module;
#include <mfem.hpp>

export module mean_field:mapping.kelvin;
export import :mapping.compactification;
export import :mapping.types;
export import :mapping.compactification.options;

export namespace mean_field::mapping::compactification {

    class KelvinCompactification final : public ExteriorDomainMap {
    public:
        explicit KelvinCompactification(options::KelvinCompactificationOptions options);

        [[nodiscard]] bool IsAffineInDisplacement() const noexcept override {
            return true;
        }

        [[nodiscard]] MappingStatus Evaluate(
            const ExteriorMapInput &input,
            ExteriorMapResult &result
        ) const override;

        [[nodiscard]] MappingStatus EvaluateVariation(
            const ExteriorMapInput &input,
            const ExteriorMapResult &result,
            const ExteriorMapDirection &direction,
            ExteriorMapVariation &variation
        ) const override;

        [[nodiscard]] std::string_view GetName() const noexcept override;

        [[nodiscard]] double GetReferenceStellarRadius() const noexcept;
        [[nodiscard]] double GetReferenceInfinityRadius() const noexcept;
        [[nodiscard]] double GetCoordinateTolerance() const noexcept;

        // Factors in delta J = scale * grad(delta u) + delta u (grad scale)^T.
        // They depend only on the fixed compactification coordinate, so prepared
        // operators can compute them once instead of evaluating the full map.
        [[nodiscard]] MappingStatus EvaluateJacobianVariationFactors(
            double coordinate,
            const mfem::Vector &coordinateGradient,
            double &scale,
            mfem::Vector &scaleGradient
        ) const;

    private:
        struct RadialFactors {
            double coordinate;
            double computational_radius;
            double scale;
            double scale_derivative;
        };

        [[nodiscard]] MappingStatus ComputeRadialFactors(
            double compactification_coordinate,
            RadialFactors &factors
        ) const;

        options::KelvinCompactificationOptions m_options;
    };
} // namespace mean_field::mapping::compactification