

        {
            const double dLambdaMass =
                    fepvals.all_lambda[FreeEnergyPerturbationCouplingType::Mass][i]
                    - lambda[static_cast<int>(FreeEnergyPerturbationCouplingType::Mass)];
            accumulateKinetic(1 + i, dLambdaMass * dhdlMass, dhdlMass);
        }
    }
}

void accumulateKineticLambdaComponents(gmx_enerdata_t*           enerd,
                                       gmx::ArrayRef<const real> lambda,
                                       const t_lambda&           fepvals)
{
    if (fepvals.separate_dvdl[FreeEnergyPerturbationCouplingType::Bonded])
    {
        enerd->term[InteractionFunction::dVbondeddLambda] +=
                enerd->term[InteractionFunction::dHdLambdaConstraint];
    }
    else
    {
        enerd->term[InteractionFunction::dVremainingdLambda] +=
                enerd->term[InteractionFunction::dHdLambdaConstraint];
    }

    // Add computed mass dH/dlambda contribution to the requested output
    set_dhdl_output(enerd, FreeEnergyPerturbationCouplingType::Mass, fepvals);

    enerd->foreignLambdaTerms.finalizeKineticContributions(
            enerd->term, enerd->dvdl_lin[FreeEnergyPerturbationCouplingType::Mass], lambda, fepvals);

    /* The constrain contribution is now included in other terms, so clear it */
    enerd->term[InteractionFunction::dHdLambdaConstraint] = 0;
}

void gmx_grppairener_t::clear()
{
    for (int i = 0; (i < static_cast<int>(NonBondedEnergyTerms::Count)); i++)
    {
        for (int j = 0; (j < nener); j++)
        {
            energyGroupPairTerms[i][j] = 0.0;
        }
    }
}

void reset_dvdl_enerdata(gmx_enerdata_t* enerd)
{
    for (auto i : keysOf(enerd->dvdl_lin))
    {
        enerd->dvdl_lin[i]    = 0.0;
        enerd->dvdl_nonlin[i] = 0.0;
    }
}

void reset_enerdata(gmx_enerdata_t* enerd)
{
    int i, j;

    /* First reset all energy components. */
    for (i = 0; (i < static_cast<int>(NonBondedEnergyTerms::Count)); i++)
    {
        for (j = 0; (j < enerd->grpp.nener); j++)
        {
            enerd->grpp.energyGroupPairTerms[i][j] = 0.0_real;
        }
    }

    /* Normal potential energy components */
    for (i = static_cast<int>(InteractionFunction::Bonds);
         (i <= static_cast<int>(InteractionFunction::PotentialEnergy));
         i++)
    {
        enerd->term[i] = 0.0_real;
    }
    enerd->term[InteractionFunction::PressureDispersionCorrection] = 0.0_real;
    enerd->term[InteractionFunction::dVremainingdLambda]           = 0.0_real;
    enerd->term[InteractionFunction::dVCoulombdLambda]             = 0.0_real;
    enerd->term[InteractionFunction::dVvanderWaalsdLambda]         = 0.0_real;
    enerd->term[InteractionFunction::dVbondeddLambda]              = 0.0_real;
    enerd->term[InteractionFunction::dVrestraintdLambda]           = 0.0_real;
    enerd->term[InteractionFunction::dEkineticdLambda]             = 0.0_real;
    enerd->foreignLambdaTerms.zeroAllTerms();
    /* reset dvdl - separate function since it is also called elsewhere */
    reset_dvdl_enerdata(enerd);
}
