index.js

const { Readable } = require('bare-stream')
const ansiEscapes = require('bare-ansi-escapes')
const KeyDecoder = require('bare-ansi-escapes/key-decoder')

const constants = {
  EOL: '\r\n'
}

const Readline = module.exports = exports = class Readline extends Readable {
  constructor (opts = {}) {
    super()

    this._prompt = opts.prompt || '> '
    this._crlfDelay = opts.crlfDelay ? Math.max(100, opts.crlfDelay) : 100

    this._oninput = this._oninput.bind(this)
    this._onkey = this._onkey.bind(this)

    this._decoder = new KeyDecoder().on('data', this._onkey)
    this._history = new History()

    this._sawReturn = 0

    this.input = opts.input.on('data', this._oninput)
    this.output = opts.output
    this.line = ''
    this.cursor = 0

    this.on('data', this._ondata).setEncoding('utf8')
  }

  prompt () {
    this.write(
      ansiEscapes.cursorPosition(0) +
      ansiEscapes.eraseLine +

      this._prompt +
      this.line +

      ansiEscapes.cursorPosition(this._prompt.length + this.cursor)
    )
  }

  close () {
    this.input.off('data', this._oninput)
    this.push(null)
  }

  write (data) {
    if (this.output) this.output.write(data)
  }

  clearLine () {
    const line = this.line
    this.write(constants.EOL)
    this.line = ''
    this.cursor = 0
    return line
  }

  _oninput (data) {
    this._decoder.write(data)
  }

  _ondata (line) {
    this.emit('line', line) // For Node.js compatibility
  }

  _online (linefeed) {
    if (linefeed) {
      if (this._sawReturn > 0 && Date.now() - this._sawReturn <= this._crlfDelay) return

      this._sawReturn = 0
    } else {
      this._sawReturn = Date.now()
    }

    const line = this.clearLine()

    const remember = line.trim() !== ''
    if (remember && line !== this._history.get(0)) this._history.unshift(line)

    this.push(line)

    if (remember) this.emit('history', this._history.entries)
  }

  _onkey (key) {
    if (key.name === 'up') return this._onup()
    if (key.name === 'down') return this._ondown()

    this._history.cursor = -1

    let characters

    switch (key.name) {
      case 'd':
        if (key.ctrl) return this.close()
        characters = key.shift ? 'D' : 'd'
        break

      case 'c':
        if (key.ctrl) return this.close()
        characters = key.shift ? 'C' : 'c'
        break

      case 'backspace': return this._onbackspace()

      case 'return': return this._online(false /* linefeed */)
      case 'linefeed': return this._online(true /* linefeed */)

      case 'right': return this._onright()
      case 'left': return this._onleft()

      case 'escape':
      case 'f1': case 'f2': case 'f3': case 'f4': case 'f5': case 'f6':
      case 'f7': case 'f8': case 'f9': case 'f10': case 'f11': case 'f12':
      case 'clear': case 'end': case 'home':
      case 'pageup': case 'pagedown':
      case 'insert': case 'delete':
      case 'tab':
      case 'undefined': return

      case 'space': characters = ' '; break

      default:
        characters = key.shift ? key.name.toUpperCase() : key.name
    }

    this.line = (
      this.line.substring(0, this.cursor) +
      characters +
      this.line.substring(this.cursor)
    )

    this.cursor += characters.length
    this.prompt()
  }

  _onbackspace () {
    if (this.cursor) {
      this.write(ansiEscapes.cursorBack(2))

      this.line = (
        this.line.substring(0, this.cursor - 1) +
        this.line.substring(this.cursor)
      )

      this.cursor--
      this.prompt()
    }
  }

  _onup () {
    if (this._history.cursor === -1 && this.line.length > 0) return
    if (this._history.length === 0) return
    if (this._history.length <= this._history.cursor + 1) return

    this._history.cursor++

    this.line = this._history.get(this._history.cursor)
    this.cursor = this.line.length
    this.prompt()
  }

  _ondown () {
    if (this._history.cursor === -1) return

    this._history.cursor--

    this.line = this._history.cursor === -1
      ? ''
      : this._history.get(this._history.cursor)
    this.cursor = this.line.length
    this.prompt()
  }

  _onright () {
    if (this.cursor < this.line.length) {
      this.cursor++
      this.write(ansiEscapes.cursorForward())
    }
  }

  _onleft () {
    if (this.cursor) {
      this.cursor--
      this.write(ansiEscapes.cursorBack())
    }
  }
}

exports.createInterface = function createInterface (opts) {
  return new Readline(opts)
}

exports.constants = constants

class History {
  constructor () {
    this.entries = []
    this.cursor = -1
  }

  get length () {
    return this.entries.length
  }

  unshift (entry) {
    this.entries.unshift(entry)
  }

  get (index) {
    if (index < 0) index += this.length
    if (index < 0 || index >= this.length) return null

    return this.entries[index]
  }
}