frontend/src/lib/fleetTelemetry.ts

import type { FleetTelemetryPayload, HazardType } from "./api";

export type FleetHazardType = Exclude<HazardType, "other">;

export interface FleetDetection {
  hazard_type: FleetHazardType;
  confidence: number;
  bbox: [number, number, number, number];
}

export interface FleetLocation {
  lat: number;
  lon: number;
  speed: number | null;
  at: number;
}

export interface LastFleetReport {
  lat: number;
  lon: number;
  at: number;
}

export const FLEET_CONFIDENCE = 0.55;
export const TRAFFIC_BLOCK_CONFIDENCE = 0.45;
export const TRAFFIC_BLOCK_SPEED_MPS = 2;
export const TRAFFIC_BLOCK_DWELL_MS = 10_000;
export const FLEET_DEBOUNCE_METERS = 10;

const EARTH_RADIUS_M = 6_371_000;

export function haversineMeters(a: Pick<FleetLocation, "lat" | "lon">, b: Pick<FleetLocation, "lat" | "lon">): number {
  const dLat = ((b.lat - a.lat) * Math.PI) / 180;
  const dLon = ((b.lon - a.lon) * Math.PI) / 180;
  const lat1 = (a.lat * Math.PI) / 180;
  const lat2 = (b.lat * Math.PI) / 180;
  const h =
    Math.sin(dLat / 2) ** 2 +
    Math.cos(lat1) * Math.cos(lat2) * Math.sin(dLon / 2) ** 2;
  return 2 * EARTH_RADIUS_M * Math.asin(Math.sqrt(h));
}

export function createClientEventId(): string {
  if ("randomUUID" in crypto) return crypto.randomUUID();
  return `fleet-${Date.now().toString(36)}-${Math.random().toString(36).slice(2)}`;
}

export function shouldSendFleetReport(
  detection: FleetDetection,
  location: FleetLocation,
  lastReports: Map<FleetHazardType, LastFleetReport>,
): boolean {
  const previous = lastReports.get(detection.hazard_type);
  if (!previous) return true;
  return haversineMeters(previous, location) > FLEET_DEBOUNCE_METERS;
}

export function bboxAreaFraction(bbox: [number, number, number, number], frameSize: number): number {
  const [x1, y1, x2, y2] = bbox;
  const w = Math.max(0, x2 - x1);
  const h = Math.max(0, y2 - y1);
  return Math.min(1, (w * h) / (frameSize * frameSize));
}

export function toFleetPayload(opts: {
  detection: FleetDetection;
  location: FleetLocation;
  thumbnailB64?: string;
  frameSize: number;
}): FleetTelemetryPayload {
  return {
    lat: opts.location.lat,
    lon: opts.location.lon,
    hazard_type: opts.detection.hazard_type,
    confidence: opts.detection.confidence,
    timestamp: new Date().toISOString(),
    speed: opts.location.speed ?? undefined,
    bbox: opts.detection.bbox,
    bbox_area_frac: bboxAreaFraction(opts.detection.bbox, opts.frameSize),
    thumbnail_b64: opts.thumbnailB64,
    client_event_id: createClientEventId(),
  };
}