/**
 * Init-script для page.addInitScript(PROBE_SCRIPT).
 * window.__perf.start() / stop() -> {long_task_n, long_task_ms, frame_n, heavy_frame_n,
 * frame_p50_ms, frame_p95_ms, duration_ms}.
 * Long task: > 50 мс (PerformanceObserver 'longtask'). Тяжёлый кадр: интервал между rAF > 50 мс.
 */
export const HEAVY_FRAME_MS = 50;

export interface ProbeMetrics {
  long_task_n: number;
  long_task_ms: number;
  frame_n: number;
  heavy_frame_n: number;
  frame_p50_ms: number;
  frame_p95_ms: number;
  duration_ms: number;
}

export const PROBE_SCRIPT = `(() => {
  if (window.__perf) return;
  const HEAVY = ${HEAVY_FRAME_MS};
  let active = false, t0 = 0, tasks = [], frames = [], last = 0, raf = 0;
  try {
    new PerformanceObserver((list) => {
      if (!active) return;
      for (const e of list.getEntries()) tasks.push(e.duration);
    }).observe({ type: 'longtask', buffered: false });
  } catch (e) {}
  const tick = (now) => {
    if (!active) return;
    if (last) frames.push(now - last);
    last = now;
    raf = requestAnimationFrame(tick);
  };
  const pct = (s, p) => s.length ? s[Math.max(Math.ceil(p * s.length), 1) - 1] : 0;
  window.__perf = {
    start() {
      tasks = []; frames = []; last = 0; t0 = performance.now(); active = true;
      raf = requestAnimationFrame(tick);
    },
    async stop() {
      // дать долгим задачам, завершившимся перед stop, доехать до observer
      await new Promise((r) => setTimeout(r, 100));
      active = false; cancelAnimationFrame(raf);
      const s = frames.slice().sort((a, b) => a - b);
      return {
        long_task_n: tasks.length,
        long_task_ms: tasks.reduce((a, b) => a + b, 0),
        frame_n: frames.length,
        heavy_frame_n: frames.filter((f) => f > HEAVY).length,
        frame_p50_ms: pct(s, 0.5),
        frame_p95_ms: pct(s, 0.95),
        duration_ms: performance.now() - t0,
      };
    },
  };
})();`;