import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
import { poll } from './poll';

beforeEach(() => vi.useFakeTimers());
afterEach(() => vi.useRealTimers());

describe('poll', () => {
  it('fetches until done, then stops', async () => {
    const values = ['queued', 'running', 'succeeded', 'never'];
    const fetch = vi.fn(async () => values.shift()!);
    const seen: string[] = [];
    poll(fetch, { intervalMs: 1000, done: (v) => v === 'succeeded', onValue: (v) => seen.push(v), onError: () => {} });

    await vi.advanceTimersByTimeAsync(5000);
    expect(seen).toEqual(['queued', 'running', 'succeeded']);
    expect(fetch).toHaveBeenCalledTimes(3);
  });

  it('never has two requests in flight when the API is slower than the interval', async () => {
    let inFlight = 0;
    let maxInFlight = 0;
    const fetch = async () => {
      inFlight++;
      maxInFlight = Math.max(maxInFlight, inFlight);
      await new Promise((r) => setTimeout(r, 2500));
      inFlight--;
      return 'running';
    };
    poll(fetch, { intervalMs: 1000, done: () => false, onValue: () => {}, onError: () => {} });

    await vi.advanceTimersByTimeAsync(10_000);
    expect(maxInFlight).toBe(1);
  });

  it('reports an error once and stops', async () => {
    const fetch = vi.fn(async () => { throw new Error('502'); });
    const onError = vi.fn();
    poll(fetch, { intervalMs: 1000, done: () => false, onValue: () => {}, onError });

    await vi.advanceTimersByTimeAsync(5000);
    expect(onError).toHaveBeenCalledOnce();
    expect(fetch).toHaveBeenCalledOnce();
  });

  it('stop() cancels future fetches, e.g. when the page unmounts', async () => {
    const fetch = vi.fn(async () => 'running');
    const stop = poll(fetch, { intervalMs: 1000, done: () => false, onValue: () => {}, onError: () => {} });

    await vi.advanceTimersByTimeAsync(1500);
    stop();
    await vi.advanceTimersByTimeAsync(10_000);
    expect(fetch).toHaveBeenCalledTimes(1);
  });
});