SkateSpots/src/lib/routing.ts

/**
 * In-app routing — OSRM client + skate-friendly distance/time formatting.
 * ─────────────────────────────────────────────────────────────────────────────
 * We deliberately do NOT hand off to Google/Apple Maps. Instead we fetch a route
 * from the keyless, account-free public OSRM server and draw it on our own
 * Leaflet map. This keeps navigation in-app, private, and dependency-light.
 *
 * SCOPE (on purpose):
 *   • We return a static route line + distance + duration summary.
 *   • We do NOT do live turn-by-turn, voice, or rerouting — that's a huge native
 *     effort and out of scope for a lean PWA.
 *
 * MODES:
 *   foot / bike / car are real OSRM profiles. "moto" (motorbike) isn't a real
 *   OSRM profile, so we route it as `car` (driving roads) and label it honestly.
 *
 * TRANSIT (subway/public transport) is intentionally NOT here: there is no free,
 * keyless, worldwide transit routing API. It needs per-city GTFS data and would
 * be empty in most cities — a worse experience than omitting it.
 */

/** Travel modes offered in the UI. */
export type TravelMode = 'foot' | 'bike' | 'moto' | 'car';

export interface TravelModeMeta {
  mode: TravelMode;
  /** OSRM routing profile actually used. */
  profile: 'foot' | 'bike' | 'car';
  label: string;
  emoji: string;
  /** True when we're being honest that the profile is an approximation. */
  approximate?: boolean;
}

export const TRAVEL_MODES: TravelModeMeta[] = [
  { mode: 'foot', profile: 'foot', label: 'Skate / Walk', emoji: '🛹' },
  { mode: 'bike', profile: 'bike', label: 'Bike', emoji: '🚲' },
  { mode: 'moto', profile: 'car', label: 'Moto', emoji: '🏍️', approximate: true },
  { mode: 'car', profile: 'car', label: 'Car', emoji: '🚗' },
];

export function travelModeMeta(mode: TravelMode): TravelModeMeta {
  return TRAVEL_MODES.find((m) => m.mode === mode) ?? TRAVEL_MODES[0];
}

export interface RouteResult {
  /** Decoded [lat, lng] path suitable for a Leaflet polyline. */
  coordinates: Array<[number, number]>;
  /** Straight-line-ish route distance in meters. */
  distanceM: number;
  /** Estimated travel time in seconds (from OSRM for the profile). */
  durationS: number;
  /** Which mode the route was requested for. */
  mode: TravelMode;
}

const OSRM_BASE = 'https://router.project-osrm.org/route/v1';
const CORS_PROXY = 'https://proxy.shakespeare.diy/?url=';

interface OsrmResponse {
  code: string;
  routes?: Array<{
    distance: number;
    duration: number;
    geometry: { coordinates: Array<[number, number]> }; // [lng, lat]
  }>;
}

/**
 * Fetch a route between two points for a given travel mode using OSRM.
 * Throws on network error or when OSRM returns no route.
 */
export async function fetchRoute(
  from: { lat: number; lng: number },
  to: { lat: number; lng: number },
  mode: TravelMode,
  signal?: AbortSignal,
): Promise<RouteResult> {
  const { profile } = travelModeMeta(mode);
  // OSRM wants lon,lat;lon,lat
  const coords = `${from.lng},${from.lat};${to.lng},${to.lat}`;
  const target = `${OSRM_BASE}/${profile}/${coords}?overview=full&geometries=geojson`;
  const url = `${CORS_PROXY}${encodeURIComponent(target)}`;

  const res = await fetch(url, { signal });
  if (!res.ok) {
    throw new Error(`Routing service returned ${res.status}`);
  }

  const data = (await res.json()) as OsrmResponse;
  if (data.code !== 'Ok' || !data.routes || data.routes.length === 0) {
    throw new Error('No route found');
  }

  const route = data.routes[0];
  // GeoJSON is [lng, lat] → Leaflet wants [lat, lng]
  const coordinates = route.geometry.coordinates.map(
    ([lng, lat]) => [lat, lng] as [number, number],
  );

  return {
    coordinates,
    distanceM: route.distance,
    durationS: route.duration,
    mode,
  };
}

// ─── Formatting helpers ──────────────────────────────────────────────────────

/**
 * Format a distance in kilometers, human-friendly.
 * e.g. 0.34 → "340 m", 3.4 → "3.4 km", 12 → "12 km"
 */
export function formatDistance(km: number): string {
  if (!isFinite(km) || km < 0) return '—';
  if (km < 1) return `${Math.round(km * 1000)} m`;
  if (km < 10) return `${km.toFixed(1)} km`;
  return `${Math.round(km)} km`;
}

/** Format a duration in seconds → "12 min", "1 h 5 min". */
export function formatDuration(seconds: number): string {
  if (!isFinite(seconds) || seconds < 0) return '—';
  const mins = Math.round(seconds / 60);
  if (mins < 1) return '<1 min';
  if (mins < 60) return `${mins} min`;
  const h = Math.floor(mins / 60);
  const m = mins % 60;
  return m > 0 ? `${h} h ${m} min` : `${h} h`;
}

/**
 * Skaters think in time, not distance. Estimate a cruising time from a
 * straight-line distance (km) at a relaxed ~10 km/h push, and phrase it in a
 * skate-native way. No routing call needed — pure formula, works offline.
 */
export function skateTime(km: number): string {
  if (!isFinite(km) || km < 0) return '';
  const CRUISE_KMH = 10; // relaxed cruising pace
  const mins = Math.round((km / CRUISE_KMH) * 60);
  if (mins < 1) return 'right here';
  if (mins < 60) return `~${mins} min cruise`;
  const h = (mins / 60).toFixed(1);
  return `~${h} h cruise`;
}

/**
 * Compact one-line readout for cards/popups given a distance in km.
 * e.g. "1.2 km · ~7 min cruise"
 */
export function distanceReadout(km: number): string {
  const d = formatDistance(km);
  const t = skateTime(km);
  return t ? `${d} · ${t}` : d;
}