// ════════════════════════════════════════════════════════════════════════
//  physics.js — Physical constants and meteorological calculations.
//
//  Exports:
//    SIGMA, EPSILON_P, A_K, ALBEDO_GRASS  (radiation constants)
//    vaporPressureHpa(Ta, RH)             Magnus formula → hPa
//    solarElevationDeg(lat, lon, dateUTC) NOAA simplified solar position
//    calcTmrt(Ta, dirRad, diffRad, globalRad, solElev)  Mean radiant temp
//    utciApprox(Ta, Tmrt, va10, ehPa)     Bröde et al. 2012 polynomial
//
//  Nothing in here should need editing unless the underlying science
//  changes. All numbers are peer-reviewed constants or coefficients.
// ════════════════════════════════════════════════════════════════════════

// ═══════════════════════════════════════════════════════════════════
// PHYSICAL CONSTANTS
// ───────────────────────────────────────────────────────────────────
// These are real-world physics values — don't change them unless you
// have a peer-reviewed reason. They're used by calcTmrt() below to
// work out how much heat your skin actually absorbs from the sun.
//   SIGMA        — Stefan–Boltzmann constant (radiates heat)
//   EPSILON_P    — emissivity of human skin (~0.97)
//   A_K          — short-wave absorption coefficient for clothing
//   ALBEDO_GRASS — how much sun grass reflects back at you (23%)
// ═══════════════════════════════════════════════════════════════════
export const SIGMA        = 5.670374419e-8;
export const EPSILON_P    = 0.97;
export const A_K          = 0.7;
export const ALBEDO_GRASS = 0.23;

// Vapour pressure (Magnus → hPa)
export function vaporPressureHpa(Ta, RH) {
  const es = 6.105 * Math.exp((17.27 * Ta) / (237.7 + Ta));
  return es * (RH / 100);
}

// Solar elevation (NOAA simplified, degrees)
export function solarElevationDeg(lat, lon, dateUTC) {
  const start = Date.UTC(dateUTC.getUTCFullYear(), 0, 0);
  const diff = dateUTC - start;
  const DOY = Math.floor(diff / 86400000);
  const hourUTC =
    dateUTC.getUTCHours() +
    dateUTC.getUTCMinutes() / 60 +
    dateUTC.getUTCSeconds() / 3600;
  const gamma = ((2 * Math.PI) / 365) * (DOY - 1 + (hourUTC - 12) / 24);
  const eqtime =
    229.18 *
    (0.000075 +
      0.001868 * Math.cos(gamma) -
      0.032077 * Math.sin(gamma) -
      0.014615 * Math.cos(2 * gamma) -
      0.040849 * Math.sin(2 * gamma));
  const decl =
    0.006918 -
    0.399912 * Math.cos(gamma) +
    0.070257 * Math.sin(gamma) -
    0.006758 * Math.cos(2 * gamma) +
    0.000907 * Math.sin(2 * gamma) -
    0.002697 * Math.cos(3 * gamma) +
    0.00148 * Math.sin(3 * gamma);
  const timeOffset = eqtime + 4 * lon;
  const tst = hourUTC * 60 + timeOffset;
  const ha = (((tst / 4) - 180) * Math.PI) / 180;
  const latRad = (lat * Math.PI) / 180;
  const cosZenith =
    Math.sin(latRad) * Math.sin(decl) +
    Math.cos(latRad) * Math.cos(decl) * Math.cos(ha);
  const zenith = Math.acos(Math.max(-1, Math.min(1, cosZenith)));
  return (Math.PI / 2 - zenith) * (180 / Math.PI);
}

// Mean radiant temperature
export function calcTmrt(Ta, dirRad, diffRad, globalRad, solElev) {
  const TaK = Ta + 273.15;
  let fp = 0;
  if (solElev > 0) {
    const h2 = solElev;
    fp = 0.308 * Math.cos((Math.PI / 180) * h2 * (0.998 - (h2 * h2) / 50000));
  }
  let DNI = 0;
  if (solElev > 1) {
    DNI = dirRad / Math.sin((solElev * Math.PI) / 180);
    DNI = Math.min(DNI, 1100);
  }
  const Sshort = A_K * (fp * DNI + 0.5 * diffRad + 0.5 * ALBEDO_GRASS * globalRad);
  const Slong = EPSILON_P * SIGMA * Math.pow(TaK, 4);
  const TmrtK = Math.pow((Sshort + Slong) / (EPSILON_P * SIGMA), 0.25);
  return TmrtK - 273.15;
}

// ═══════════════════════════════════════════════════════════════════
// UTCI POLYNOMIAL — DO NOT EDIT (or be VERY careful if you do)
// ───────────────────────────────────────────────────────────────────
// This is the official 210-term Bröde et al. (2012) approximation.
// It takes air temp, mean radiant temp, wind, and humidity and returns
// the "felt" temperature. Every number is a peer-reviewed coefficient.
// Scroll past it — there's nothing here you'll want to change.
// ═══════════════════════════════════════════════════════════════════
export function utciApprox(Ta, Tmrt, va10, ehPa) {
  const va = Math.max(0.5, Math.min(17, va10));
  const D_Tmrt = Tmrt - Ta;
  const Pa = ehPa / 10;
  const T = Ta, V = va, D = D_Tmrt, P = Pa;
  const T2=T*T, T3=T2*T, T4=T3*T, T5=T4*T, T6=T5*T;
  const V2=V*V, V3=V2*V, V4=V3*V, V5=V4*V, V6=V5*V;
  const D2=D*D, D3=D2*D, D4=D3*D, D5=D4*D, D6=D5*D;
  const P2=P*P, P3=P2*P, P4=P3*P, P5=P4*P, P6=P5*P;
  return T +
    6.07562052e-1 +
    -2.27712343e-2 * T + 8.06470249e-4 * T2 + -1.54271372e-4 * T3 +
    -3.24651735e-6 * T4 + 7.32602852e-8 * T5 + 1.35959073e-9 * T6 +
    -2.25836520e0 * V + 8.80326035e-2 * T*V + 2.16844454e-3 * T2*V +
    -1.53347087e-5 * T3*V + -5.72983704e-7 * T4*V + -2.55090145e-9 * T5*V +
    -7.51269505e-1 * V2 + -4.08350271e-3 * T*V2 + -5.21670675e-5 * T2*V2 +
    1.94544667e-6 * T3*V2 + 1.14099531e-8 * T4*V2 +
    1.58137256e-1 * V3 + -6.57263143e-5 * T*V3 + 2.22697524e-7 * T2*V3 +
    -4.16117031e-8 * T3*V3 +
    -1.27762753e-2 * V4 + 9.66891875e-6 * T*V4 + 2.52785852e-9 * T2*V4 +
    4.56306672e-4 * V5 + -1.74202546e-7 * T*V5 +
    -5.91491269e-6 * V6 +
    3.98374029e-1 * D + 1.83945314e-4 * T*D + -1.73754510e-4 * T2*D +
    -7.60781159e-7 * T3*D + 3.77830287e-8 * T4*D + 5.43079673e-10 * T5*D +
    -2.00518269e-2 * V*D + 8.92859837e-4 * T*V*D + 3.45433048e-6 * T2*V*D +
    -3.77925774e-7 * T3*V*D + -1.69699377e-9 * T4*V*D +
    1.69992415e-4 * V2*D + -4.99204314e-5 * T*V2*D + 2.47417178e-7 * T2*V2*D +
    1.07596466e-8 * T3*V2*D +
    8.49242932e-5 * V3*D + 1.35191328e-6 * T*V3*D + -6.21531254e-9 * T2*V3*D +
    -4.99410301e-6 * V4*D + -1.89489258e-8 * T*V4*D +
    8.15300114e-8 * V5*D +
    7.55043090e-4 * D2 + -5.65095215e-5 * T*D2 + -4.52166564e-7 * T2*D2 +
    2.46688878e-8 * T3*D2 + 2.42674348e-10 * T4*D2 +
    1.54547250e-4 * V*D2 + 5.24110970e-6 * T*V*D2 + -8.75874982e-8 * T2*V*D2 +
    -1.50743064e-9 * T3*V*D2 +
    -1.56236307e-5 * V2*D2 + -1.33895614e-7 * T*V2*D2 + 2.49709824e-9 * T2*V2*D2 +
    6.51711721e-7 * V3*D2 + 1.94960053e-9 * T*V3*D2 +
    -1.00361113e-8 * V4*D2 +
    -1.21206673e-5 * D3 + -2.18203660e-7 * T*D3 + 7.51269482e-9 * T2*D3 +
    9.79063848e-11 * T3*D3 +
    1.25006734e-6 * V*D3 + -1.81584736e-9 * T*V*D3 + -3.52197671e-10 * T2*V*D3 +
    -3.36514630e-8 * V2*D3 + 1.35908359e-10 * T*V2*D3 +
    4.17032620e-10 * V3*D3 +
    -1.30369025e-9 * D4 + 4.13908461e-10 * T*D4 + 9.22652254e-12 * T2*D4 +
    -5.08220384e-9 * V*D4 + -2.24730961e-11 * T*V*D4 +
    1.17139133e-10 * V2*D4 +
    6.62154879e-10 * D5 + 4.03863260e-13 * T*D5 + 1.95087203e-12 * V*D5 +
    -4.73602469e-12 * D6 +
    5.12733497e0 * P + -3.12788561e-1 * T*P + -1.96701861e-2 * T2*P +
    9.99690870e-4 * T3*P + 9.51738512e-6 * T4*P + -4.66426341e-7 * T5*P +
    5.48050612e-1 * V*P + -3.30552823e-3 * T*V*P + -1.64119440e-3 * T2*V*P +
    -5.16670694e-6 * T3*V*P + 9.52692432e-7 * T4*V*P +
    -4.29223622e-2 * V2*P + 5.00845667e-3 * T*V2*P + 1.00601257e-6 * T2*V2*P +
    -1.81748644e-6 * T3*V2*P +
    -1.25813502e-3 * V3*P + -1.79330391e-4 * T*V3*P + 2.34994441e-6 * T2*V3*P +
    1.29735808e-4 * V4*P + 1.29064870e-6 * T*V4*P +
    -2.28558686e-6 * V5*P +
    -3.69476348e-2 * D*P + 1.62325322e-3 * T*D*P + -3.14279680e-5 * T2*D*P +
    2.59835559e-6 * T3*D*P + -4.77136523e-8 * T4*D*P +
    8.64203390e-3 * V*D*P + -6.87405181e-4 * T*V*D*P + -9.13863872e-6 * T2*V*D*P +
    5.15916806e-7 * T3*V*D*P +
    -3.59217476e-5 * V2*D*P + 3.28696511e-5 * T*V2*D*P + -7.10542454e-7 * T2*V2*D*P +
    -1.24382300e-5 * V3*D*P + -7.38584400e-9 * T*V3*D*P +
    2.20609296e-7 * V4*D*P +
    -7.32469180e-4 * D2*P + -1.87381964e-5 * T*D2*P + 4.80925239e-6 * T2*D2*P +
    -8.75492040e-8 * T3*D2*P +
    2.77862930e-5 * V*D2*P + -5.06004592e-6 * T*V*D2*P + 1.14325367e-7 * T2*V*D2*P +
    2.53016723e-6 * V2*D2*P + -1.72857035e-8 * T*V2*D2*P +
    -3.95079398e-8 * V3*D2*P +
    -3.59413173e-7 * D3*P + 7.04388046e-7 * T*D3*P + -1.89309167e-8 * T2*D3*P +
    -4.79768731e-7 * V*D3*P + 7.96079978e-9 * T*V*D3*P +
    1.62897058e-9 * V2*D3*P +
    3.94367674e-8 * D4*P + -1.18566247e-9 * T*D4*P +
    3.34678041e-10 * V*D4*P +
    -1.15606447e-10 * D5*P +
    -2.80626406e0 * P2 + 5.48712484e-1 * T*P2 + -3.99428410e-3 * T2*P2 +
    -9.54009191e-4 * T3*P2 + 1.93090978e-5 * T4*P2 +
    -3.08806365e-1 * V*P2 + 1.16952364e-2 * T*V*P2 + 4.95271903e-4 * T2*V*P2 +
    -1.90710882e-5 * T3*V*P2 +
    2.10787756e-3 * V2*P2 + -6.98445738e-4 * T*V2*P2 + 2.30109073e-5 * T2*V2*P2 +
    4.17856590e-4 * V3*P2 + -1.27043871e-5 * T*V3*P2 +
    -3.04620472e-6 * V4*P2 +
    5.14507424e-2 * D*P2 + -4.32510997e-3 * T*D*P2 + 8.99281156e-5 * T2*D*P2 +
    -7.14663943e-7 * T3*D*P2 +
    -2.66016305e-4 * V*D*P2 + 2.63789586e-4 * T*V*D*P2 + -7.01199003e-6 * T2*V*D*P2 +
    -1.06823306e-4 * V2*D*P2 + 3.61341136e-6 * T*V2*D*P2 +
    2.29748967e-7 * V3*D*P2 +
    3.04788893e-4 * D2*P2 + -6.42070836e-5 * T*D2*P2 + 1.16257971e-6 * T2*D2*P2 +
    7.68023384e-6 * V*D2*P2 + -5.47446896e-7 * T*V*D2*P2 +
    -3.59937910e-8 * V2*D2*P2 +
    -4.36497725e-6 * D3*P2 + 1.68737969e-7 * T*D3*P2 +
    2.67489271e-8 * V*D3*P2 +
    3.23926897e-9 * D4*P2 +
    -3.53874123e-2 * P3 + -2.21201190e-1 * T*P3 + 1.55126038e-2 * T2*P3 +
    -2.63917279e-4 * T3*P3 +
    4.53433455e-2 * V*P3 + -4.32943862e-3 * T*V*P3 + 1.45389826e-4 * T2*V*P3 +
    2.17508610e-4 * V2*P3 + -6.66724702e-5 * T*V2*P3 +
    3.33217140e-5 * V3*P3 +
    -2.26921615e-3 * D*P3 + 3.80261982e-4 * T*D*P3 + -5.45314314e-9 * T2*D*P3 +
    -7.96355448e-4 * V*D*P3 + 2.53458034e-5 * T*V*D*P3 +
    -6.31223658e-6 * V2*D*P3 +
    3.02122035e-4 * D2*P3 + -4.77403547e-6 * T*D2*P3 +
    1.73825715e-6 * V*D2*P3 +
    -4.09087898e-7 * D3*P3 +
    6.14155345e-1 * P4 + -6.16755931e-2 * T*P4 + 1.33374846e-3 * T2*P4 +
    3.55375387e-3 * V*P4 + -5.13027851e-4 * T*V*P4 +
    1.02449757e-4 * V2*P4 +
    -1.48526421e-3 * D*P4 + -4.11469183e-5 * T*D*P4 +
    -6.80434415e-6 * V*D*P4 +
    -9.77675906e-6 * D2*P4 +
    8.82773108e-2 * P5 + -3.01859306e-3 * T*P5 +
    1.04452989e-3 * V*P5 +
    2.47090539e-4 * D*P5 +
    1.48348065e-3 * P6;
}