import { promises as fs } from 'node:fs';
import path from 'node:path';
import { haversineKm } from './geo';

export type CsvRow = Record<string, string>;

// Minimal RFC-4180-ish parser: quoted fields, escaped quotes (""), CRLF.
export function parseCsv(text: string): CsvRow[] {
  const rows: string[][] = [];
  let row: string[] = [];
  let field = '';
  let inQuotes = false;

  for (let i = 0; i < text.length; i++) {
    const c = text[i];
    if (inQuotes) {
      if (c === '"') {
        if (text[i + 1] === '"') {
          field += '"';
          i++;
        } else {
          inQuotes = false;
        }
      } else {
        field += c;
      }
    } else if (c === '"') {
      inQuotes = true;
    } else if (c === ',') {
      row.push(field);
      field = '';
    } else if (c === '\n') {
      row.push(field);
      rows.push(row);
      row = [];
      field = '';
    } else if (c !== '\r') {
      field += c;
    }
  }
  if (field.length > 0 || row.length > 0) {
    row.push(field);
    rows.push(row);
  }

  const [header, ...rest] = rows;
  return rest
    .filter((r) => r.length === header.length && !(r.length === 1 && r[0] === ''))
    .map((r) => Object.fromEntries(header.map((h, i) => [h, r[i]])));
}

// OurAirports types kept for the sim: all fixed-wing airports plus seaplane bases.
// 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 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;
  lat: number;
  lon: number;
}

export interface GeoJsonFeature {
  type: 'Feature';
  geometry: { type: 'Point'; coordinates: [number, number] };
  properties: AirportProperties;
}

export interface GeoJsonFeatureCollection {
  type: 'FeatureCollection';
  features: GeoJsonFeature[];
}

export function toGeoJson(rows: CsvRow[]): GeoJsonFeatureCollection {
  const features: GeoJsonFeature[] = [];
  for (const r of rows) {
    // OurAirports schema: latitude_deg / longitude_deg; ICAO in icao_code, ident as fallback.
    const lat = Number(r.latitude_deg);
    const lon = Number(r.longitude_deg);
    if (!r.ident || !r.name || !Number.isFinite(lat) || !Number.isFinite(lon)) continue;
    features.push({
      type: 'Feature',
      geometry: { type: 'Point', coordinates: [lon, lat] },
      properties: { name: r.name, icao: r.icao_code || r.ident, lat, lon },
    });
  }
  return { type: 'FeatureCollection', features };
}

// Three consumers key features by ICAO with silent-overwrite semantics (the map's airport
// index, the route/queue GeoJSON builders and the sim's airport lookups) — a duplicate would
// corrupt state without any error, so fail loud at load instead.
export function assertUniqueIcaos(fc: GeoJsonFeatureCollection): void {
  const seen = new Set<string>();
  for (const f of fc.features) {
    if (seen.has(f.properties.icao)) throw new Error(`duplicate ICAO in airport dataset: ${f.properties.icao}`);
    seen.add(f.properties.icao);
  }
}

let cached: GeoJsonFeatureCollection | null = null;

export async function loadAirportsGeoJson(): Promise<GeoJsonFeatureCollection> {
  if (cached) return cached;
  const file = path.join(process.cwd(), 'data', 'airports_world.csv');
  const text = await fs.readFile(file, 'utf8');
  const fc = toGeoJson(filterWorldAirports(parseCsv(text)));
  assertUniqueIcaos(fc);
  cached = fc;
  return cached;
}

export async function airportsHandler(): Promise<Response> {
  try {
    const fc = await loadAirportsGeoJson();
    return Response.json(fc);
  } catch (err) {
    console.error('failed to load airport data', err);
    return Response.json({ error: 'failed to load airport data' }, { status: 500 });
  }
}