module;
#include <mfem.hpp>
module mean_field;

namespace mean_field::integrators {
    GravityForceIntegrator::GravityForceIntegrator(
        const mapping::DomainMapper& map,
        const mfem::GridFunction& phi
    ): m_map(map), m_phi(&phi) {}

    void GravityForceIntegrator::SetPotential(const mfem::GridFunction& phi) { m_phi = &phi; };

    void GravityForceIntegrator::AssembleElementVector(
        const mfem::Array<const mfem::FiniteElement *> &el,
        mfem::ElementTransformation &Tr,
        const mfem::Array<const mfem::Vector *> &elfun,
        const mfem::Array<mfem::Vector *> &elvec
    ) {

        if (utils::is_vacuum(Tr, elvec)) {
            return;
        }

        const mfem::FiniteElement* fe_v = el[0];
        const mfem::FiniteElement* fe_rho = el[1];

        const int dof_v = fe_v->GetDof();
        const int dof_rho = fe_rho->GetDof();
        const int dim = Tr.GetSpaceDim();

        const mfem::Vector& rho_dofs = *elfun[1];

        mfem::Vector& r_v = *elvec[0];
        r_v.SetSize(dof_v * dim);
        r_v = 0.0;
        if (elvec[1]) {
            elvec[1]->SetSize(dof_rho);
            *elvec[1] = 0.0;
        }

        mfem::Vector shape_v(dof_v), shape_rho(dof_rho);
        mfem::Vector grad_phi_ref(dim), grad_phi_phys(dim), grad_phi_elem(dim);

        const mfem::IntegrationRule* ir = &mfem::IntRules.Get(fe_v->GetGeomType(), 2 * fe_v->GetOrder());

        for (int q = 0; q < ir->GetNPoints(); ++q) {
            const mfem::IntegrationPoint& ip = ir->IntPoint(q);
            Tr.SetIntPoint(&ip);

            auto [J_inv, detJ, weight] = m_map.GetQuadratureContext(Tr, ip);
            m_phi->GetGradient(Tr, grad_phi_elem);
            mfem::DenseMatrix J_map(dim, dim), J_map_inv(dim, dim);
            m_map.ComputeJacobian(Tr, J_map);
            mfem::CalcInverse(J_map, J_map_inv);
            J_map_inv.MultTranspose(grad_phi_elem, grad_phi_phys);

            fe_v->CalcShape(ip, shape_v);
            fe_rho->CalcShape(ip, shape_rho);

            double rho_val = 0.0;
            for (int i = 0; i < dof_rho; ++i) {
                rho_val += rho_dofs(i) * shape_rho(i);
            }

            for (int i = 0;  i < dof_v; ++i) {
                for (int c = 0; c < dim; ++c) {
                    r_v(i + c * dof_v) += shape_v(i) * rho_val * grad_phi_phys(c) * weight;
                }
            }
        }
    }

    void GravityForceIntegrator::AssembleElementGrad(
        const mfem::Array<const mfem::FiniteElement *> &el,
        mfem::ElementTransformation &Tr,
        const mfem::Array<const mfem::Vector *> &elfun,
        const mfem::Array2D<mfem::DenseMatrix *> &elmats
    ) {
        const mfem::FiniteElement* fe_v = el[0];
        const mfem::FiniteElement* fe_rho = el[1];

        const int dof_v = fe_v->GetDof();
        const int dof_rho = fe_rho->GetDof();
        const int dim = Tr.GetSpaceDim();

        mfem::DenseMatrix* dv_dv = elmats(0, 0);
        mfem::DenseMatrix* dv_drho = elmats(0, 1);

        if (dv_dv) *dv_dv = 0.0;
        if (dv_drho) *dv_drho = 0.0;

        if (!dv_drho) return;

        mfem::Vector shape_v(dof_v), shape_rho(dof_rho);
        mfem::Vector grad_phi_ref(dim), grad_phi_phys(dim), grad_phi_elem(dim);

        const mfem::IntegrationRule* ir = &mfem::IntRules.Get(fe_v->GetGeomType(), 2 * fe_v->GetOrder());

        for (int q = 0; q < ir->GetNPoints(); ++q) {
            const mfem::IntegrationPoint& ip = ir->IntPoint(q);
            Tr.SetIntPoint(&ip);

            auto [J_inv, detJ, weight] = m_map.GetQuadratureContext(Tr, ip);
            m_phi->GetGradient(Tr, grad_phi_elem);
            mfem::DenseMatrix J_map(dim, dim), J_map_inv(dim, dim);
            m_map.ComputeJacobian(Tr, J_map);
            mfem::CalcInverse(J_map, J_map_inv);
            J_map_inv.MultTranspose(grad_phi_elem, grad_phi_phys);

            fe_v->CalcShape(ip, shape_v);
            fe_rho->CalcShape(ip, shape_rho);


            for (int i = 0; i < dof_v; ++i) {
                for (int c = 0; c < dim; ++c) {
                    const int row = i + c * dof_v;
                    for (int j = 0; j < dof_rho; ++j) {
                        (*dv_drho)(row, j) += shape_v(i) * shape_rho(j) * grad_phi_phys(c) * weight;
                    }
                }
            }
        }
    }
}