import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
import { startIntervalRunner } from "./interval-runner.ts";

beforeEach(() => {
  vi.useFakeTimers();
});

afterEach(() => {
  vi.useRealTimers();
});

/** A run that stays in flight until the test lets it go. */
function heldRun() {
  let release!: () => void;
  let finished = false;
  const run = vi.fn(
    () =>
      new Promise<void>((resolve) => {
        release = () => {
          finished = true;
          resolve();
        };
      }),
  );
  return { run, release: () => release(), finished: () => finished };
}

describe("startIntervalRunner", () => {
  it("never overlaps two ticks", async () => {
    const held = heldRun();
    const handle = startIntervalRunner({ name: "test", tickMs: 100, run: held.run });
    await vi.advanceTimersByTimeAsync(350);
    expect(held.run).toHaveBeenCalledTimes(1);
    held.release();
    await handle.stop();
  });

  it("waits on the tick still running when the interval fired during it", async () => {
    const held = heldRun();
    const handle = startIntervalRunner({ name: "test", tickMs: 100, run: held.run });
    // Several interval fires land while the first tick is still running.
    await vi.advanceTimersByTimeAsync(350);

    let stopped = false;
    const stopping = handle.stop(5_000).then(() => {
      stopped = true;
    });
    await vi.advanceTimersByTimeAsync(10);
    expect(stopped).toBe(false);

    held.release();
    await stopping;
    expect(held.finished()).toBe(true);
  });

  it("gives up waiting after the timeout", async () => {
    const held = heldRun();
    const handle = startIntervalRunner({ name: "test", tickMs: 100, run: held.run });
    const stopping = handle.stop(2_000);
    await vi.advanceTimersByTimeAsync(2_000);
    await stopping;
    expect(held.finished()).toBe(false);
  });

  it("starts no tick after stop", async () => {
    const run = vi.fn().mockResolvedValue(undefined);
    const handle = startIntervalRunner({ name: "test", tickMs: 100, run });
    await handle.stop();
    await vi.advanceTimersByTimeAsync(500);
    expect(run).toHaveBeenCalledTimes(1);
  });
});