const support_system_file_fs = require('fs')

// like `readLine` without the overhead of copying characters.
// returns int (success 0, failure -1) to align with the C counterpart.
function support_system_file_seekLine (file_ptr) {
  const LF = 0x0a
  const readBuf = Buffer.alloc(1)
  let lineEnd = file_ptr.buffer.indexOf(LF)
  while (lineEnd === -1) {
    const bytesRead = support_system_file_fs.readSync(file_ptr.fd, readBuf, 0, 1, null)
    if (bytesRead === 0) {
      file_ptr.eof = true
      file_ptr.buffer = Buffer.alloc(0)
      return 0n
    }
    file_ptr.buffer = Buffer.concat([file_ptr.buffer, readBuf.slice(0, bytesRead)])
    lineEnd = file_ptr.buffer.indexOf(LF)
  }
  file_ptr.buffer = file_ptr.buffer.slice(lineEnd + 1)
  return 0n
}

function support_system_file_readLine (file_ptr) {
  const LF = 0x0a
  const readBuf = Buffer.alloc(1)
  let lineEnd = file_ptr.buffer.indexOf(LF)
  while (lineEnd === -1) {
    const bytesRead = support_system_file_fs.readSync(file_ptr.fd, readBuf, 0, 1, null)
    if (bytesRead === 0) {
      file_ptr.eof = true
      const line = file_ptr.buffer.toString('utf-8')
      file_ptr.buffer = Buffer.alloc(0)
      return line
    }
    file_ptr.buffer = Buffer.concat([file_ptr.buffer, readBuf.slice(0, bytesRead)])
    lineEnd = file_ptr.buffer.indexOf(LF)
  }
  const line = file_ptr.buffer.slice(0, lineEnd + 1).toString('utf-8')
  file_ptr.buffer = file_ptr.buffer.slice(lineEnd + 1)
  return line
}

function support_system_file_getStr () {
  return support_system_file_readLine({ fd: 0, buffer: Buffer.alloc(0), name: '<stdin>', eof: false })
}

function support_system_file_openFile (n, m) {
  try {
    const fd = support_system_file_fs.openSync(n, m)
    return { fd: fd, buffer: Buffer.alloc(0), name: n, eof: false }
  } catch (e) {
    process.__lasterr = e
    return null
  }
}

function support_system_file_chmod (filename, mode) {
  try {
    support_system_file_fs.chmodSync(filename, Number(mode))
    return 0n
  } catch (e) {
    process.__lasterr = e
    return 1n
  }
}