Location Cloudflare Durable Objects close to users based on continent and latitude/longitude.

location.ts

export function getLocationHint(location: Location = {}) {
  if (!location.continentCode && !location.point) return 'enam';
  const areas = continentCodes[location.continentCode || 'AN'];
  let closest = areas[0];
  let shortestDistance = Infinity;

  if (areas.length === 1 || !location.point) return closest;

  const { lat, lon } = location.point;
  const userLatLong = [lat, lon] as [number, number];
  areas.forEach(area => {
    const latLong = locationLatLongs[area];
    const distance = getDistance(latLong, userLatLong);
    if (distance < shortestDistance) {
      shortestDistance = distance;
      closest = area;
    }
  });

  return closest;
}

interface Location {
  continentCode?: string;
  point?: { lat: number; lon: number };
}

type Locations = keyof typeof locationLatLongs;

const locationLatLongs: Record<string, [number, number]> = {
  wnam: [37.797958, -122.238303], // Western North America
  enam: [39.082657, -77.658312], // Eastern North America
  sam: [-9.07816, -59.0535], // South America
  weur: [48.851311, 2.295185], // Western Europe
  eeur: [44.347606, 25.674957], // Eastern Europe
  apac: [1.415, 104.021515], // Asia-Pacific
  oc: [-23.045663, 134.341405], // Oceania
  afr: [18.598045, 17.183202], // Africa
  me: [31.610075, 48.911718], // Middle East
};

const continentCodes: Record<string, Locations[]> = {
  AF: ['afr'], // Africa
  AN: ['afr', 'apac', 'weur', 'eeur', 'wnam', 'enam', 'oc', 'sam'], // Antarctica
  AS: ['apac'], // Asia
  EU: ['weur', 'eeur'], // Europe
  NA: ['wnam', 'enam'], // North america
  OC: ['oc'], // Oceania
  SA: ['sam'], // South america
};

// Returns the distance between to lat/long coordinates in km
function getDistance(pos1: [number, number], pos2: [number, number]) {
  var R = 6371; // Radius of the earth in km
  var dLat = deg2rad(pos2[0] - pos1[0]); // deg2rad below
  var dLon = deg2rad(pos2[1] - pos1[1]);
  var a =
    Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(deg2rad(pos1[0])) * Math.cos(deg2rad(pos2[0])) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  var d = R * c; // Distance in km
  return d;
}

function deg2rad(deg: number) {
  return deg * (Math.PI / 180);
}