/**
 * Reverse geocoding for spot/shop location tags
 * ─────────────────────────────────────────────────────────────────────────────
 * Turns a pin into `city` / `country` / `country_code` tags so the map AND the
 * community stats agree on where a spot is. This is the **single source of truth**
 * for the request, used by spot create/edit and shop create/edit.
 *
 * Two providers, tried in order, so a new spot is tagged by default:
 *   1. OpenStreetMap **Nominatim** (primary — matches existing data).
 *   2. **BigDataCloud** `reverse-geocode-client` (fallback — client-friendly, no
 *      key). Nominatim's usage policy forbids per-viewer volume and can 429; a
 *      single create/edit call is fine, but we don't want a failure to mean an
 *      untagged spot, so we fall back.
 *
 * Best-effort by design — it **never throws**, so a geocoder outage can never
 * block a publish. If both providers fail the spot still publishes (with its
 * geohash); the stats' read-time derivation can still place it.
 *
 * ⚠️ Both providers see the caller's IP. Disclosed in `/privacy` →
 * "What leaves your device" → *Spot/shop geocoding*. The coordinates are the
 * **spot/shop pin**, never the device's live GPS.
 */

export interface GeocodedRegions {
  /** Best available human city/town/village/county name. */
  city: string;
  /** Nominatim's display country name (e.g. "United Kingdom"). */
  country: string;
  /** Region/state, used to build a readable location string. */
  state: string;
  /** ISO-3166-1 alpha-2, uppercased (e.g. "GB"). The stable stats grouping key. */
  countryCode: string;
}

const EMPTY: GeocodedRegions = { city: '', country: '', state: '', countryCode: '' };

const NOMINATIM_TIMEOUT_MS = 6000;
const BIGDATA_TIMEOUT_MS = 8000;

/** Primary: OpenStreetMap Nominatim. Never throws. */
async function geocodeNominatim(lat: number, lng: number): Promise<GeocodedRegions> {
  try {
    const res = await fetch(
      `https://nominatim.openstreetmap.org/reverse?lat=${lat}&lon=${lng}&format=json&zoom=10`,
      {
        headers: { 'Accept-Language': 'en', 'User-Agent': 'SkateSpots/1.0' },
        signal: AbortSignal.timeout(NOMINATIM_TIMEOUT_MS),
      },
    );
    if (!res.ok) return EMPTY;
    const data = (await res.json()) as { address?: Record<string, string> };
    const addr = data.address ?? {};
    return {
      city: addr.city ?? addr.town ?? addr.village ?? addr.county ?? '',
      country: addr.country ?? '',
      state: addr.state ?? '',
      countryCode: String(addr.country_code ?? '').trim().toUpperCase(),
    };
  } catch {
    return EMPTY;
  }
}

/**
 * Fallback: BigDataCloud client-side reverse geocoding (no key, CORS `*`).
 * Also used directly by the stats' read-time derivation (`lib/derivedRegions`),
 * where Nominatim must NOT be used. Never throws.
 */
export async function geocodeBigDataCloud(lat: number, lng: number): Promise<GeocodedRegions> {
  try {
    const res = await fetch(
      `https://api.bigdatacloud.net/data/reverse-geocode-client?latitude=${lat}&longitude=${lng}&localityLanguage=en`,
      { signal: AbortSignal.timeout(BIGDATA_TIMEOUT_MS) },
    );
    if (!res.ok) return EMPTY;
    const data = (await res.json()) as {
      city?: string;
      locality?: string;
      countryName?: string;
      countryCode?: string;
      principalSubdivision?: string;
    };
    return {
      city: data.city || data.locality || '',
      country: data.countryName || '',
      state: data.principalSubdivision || '',
      countryCode: String(data.countryCode ?? '').trim().toUpperCase(),
    };
  } catch {
    return EMPTY;
  }
}

/**
 * Reverse geocode a pin. Nominatim first, then BigDataCloud. Resolves to empty
 * strings only when BOTH providers fail.
 */
export async function reverseGeocodeRegions(lat: number, lng: number): Promise<GeocodedRegions> {
  const primary = await geocodeNominatim(lat, lng);
  if (primary.city || primary.country || primary.countryCode) return primary;
  return geocodeBigDataCloud(lat, lng);
}

/** Push the region tags onto an event tag list, skipping empty values. */
export function pushRegionTags(tags: string[][], geo: GeocodedRegions): void {
  if (geo.city) tags.push(['city', geo.city]);
  if (geo.country) tags.push(['country', geo.country]);
  if (geo.countryCode) tags.push(['country_code', geo.countryCode]);
}