// src/services/voiceDiag/checks/wan/wanLatency.js
//
// Per-path WAN latency (LQM one-way average, milliseconds) vs
// ITU-T G.114 references:
//   - <= 150ms  : good (no perceptible degradation)
//   - 150-400ms : warn (audible echo/lag, still usable)
//   - > 400ms   : error (voice becomes duplex-half, users stop
//                  talking over each other and start waiting)
//
// Both thresholds are env-configurable via WAN_STANDARD_LATENCY_*
// (see .env.example). Worst path drives severity — a single bad
// path takes precedence over three good ones because that's the
// one your voice ticket is routed over.

import {
  maybeSkippedByKillSwitch,
  getLinks,
  getLatencyWarnMs,
  getLatencyErrorMs,
  evaluatePerLinkMetric,
} from './_helpers.js';

// Standards frozen as a plain constant so the README standards
// table + regression guards can read it without invoking the
// accessors. Same values as `getLatencyWarnMs()` / `getLatencyErrorMs()`
// unless the operator overrode via env.
export const WAN_LATENCY_STANDARDS = Object.freeze({
  maxWarnMs: 150,
  maxErrorMs: 400,
  unit: 'ms',
  reference: 'ITU-T G.114',
});

export const wanLatencyCheck = {
  id: 'wanLatency',
  label: 'SD-WAN Latency (per path)',
  requires: ['sdwanSite'],
  scope: null,
  standards: WAN_LATENCY_STANDARDS,

  async run(ctx) {
    const skip = maybeSkippedByKillSwitch(wanLatencyCheck);
    if (skip) return skip;

    const warnThresh = getLatencyWarnMs();
    const errorThresh = getLatencyErrorMs();
    return evaluatePerLinkMetric({
      links: getLinks(ctx),
      metricKey: 'latencyMs',
      label: 'latency',
      unit: 'ms',
      warnThresh,
      errorThresh,
      lowIsBad: false,
      standardLabel: `warn > ${warnThresh}ms, error > ${errorThresh}ms`,
    });
  },
};