meson-mfem/src/include/serif/dimensions/partial.hpp

#pragma once

#include "serif/dimensions/quantities.hpp"
#include "serif/utils/misc/concepts/numeric.hpp"

namespace serif::dimensions {
    template <ThermodynamicQuantityType Quantity>
    struct WithRespectTo final {};

    template <ThermodynamicQuantityType OutputQuantity, ThermodynamicQuantityType InputQuantity>
    class PartialDerivative final {
    public:
        explicit constexpr PartialDerivative(const double value) noexcept : m_value(value){}

        [[nodiscard]] constexpr double value() const noexcept {
            return m_value;
        }

        friend constexpr PartialDerivative<OutputQuantity, InputQuantity> operator+(
            const PartialDerivative<OutputQuantity, InputQuantity>& lhs,
            const PartialDerivative<OutputQuantity, InputQuantity>& rhs
        ) noexcept {
            return PartialDerivative<OutputQuantity, InputQuantity>{lhs.m_value + rhs.m_value};
        }

        friend constexpr PartialDerivative<OutputQuantity, InputQuantity> operator-(
            const PartialDerivative<OutputQuantity, InputQuantity>& lhs,
            const PartialDerivative<OutputQuantity, InputQuantity>& rhs
        ) noexcept {
            return PartialDerivative<OutputQuantity, InputQuantity>{lhs.m_value - rhs.m_value};
        }

        template <utils::misc::concepts::IsNumeric Scalar>
        friend constexpr PartialDerivative<OutputQuantity, InputQuantity> operator*(
            const PartialDerivative<OutputQuantity, InputQuantity>& lhs,
            const Scalar& rhs
        ) noexcept {
            return PartialDerivative<OutputQuantity, InputQuantity>{lhs.m_value * rhs};
        }

        template <utils::misc::concepts::IsNumeric Scalar>
        friend constexpr PartialDerivative<OutputQuantity, InputQuantity> operator*(
            const Scalar& lhs,
            const PartialDerivative<OutputQuantity, InputQuantity>& rhs
        ) noexcept {
            return PartialDerivative<OutputQuantity, InputQuantity>{lhs * rhs.m_value};
        }

        template <utils::misc::concepts::IsNumeric Scalar>
        friend constexpr PartialDerivative<OutputQuantity, InputQuantity> operator/(
            const PartialDerivative<OutputQuantity, InputQuantity>& lhs,
            const Scalar& rhs
        ) noexcept {
            return PartialDerivative<OutputQuantity, InputQuantity>{lhs.m_value / rhs};
        }

        template <utils::misc::concepts::IsNumeric Scalar>
        friend constexpr std::partial_ordering operator<=>(
            const PartialDerivative<OutputQuantity, InputQuantity>& lhs,
            Scalar rhs
        ) noexcept {
            return lhs.m_value <=> rhs;
        }

        template <utils::misc::concepts::IsNumeric Scalar>
        friend constexpr std::partial_ordering operator<=>(
            Scalar lhs,
            const PartialDerivative<OutputQuantity, InputQuantity>& rhs
        ) noexcept {
            return lhs <=> rhs.m_value;
        }

        friend constexpr std::partial_ordering operator<=>(
            const PartialDerivative<OutputQuantity, InputQuantity> &lhs,
            const PartialDerivative<OutputQuantity, InputQuantity> &rhs
        ) noexcept {
            return lhs.m_value <=> rhs.m_value;
        }

    private:
        double m_value;
    };
}