export function percentile(values, fraction) {
  if (values.length === 0) return 0;
  const sorted = [...values].sort((a, b) => a - b);
  return sorted[Math.min(sorted.length - 1, Math.floor(sorted.length * fraction))];
}

export function median(values) {
  return percentile(values, 0.5);
}

export function linearSlopePerHour(samples, field) {
  if (samples.length < 2) return 0;
  const xs = samples.map((sample) => sample.elapsedMs / 3_600_000);
  const ys = samples.map((sample) => sample[field]);
  const meanX = xs.reduce((sum, value) => sum + value, 0) / xs.length;
  const meanY = ys.reduce((sum, value) => sum + value, 0) / ys.length;
  const denominator = xs.reduce((sum, value) => sum + ((value - meanX) ** 2), 0);
  if (denominator === 0) return 0;
  return xs.reduce((sum, value, index) => sum + ((value - meanX) * (ys[index] - meanY)), 0) / denominator;
}

export function buildSoakSummary({ samples, reconnects, startedAt, completedAt, durationHours, sampleSeconds, counters, requireWallboardTitle = false }) {
  if (samples.length === 0) throw new Error('at least one wallboard sample is required');
  const hourly = samples.filter((sample) => sample.forcedGC);
  if (hourly.length === 0) throw new Error('at least one forced-GC sample is required');
  const quarterSize = Math.max(1, Math.ceil(hourly.length / 4));
  const firstQuarter = hourly.slice(0, quarterSize).map((sample) => sample.usedHeapBytes);
  const lastQuarter = hourly.slice(-quarterSize).map((sample) => sample.usedHeapBytes);
  const retainedGrowthBytes = median(lastQuarter) - median(firstQuarter);
  const heapSlopeBytesPerHour = linearSlopePerHour(hourly, 'usedHeapBytes');
  const maxAllowedGrowthBytes = Math.max(16 * 1024 * 1024, median(firstQuarter) * 0.20);
  const elapsedHours = (completedAt.getTime() - startedAt.getTime()) / 3_600_000;
  const expectedSampleCount = durationHours * 3_600 / sampleSeconds;
  const minimumSampleCount = Math.floor(Math.min(expectedSampleCount * 0.99, Math.max(1, expectedSampleCount - 2)));
  const sampleGapsSeconds = samples.slice(1).map((sample, index) => (sample.elapsedMs - samples[index].elapsedMs) / 1_000);
  const maxSampleGapSeconds = Math.max(0, ...sampleGapsSeconds);
  const maxAllowedSampleGapSeconds = sampleSeconds + 15;
  const summary = {
    status: 'pass',
    startedAt: startedAt.toISOString(),
    completedAt: completedAt.toISOString(),
    elapsedHours,
    sampleCount: samples.length,
    forcedGCSampleCount: hourly.length,
    expectedSampleCount,
    minimumSampleCount,
    maxSampleGapSeconds,
    maxAllowedSampleGapSeconds,
    reconnectCount: reconnects.length,
    reconnectFailures: reconnects.filter((item) => !item.recovered).length,
    reconnectP95Ms: percentile(reconnects.map((item) => item.durationMs), 0.95),
    retainedGrowthBytes,
    heapSlopeBytesPerHour,
    maxAllowedGrowthBytes,
    fpsP05: percentile(samples.map((sample) => sample.fps), 0.05),
    frameP95WorstMs: Math.max(...samples.map((sample) => sample.frameP95Ms)),
    longestTaskMs: Math.max(...samples.map((sample) => sample.longestTaskMs)),
    maxActiveSockets: counters.maxActiveSockets,
    openedSockets: counters.openedSockets,
    closedSockets: counters.closedSockets,
    websocketErrors: counters.websocketErrors ?? 0,
    socketChurnBudget: reconnects.length + 4,
    pageErrors: counters.pageErrors,
    apiFailures: counters.apiFailures,
    maxDOMNodes: Math.max(...samples.map((sample) => sample.nodes)),
    horizontalOverflowSamples: samples.filter((sample) => sample.bodyWidth > sample.viewportWidth).length,
    verticalOverflowSamples: samples.filter((sample) => sample.bodyHeight != null && sample.viewportHeight != null && sample.bodyHeight > sample.viewportHeight).length,
    invalidWallboardSamples: samples.filter((sample) => {
      if (sample.wallboardTitle == null || sample.activeDashboard == null) return requireWallboardTitle;
      return sample.wallboardTitle !== 'Operationeel wallboard' || !/^Wallboard soak [12]$/.test(sample.activeDashboard);
    }).length,
  };
  const failures = [];
  if (summary.elapsedHours < durationHours) failures.push('elapsed duration shorter than requested');
  if (summary.sampleCount < minimumSampleCount || maxSampleGapSeconds > maxAllowedSampleGapSeconds) failures.push('sample coverage or continuity fell below the uninterrupted-run budget');
  if (retainedGrowthBytes > maxAllowedGrowthBytes || heapSlopeBytesPerHour > 1024 * 1024) failures.push('retained heap growth exceeded the bounded budget');
  if (summary.reconnectFailures > 0 || summary.reconnectP95Ms > 10_000) failures.push('WebSocket reconnect exceeded 10 seconds');
  if (summary.frameP95WorstMs > 50 || summary.fpsP05 < 30 || summary.longestTaskMs > 250) failures.push('visible-jank budget exceeded');
  if (summary.maxActiveSockets > 2) failures.push('active WebSocket count was unbounded');
  if (summary.openedSockets > summary.socketChurnBudget) failures.push('WebSocket lifecycle churn exceeded the bounded budget');
  if (summary.websocketErrors > 0 || summary.pageErrors > 0 || summary.apiFailures > 0) failures.push('runtime browser, API or WebSocket failures occurred');
  if (summary.horizontalOverflowSamples > 0 || summary.verticalOverflowSamples > 0) failures.push('wallboard overflowed the viewport');
  if (summary.invalidWallboardSamples > 0) failures.push('wallboard content disappeared during the soak');
  if (failures.length > 0) {
    summary.status = 'fail';
    summary.failures = failures;
  }
  return summary;
}