waseel/lib/use-nearby-drivers.ts

// Progressive nearby-driver search for the rider side.
//
// /(api)/driver/nearby is bounded by a radius, so a single fixed value is
// always wrong in one direction: too tight and a rider in a quiet area sees an
// empty map, too wide and a rider in Beirut gets pins from cars that are forty
// minutes away and will never be matched to them.
//
// So the search starts tight — the handful of cars actually near the rider —
// and only widens when that comes back empty, in 5 km steps, until it finds
// someone or hits the cap. A rider in a busy street gets a close, honest map;
// a rider in the mountains still gets an answer a few seconds later.
//
// The radius is reported back so the UI can say what it's doing rather than
// showing a spinner that looks stuck.

import { useEffect, useRef, useState } from "react";

import { fetchAPI } from "@/lib/fetch";
import type { Driver } from "@/types/type";

/** First pass: only cars genuinely next to the rider. */
export const SEARCH_START_RADIUS_M = 2000;
/** Each unsuccessful pass widens the net by this much. */
export const SEARCH_STEP_M = 5000;
/** Ceiling, matching the server's own cap on the endpoint. */
export const SEARCH_MAX_RADIUS_M = 20000;

// Gap between widening attempts. Long enough not to hammer the endpoint with
// four requests in a single frame, short enough that a rider in an empty area
// reaches the full radius in a few seconds rather than half a minute.
const EXPAND_DELAY_MS = 1200;

// Once drivers are found (or the search has run out of room to widen), settle
// into a steady poll so the map keeps up with cars moving and going offline.
//
// Matched to the driver heartbeat (lib/use-driver-location PING_INTERVAL_MS):
// polling faster than drivers report would burn requests to redraw identical
// positions, and polling slower is what made the map look static — at 10s a
// car in traffic jumped a whole block between frames, which reads as a glitch
// rather than as movement. The markers interpolate between these updates, so
// this is the rate at which truth arrives, not the frame rate.
const SETTLED_POLL_MS = 5000;

// Rounding the rider's position to ~110 m before using it as an effect key.
// Raw GPS jitters by a few metres constantly, and without this every jitter
// would restart the search from the beginning and the radius would never
// climb.
const QUANTIZE = 1e3;
const quantize = (v: number): number => Math.round(v * QUANTIZE) / QUANTIZE;

export type NearbySearch = {
  drivers: Driver[];
  /** Radius the current result set came from, in metres. */
  radius: number;
  /** True while widening — i.e. nothing found yet and there's room to grow. */
  expanding: boolean;
  /** True until the first response lands, so callers can tell "none" from "not yet". */
  loading: boolean;
};

export const useNearbyDrivers = (
  service: string,
  latitude: number | null,
  longitude: number | null,
): NearbySearch => {
  const [drivers, setDrivers] = useState<Driver[]>([]);
  const [radius, setRadius] = useState(SEARCH_START_RADIUS_M);
  const [expanding, setExpanding] = useState(false);
  const [loading, setLoading] = useState(true);

  // Quantized so GPS jitter doesn't restart the search; the raw values are
  // still what gets sent to the server.
  const latKey = latitude === null ? null : quantize(latitude);
  const lngKey = longitude === null ? null : quantize(longitude);
  const coords = useRef({ latitude, longitude });
  coords.current = { latitude, longitude };

  useEffect(() => {
    if (latKey === null || lngKey === null) return;

    let cancelled = false;
    let timer: ReturnType<typeof setTimeout>;
    let current = SEARCH_START_RADIUS_M;

    setRadius(SEARCH_START_RADIUS_M);
    setLoading(true);

    const run = async () => {
      const { latitude: lat, longitude: lng } = coords.current;
      if (lat === null || lng === null) return;

      try {
        const res = await fetchAPI(
          `/(api)/driver/nearby?service=${service}&lat=${lat}&lng=${lng}&radius=${current}`,
        );
        if (cancelled) return;

        const found = (res.data ?? []) as Driver[];
        setDrivers(found);
        setRadius(current);
        setLoading(false);

        if (found.length === 0 && current < SEARCH_MAX_RADIUS_M) {
          current = Math.min(current + SEARCH_STEP_M, SEARCH_MAX_RADIUS_M);
          setExpanding(true);
          timer = setTimeout(run, EXPAND_DELAY_MS);
          return;
        }

        setExpanding(false);
        timer = setTimeout(run, SETTLED_POLL_MS);
      } catch {
        // A failed request shouldn't collapse the search back to the start —
        // retry at the same radius on the slow cadence.
        if (cancelled) return;
        setLoading(false);
        setExpanding(false);
        timer = setTimeout(run, SETTLED_POLL_MS);
      }
    };

    void run();

    return () => {
      cancelled = true;
      clearTimeout(timer);
    };
  }, [service, latKey, lngKey]);

  return { drivers, radius, expanding, loading };
};

/** "2 km" / "20 km" — the radius as riders should read it. */
export const radiusKm = (meters: number): number => Math.round(meters / 1000);