'use strict'

const {
  Duplex: DuplexStream,
  Readable: ReadableStream,
  Writable: WritableStream
} = require('bare-node-stream')

const {
  CHANNEL_EXTENDED_DATATYPE: { STDERR }
} = require('./protocol/constants.js')
const { bufferSlice } = require('./protocol/utils.js')

const PACKET_SIZE = 32 * 1024
const MAX_WINDOW = 2 * 1024 * 1024
const WINDOW_THRESHOLD = MAX_WINDOW / 2

class ClientStderr extends ReadableStream {
  constructor(channel, streamOpts) {
    super(streamOpts)

    this._channel = channel
  }
  _read(n) {
    if (this._channel._waitChanDrain) {
      this._channel._waitChanDrain = false
      if (this._channel.incoming.window <= WINDOW_THRESHOLD) windowAdjust(this._channel)
    }
  }
}

class ServerStderr extends WritableStream {
  constructor(channel) {
    super({ highWaterMark: MAX_WINDOW })

    this._channel = channel
  }

  _write(data, encoding, cb) {
    const channel = this._channel
    const protocol = channel._client._protocol
    const outgoing = channel.outgoing
    const packetSize = outgoing.packetSize
    const id = outgoing.id
    let window = outgoing.window
    const len = data.length
    let p = 0

    if (outgoing.state !== 'open') return

    while (len - p > 0 && window > 0) {
      let sliceLen = len - p
      if (sliceLen > window) sliceLen = window
      if (sliceLen > packetSize) sliceLen = packetSize

      if (p === 0 && sliceLen === len) protocol.channelExtData(id, data, STDERR)
      else protocol.channelExtData(id, bufferSlice(data, p, p + sliceLen), STDERR)

      p += sliceLen
      window -= sliceLen
    }

    outgoing.window = window

    if (len - p > 0) {
      if (window === 0) channel._waitWindow = true
      if (p > 0) channel._chunkErr = bufferSlice(data, p, len)
      else channel._chunkErr = data
      channel._chunkcbErr = cb
      return
    }

    cb()
  }
}

class Channel extends DuplexStream {
  constructor(client, info, opts) {
    const streamOpts = {
      highWaterMark: MAX_WINDOW,
      allowHalfOpen: !opts || (opts && opts.allowHalfOpen !== false),
      emitClose: false
    }
    super(streamOpts)
    this.allowHalfOpen = streamOpts.allowHalfOpen

    const server = !!(opts && opts.server)

    this.server = server
    this.type = info.type
    this.subtype = undefined

    /*
      incoming and outgoing contain these properties:
      {
        id: undefined,
        window: undefined,
        packetSize: undefined,
        state: 'closed'
      }
    */
    this.incoming = info.incoming
    this.outgoing = info.outgoing
    this._callbacks = []

    this._client = client
    this._hasX11 = false
    this._exit = {
      code: undefined,
      signal: undefined,
      dump: undefined,
      desc: undefined
    }

    this.stdin = this.stdout = this

    if (server) this.stderr = new ServerStderr(this)
    else this.stderr = new ClientStderr(this, streamOpts)

    // Outgoing data
    this._waitWindow = false // SSH-level backpressure

    // Incoming data
    this._waitChanDrain = false // Channel Readable side backpressure

    this._chunk = undefined
    this._chunkcb = undefined
    this._chunkErr = undefined
    this._chunkcbErr = undefined

    this.on('finish', onFinish).on('prefinish', onFinish) // For node v0.11+

    this.on('end', onEnd).on('close', onEnd)
  }

  _read(n) {
    if (this._waitChanDrain) {
      this._waitChanDrain = false
      if (this.incoming.window <= WINDOW_THRESHOLD) windowAdjust(this)
    }
  }

  _write(data, encoding, cb) {
    const protocol = this._client._protocol
    const outgoing = this.outgoing
    const packetSize = outgoing.packetSize
    const id = outgoing.id
    let window = outgoing.window
    const len = data.length
    let p = 0

    if (outgoing.state !== 'open') return

    while (len - p > 0 && window > 0) {
      let sliceLen = len - p
      if (sliceLen > window) sliceLen = window
      if (sliceLen > packetSize) sliceLen = packetSize

      if (p === 0 && sliceLen === len) protocol.channelData(id, data)
      else protocol.channelData(id, bufferSlice(data, p, p + sliceLen))

      p += sliceLen
      window -= sliceLen
    }

    outgoing.window = window

    if (len - p > 0) {
      if (window === 0) this._waitWindow = true
      if (p > 0) this._chunk = bufferSlice(data, p, len)
      else this._chunk = data
      this._chunkcb = cb
      return
    }

    cb()
  }

  eof() {
    if (this.outgoing.state === 'open') {
      this.outgoing.state = 'eof'
      this._client._protocol.channelEOF(this.outgoing.id)
    }
  }

  close() {
    if (this.outgoing.state === 'open' || this.outgoing.state === 'eof') {
      this.outgoing.state = 'closing'
      this._client._protocol.channelClose(this.outgoing.id)
    }
  }

  destroy() {
    this.end()
    this.close()
    return this
  }

  // Session type-specific methods =============================================
  setWindow(rows, cols, height, width) {
    if (this.server) throw new Error('Client-only method called in server mode')

    if (
      this.type === 'session' &&
      (this.subtype === 'shell' || this.subtype === 'exec') &&
      this.writable &&
      this.outgoing.state === 'open'
    ) {
      this._client._protocol.windowChange(this.outgoing.id, rows, cols, height, width)
    }
  }

  signal(signalName) {
    if (this.server) throw new Error('Client-only method called in server mode')

    if (this.type === 'session' && this.writable && this.outgoing.state === 'open') {
      this._client._protocol.signal(this.outgoing.id, signalName)
    }
  }

  exit(statusOrSignal, coreDumped, msg) {
    if (!this.server) throw new Error('Server-only method called in client mode')

    if (this.type === 'session' && this.writable && this.outgoing.state === 'open') {
      if (typeof statusOrSignal === 'number') {
        this._client._protocol.exitStatus(this.outgoing.id, statusOrSignal)
      } else {
        this._client._protocol.exitSignal(this.outgoing.id, statusOrSignal, coreDumped, msg)
      }
    }
  }
}

function onFinish() {
  this.eof()
  if (this.server || !this.allowHalfOpen) this.close()
  try {
    this.writable = false
  } catch (_) {
    /* bare-node-stream / streamx: writable may be getter-only */
  }
}

function onEnd() {
  try {
    this.readable = false
  } catch (_) {
    /* bare-node-stream / streamx: readable is getter-only */
  }
}

function windowAdjust(self) {
  if (self.outgoing.state === 'closed') return
  const amt = MAX_WINDOW - self.incoming.window
  if (amt <= 0) return
  self.incoming.window += amt
  self._client._protocol.channelWindowAdjust(self.outgoing.id, amt)
}

module.exports = {
  Channel,
  MAX_WINDOW,
  PACKET_SIZE,
  windowAdjust,
  WINDOW_THRESHOLD
}