waseel/lib/use-service-availability.ts

// Which services actually have a driver near the rider.
//
// The map only ever shows the selected service, so an empty map means both
// "nobody is driving tonight" and "nobody is on a moto, though three cars are
// a street away" — and the rider has no way to tell which. That ambiguity is
// what leaves someone staring at a blank map instead of switching service and
// getting a ride.
//
// This answers it once for every service, so the picker can show availability
// and the request screen can point at a service that would actually work.

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

import { SERVICES, type ServiceId } from "@/constants/services";
import { fetchAPI } from "@/lib/fetch";
import { SEARCH_MAX_RADIUS_M } from "@/lib/use-nearby-drivers";

// Slower than the map's own poll: this drives a hint, not the pins, and it
// scans every service rather than one.
const POLL_MS = 15000;

// ~110 m, so GPS jitter doesn't restart the request loop on every fix.
const QUANTIZE = 1e3;
const quantize = (v: number): number => Math.round(v * QUANTIZE) / QUANTIZE;

export type ServiceAvailability = {
  /** Driver count per service, every service present (zeros included). */
  counts: Record<ServiceId, number>;
  /** Services with at least one driver in range. */
  available: ServiceId[];
  /** Radius the counts were measured over, in metres. */
  radius: number;
  loading: boolean;
};

const emptyCounts = (): Record<ServiceId, number> => {
  const counts = {} as Record<ServiceId, number>;
  for (const service of SERVICES) counts[service.id] = 0;
  return counts;
};

export const useServiceAvailability = (
  latitude: number | null,
  longitude: number | null,
): ServiceAvailability => {
  const [counts, setCounts] = useState<Record<ServiceId, number>>(emptyCounts);
  const [radius, setRadius] = useState(SEARCH_MAX_RADIUS_M);
  const [loading, setLoading] = useState(true);

  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>;

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

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

        const data = res.data as {
          radius: number;
          counts: Record<string, number>;
        };

        // Merge onto a full set of zeros so a service the server didn't
        // mention still renders as "none nearby" rather than blank.
        const next = emptyCounts();
        for (const service of SERVICES) {
          next[service.id] = data.counts?.[service.id] ?? 0;
        }

        setCounts(next);
        setRadius(data.radius ?? SEARCH_MAX_RADIUS_M);
      } catch {
        // Leave the last known counts in place — a dropped request shouldn't
        // flash "no drivers anywhere" at the rider.
      } finally {
        if (!cancelled) {
          setLoading(false);
          timer = setTimeout(run, POLL_MS);
        }
      }
    };

    void run();

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

  const available = SERVICES.map((s) => s.id).filter((id) => counts[id] > 0);

  return { counts, available, radius, loading };
};