/**
 * Rolling z-score helpers for anomaly retrain / hybrid detection.
 */

/**
 * @param {number[]} values
 * @returns {{ mean: number, stdev: number, n: number }}
 */
export function stats(values) {
  const xs = values.filter((v) => v != null && Number.isFinite(v))
  const n = xs.length
  if (!n) return { mean: 0, stdev: 0, n: 0 }
  const mean = xs.reduce((a, b) => a + b, 0) / n
  if (n < 2) return { mean, stdev: 0, n }
  let sumSq = 0
  for (const v of xs) sumSq += (v - mean) ** 2
  const stdev = Math.sqrt(sumSq / (n - 1))
  return { mean, stdev, n }
}

/**
 * @param {number} value
 * @param {number} mean
 * @param {number} stdev
 */
export function zScore(value, mean, stdev) {
  if (!Number.isFinite(value) || !Number.isFinite(mean)) return 0
  if (!stdev || stdev < 1e-9) return value === mean ? 0 : value > mean ? 3 : -3
  return (value - mean) / stdev
}

/**
 * Derive warn/crit absolute thresholds from baseline + z multipliers.
 * For `>` comparator: warn = mean + warnZ*stdev, crit = mean + critZ*stdev
 * For `<` comparator: warn = mean - warnZ*stdev, crit = mean - critZ*stdev
 *
 * @param {{ mean: number, stdev: number }} s
 * @param {string} comparator
 * @param {{ warnZ?: number, critZ?: number, minStdev?: number }} [opts]
 */
export function thresholdsFromStats(s, comparator, opts = {}) {
  const warnZ = opts.warnZ ?? 2
  const critZ = opts.critZ ?? 3
  const minStdev = opts.minStdev ?? 0.01
  const stdev = Math.max(s.stdev, minStdev)
  const op = comparator || '>'
  if (op === '<' || op === '<=') {
    return {
      warn: s.mean - warnZ * stdev,
      crit: s.mean - critZ * stdev,
      mean: s.mean,
      stdev,
    }
  }
  return {
    warn: s.mean + warnZ * stdev,
    crit: s.mean + critZ * stdev,
    mean: s.mean,
    stdev,
  }
}

/**
 * Extract numeric dimension series from MetricStore points.
 * @param {import('./store.js').MetricStore} store
 * @param {string} chart
 * @param {string} dimension
 * @param {number} [maxPoints]
 * @returns {number[]}
 */
export function seriesFromStore(store, chart, dimension, maxPoints = 300) {
  const entry = store.series?.get?.(chart)
  const points = entry?.points || []
  const slice = points.slice(-maxPoints)
  /** @type {number[]} */
  const out = []
  for (const p of slice) {
    const v = p.values?.[dimension]
    if (v != null && Number.isFinite(v)) out.push(v)
  }
  return out
}