/**
 * A wheel step on one axis of a music tab, once as a jump and once as a transition of 1000 ms (#377).
 * `read` returns `{ scale, moving }` – the zoom of that axis and whether a transition is on its way.
 * The step is taken back each time with the opposite wheel, so the view ends where it started.
 */
export async function sampleZoom(t, at, read, dy = -100) {
  const { evaluate, json, mouse, settle, wheel, waitUntil } = t;
  const now = () => json(read);
  await evaluate('__gm.zoomTransition(0)');
  const start = await now();
  await wheel(at.x, at.y, dy);
  const jumped = await now();
  await wheel(at.x, at.y, -dy);
  const back = await now();
  await evaluate('__gm.zoomTransition(1000)');
  await mouse('mouseMoved', at.x, at.y);
  await mouse('mouseWheel', at.x, at.y, 'none', { deltaX: 0, deltaY: dy });
  await settle(2);
  const midway = await now();
  await waitUntil(`!(${read}).moving`, { label: 'the zoom transition ended' });
  const landed = await now();
  await evaluate('__gm.zoomTransition(0)');
  await wheel(at.x, at.y, -dy);
  const between = (v, a, b) => v > Math.min(a, b) && v < Math.max(a, b);
  const ok =
    jumped.scale !== start.scale &&
    Math.abs(back.scale - start.scale) < 1e-9 &&
    midway.moving === true &&
    between(midway.scale, start.scale, jumped.scale) &&
    landed.moving === false &&
    Math.abs(landed.scale - jumped.scale) < 1e-9;
  const samples = { start, jumped, back, midway, landed };
  return { ok, samples, detail: JSON.stringify(samples) };
}