/**
 * Geometry helpers shared by the globe: geodetic → unit-sphere coordinates (Three.js is Y-up), the compressed
 * altitude scale used for legibility, sun direction for the day/night terminator and CSS-token colour lookup.
 *
 * Altitude scale (documented in the UI tooltip): r = 1 + 0.06 + ln(1 + alt/400) × 0.12 with alt in km.
 * LEO (400 km) → 1.143 · 1 000 km → 1.21 · MEO (20 000 km) → 1.53 · GEO (35 786 km) → 1.60. It exaggerates low
 * shells so that the LEO swarm does not sit on the surface, and compresses MEO/GEO so the GEO ring stays on screen.
 */
import type { Vector3 } from 'three';

export const EARTH_RADIUS_KM = 6371;
export const DEG = Math.PI / 180;

export function altToRadius(altKm: number): number {
  const a = Math.max(0, altKm);
  return 1 + 0.06 + Math.log1p(a / 400) * 0.12;
}

/** lon/lat (deg) at radius r → xyz (Y-up, prime meridian at +X, east positive). Writes into `out` (Float32Array|number[]). */
export function llaToXyz(latDeg: number, lonDeg: number, r: number, out: Float32Array | number[], off = 0): void {
  const lat = latDeg * DEG;
  const lon = lonDeg * DEG;
  const c = Math.cos(lat);
  out[off] = r * c * Math.cos(lon);
  out[off + 1] = r * Math.sin(lat);
  out[off + 2] = -r * c * Math.sin(lon);
}

export function llaToVec(latDeg: number, lonDeg: number, r: number, v: Vector3): Vector3 {
  const lat = latDeg * DEG;
  const lon = lonDeg * DEG;
  const c = Math.cos(lat);
  return v.set(r * c * Math.cos(lon), r * Math.sin(lat), -r * c * Math.sin(lon));
}

/**
 * Sub-solar point (approximate, ±0.5°): low-precision solar coordinates (Astronomical Almanac) + GMST.
 * Returns a unit vector in the same Y-up frame as `llaToXyz` — cheap enough to recompute every frame.
 */
export function sunDirection(date: Date, out: Vector3): Vector3 {
  const jd = date.getTime() / 86400000 + 2440587.5;
  const d = jd - 2451545.0;
  const g = ((357.529 + 0.98560028 * d) % 360) * DEG;
  const q = (280.459 + 0.98564736 * d) % 360;
  const L = (q + 1.915 * Math.sin(g) + 0.02 * Math.sin(2 * g)) * DEG;
  const e = (23.439 - 0.00000036 * d) * DEG;
  const ra = Math.atan2(Math.cos(e) * Math.sin(L), Math.cos(L));
  const dec = Math.asin(Math.sin(e) * Math.sin(L));
  const gmst = ((280.46061837 + 360.98564736629 * d) % 360) * DEG;
  const lon = ra - gmst; // sub-solar longitude (rad)
  const c = Math.cos(dec);
  return out.set(c * Math.cos(lon), Math.sin(dec), -c * Math.sin(lon)).normalize();
}

/** Resolve a CSS custom property (design token) to a colour string usable by Three. */
export function cssVar(name: string, fallback: string): string {
  if (typeof window === 'undefined') return fallback;
  const v = getComputedStyle(document.documentElement).getPropertyValue(name).trim();
  return v || fallback;
}

export const TOKEN_FALLBACKS: Record<string, string> = {
  '--leo': '#38d3ff',
  '--meo': '#8f7dff',
  '--geo': '#f5b544',
  '--heo': '#ff7ab6',
  '--other': '#7c869e',
  '--accent': '#38d3ff',
  '--accent-2': '#8f7dff',
  '--ink-3': '#6b7694',
  '--rule-strong': 'rgba(160, 180, 230, 0.28)',
  '--plane': '#0b1020',
  '--plane-2': '#111830',
  '--space': '#060912',
};

export function token(name: keyof typeof TOKEN_FALLBACKS): string {
  return cssVar(name, TOKEN_FALLBACKS[name] ?? '#ffffff');
}

/** Detect WebGL support without creating a persistent context (headless / old GPUs / blocked GL). */
export function hasWebGL(): boolean {
  if (typeof window === 'undefined') return false;
  try {
    const c = document.createElement('canvas');
    const gl = c.getContext('webgl2') ?? c.getContext('webgl');
    if (!gl) return false;
    const ext = gl.getExtension('WEBGL_lose_context');
    ext?.loseContext();
    return true;
  } catch {
    return false;
  }
}

export function prefersReducedMotion(): boolean {
  return typeof window !== 'undefined' && window.matchMedia('(prefers-reduced-motion: reduce)').matches;
}

/** Low-power heuristic: cap rendered points on small screens / few cores. */
export function isLowPower(): boolean {
  if (typeof window === 'undefined') return false;
  const cores = navigator.hardwareConcurrency ?? 8;
  return cores <= 4 || window.innerWidth < 768;
}