waseel/app/(api)/ride/[id]/offer+api.ts

import { requireApprovedDriver } from "@/lib/driver";
import { sql, transaction } from "@/lib/db";
import { sendPushToUser } from "@/lib/push";
import { DRIVER_BUSY_ARRAY } from "@/lib/ride-lifecycle";
import { haversine } from "@/lib/utils";

// POST — a driver's answer to a broadcast request.
//
//   { action: 'offer' }    — volunteer for it. The rider sees this driver
//                            appear in their list of offers and may pick them.
//   { action: 'withdraw' } — take the offer back, before the rider picks.
//
// Offering is not an assignment: several drivers can be offered on the same
// request at once and none of them is committed until the rider chooses. That
// is why offering doesn't take a driver off the board, and why withdrawing is
// free — the cost of a driver changing their mind lands here rather than on a
// rider whose ride was already promised away.
export async function POST(req: Request, { id }: { id: string }) {
  const rideId = Number(id);
  if (!Number.isInteger(rideId)) {
    return Response.json({ error: "Invalid ride id." }, { status: 400 });
  }

  // Approval is re-checked here, not just at broadcast time: a driver
  // suspended between seeing a request and tapping Offer must not be able to
  // put themselves in front of a rider. (Rides already under way stay under
  // requireDriverProfile — a suspension must never strand a rider who is
  // sitting in the car.)
  const result = await requireApprovedDriver(req);
  if ("error" in result) return result.error;

  const { driverId } = result;

  let body: { action?: string };
  try {
    body = await req.json();
  } catch {
    return Response.json({ error: "Invalid JSON body." }, { status: 400 });
  }

  const action = body.action;
  if (action !== "offer" && action !== "withdraw") {
    return Response.json(
      { error: "action must be 'offer' or 'withdraw'." },
      { status: 400 },
    );
  }

  try {
    if (action === "withdraw") {
      const withdrawn = await sql<{ id: number }>`
        UPDATE ride_offers
        SET status = 'withdrawn', responded_at = CURRENT_TIMESTAMP
        WHERE ride_id = ${rideId}
          AND driver_id = ${driverId}
          AND status = 'offered'
        RETURNING id
      `;
      if (!withdrawn[0]) {
        return Response.json(
          { error: "There is no live offer to withdraw." },
          { status: 409 },
        );
      }
      return Response.json({ data: { status: "withdrawn" } });
    }

    const offered = await transaction<{
      userId: string;
      alreadyOffered: boolean;
    } | null>(async (tx) => {
      // Lock the request so a rider picking someone else at this exact moment
      // and this driver offering can't both believe they won.
      const rides = await tx<{
        status: string;
        user_id: string;
        service: string;
        lat: number;
        lng: number;
      }>`
        SELECT status, user_id, service,
               origin_latitude AS lat, origin_longitude AS lng
        FROM rides WHERE ride_id = ${rideId} FOR UPDATE
      `;
      const ride = rides[0];
      if (!ride || ride.status !== "requested") return null;

      // The driver's own state has to be re-read here rather than trusted from
      // the dashboard that drew the button: service, liveness and — above all
      // — whether they picked up another ride in the meantime.
      const drivers = await tx<{
        service: string;
        online: boolean;
        latitude: number | null;
        longitude: number | null;
      }>`
        SELECT service, online, latitude, longitude
        FROM drivers WHERE id = ${driverId}
      `;
      const driver = drivers[0];
      if (!driver || !driver.online || driver.service !== ride.service) {
        return null;
      }

      const busy = await tx<{ n: number }>`
        SELECT COUNT(*)::int AS n FROM rides
        WHERE driver_id = ${driverId}
          AND status = ANY(${DRIVER_BUSY_ARRAY}::text[])
      `;
      if ((busy[0]?.n ?? 0) > 0) return null;

      const distance =
        driver.latitude === null || driver.longitude === null
          ? null
          : Math.round(
              haversine(ride.lat, ride.lng, driver.latitude, driver.longitude),
            );

      // ON CONFLICT rather than an existence check: the unique index is the
      // real guard, and a driver who taps Offer twice (or re-offers after
      // withdrawing) should end up with one live offer either way.
      const rows = await tx<{ inserted: boolean }>`
        INSERT INTO ride_offers (ride_id, driver_id, status, pickup_distance_m)
        VALUES (${rideId}, ${driverId}, 'offered', ${distance})
        ON CONFLICT (ride_id, driver_id) DO UPDATE
          SET status = 'offered',
              offered_at = CURRENT_TIMESTAMP,
              responded_at = NULL,
              pickup_distance_m = EXCLUDED.pickup_distance_m
          WHERE ride_offers.status IN ('withdrawn', 'offered')
        RETURNING (xmax = 0) AS inserted
      `;
      // No row means the conflict target existed in a state we refuse to
      // revive — the rider already picked someone, or this offer was closed
      // with the request.
      if (!rows[0]) return null;

      return { userId: ride.user_id, alreadyOffered: !rows[0].inserted };
    });

    if (!offered) {
      return Response.json(
        { error: "This request is no longer open." },
        { status: 409 },
      );
    }

    // Nudge the rider — they are sitting on a screen watching for exactly
    // this. Only for the first offer on the request: the rest arrive on the
    // list they are already looking at, and a buzz per driver would turn a
    // busy street into a nuisance.
    if (!offered.alreadyOffered) {
      const [count] = await sql<{ n: number }>`
        SELECT COUNT(*)::int AS n FROM ride_offers
        WHERE ride_id = ${rideId} AND status = 'offered'
      `;
      if ((count?.n ?? 0) === 1) {
        void sendPushToUser(offered.userId, {
          title: "A driver is available",
          body: "Open your ride to see who can pick you up.",
          data: { type: "ride_offer_received", rideId },
        });
      }
    }

    return Response.json({ data: { status: "offered" } });
  } catch (error) {
    console.error("[RIDE_OFFER]: ", error);
    return Response.json({ error: "Internal Server Error" }, { status: 500 });
  }
}