deadhead-space-freight-tycoon/packages/engine/test/core.test.ts

import type { SaveDocument } from "@deadhead/schema";
import { describe, expect, it } from "vitest";
import { fullSave } from "../../schema/test/save-fixture";
import {
  EngineCore,
  GameLockedError,
  MemoryBackend,
  SaveStorage,
  TabLock,
  type LockManagerLike,
} from "../src/index";

const fixedClock = (t = 5_000_000) => ({ now: () => t });

async function engineWith(save: SaveDocument, backend = new MemoryBackend()) {
  const storage = new SaveStorage(backend);
  await storage.save(save);
  return { engine: new EngineCore({ storage, clock: fixedClock() }), storage, backend };
}

/** A purchase: refuses unless the credits cover it (as the real command will). */
const buy = (engine: EngineCore, price: number) =>
  engine.write((save) => {
    if (!save) throw new Error("no company");
    if (save.company.credits < price) throw new Error("insufficient-funds");
    save.company.credits -= price;
    save.bays.push({ id: `bay-${save.bays.length}`, locationId: "moon", createdAt: 0 });
    return { save, result: save.company.credits };
  });

describe("mutation queue (Step 14.4, decision 0.5.90)", () => {
  it("runs two rapid purchases one at a time: only the affordable one happens", async () => {
    const start = { ...fullSave(), company: { ...fullSave().company, credits: 1_500 } };
    const { engine, storage } = await engineWith(start);
    const results = await Promise.allSettled([buy(engine, 1_000), buy(engine, 1_000)]);
    expect(results.map((r) => r.status)).toEqual(["fulfilled", "rejected"]);
    const saved = await storage.load();
    expect(saved.status === "loaded" && saved.save.company.credits).toBe(500);
    expect(saved.status === "loaded" && saved.save.bays.length).toBe(start.bays.length + 1);
  });

  it("leaves the save and the engine's copy unchanged when a command throws", async () => {
    const { engine, backend } = await engineWith(fullSave());
    const before = backend.slots.get("main");
    await expect(
      engine.write((save) => {
        save!.company.credits = 0;
        throw new Error("boom");
      }),
    ).rejects.toThrow("boom");
    expect(backend.slots.get("main")).toBe(before);
    expect(await engine.read((save) => save!.company.credits)).toBe(fullSave().company.credits);
  });

  it("refuses to save a state that doesn't validate", async () => {
    const { engine, backend } = await engineWith(fullSave());
    const before = backend.slots.get("main");
    await expect(
      engine.write((save) => ({ save: { ...save!, company: null as never }, result: 0 })),
    ).rejects.toThrow();
    expect(backend.slots.get("main")).toBe(before);
  });

  it("records the time it last saw, never going below the save's", async () => {
    const lastSeen = fullSave().lastTimeSeen;
    for (const [clockAt, expected] of [
      [lastSeen + 60_000, lastSeen + 60_000],
      [lastSeen - 60_000, lastSeen],
    ]) {
      const storage = new SaveStorage(new MemoryBackend());
      await storage.save(fullSave());
      const engine = new EngineCore({ storage, clock: fixedClock(clockAt) });
      await engine.write((save) => ({ save: save!, result: null }));
      const saved = await storage.load();
      expect(saved.status === "loaded" && saved.save.lastTimeSeen).toBe(expected);
    }
  });
});

/** Web Locks semantics: one holder; ifAvailable gets null when held; steal aborts the holder. */
class FakeLocks implements LockManagerLike {
  #holder: { reject: (e: Error) => void } | null = null;
  request(
    _name: string,
    options: { ifAvailable?: boolean; steal?: boolean },
    callback: (lock: unknown) => unknown,
  ): Promise<unknown> {
    if (this.#holder && options.ifAvailable) return Promise.resolve(callback(null));
    if (this.#holder && options.steal) {
      this.#holder.reject(new DOMException("Lock broken by another request", "AbortError"));
      this.#holder = null;
    }
    return new Promise((resolve, reject) => {
      const holder = { reject };
      this.#holder = holder;
      Promise.resolve(callback({ name: "deadhead-game" })).then((value) => {
        if (this.#holder === holder) this.#holder = null;
        resolve(value);
      });
    });
  }
}

describe("one tab runs the game (Step 14.4)", () => {
  it("lets a second tab run commands only after it takes over", async () => {
    const backend = new MemoryBackend();
    const storage = new SaveStorage(backend);
    await storage.save(fullSave());
    const locks = new FakeLocks();
    const lockA = new TabLock(locks);
    const lockB = new TabLock(locks);
    const tabA = new EngineCore({ storage, clock: fixedClock(), canWrite: () => lockA.held });
    const tabB = new EngineCore({ storage, clock: fixedClock(), canWrite: () => lockB.held });
    let aLost = false;
    lockA.onLost(() => (aLost = true));

    expect(await lockA.acquire()).toBe(true);
    expect(await lockB.acquire()).toBe(false);
    await buy(tabA, 100);
    await expect(buy(tabB, 100)).rejects.toBeInstanceOf(GameLockedError);

    // "Use here" in tab B.
    expect(await lockB.acquire({ takeOver: true })).toBe(true);
    await Promise.resolve();
    expect(aLost).toBe(true);
    expect(lockA.held).toBe(false);
    await expect(buy(tabA, 100)).rejects.toBeInstanceOf(GameLockedError);

    // Tab B picks up what tab A saved.
    tabB.reload();
    expect(await buy(tabB, 100)).toBe(fullSave().company.credits - 200);
  });

  it("always holds the game where Web Locks don't exist", async () => {
    const lock = new TabLock(undefined);
    expect(lock.held).toBe(true);
    expect(await lock.acquire()).toBe(true);
  });
});