ERP/tests/concurrency.test.ts

import { describe, expect, it } from "vitest";
import { stockOf } from "@/lib/server/stock";
import { StockTransfer } from "@/lib/server/models/StockTransfer";
import { StockLock } from "@/lib/server/models/StockLock";
import * as adjustments from "@/app/api/stock/adjustments/route";
import * as transfers from "@/app/api/stock/transfers/route";
import { makeTenant, req, uuid, type Tenant } from "./helpers";

async function openingStock(t: Tenant, quantity: number) {
  await adjustments.POST(
    req("POST", "/x", {
      as: t.owner,
      body: { clientUuid: uuid(), branchId: t.branchA, productId: t.water20, mode: "DELTA", quantity },
    })
  );
}

const transferOut = (t: Tenant, quantity: number) =>
  transfers.POST(
    req("POST", "/x", {
      as: t.owner,
      body: { clientUuid: uuid(), fromBranchId: t.branchA, toBranchId: t.branchB, productId: t.water20, quantity },
    })
  );

describe("concurrent stock changes", () => {
  it("never lets simultaneous transfers send more than the branch holds", async () => {
    const t = await makeTenant();
    await openingStock(t, 10);

    // Five managers press "Record transfer" for 4 units at the same moment.
    const statuses = (await Promise.all(Array.from({ length: 5 }, () => transferOut(t, 4)))).map((r) => r.status);

    expect(statuses.filter((s) => s === 201)).toHaveLength(2);
    expect(statuses.filter((s) => s === 409)).toHaveLength(3);
    expect(await stockOf(t.businessId, t.branchA, t.water20)).toBe(2);
    expect(await stockOf(t.businessId, t.branchB, t.water20)).toBe(8);
    expect(await StockTransfer.countDocuments({})).toBe(2);
  });

  it("holds across repeated races, not just once", async () => {
    for (let round = 0; round < 5; round++) {
      const t = await makeTenant("Round" + round);
      await openingStock(t, 9);
      const statuses = (await Promise.all(Array.from({ length: 4 }, () => transferOut(t, 3)))).map((r) => r.status);
      expect(statuses.filter((s) => s === 201)).toHaveLength(3);
      expect(await stockOf(t.businessId, t.branchA, t.water20)).toBe(0);
    }
  });

  it("applies a double-tapped transfer once even when both taps race", async () => {
    const t = await makeTenant();
    await openingStock(t, 10);
    const body = { clientUuid: uuid(), fromBranchId: t.branchA, toBranchId: t.branchB, productId: t.water20, quantity: 6 };
    const statuses = (
      await Promise.all([
        transfers.POST(req("POST", "/x", { as: t.owner, body })),
        transfers.POST(req("POST", "/x", { as: t.owner, body })),
      ])
    ).map((r) => r.status);
    expect(statuses.sort()).toEqual([200, 201]);
    expect(await stockOf(t.businessId, t.branchA, t.water20)).toBe(4);
  });

  it("takes over a lock left behind by a crashed request once it expires", async () => {
    const t = await makeTenant();
    await openingStock(t, 10);
    await StockLock.create({
      _id: `${t.businessId}:${t.branchA}:${t.water20}`,
      owner: "crashed-request",
      lockedUntil: new Date(Date.now() - 1000),
    });
    expect((await transferOut(t, 3)).status).toBe(201);
    expect(await StockLock.countDocuments({})).toBe(0);
  });

  it("serialises a physical count with a transfer, so the count is never applied to a stale balance", async () => {
    const t = await makeTenant();
    await openingStock(t, 10);

    // A count of 10 and a transfer of 6 race. Whichever runs second must
    // see the first: either the count resets 4 back to 10 after the
    // transfer, or the transfer moves 6 out of the counted 10.
    const [count, transfer] = await Promise.all([
      adjustments.POST(
        req("POST", "/x", {
          as: t.owner,
          body: { clientUuid: uuid(), branchId: t.branchA, productId: t.water20, mode: "COUNT", quantity: 10 },
        })
      ),
      transferOut(t, 6),
    ]);
    expect([count.status, transfer.status]).toEqual([201, 201]);
    const a = await stockOf(t.businessId, t.branchA, t.water20);
    expect([4, 10]).toContain(a);
    expect(await stockOf(t.businessId, t.branchB, t.water20)).toBe(6);
  });

  it("does not block transfers of different products or branches on each other", async () => {
    const t = await makeTenant();
    await openingStock(t, 10);
    await adjustments.POST(
      req("POST", "/x", {
        as: t.owner,
        body: { clientUuid: uuid(), branchId: t.branchA, productId: t.water5, mode: "DELTA", quantity: 10 },
      })
    );
    const results = await Promise.all([
      transferOut(t, 5),
      transfers.POST(
        req("POST", "/x", {
          as: t.owner,
          body: { clientUuid: uuid(), fromBranchId: t.branchA, toBranchId: t.branchB, productId: t.water5, quantity: 5 },
        })
      ),
    ]);
    expect(results.map((r) => r.status)).toEqual([201, 201]);
  });
});