/**
 * Last-known-location cache.
 * ─────────────────────────────────────────────────────────────────────────────
 * Getting a fresh GPS fix takes time. To make the map feel instant we remember
 * the user's last successful location in localStorage and use it to:
 *   1. Open the map ALREADY centered on their area (optimistic initial view).
 *   2. Give "Near Me" something to fly to immediately while the fresh fix
 *      resolves in the background.
 *
 * This is a coarse convenience cache, not a source of truth — a fresh fix always
 * supersedes it. We never store accuracy or timestamps beyond what's needed and
 * it lives only in this browser/app.
 */

export interface LastLocation {
  lat: number;
  lng: number;
  /** Epoch ms when this fix was captured. */
  at: number;
}

const KEY = 'skatespots:last-location';

/** Consider a cached location "usable for centering" for 30 days. */
const MAX_AGE = 30 * 24 * 60 * 60 * 1000;

/** Persist a successful location fix. Never throws. */
export function saveLastLocation(lat: number, lng: number): void {
  try {
    if (
      typeof lat !== 'number' ||
      typeof lng !== 'number' ||
      Number.isNaN(lat) ||
      Number.isNaN(lng) ||
      (lat === 0 && lng === 0)
    ) {
      return;
    }
    const payload: LastLocation = { lat, lng, at: Date.now() };
    localStorage.setItem(KEY, JSON.stringify(payload));
  } catch {
    // ignore private-mode / quota failures
  }
}

/**
 * Read the cached location if present and not expired. Returns null otherwise.
 * Never throws.
 */
export function getLastLocation(): LastLocation | null {
  try {
    const raw = localStorage.getItem(KEY);
    if (!raw) return null;
    const parsed = JSON.parse(raw) as Partial<LastLocation>;
    if (
      typeof parsed?.lat !== 'number' ||
      typeof parsed?.lng !== 'number' ||
      typeof parsed?.at !== 'number'
    ) {
      return null;
    }
    if (Date.now() - parsed.at > MAX_AGE) return null;
    return { lat: parsed.lat, lng: parsed.lng, at: parsed.at };
  } catch {
    return null;
  }
}