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

/* 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
}

/**
 * head — first lines or bytes of files.
 */

function bareHeadBytesSlice(u8, n) {
  if (!u8 || !u8.byteLength || n <= 0) return new Uint8Array(0)
  const end = Math.min(u8.byteLength, n)
  return u8.subarray(0, end)
}

async function run(ctx, argv) {
  const vfs = ctx.vfs
  let n = 10
  /** @type {'lines' | 'bytes'} */
  let mode = 'lines'
  let i = 1

  while (i < argv.length) {
    const a = argv[i]
    if (a === '--') {
      i++
      break
    }
    if (a === '-n' || a === '--lines') {
      const v = argv[i + 1]
      if (v == null) {
        ctx.console.error('head: option requires an argument -- n')
        ctx.exitCode = 1
        return
      }
      n = Number.parseInt(v, 10) || 10
      mode = 'lines'
      i += 2
      continue
    }
    if (a.startsWith('-n') && a.length > 2) {
      n = Number.parseInt(a.slice(2), 10) || 10
      mode = 'lines'
      i++
      continue
    }
    if (a === '-c' || a === '--bytes') {
      const v = argv[i + 1]
      if (v == null) {
        ctx.console.error('head: option requires an argument -- c')
        ctx.exitCode = 1
        return
      }
      n = Number.parseInt(v, 10) || 0
      mode = 'bytes'
      i += 2
      continue
    }
    if (a.startsWith('-c') && a.length > 2) {
      n = Number.parseInt(a.slice(2), 10) || 0
      mode = 'bytes'
      i++
      continue
    }
    if (a && /^-\d+$/.test(a)) {
      n = Number.parseInt(a.slice(1), 10) || 10
      mode = 'lines'
      i++
      continue
    }
    if (a.startsWith('-')) {
      ctx.console.error('head: unrecognized option: ' + a)
      ctx.exitCode = 1
      return
    }
    break
  }

  const files = argv.slice(i).filter((x) => x !== '--')

  const takeString = (s) => {
    if (mode === 'bytes') {
      const u8 = ctx.b4a.from(s, 'utf8')
      const slice = bareHeadBytesSlice(u8, n)
      const out = ctx.b4a.toString(slice)
      if (out) ctx.console.log(out)
      return
    }
    const lines = s.split('\n')
    const out = lines.slice(0, n).join('\n')
    ctx.console.log(
      out + (out && !out.endsWith('\n') && lines.length > n ? '\n' : '')
    )
  }

  const takeU8 = (u8) => {
    if (mode === 'bytes') {
      const slice = bareHeadBytesSlice(
        u8 instanceof Uint8Array ? u8 : ctx.b4a.from(u8),
        n
      )
      const out = ctx.b4a.toString(slice)
      if (out) ctx.console.log(out)
      return
    }
    takeString(ctx.b4a.toString(u8))
  }

  if (!files.length) {
    takeString(bareStdin(ctx))
    return
  }
  for (const f of files) {
    const buf = await vfs.readFile(f)
    if (!buf) {
      ctx.console.error('head: ' + f + ': No such file')
      continue
    }
    if (files.length > 1) ctx.console.log('==> ' + f + ' <==')
    takeU8(buf)
  }
}