Special remote airports + isRemote curation (ISS-097, v0.61.0)

lib/airports.ts

@@ -1,5 +1,6 @@
 import { promises as fs } from 'node:fs';
 import path from 'node:path';
+import { haversineKm } from './geo';
 
 export type CsvRow = Record<string, string>;
 
@@ -52,15 +53,38 @@ export function parseCsv(text: string): CsvRow[] {
 // The 2026 schema splits "airport" into small/medium/large_airport (older dumps used a
 // single "airport" type + category column) — both spellings are accepted. Heliports are
 // excluded — no fixed-wing transport ops; other types (closed, balloonport, ...) are
-// irrelevant to an airline-ops game. The committed dataset is pre-curated to large_airport
-// only (scripts/build-world-airports.mjs); this check stays as a cheap guard against an
-// uncurated dump being swapped in.
+// irrelevant to an airline-ops game. The committed dataset is pre-curated by
+// scripts/build-world-airports.mjs: every large_airport plus the small/medium/seaplane rows
+// that are REMOTE (see isRemote) — this check stays as a cheap guard against an uncurated
+// dump being swapped in.
 const INCLUDED_TYPES = new Set(['airport', 'small_airport', 'medium_airport', 'large_airport', 'seaplane_base']);
 
 export function filterWorldAirports(rows: CsvRow[]): CsvRow[] {
   return rows.filter((r) => INCLUDED_TYPES.has(r.type));
 }
 
+// v0.61.0 (ISS-097): "special" remote airports — the issue's loneliness test: an airport is
+// remote when no other member of `airports` sits within this radius, so it stands alone in a
+// genuinely empty region (Antarctica, high Arctic, far islands) rather than being one of many.
+export const REMOTE_RADIUS_KM = 1000;
+
+export interface RemoteAirport {
+  icao: string;
+  lat: number;
+  lon: number;
+}
+
+// True when the airport with this ICAO has no OTHER member of `airports` within REMOTE_RADIUS_KM
+// (haversine). Unknown ICACOs are not remote — callers only pass rows they intend to include.
+export function isRemote(airports: readonly RemoteAirport[], icao: string): boolean {
+  const a = airports.find((x) => x.icao === icao);
+  if (!a) return false;
+  for (const b of airports) {
+    if (b.icao !== a.icao && haversineKm(a.lat, a.lon, b.lat, b.lon) <= REMOTE_RADIUS_KM) return false;
+  }
+  return true;
+}
+
 export interface AirportProperties {
   name: string;
   icao: string;