static _riskPercentiles()

in src/sdk/lh-trace-processor.ts [289:345]
43 lines of code
9 McCabe index (conditional complexity)

  static _riskPercentiles(
    durations,
    totalTime,
    percentiles,
    clippedLength = 0
  ) {
    let busyTime = 0;
    for (let i = 0; i < durations.length; i++) {
      busyTime += durations[i];
    }
    busyTime -= clippedLength;

    // Start with idle time already complete.
    let completedTime = totalTime - busyTime;
    let duration = 0;
    let cdfTime = completedTime;
    const results = [];

    let durationIndex = -1;
    let remainingCount = durations.length + 1;
    if (clippedLength > 0) {
      // If there was a clipped duration, one less in count since one hasn't started yet.
      remainingCount--;
    }

    // Find percentiles of interest, in order.
    for (const percentile of percentiles) {
      // Loop over durations, calculating a CDF value for each until it is above
      // the target percentile.
      const percentileTime = percentile * totalTime;
      while (cdfTime < percentileTime && durationIndex < durations.length - 1) {
        completedTime += duration;
        remainingCount -= duration < 0 ? -1 : 1;

        if (clippedLength > 0 && clippedLength < durations[durationIndex + 1]) {
          duration = -clippedLength;
          clippedLength = 0;
        } else {
          durationIndex++;
          duration = durations[durationIndex];
        }

        // Calculate value of CDF (multiplied by totalTime) for the end of this duration.
        cdfTime = completedTime + Math.abs(duration) * remainingCount;
      }

      // Negative results are within idle time (0ms wait by definition), so clamp at zero.
      results.push({
        percentile,
        time:
          Math.max(0, (percentileTime - completedTime) / remainingCount) +
          BASE_RESPONSE_LATENCY,
      });
    }

    return results;
  }