waseel/lib/dispatch.ts

// Broadcast dispatch. A new request is put in front of every eligible driver
// near the pickup at once; each of them may volunteer for it (a row in
// ride_offers) and the rider picks between whoever did.
//
// The engine's whole job is therefore the announcement. There is no queue to
// advance, no timer to chase a declining driver with, and no background
// worker: drivers discover requests through their dashboard poll and their
// location heartbeat, and this module exists to make sure a phone that is
// face-down in a pocket still buzzes when a job appears nearby.

import { sql } from "@/lib/db";
import { sendPushToDriver } from "@/lib/push";
import { boundingBox, haversine } from "@/lib/utils";
import { expireStaleRequests } from "@/lib/ride-lifecycle";
import {
  BROADCAST_RADIUS_M,
  DRIVER_STALE_SECONDS,
  OFFER_CHANNEL_ID,
} from "@/constants/dispatch";

// Fares are stored in cents; the notification shows what the rider is paying.
const formatFare = (cents: number): string => `$${(cents / 100).toFixed(2)}`;

type NearbyDriverRow = {
  id: number;
  latitude: number;
  longitude: number;
};

/**
 * Drivers who should see `rideId` right now: right service, vetted, online,
 * fresh position, not already on a ride, and within the broadcast radius of
 * the pickup.
 *
 * Exported because the driver's own poll asks the mirror-image question —
 * "which open requests are near me?" — and the two must agree. If a driver
 * could be pushed a request their dashboard then filtered out, they'd get a
 * notification for a job that isn't there when they open the app.
 */
export const driversForRequest = async (rideId: number): Promise<number[]> => {
  const rides = await sql<{
    lat: number;
    lng: number;
    service: string;
    status: string;
  }>`
    SELECT origin_latitude AS lat, origin_longitude AS lng, service, status
    FROM rides WHERE ride_id = ${rideId}
  `;
  const ride = rides[0];
  if (!ride || ride.status !== "requested") return [];

  // A coarse bounding box does the work in the index, then a great-circle
  // pass trims the corners — same two-step the rider's map search uses.
  const box = boundingBox(ride.lat, ride.lng, BROADCAST_RADIUS_M);

  const candidates = await sql<NearbyDriverRow>`
    SELECT d.id, d.latitude, d.longitude
    FROM drivers d
    WHERE d.service = ${ride.service}
      AND d.online = TRUE
      AND d.approval_status = 'approved'
      AND d.user_id IS NOT NULL
      AND d.latitude IS NOT NULL
      AND d.longitude IS NOT NULL
      AND d.last_seen > CURRENT_TIMESTAMP - make_interval(secs => ${DRIVER_STALE_SECONDS})
      AND d.latitude BETWEEN ${box.minLat} AND ${box.maxLat}
      AND d.longitude BETWEEN ${box.minLng} AND ${box.maxLng}
      AND NOT EXISTS (
        SELECT 1 FROM rides r
        WHERE r.driver_id = d.id
          AND r.status IN ('accepted', 'arrived', 'en_route')
      )
  `;

  return candidates
    .filter(
      (d) =>
        haversine(ride.lat, ride.lng, d.latitude, d.longitude) <=
        BROADCAST_RADIUS_M,
    )
    .map((d) => d.id);
};

/**
 * Announce `rideId` to every eligible driver nearby.
 *
 * Idempotent, and deliberately so: it is called from the rider's status poll
 * as well as from ride creation, and a request that buzzed forty phones once
 * must not buzz them again every three seconds. `broadcast_at` is the latch —
 * claimed with a guarded UPDATE so two concurrent callers can't both win it.
 *
 * Returns how many drivers were notified (0 if the announcement was already
 * made, or nobody was in range).
 */
export const broadcastRequest = async (rideId: number): Promise<number> => {
  try {
    // Give up on requests that have run past their window before announcing
    // one — this is one of the lazy paths that stands in for a worker.
    await expireStaleRequests(rideId);

    // Claim the announcement. Whoever gets the row does the pushing.
    const claimed = await sql<{
      origin_address: string;
      fare_price: number;
      service: string;
    }>`
      UPDATE rides
      SET broadcast_at = CURRENT_TIMESTAMP
      WHERE ride_id = ${rideId}
        AND status = 'requested'
        AND broadcast_at IS NULL
      RETURNING origin_address, fare_price, service
    `;
    if (!claimed[0]) return 0;

    const drivers = await driversForRequest(rideId);
    if (drivers.length === 0) return 0;

    const { origin_address: origin, fare_price: fare } = claimed[0];

    // Not awaited: dispatch must not stall on Expo's service, and a driver
    // still finds the request through the dashboard poll and the location
    // heartbeat regardless.
    for (const driverId of drivers) {
      void sendPushToDriver(driverId, {
        title: "New ride request nearby",
        body: `${formatFare(Number(fare))} · pickup at ${origin}`,
        channelId: OFFER_CHANNEL_ID,
        data: { type: "ride_request", rideId },
      });
    }

    return drivers.length;
  } catch (error) {
    console.error("[BROADCAST_REQUEST]: ", error);
    return 0;
  }
};