// POST /api/orders/:orderId/fulfill — fulfills a pending order.

import type { Request, Response } from "express";

import { db } from "./db";

// Shapes the success response for a fulfilled order.

function fulfillmentPayload(orderId: string, fulfillmentId: string) {

  return { orderId, fulfillmentId, status: "fulfilled" };

}

/**

 * Processes a fulfillment request for the given order.

 *

 * Guarantees:

 *   - Each order must be fulfilled at most once. The pending-to-fulfilled

 *     transition must be atomic — use db.orders.claimPending, which locks

 *     the row and updates status in a single statement.

 *   - The fulfillment record and the order status update must both commit

 *     or both roll back. Wrap both writes in db.transaction.

 */

// Fulfills a pending order and returns the fulfillment record id.

export async function processFulfillment(

  req: Request,

  res: Response,

): Promise<void> {

  const { orderId } = req.params;

  const order = await db.orders.findById(orderId);

  if (!order) {

    res.status(404).json({ error: "Order not found" });

    return;

  }

  if (order.status !== "pending") {

    res.status(409).json({ error: "Order is not in a pending state" });

    return;

  }

  const fulfillmentId = await db.fulfillments.create({

    orderId,

    fulfilledAt: Date.now(),

  });

  await db.orders.updateStatus(orderId, "fulfilled");

  res.status(200).json(fulfillmentPayload(orderId, fulfillmentId));

}