/**
 * Ring buffer of message-processing RTTs (ms) for planning percentiles.
 * @module rtt
 */

export class RttWindow {
  /**
   * @param {number} [cap=400]
   */
  constructor(cap = 400) {
    this.cap = cap;
    /** @type {number[]} */
    this.samples = [];
  }

  add(ms) {
    const n = Number(ms);
    if (!Number.isFinite(n) || n < 0) return;
    this.samples.push(n);
    if (this.samples.length > this.cap) this.samples.splice(0, this.samples.length - this.cap);
  }

  stats() {
    return summarizeRtt(this.samples);
  }
}

/**
 * @param {number[]} samples
 */
export function summarizeRtt(samples) {
  const xs = samples.filter((n) => Number.isFinite(n) && n >= 0).slice().sort((a, b) => a - b);
  if (!xs.length) {
    return { count: 0, minMs: null, avgMs: null, p50Ms: null, p90Ms: null };
  }
  const sum = xs.reduce((a, b) => a + b, 0);
  return {
    count: xs.length,
    minMs: round1(xs[0]),
    avgMs: round1(sum / xs.length),
    p50Ms: round1(percentile(xs, 0.5)),
    p90Ms: round1(percentile(xs, 0.9)),
  };
}

function percentile(sorted, p) {
  if (sorted.length === 1) return sorted[0];
  const idx = (sorted.length - 1) * p;
  const lo = Math.floor(idx);
  const hi = Math.ceil(idx);
  if (lo === hi) return sorted[lo];
  return sorted[lo] + (sorted[hi] - sorted[lo]) * (idx - lo);
}

function round1(n) {
  return Math.round(n * 10) / 10;
}