module;

#include <vector>

#include <mfem.hpp>

export module mean_field:model.structure.polytropic;

export import :eos.polytrope;
export import :model.structure.base;

import :utils.misc;

export namespace mean_field::models::structure {
    class PolytropicStructure final : public StructureBase {
    public:
        explicit PolytropicStructure(
            eos::Polytrope equationOfState,
            double targetMass
        );

        [[nodiscard]] const eos::EquationOfState &equationOfState() const noexcept override;

        [[nodiscard]] double targetMass() const noexcept override;

        [[nodiscard]] StructureSeed makeInitialSeed(const StructureSeedRequest &request) const override;

        void validate() const override;

    private:
        struct LaneEmdenPoint {
            double coordinate{0.0};
            double value{0.0};
            double derivative{0.0};
        };

        struct LaneEmdenDerivative {
            double value{0.0};
            double derivative{0.0};
        };

        static void validateSeedRequest(const StructureSeedRequest &request);

        [[nodiscard]] static LaneEmdenDerivative evaluateLaneEmdenRhs(
            double coordinate,
            double value,
            double derivative,
            double polytropicIndex
        );

        [[nodiscard]] static LaneEmdenPoint takeLaneEmdenStep(
            const LaneEmdenPoint &point,
            double step,
            double polytropicIndex
        );

        [[nodiscard]] static std::vector<LaneEmdenPoint> solveLaneEmden(double polytropicIndex);

        [[nodiscard]] static double interpolateLaneEmdenValue(
            const std::vector<LaneEmdenPoint> &solution,
            double coordinate,
            std::size_t &lowerIndex
        );

        eos::Polytrope m_equationOfState;
        double m_targetMass;
    };
} // namespace mean_field::models::structure