fs.open flags

index.js

export const O_APPEND = 1024
export const O_CREAT = 64
export const O_EXCL = 128
export const O_RDONLY = 0
export const O_RDWR = 2
export const O_SYNC = 1052672
export const O_TRUNC = 512
export const O_WRONLY = 1

// https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-createfilea
export const CREATE_ALWAYS = O_RDWR | O_CREAT | O_TRUNC
export const CREATE_NEW = O_RDWR | O_CREAT | O_EXCL
export const OPEN_ALWAYS = O_RDWR | CREATE_ALWAYS | O_APPEND
export const OPEN_EXISTING = O_RDWR | O_APPEND
export const TRUNCATE_EXISTING = O_RDWR | O_TRUNC

class Flags {
  constructor(append, create, exclusive, read, sync, write) {
    this.append = append
    this.create = create
    this.exclusive = exclusive
    this.read = read
    this.sync = sync
    this.write = write
  }

  get truncate() {
    return !this.append
  }

  set truncate(truncate) {
    this.append = !truncate
  }

  toNumber() {
    let flags = this.read ? (this.write ? O_RDWR : O_RDONLY) : O_WRONLY
    if (this.create) {
      flags |= O_CREAT | (this.append ? O_APPEND : O_TRUNC)
      if (this.exclusive) {
        flags |= O_EXCL
      }
    }
    if (this.sync) {
      flags |= O_SYNC
    }
    return flags
  }

  toString() {
    if (this.create) {
      let flags = this.append ? 'a' : 'w'
      if (this.exclusive) {
        flags += 'x'
      } else if (this.sync) {
        flags += 's'
      }
      if (this.read) {
        flags += '+'
      }
      return flags
    }
    return this.write ? 'r+' : 'r'
  }
}

export const fromNumber = flags => {
  return new Flags(
    (flags & O_APPEND) !== 0,
    (flags & O_CREAT) !== 0,
    (flags & O_EXCL) !== 0,
    (flags & O_WRONLY) === 0,
    (flags & O_SYNC) !== 0,
    (flags & (O_RDWR | O_WRONLY)) !== 0
  )
}

const parse = flags => {
  const result = { __proto__: null }
  for (let i = 0, n = flags.length; i < n; ++i) {
    result[flags[i]] = true
  }
  return result
}
export const fromString = flags => {
  flags = parse(flags)
  const sync = 's' in flags

  return 'r' in flags
    ? new Flags(false, false, false, true, sync, '+' in flags)
    : new Flags('a' in flags, true, 'x' in flags, '+' in flags, sync, true)
}