import { test } from "node:test";
import assert from "node:assert/strict";
import { mapInYieldingChunks } from "./channelSnapshot";

// Run with:
//   pnpm --filter yt-dlp-transcript-common exec tsx --test controller/snapshotYield.test.ts
//
// THE WALK YIELDS BETWEEN CHUNKS (release 17 slice D0). A macrotask queued
// while the first chunk runs — a request's I/O callback, here a setImmediate
// probe — runs before the second chunk's first unit starts. Without the yield
// every unit below would finish in microtasks before the probe ever ran.

test("a macrotask queued during chunk 1 runs before chunk 2 starts", async () => {
  const events: string[] = [];
  const items = Array.from({ length: 64 }, (_, i) => i);
  const out = await mapInYieldingChunks(items, 32, async (i) => {
    if (i === 0) setImmediate(() => events.push("probe"));
    events.push(`unit ${i}`);
    await Promise.resolve();
    return i * 2;
  });
  assert.deepEqual(out, items.map((i) => i * 2), "results in order");
  const probe = events.indexOf("probe");
  assert.ok(probe > events.indexOf("unit 31"), "after the first chunk");
  assert.ok(probe < events.indexOf("unit 32"), "before the second chunk");
});

test("one chunk, no yield; an empty list, no call", async () => {
  let calls = 0;
  assert.deepEqual(
    await mapInYieldingChunks([1, 2, 3], 32, async (i) => {
      calls++;
      return i;
    }),
    [1, 2, 3],
  );
  assert.equal(calls, 3);
  assert.deepEqual(await mapInYieldingChunks([], 32, async (i: number) => i), []);
});