/**
 * Human-readable metric formatting with automatic unit scaling.
 */

/**
 * @param {number} n
 * @param {number} digits
 */
function trimFixed(n, digits) {
  const s = n.toFixed(digits)
  if (!s.includes('.')) return s
  return s.replace(/0+$/, '').replace(/\.$/, '')
}

/**
 * Pick decimal places from magnitude after scaling.
 * @param {number} n
 */
function autoDigits(n) {
  const a = Math.abs(n)
  if (a >= 100) return 0
  if (a >= 10) return 1
  return 2
}

/**
 * Scale a magnitude through a unit ladder.
 * @param {number} value absolute magnitude in base units
 * @param {string[]} units
 * @param {number} base
 * @returns {{ n: number, unit: string }}
 */
function scaleUnit(value, units, base) {
  let n = Math.abs(value)
  let i = 0
  while (n >= base && i < units.length - 1) {
    n /= base
    i++
  }
  return { n: value < 0 ? -n : n, unit: units[i] }
}

/**
 * Format memory stored as MiB → B / KiB / MiB / GiB / TiB / PiB.
 * @param {number|null|undefined} mib
 * @returns {string}
 */
export function formatMib(mib) {
  if (mib == null || !Number.isFinite(Number(mib))) return '—'
  const bytes = Number(mib) * 1024 * 1024
  if (bytes === 0) return '0 B'
  const { n, unit } = scaleUnit(bytes, ['B', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB'], 1024)
  return `${trimFixed(n, autoDigits(n))} ${unit}`
}

/**
 * Format network rate stored as kilobits/s → b/s / kb/s / Mb/s / Gb/s / Tb/s.
 * @param {number|null|undefined} kbps
 * @returns {string}
 */
export function formatKilobitsPerSec(kbps) {
  if (kbps == null || !Number.isFinite(Number(kbps))) return '—'
  const bps = Number(kbps) * 1000
  if (bps === 0) return '0 b/s'
  const { n, unit } = scaleUnit(bps, ['b/s', 'kb/s', 'Mb/s', 'Gb/s', 'Tb/s'], 1000)
  return `${trimFixed(n, autoDigits(n))} ${unit}`
}

/**
 * Format raw bytes → B / KiB / MiB / GiB / TiB / PiB.
 * @param {number|null|undefined} bytes
 * @returns {string}
 */
export function formatBytes(bytes) {
  if (bytes == null || !Number.isFinite(Number(bytes))) return '—'
  const n0 = Number(bytes)
  if (n0 === 0) return '0 B'
  const { n, unit } = scaleUnit(n0, ['B', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB'], 1024)
  return `${trimFixed(n, autoDigits(n))} ${unit}`
}