module;
#include <cstdint>
#include <memory>
#include <mfem.hpp>
#include <vector>

export module mean_field:operators.prepared_gravity_source;
export import :fem;
export import :mapping.domain_mapper;

export namespace mean_field::operators {
    class PreparedMappedGravitySourceOperator final : public mfem::Operator {
    public:
        PreparedMappedGravitySourceOperator(
            const fem::FEM &f,
            const mapping::DomainMapperStateless &domain_mapper
        );

        void Prepare(const mfem::Vector &displacement_true);
        void Mult(
            const mfem::Vector &density_true,
            mfem::Vector &action
        ) const override;

        [[nodiscard]] bool IsPrepared() const noexcept;
        [[nodiscard]] std::uint64_t GetPreparationCount() const noexcept;

        void MultTranspose(
            const mfem::Vector &potential_true,
            mfem::Vector &action
        ) const override;

    private:
        struct ElementPAData {
            int element_id{-1};

            mfem::Array<int> density_dofs;
            mfem::Array<int> potential_dofs;

            mfem::DofTransformation *density_dof_transformation{nullptr};
            mfem::DofTransformation *potential_dof_transformation{nullptr};

            // Rows are quadrature points; columns are element DOFs.
            mfem::DenseMatrix density_basis;
            mfem::DenseMatrix potential_basis;

            // Contains quadrature weight, mesh Jacobian, mapped Jacobian,
            // and 4*pi*G.
            mfem::Vector quadrature_data;
        };

        const fem::FEM &m_fem;
        const mapping::DomainMapperStateless &m_domain_mapper;

        mfem::Array<int> m_stellar_marker;
        std::vector<ElementPAData> m_elements;

        std::uint64_t m_preparation_count{0};
        bool m_is_prepared{false};
    };
} // namespace mean_field::operators