Mini Shell

'use strict'
const EE = require('events')
const Yallist = require('yallist')
const EOF = Symbol('EOF')
const MAYBE_EMIT_END = Symbol('maybeEmitEnd')
const EMITTED_END = Symbol('emittedEnd')
const CLOSED = Symbol('closed')
const READ = Symbol('read')
const FLUSH = Symbol('flush')
const doIter = process.env._MP_NO_ITERATOR_SYMBOLS_  !== '1'
const ASYNCITERATOR = doIter && Symbol.asyncIterator || Symbol('asyncIterator not implemented')
const ITERATOR = doIter && Symbol.iterator || Symbol('iterator not implemented')
const FLUSHCHUNK = Symbol('flushChunk')
const SD = require('string_decoder').StringDecoder
const ENCODING = Symbol('encoding')
const DECODER = Symbol('decoder')
const FLOWING = Symbol('flowing')
const RESUME = Symbol('resume')
const BUFFERLENGTH = Symbol('bufferLength')
const BUFFERPUSH = Symbol('bufferPush')
const BUFFERSHIFT = Symbol('bufferShift')
const OBJECTMODE = Symbol('objectMode')
const SILENT_END = Symbol('silentEnd')

// Buffer in node 4.x < 4.5.0 doesn't have working Buffer.from
// or Buffer.alloc, and Buffer in node 10 deprecated the ctor.
// .M, this is fine .\^/M..
let B = Buffer
/* istanbul ignore next */
if (!B.alloc) {
  B = require('safe-buffer').Buffer
}

module.exports = class MiniPass extends EE {
  constructor (options) {
    super()
    this[SILENT_END] = false
    this[FLOWING] = false
    this.pipes = new Yallist()
    this.buffer = new Yallist()
    this[OBJECTMODE] = options && options.objectMode || false
    if (this[OBJECTMODE])
      this[ENCODING] = null
    else
      this[ENCODING] = options && options.encoding || null
    if (this[ENCODING] === 'buffer')
      this[ENCODING] = null
    this[DECODER] = this[ENCODING] ? new SD(this[ENCODING]) : null
    this[EOF] = false
    this[EMITTED_END] = false
    this[CLOSED] = false
    this.writable = true
    this.readable = true
    this[BUFFERLENGTH] = 0
  }

  get bufferLength () { return this[BUFFERLENGTH] }

  get encoding () { return this[ENCODING] }
  set encoding (enc) {
    if (this[OBJECTMODE])
      throw new Error('cannot set encoding in objectMode')

    if (this[ENCODING] && enc !== this[ENCODING] &&
        (this[DECODER] && this[DECODER].lastNeed || this[BUFFERLENGTH]))
      throw new Error('cannot change encoding')

    if (this[ENCODING] !== enc) {
      this[DECODER] = enc ? new SD(enc) : null
      if (this.buffer.length)
        this.buffer = this.buffer.map(chunk => this[DECODER].write(chunk))
    }

    this[ENCODING] = enc
  }

  setEncoding (enc) {
    this.encoding = enc
  }

  write (chunk, encoding, cb) {
    if (this[EOF])
      throw new Error('write after end')

    if (typeof encoding === 'function')
      cb = encoding, encoding = 'utf8'

    if (!encoding)
      encoding = 'utf8'

    // fast-path writing strings of same encoding to a stream with
    // an empty buffer, skipping the buffer/decoder dance
    if (typeof chunk === 'string' && !this[OBJECTMODE] &&
        // unless it is a string already ready for us to use
        !(encoding === this[ENCODING] && !this[DECODER].lastNeed)) {
      chunk = B.from(chunk, encoding)
    }

    if (B.isBuffer(chunk) && this[ENCODING])
      chunk = this[DECODER].write(chunk)

    try {
      return this.flowing
        ? (this.emit('data', chunk), this.flowing)
        : (this[BUFFERPUSH](chunk), false)
    } finally {
      this.emit('readable')
      if (cb)
        cb()
    }
  }

  read (n) {
    try {
      if (this[BUFFERLENGTH] === 0 || n === 0 || n > this[BUFFERLENGTH])
        return null

      if (this[OBJECTMODE])
        n = null

      if (this.buffer.length > 1 && !this[OBJECTMODE]) {
        if (this.encoding)
          this.buffer = new Yallist([
            Array.from(this.buffer).join('')
          ])
        else
          this.buffer = new Yallist([
            B.concat(Array.from(this.buffer), this[BUFFERLENGTH])
          ])
      }

      return this[READ](n || null, this.buffer.head.value)
    } finally {
      this[MAYBE_EMIT_END]()
    }
  }

  [READ] (n, chunk) {
    if (n === chunk.length || n === null)
      this[BUFFERSHIFT]()
    else {
      this.buffer.head.value = chunk.slice(n)
      chunk = chunk.slice(0, n)
      this[BUFFERLENGTH] -= n
    }

    this.emit('data', chunk)

    if (!this.buffer.length && !this[EOF])
      this.emit('drain')

    return chunk
  }

  end (chunk, encoding, cb) {
    if (typeof chunk === 'function')
      cb = chunk, chunk = null
    if (typeof encoding === 'function')
      cb = encoding, encoding = 'utf8'
    if (chunk)
      this.write(chunk, encoding)
    if (cb)
      this.once('end', cb)
    this[EOF] = true
    this.writable = false
    if (this.flowing)
      this[MAYBE_EMIT_END]()
  }

  // don't let the internal resume be overwritten
  [RESUME] () {
    this[FLOWING] = true
    this.emit('resume')
    if (this.buffer.length)
      this[FLUSH]()
    else if (this[EOF])
      this[MAYBE_EMIT_END]()
    else
      this.emit('drain')
  }

  resume () {
    return this[RESUME]()
  }

  pause () {
    this[FLOWING] = false
  }

  get flowing () {
    return this[FLOWING]
  }

  [BUFFERPUSH] (chunk) {
    if (this[OBJECTMODE])
      this[BUFFERLENGTH] += 1
    else
      this[BUFFERLENGTH] += chunk.length
    return this.buffer.push(chunk)
  }

  [BUFFERSHIFT] () {
    if (this.buffer.length) {
      if (this[OBJECTMODE])
        this[BUFFERLENGTH] -= 1
      else
        this[BUFFERLENGTH] -= this.buffer.head.value.length
    }
    return this.buffer.shift()
  }

  [FLUSH] () {
    do {} while (this[FLUSHCHUNK](this[BUFFERSHIFT]()))

    if (!this.buffer.length && !this[EOF])
      this.emit('drain')
  }

  [FLUSHCHUNK] (chunk) {
    return chunk ? (this.emit('data', chunk), this.flowing) : false
  }

  pipe (dest, opts) {
    if (dest === process.stdout || dest === process.stderr)
      (opts = opts || {}).end = false
    const p = { dest: dest, opts: opts, ondrain: _ => this[RESUME]() }
    this.pipes.push(p)

    dest.on('drain', p.ondrain)
    this[RESUME]()
    return dest
  }

  addListener (ev, fn) {
    return this.on(ev, fn)
  }

  on (ev, fn) {
    try {
      return super.on(ev, fn)
    } finally {
      if (ev === 'data' && !this.pipes.length && !this.flowing)
        this[RESUME]()
      else if (ev === 'end' && this[SILENT_END] && this[EMITTED_END]) {
        this[SILENT_END] = false
        super.emit('end')
      }
    }
  }

  get emittedEnd () {
    return this[EMITTED_END]
  }

  [MAYBE_EMIT_END] () {
    if (!this[EMITTED_END] && this.buffer.length === 0 && this[EOF]) {
      this.emit('end')
      this.emit('prefinish')
      this.emit('finish')
      if (this[CLOSED])
        this.emit('close')
    }
  }

  emit (ev, data) {
    if (ev === 'data') {
      if (!data)
        return

      if (this.pipes.length)
        this.pipes.forEach(p => p.dest.write(data) || this.pause())
    } else if (ev === 'end') {
      if (this[EMITTED_END] === true)
        return

      this[EMITTED_END] = true
      this.readable = false

      if (this[DECODER]) {
        data = this[DECODER].end()
        if (data) {
          this.pipes.forEach(p => p.dest.write(data))
          super.emit('data', data)
        }
      }

      this.pipes.forEach(p => {
        p.dest.removeListener('drain', p.ondrain)
        if (!p.opts || p.opts.end !== false)
          p.dest.end()
      })
    } else if (ev === 'close') {
      this[CLOSED] = true
      // don't emit close before 'end' and 'finish'
      if (!this[EMITTED_END])
        return
    }

    const args = new Array(arguments.length)
    args[0] = ev
    args[1] = data
    if (arguments.length > 2) {
      for (let i = 2; i < arguments.length; i++) {
        args[i] = arguments[i]
      }
    }

    try {
      const ret = super.emit.apply(this, args)
      if (ev === 'end' && ret === false)
        this[SILENT_END] = true
      return ret
    } finally {
      if (ev !== 'end')
        this[MAYBE_EMIT_END]()
    }
  }

  // const all = await stream.collect()
  collect () {
    return new Promise((resolve, reject) => {
      const buf = []
      this.on('data', c => buf.push(c))
      this.on('end', () => resolve(buf))
      this.on('error', reject)
    })
  }

  // for await (let chunk of stream)
  [ASYNCITERATOR] () {
    const next = () => {
      const res = this.read()
      if (res !== null)
        return Promise.resolve({ done: false, value: res })

      if (this[EOF])
        return Promise.resolve({ done: true })

      let resolve = null
      let reject = null
      const onerr = er => {
        this.removeListener('data', ondata)
        this.removeListener('end', onend)
        reject(er)
      }
      const ondata = value => {
        this.removeListener('error', onerr)
        this.removeListener('end', onend)
        this.pause()
        resolve({ value: value, done: !!this[EOF] })
      }
      const onend = () => {
        this.removeListener('error', onerr)
        this.removeListener('data', ondata)
        resolve({ done: true })
      }
      return new Promise((res, rej) => {
        reject = rej
        resolve = res
        this.once('error', onerr)
        this.once('end', onend)
        this.once('data', ondata)
        this.resume()
      })
    }

    return { next }
  }

  // for (let chunk of stream)
  [ITERATOR] () {
    const next = () => {
      const value = this.read()
      const done = value === null
      return { value, done }
    }
    return { next }
  }
}