// src/services/voiceDiag/checks/wan/wanMos.js
//
// Per-path Mean Opinion Score (MOS, 1.0-5.0). MOS is Prisma's
// composite quality score derived from LQM latency+jitter+loss;
// it's the number to correlate with user-reported "voice sounds
// bad" tickets because it factors all the physical-layer signals
// into one number.
//
//   - >= 4.0 : good ("toll quality")
//   - 3.5-4.0: warn ("acceptable, users notice")
//   - < 3.5  : error ("degraded, users struggle")
//
// Unlike latency/jitter/loss, MOS is inverted: LOW is bad. The
// shared evaluator honours the `lowIsBad: true` flag.

import {
  maybeSkippedByKillSwitch,
  getLinks,
  getMosWarn,
  getMosError,
  evaluatePerLinkMetric,
} from './_helpers.js';

export const WAN_MOS_STANDARDS = Object.freeze({
  minWarn: 4.0,
  minError: 3.5,
  unit: '',
  reference: 'ITU-T P.800 MOS scale',
});

export const wanMosCheck = {
  id: 'wanMos',
  label: 'SD-WAN MOS (per path)',
  requires: ['sdwanSite'],
  scope: null,
  standards: WAN_MOS_STANDARDS,

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

    const warnThresh = getMosWarn();
    const errorThresh = getMosError();
    return evaluatePerLinkMetric({
      links: getLinks(ctx),
      metricKey: 'mos',
      label: 'MOS',
      unit: '',
      warnThresh,
      errorThresh,
      lowIsBad: true,
      standardLabel: `warn < ${warnThresh}, error < ${errorThresh}`,
    });
  },
};