interface PerfSample {
  metric: string;
  operation: string;
  value: number;
}

const FLUSH_INTERVAL_MS = 30_000;
let batch: PerfSample[] = [];
let flushTimer: ReturnType<typeof setInterval> | null = null;

export function record(metric: string, operation: string, value: number): void {
  batch.push({ metric, operation, value });
}

function flush(): void {
  if (batch.length === 0) return;
  const blob = new Blob([JSON.stringify(batch)], { type: 'application/json' });
  batch = [];

  if (navigator.sendBeacon) {
    navigator.sendBeacon('/api/perf', blob);
  } else {
    fetch('/api/perf', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: blob,
      keepalive: true,
    }).catch(() => {});
  }
}

export function startCollector(): void {
  if (flushTimer) return;
  flushTimer = setInterval(flush, FLUSH_INTERVAL_MS);
  document.addEventListener('visibilitychange', () => {
    if (document.visibilityState === 'hidden') flush();
  });
}

export function stopCollector(): void {
  if (flushTimer) {
    clearInterval(flushTimer);
    flushTimer = null;
  }
  flush();
}