metatrondelivery/app/lib/geo.ts

// Pure geographic math — no network, no DB (CLAUDE.md: pure functions,
// inject data, no I/O in the math). Geocoding itself (address -> lat/lng)
// is I/O and lives in services/zones.server.ts; this file is just the
// distance/eligibility arithmetic once coordinates are known.

export interface Coordinates {
  lat: number;
  lng: number;
}

const EARTH_RADIUS_KM = 6371;

function toRadians(degrees: number): number {
  return (degrees * Math.PI) / 180;
}

/** Great-circle (straight-line) distance between two points, in kilometers. */
export function haversineDistanceKm(a: Coordinates, b: Coordinates): number {
  const dLat = toRadians(b.lat - a.lat);
  const dLng = toRadians(b.lng - a.lng);
  const lat1 = toRadians(a.lat);
  const lat2 = toRadians(b.lat);

  const h = Math.sin(dLat / 2) ** 2 + Math.cos(lat1) * Math.cos(lat2) * Math.sin(dLng / 2) ** 2;
  const c = 2 * Math.atan2(Math.sqrt(h), Math.sqrt(1 - h));

  return EARTH_RADIUS_KM * c;
}

export function isWithinRadiusKm(point: Coordinates, center: Coordinates, radiusKm: number): boolean {
  return haversineDistanceKm(point, center) <= radiusKm;
}

/** Loose normalization for postal/ZIP comparison: uppercase, strip spaces. Matches "V6B 1A1" against "v6b1a1". */
export function normalizePostalCode(code: string): string {
  return code.toUpperCase().replace(/\s+/g, "");
}

export function isPostalCodeListed(postalCode: string, listed: string[]): boolean {
  const normalized = normalizePostalCode(postalCode);
  return listed.some((entry) => normalizePostalCode(entry) === normalized);
}

/** Sorts locations by distance from a point, nearest first. */
export function sortByDistance<T extends { coordinates: Coordinates }>(point: Coordinates, items: T[]): T[] {
  return [...items].sort(
    (a, b) => haversineDistanceKm(point, a.coordinates) - haversineDistanceKm(point, b.coordinates),
  );
}