centers.hpp

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#pragma once
 
#include "ffi_core.hpp"
 
namespace siderust {
 
// Forward declaration for Geodetic (defined in coordinates/geodetic.hpp)
struct Geodetic;
 
namespace centers {
 
// ============================================================================
// Center Trait
// ============================================================================
 
template <typename C>
struct CenterTraits; // primary — intentionally undefined
 
template <typename C, typename = void>
struct is_center : std::false_type {};
 
template <typename C>
struct is_center<C, std::void_t<decltype(CenterTraits<C>::ffi_id)>> : std::true_type {};
 
template <typename C>
inline constexpr bool is_center_v = is_center<C>::value;
 
// ============================================================================
// Center Tag Definitions
// ============================================================================
 
struct Barycentric {};
struct Heliocentric {};
struct Geocentric {};
struct Topocentric {};
struct Bodycentric {};
 
// ============================================================================
// CenterTraits Specializations
// ============================================================================
 
struct NoParams {};
 
template <>
struct CenterTraits<Barycentric> {
    static constexpr siderust_center_t ffi_id = SIDERUST_CENTER_T_BARYCENTRIC;
    using Params                              = NoParams;
    static constexpr const char* name() { return "Barycentric"; }
};
 
template <>
struct CenterTraits<Heliocentric> {
    static constexpr siderust_center_t ffi_id = SIDERUST_CENTER_T_HELIOCENTRIC;
    using Params                              = NoParams;
    static constexpr const char* name() { return "Heliocentric"; }
};
 
template <>
struct CenterTraits<Geocentric> {
    static constexpr siderust_center_t ffi_id = SIDERUST_CENTER_T_GEOCENTRIC;
    using Params                              = NoParams;
    static constexpr const char* name() { return "Geocentric"; }
};
 
template <>
struct CenterTraits<Topocentric> {
    static constexpr siderust_center_t ffi_id = SIDERUST_CENTER_T_TOPOCENTRIC;
    using Params                              = Geodetic; // forward-declared
    static constexpr const char* name() { return "Topocentric"; }
};
 
template <>
struct CenterTraits<Bodycentric> {
    static constexpr siderust_center_t ffi_id = SIDERUST_CENTER_T_BODYCENTRIC;
    using Params                              = NoParams; // placeholder for BodycentricParams
    static constexpr const char* name() { return "Bodycentric"; }
};
 
// ============================================================================
// Center-shift Valid Predicate
// ============================================================================
 
template <typename From, typename To>
struct has_center_transform : std::false_type {};
 
template <typename C>
struct has_center_transform<C, C> : std::true_type {};
 
#define SIDERUST_CENTER_TRANSFORM_PAIR(A, B)               \
    template <>                                            \
    struct has_center_transform<A, B> : std::true_type {}; \
    template <>                                            \
    struct has_center_transform<B, A> : std::true_type {}
 
SIDERUST_CENTER_TRANSFORM_PAIR(Barycentric, Heliocentric);
SIDERUST_CENTER_TRANSFORM_PAIR(Barycentric, Geocentric);
SIDERUST_CENTER_TRANSFORM_PAIR(Heliocentric, Geocentric);
 
#undef SIDERUST_CENTER_TRANSFORM_PAIR
 
template <typename From, typename To>
inline constexpr bool has_center_transform_v = has_center_transform<From, To>::value;
 
} // namespace centers
} // namespace siderust