Units.hpp

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// Vulcan Unit Conversions
// Common aerospace unit conversion utilities
#pragma once
 
#include <janus/math/Arithmetic.hpp>
#include <janus/math/Logic.hpp>
#include <vulcan/core/Constants.hpp>
 
namespace vulcan::units {
 
// =============================================================================
// Angular Conversions
// =============================================================================

template <typename Scalar> constexpr Scalar deg_to_rad(const Scalar &deg) {
    return deg * constants::angle::deg2rad;
}

template <typename Scalar> constexpr Scalar rad_to_deg(const Scalar &rad) {
    return rad * constants::angle::rad2deg;
}

template <typename Scalar> constexpr Scalar wrap_to_2pi(const Scalar &angle) {
    const double two_pi = 2.0 * constants::angle::pi;
    Scalar wrapped = janus::fmod(angle, Scalar(two_pi));
    return janus::where(wrapped < 0.0, wrapped + two_pi, wrapped);
}

template <typename Scalar> constexpr Scalar wrap_to_pi(const Scalar &angle) {
    // Wrap to [0, 2pi), then shift to [-pi, pi)?
    // Actually, simple fmod logic:
    // angle - 2pi * floor((angle + pi) / 2pi)
    // janus doesn't guarantee floor?
    // let's use the 2pi wrap shifting.
    return wrap_to_2pi(angle + constants::angle::pi) - constants::angle::pi;
}

template <typename Scalar>
constexpr Scalar wrap_to_180(const Scalar &angle_deg) {
    const double three_sixty = 360.0;
    Scalar wrapped = janus::fmod(angle_deg, Scalar(three_sixty));
    wrapped =
        janus::where(wrapped < 0.0, wrapped + three_sixty, wrapped); // [0, 360)
    // shift to [-180, 180)
    return janus::where(wrapped >= 180.0, wrapped - three_sixty, wrapped);
    // Wait, simpler: wrap_to_360(angle + 180) - 180
    // reuse logic
    // Scalar w = janus::fmod(angle_deg + 180.0, 360.0);
    // w = janus::where(w < 0.0, w + 360.0, w);
    // return w - 180.0;
}
 
// =============================================================================
// Length Conversions
// =============================================================================

template <typename Scalar> constexpr Scalar ft_to_m(const Scalar &ft) {
    return ft * 0.3048;
}

template <typename Scalar> constexpr Scalar m_to_ft(const Scalar &m) {
    return m / 0.3048;
}

template <typename Scalar> constexpr Scalar nm_to_m(const Scalar &nm) {
    return nm * 1852.0;
}

template <typename Scalar> constexpr Scalar m_to_nm(const Scalar &m) {
    return m / 1852.0;
}

template <typename Scalar> constexpr Scalar km_to_m(const Scalar &km) {
    return km * 1000.0;
}

template <typename Scalar> constexpr Scalar m_to_km(const Scalar &m) {
    return m / 1000.0;
}
 
// =============================================================================
// Speed Conversions
// =============================================================================

template <typename Scalar> constexpr Scalar kts_to_mps(const Scalar &kts) {
    return kts * 0.514444;
}

template <typename Scalar> constexpr Scalar mps_to_kts(const Scalar &mps) {
    return mps / 0.514444;
}

template <typename Scalar> constexpr Scalar fps_to_mps(const Scalar &fps) {
    return fps * 0.3048;
}

template <typename Scalar> constexpr Scalar mps_to_fps(const Scalar &mps) {
    return mps / 0.3048;
}
 
// =============================================================================
// Mass/Force Conversions
// =============================================================================

template <typename Scalar> constexpr Scalar lbm_to_kg(const Scalar &lbm) {
    return lbm * 0.45359237;
}

template <typename Scalar> constexpr Scalar kg_to_lbm(const Scalar &kg) {
    return kg / 0.45359237;
}

template <typename Scalar> constexpr Scalar slug_to_kg(const Scalar &slug) {
    return slug * 14.593903;
}

template <typename Scalar> constexpr Scalar kg_to_slug(const Scalar &kg) {
    return kg / 14.593903;
}

template <typename Scalar> constexpr Scalar slug_to_lbm(const Scalar &slug) {
    return slug * 32.17405;
}

template <typename Scalar> constexpr Scalar lbm_to_slug(const Scalar &lbm) {
    return lbm / 32.17405;
}

template <typename Scalar> constexpr Scalar lbf_to_N(const Scalar &lbf) {
    return lbf * 4.4482216;
}

template <typename Scalar> constexpr Scalar N_to_lbf(const Scalar &N) {
    return N / 4.4482216;
}
 
// =============================================================================
// Inertia (Moment of Inertia) Conversions
// =============================================================================

template <typename Scalar>
constexpr Scalar slugft2_to_kgm2(const Scalar &slugft2) {
    // 1 slug-ft² = 14.593903 kg * (0.3048 m)² = 1.35582 kg·m²
    return slugft2 * 1.3558179;
}

template <typename Scalar>
constexpr Scalar kgm2_to_slugft2(const Scalar &kgm2) {
    return kgm2 / 1.3558179;
}

template <typename Scalar>
constexpr Scalar lbmft2_to_kgm2(const Scalar &lbmft2) {
    // 1 lbm-ft² = 0.45359237 kg * (0.3048 m)² = 0.042140 kg·m²
    return lbmft2 * 0.04214011;
}

template <typename Scalar> constexpr Scalar kgm2_to_lbmft2(const Scalar &kgm2) {
    return kgm2 / 0.04214011;
}

template <typename Scalar>
constexpr Scalar lbmin2_to_kgm2(const Scalar &lbmin2) {
    // 1 lbm-in² = 0.45359237 kg * (0.0254 m)² = 2.9264e-4 kg·m²
    return lbmin2 * 2.9263966e-4;
}

template <typename Scalar> constexpr Scalar kgm2_to_lbmin2(const Scalar &kgm2) {
    return kgm2 / 2.9263966e-4;
}

template <typename Scalar>
constexpr Scalar slugin2_to_kgm2(const Scalar &slugin2) {
    // 1 slug-in² = 14.593903 kg * (0.0254 m)² = 9.4154e-3 kg·m²
    return slugin2 * 9.4154069e-3;
}

template <typename Scalar>
constexpr Scalar kgm2_to_slugin2(const Scalar &kgm2) {
    return kgm2 / 9.4154069e-3;
}
 
// =============================================================================
// Pressure Conversions
// =============================================================================

template <typename Scalar> constexpr Scalar psi_to_Pa(const Scalar &psi) {
    return psi * 6894.76;
}

template <typename Scalar> constexpr Scalar Pa_to_psi(const Scalar &Pa) {
    return Pa / 6894.76;
}

template <typename Scalar> constexpr Scalar atm_to_Pa(const Scalar &atm) {
    return atm * 101325.0;
}

template <typename Scalar> constexpr Scalar Pa_to_atm(const Scalar &Pa) {
    return Pa / 101325.0;
}
 
// =============================================================================
// Temperature Conversions
// =============================================================================

template <typename Scalar> constexpr Scalar C_to_K(const Scalar &C) {
    return C + 273.15;
}

template <typename Scalar> constexpr Scalar K_to_C(const Scalar &K) {
    return K - 273.15;
}

template <typename Scalar> constexpr Scalar F_to_K(const Scalar &F) {
    return (F - 32.0) * 5.0 / 9.0 + 273.15;
}

template <typename Scalar> constexpr Scalar K_to_F(const Scalar &K) {
    return (K - 273.15) * 9.0 / 5.0 + 32.0;
}

template <typename Scalar> constexpr Scalar R_to_K(const Scalar &R) {
    return R * 5.0 / 9.0;
}

template <typename Scalar> constexpr Scalar K_to_R(const Scalar &K) {
    return K * 9.0 / 5.0;
}
 
} // namespace vulcan::units