bare-operating-system/packages/bare-os-seeder/kernel/bin/truncate

/* BARE_OS_BIN_API 1.0.0 — bump when staged /bin script semantics change (see developer guide). */
/** Shared helpers for drive-resident /bin scripts (prepended before each command). */
function bareStdin(ctx) {
  return typeof ctx.shellStdin === 'string' ? ctx.shellStdin : ''
}

/** @param {number} mode @param {'file' | 'directory' | 'symlink'} type */
function bareFormatModeString(mode, type) {
  const typeChar = type === 'directory' ? 'd' : type === 'symlink' ? 'l' : '-'
  const perm = mode & 0o777
  const r = (bit) => (perm & bit ? 'r' : '-')
  const w = (bit) => (perm & bit ? 'w' : '-')
  const x = (bit) => (perm & bit ? 'x' : '-')
  return (
    typeChar +
    r(0o400) +
    w(0o200) +
    x(0o100) +
    r(0o040) +
    w(0o020) +
    x(0o010) +
    r(0o004) +
    w(0o002) +
    x(0o001)
  )
}

/** @param {number} mtimeMs @param {number} [nowMs] */
function bareFormatLsMtime(mtimeMs, nowMs) {
  const now = nowMs != null ? nowMs : Date.now()
  const d = new Date(mtimeMs)
  const months = [
    'Jan',
    'Feb',
    'Mar',
    'Apr',
    'May',
    'Jun',
    'Jul',
    'Aug',
    'Sep',
    'Oct',
    'Nov',
    'Dec'
  ]
  const mon = months[d.getMonth()]
  const day = String(d.getDate()).padStart(2, ' ')
  const sixMo = 180 * 24 * 3600 * 1000
  if (Math.abs(now - mtimeMs) > sixMo) {
    const yr = String(d.getFullYear()).padStart(4, ' ')
    return mon + ' ' + day + '  ' + yr
  }
  const hh = String(d.getHours()).padStart(2, '0')
  const mm = String(d.getMinutes()).padStart(2, '0')
  return mon + ' ' + day + ' ' + hh + ':' + mm
}

/** @param {number} size */
function barePosixBlocks(size) {
  return Math.ceil(Number(size) / 512) || 0
}

/**
 * Raw stdout for NUL/binary when **`process.stdout.write`** is missing.
 * If **`ctx.bareOsBinWrite(Uint8Array|string)`** is set (tests / host), use it.
 * @param {Record<string, unknown>} ctx
 * @param {string | Uint8Array} chunk
 * @returns {boolean}
 */
function bareOsEmitRaw(ctx, chunk) {
  if (typeof ctx.bareOsBinWrite === 'function') {
    const b4 = ctx.b4a
    const u8 =
      typeof chunk === 'string'
        ? b4 && typeof b4.from === 'function'
          ? b4.from(chunk)
          : new TextEncoder().encode(chunk)
        : chunk
    ctx.bareOsBinWrite(u8 instanceof Uint8Array ? u8 : new Uint8Array(u8))
    return true
  }
  const w = globalThis.process?.stdout?.write
  if (typeof w === 'function') {
    w.call(globalThis.process.stdout, chunk)
    return true
  }
  return false
}

/**
 * @param {string} raw
 * @param {number} curLen
 * @returns {number | null}
 */
function resolveTruncateSize(raw, curLen) {
  const s = String(raw).trim()
  if (!s) return null
  if (/%$/.test(s)) {
    const inner = s.startsWith('+') || s.startsWith('-') ? s.slice(1) : s
    const pct = Number.parseFloat(inner.replace(/%$/, ''))
    if (!Number.isFinite(pct)) return null
    const delta = Math.floor((curLen * pct) / 100)
    if (s.startsWith('+')) return Math.max(0, curLen + delta)
    if (s.startsWith('-')) return Math.max(0, curLen - delta)
    return Math.max(0, Math.floor((curLen * pct) / 100))
  }
  if (s.startsWith('+')) {
    const n = Number.parseInt(s.slice(1), 10)
    if (!Number.isFinite(n)) return null
    return Math.max(0, curLen + n)
  }
  if (s.startsWith('-')) {
    const n = Number.parseInt(s.slice(1), 10)
    if (!Number.isFinite(n)) return null
    return Math.max(0, curLen - n)
  }
  const abs = Number.parseInt(s, 10)
  if (!Number.isFinite(abs) || abs < 0) return null
  return abs
}

async function run(ctx, argv) {
  /** @type {string | null} */
  let sizeSpec = null
  const paths = []
  for (let i = 1; i < argv.length; i++) {
    const a = argv[i]
    if (a === '-h' || a === '--help') {
      ctx.console.log(
        'usage: truncate -s SIZE FILE\n' +
          'SIZE: bytes, +N, -N, +N%, -N%, or N% (of current length).\n' +
          'Sets file length (padded with zeros if growing).'
      )
      return
    }
    if ((a === '-s' || a === '--size') && argv[i + 1]) {
      sizeSpec = argv[++i]
      continue
    }
    if (a.startsWith('-')) {
      ctx.console.error('truncate: unsupported option ' + a)
      ctx.exitCode = 1
      return
    }
    paths.push(a)
  }
  if (!sizeSpec || paths.length !== 1) {
    ctx.console.error('usage: truncate -s SIZE FILE')
    ctx.exitCode = 1
    return
  }
  const file = paths[0]
  let cur = new Uint8Array(0)
  try {
    const b = await ctx.vfs.readFile(file)
    if (b) cur = b instanceof Uint8Array ? b : new Uint8Array(b)
  } catch {
    /* new file — relative sizes use curLen 0 */
  }
  const size = resolveTruncateSize(sizeSpec, cur.length)
  if (size == null) {
    ctx.console.error('truncate: invalid size: ' + sizeSpec)
    ctx.exitCode = 1
    return
  }
  const out = new Uint8Array(size)
  out.set(cur.subarray(0, Math.min(cur.length, size)))
  try {
    await ctx.vfs.writeFile(file, out)
  } catch (e) {
    ctx.console.error('truncate: ' + (e.message || e))
    ctx.exitCode = 1
  }
}