// units.js — SI ↔ optional in-world units (spans, leagues; from /api/meta at startup). Without them: SI only.
export const UNITS = { span_m: null, moment_s: null, league_km: null, day_hours: 24 };
export function setUnits(u) { Object.assign(UNITS, u || {}); }
export const kmToLeagues = km => km / UNITS.league_km;
export const mToSpans = m => m / UNITS.span_m;
export const km2ToSqLeagues = a => a / UNITS.league_km ** 2;
export const walkDays = (km, kmPerDay = 30) => km / kmPerDay;
const num = (v, d) => v.toLocaleString('en-US', { minimumFractionDigits: d, maximumFractionDigits: d });
const spans = m => (UNITS.span_m ? ` · ${num(mToSpans(m), 0)} spans` : '');
const leagues = (km, d) => (UNITS.league_km ? ` · ${num(kmToLeagues(km), d)} leagues` : '');
export const fmtDistance = km => (km < 1
  ? `${num(km * 1000, 0)} m${spans(km * 1000)}`
  : `${num(km, km < 100 ? 1 : 0)} km${leagues(km, km < 100 ? 2 : 1)}`);
export const fmtElev = m => `${num(m, 0)} m${spans(m)}`;
export const fmtArea = km2 => `${num(km2, 0)} km²${UNITS.league_km ? ` · ${num(km2ToSqLeagues(km2), 0)} sq leagues` : ''}`;
export function fmtWalk(km) { const d = walkDays(km); return `${num(d, d < 10 ? 1 : 0)} days on foot`; }
export const fmtLatLon = (lat, lon) =>
  `${Math.abs(lat).toFixed(3)}° ${lat >= 0 ? 'N' : 'S'}, ${Math.abs(lon).toFixed(3)}° ${lon >= 0 ? 'E' : 'W'}`;
export function niceKm(km) {
  const p = 10 ** Math.floor(Math.log10(km));
  return p * [1, 2, 5].findLast(m => m * p <= km * (1 + 1e-12));
}