const { EventEmitter } = require('events')
const STREAM_DESTROYED = new Error('Stream was destroyed')
const PREMATURE_CLOSE = new Error('Premature close')

const FIFO = require('fast-fifo')
const TextDecoder = require('text-decoder')

// if we do a future major, expect queue microtask to be there always, for now a bit defensive
const qmt = typeof queueMicrotask === 'undefined' ? fn => global.process.nextTick(fn) : queueMicrotask

/* eslint-disable no-multi-spaces */

// 29 bits used total (4 from shared, 14 from read, and 11 from write)
const MAX = ((1 << 29) - 1)

// Shared state
const OPENING       = 0b0001
const PREDESTROYING = 0b0010
const DESTROYING    = 0b0100
const DESTROYED     = 0b1000

const NOT_OPENING = MAX ^ OPENING
const NOT_PREDESTROYING = MAX ^ PREDESTROYING

// Read state (4 bit offset from shared state)
const READ_ACTIVE           = 0b00000000000001 << 4
const READ_UPDATING         = 0b00000000000010 << 4
const READ_PRIMARY          = 0b00000000000100 << 4
const READ_QUEUED           = 0b00000000001000 << 4
const READ_RESUMED          = 0b00000000010000 << 4
const READ_PIPE_DRAINED     = 0b00000000100000 << 4
const READ_ENDING           = 0b00000001000000 << 4
const READ_EMIT_DATA        = 0b00000010000000 << 4
const READ_EMIT_READABLE    = 0b00000100000000 << 4
const READ_EMITTED_READABLE = 0b00001000000000 << 4
const READ_DONE             = 0b00010000000000 << 4
const READ_NEXT_TICK        = 0b00100000000000 << 4
const READ_NEEDS_PUSH       = 0b01000000000000 << 4
const READ_READ_AHEAD       = 0b10000000000000 << 4

// Combined read state
const READ_FLOWING = READ_RESUMED | READ_PIPE_DRAINED
const READ_ACTIVE_AND_NEEDS_PUSH = READ_ACTIVE | READ_NEEDS_PUSH
const READ_PRIMARY_AND_ACTIVE = READ_PRIMARY | READ_ACTIVE
const READ_EMIT_READABLE_AND_QUEUED = READ_EMIT_READABLE | READ_QUEUED
const READ_RESUMED_READ_AHEAD = READ_RESUMED | READ_READ_AHEAD

const READ_NOT_ACTIVE             = MAX ^ READ_ACTIVE
const READ_NON_PRIMARY            = MAX ^ READ_PRIMARY
const READ_NON_PRIMARY_AND_PUSHED = MAX ^ (READ_PRIMARY | READ_NEEDS_PUSH)
const READ_PUSHED                 = MAX ^ READ_NEEDS_PUSH
const READ_PAUSED                 = MAX ^ READ_RESUMED
const READ_NOT_QUEUED             = MAX ^ (READ_QUEUED | READ_EMITTED_READABLE)
const READ_NOT_ENDING             = MAX ^ READ_ENDING
const READ_PIPE_NOT_DRAINED       = MAX ^ READ_FLOWING
const READ_NOT_NEXT_TICK          = MAX ^ READ_NEXT_TICK
const READ_NOT_UPDATING           = MAX ^ READ_UPDATING
const READ_NO_READ_AHEAD          = MAX ^ READ_READ_AHEAD
const READ_PAUSED_NO_READ_AHEAD   = MAX ^ READ_RESUMED_READ_AHEAD

// Write state (18 bit offset, 4 bit offset from shared state and 14 from read state)
const WRITE_ACTIVE     = 0b00000000001 << 18
const WRITE_UPDATING   = 0b00000000010 << 18
const WRITE_PRIMARY    = 0b00000000100 << 18
const WRITE_QUEUED     = 0b00000001000 << 18
const WRITE_UNDRAINED  = 0b00000010000 << 18
const WRITE_DONE       = 0b00000100000 << 18
const WRITE_EMIT_DRAIN = 0b00001000000 << 18
const WRITE_NEXT_TICK  = 0b00010000000 << 18
const WRITE_WRITING    = 0b00100000000 << 18
const WRITE_FINISHING  = 0b01000000000 << 18
const WRITE_CORKED     = 0b10000000000 << 18

const WRITE_NOT_ACTIVE    = MAX ^ (WRITE_ACTIVE | WRITE_WRITING)
const WRITE_NON_PRIMARY   = MAX ^ WRITE_PRIMARY
const WRITE_NOT_FINISHING = MAX ^ (WRITE_ACTIVE | WRITE_FINISHING)
const WRITE_DRAINED       = MAX ^ WRITE_UNDRAINED
const WRITE_NOT_QUEUED    = MAX ^ WRITE_QUEUED
const WRITE_NOT_NEXT_TICK = MAX ^ WRITE_NEXT_TICK
const WRITE_NOT_UPDATING  = MAX ^ WRITE_UPDATING
const WRITE_NOT_CORKED    = MAX ^ WRITE_CORKED

// Combined shared state
const ACTIVE = READ_ACTIVE | WRITE_ACTIVE
const NOT_ACTIVE = MAX ^ ACTIVE
const DONE = READ_DONE | WRITE_DONE
const DESTROY_STATUS = DESTROYING | DESTROYED | PREDESTROYING
const OPEN_STATUS = DESTROY_STATUS | OPENING
const AUTO_DESTROY = DESTROY_STATUS | DONE
const NON_PRIMARY = WRITE_NON_PRIMARY & READ_NON_PRIMARY
const ACTIVE_OR_TICKING = WRITE_NEXT_TICK | READ_NEXT_TICK
const TICKING = ACTIVE_OR_TICKING & NOT_ACTIVE
const IS_OPENING = OPEN_STATUS | TICKING

// Combined shared state and read state
const READ_PRIMARY_STATUS = OPEN_STATUS | READ_ENDING | READ_DONE
const READ_STATUS = OPEN_STATUS | READ_DONE | READ_QUEUED
const READ_ENDING_STATUS = OPEN_STATUS | READ_ENDING | READ_QUEUED
const READ_READABLE_STATUS = OPEN_STATUS | READ_EMIT_READABLE | READ_QUEUED | READ_EMITTED_READABLE
const SHOULD_NOT_READ = OPEN_STATUS | READ_ACTIVE | READ_ENDING | READ_DONE | READ_NEEDS_PUSH | READ_READ_AHEAD
const READ_BACKPRESSURE_STATUS = DESTROY_STATUS | READ_ENDING | READ_DONE
const READ_UPDATE_SYNC_STATUS = READ_UPDATING | OPEN_STATUS | READ_NEXT_TICK | READ_PRIMARY
const READ_NEXT_TICK_OR_OPENING = READ_NEXT_TICK | OPENING

// Combined write state
const WRITE_PRIMARY_STATUS = OPEN_STATUS | WRITE_FINISHING | WRITE_DONE
const WRITE_QUEUED_AND_UNDRAINED = WRITE_QUEUED | WRITE_UNDRAINED
const WRITE_QUEUED_AND_ACTIVE = WRITE_QUEUED | WRITE_ACTIVE
const WRITE_DRAIN_STATUS = WRITE_QUEUED | WRITE_UNDRAINED | OPEN_STATUS | WRITE_ACTIVE
const WRITE_STATUS = OPEN_STATUS | WRITE_ACTIVE | WRITE_QUEUED | WRITE_CORKED
const WRITE_PRIMARY_AND_ACTIVE = WRITE_PRIMARY | WRITE_ACTIVE
const WRITE_ACTIVE_AND_WRITING = WRITE_ACTIVE | WRITE_WRITING
const WRITE_FINISHING_STATUS = OPEN_STATUS | WRITE_FINISHING | WRITE_QUEUED_AND_ACTIVE | WRITE_DONE
const WRITE_BACKPRESSURE_STATUS = WRITE_UNDRAINED | DESTROY_STATUS | WRITE_FINISHING | WRITE_DONE
const WRITE_UPDATE_SYNC_STATUS = WRITE_UPDATING | OPEN_STATUS | WRITE_NEXT_TICK | WRITE_PRIMARY
const WRITE_DROP_DATA = WRITE_FINISHING | WRITE_DONE | DESTROY_STATUS

const asyncIterator = Symbol.asyncIterator || Symbol('asyncIterator')

class WritableState {
  constructor (stream, { highWaterMark = 16384, map = null, mapWritable, byteLength, byteLengthWritable } = {}) {
    this.stream = stream
    this.queue = new FIFO()
    this.highWaterMark = highWaterMark
    this.buffered = 0
    this.error = null
    this.pipeline = null
    this.drains = null // if we add more seldomly used helpers we might them into a subobject so its a single ptr
    this.byteLength = byteLengthWritable || byteLength || defaultByteLength
    this.map = mapWritable || map
    this.afterWrite = afterWrite.bind(this)
    this.afterUpdateNextTick = updateWriteNT.bind(this)
  }

  get ended () {
    return (this.stream._duplexState & WRITE_DONE) !== 0
  }

  push (data) {
    if ((this.stream._duplexState & WRITE_DROP_DATA) !== 0) return false
    if (this.map !== null) data = this.map(data)

    this.buffered += this.byteLength(data)
    this.queue.push(data)

    if (this.buffered < this.highWaterMark) {
      this.stream._duplexState |= WRITE_QUEUED
      return true
    }

    this.stream._duplexState |= WRITE_QUEUED_AND_UNDRAINED
    return false
  }

  shift () {
    const data = this.queue.shift()

    this.buffered -= this.byteLength(data)
    if (this.buffered === 0) this.stream._duplexState &= WRITE_NOT_QUEUED

    return data
  }

  end (data) {
    if (typeof data === 'function') this.stream.once('finish', data)
    else if (data !== undefined && data !== null) this.push(data)
    this.stream._duplexState = (this.stream._duplexState | WRITE_FINISHING) & WRITE_NON_PRIMARY
  }

  autoBatch (data, cb) {
    const buffer = []
    const stream = this.stream

    buffer.push(data)
    while ((stream._duplexState & WRITE_STATUS) === WRITE_QUEUED_AND_ACTIVE) {
      buffer.push(stream._writableState.shift())
    }

    if ((stream._duplexState & OPEN_STATUS) !== 0) return cb(null)
    stream._writev(buffer, cb)
  }

  update () {
    const stream = this.stream

    stream._duplexState |= WRITE_UPDATING

    do {
      while ((stream._duplexState & WRITE_STATUS) === WRITE_QUEUED) {
        const data = this.shift()
        stream._duplexState |= WRITE_ACTIVE_AND_WRITING
        stream._write(data, this.afterWrite)
      }

      if ((stream._duplexState & WRITE_PRIMARY_AND_ACTIVE) === 0) this.updateNonPrimary()
    } while (this.continueUpdate() === true)

    stream._duplexState &= WRITE_NOT_UPDATING
  }

  updateNonPrimary () {
    const stream = this.stream

    if ((stream._duplexState & WRITE_FINISHING_STATUS) === WRITE_FINISHING) {
      stream._duplexState = stream._duplexState | WRITE_ACTIVE
      stream._final(afterFinal.bind(this))
      return
    }

    if ((stream._duplexState & DESTROY_STATUS) === DESTROYING) {
      if ((stream._duplexState & ACTIVE_OR_TICKING) === 0) {
        stream._duplexState |= ACTIVE
        stream._destroy(afterDestroy.bind(this))
      }
      return
    }

    if ((stream._duplexState & IS_OPENING) === OPENING) {
      stream._duplexState = (stream._duplexState | ACTIVE) & NOT_OPENING
      stream._open(afterOpen.bind(this))
    }
  }

  continueUpdate () {
    if ((this.stream._duplexState & WRITE_NEXT_TICK) === 0) return false
    this.stream._duplexState &= WRITE_NOT_NEXT_TICK
    return true
  }

  updateCallback () {
    if ((this.stream._duplexState & WRITE_UPDATE_SYNC_STATUS) === WRITE_PRIMARY) this.update()
    else this.updateNextTick()
  }

  updateNextTick () {
    if ((this.stream._duplexState & WRITE_NEXT_TICK) !== 0) return
    this.stream._duplexState |= WRITE_NEXT_TICK
    if ((this.stream._duplexState & WRITE_UPDATING) === 0) qmt(this.afterUpdateNextTick)
  }
}

class ReadableState {
  constructor (stream, { highWaterMark = 16384, map = null, mapReadable, byteLength, byteLengthReadable } = {}) {
    this.stream = stream
    this.queue = new FIFO()
    this.highWaterMark = highWaterMark === 0 ? 1 : highWaterMark
    this.buffered = 0
    this.readAhead = highWaterMark > 0
    this.error = null
    this.pipeline = null
    this.byteLength = byteLengthReadable || byteLength || defaultByteLength
    this.map = mapReadable || map
    this.pipeTo = null
    this.afterRead = afterRead.bind(this)
    this.afterUpdateNextTick = updateReadNT.bind(this)
  }

  get ended () {
    return (this.stream._duplexState & READ_DONE) !== 0
  }

  pipe (pipeTo, cb) {
    if (this.pipeTo !== null) throw new Error('Can only pipe to one destination')
    if (typeof cb !== 'function') cb = null

    this.stream._duplexState |= READ_PIPE_DRAINED
    this.pipeTo = pipeTo
    this.pipeline = new Pipeline(this.stream, pipeTo, cb)

    if (cb) this.stream.on('error', noop) // We already error handle this so supress crashes

    if (isStreamx(pipeTo)) {
      pipeTo._writableState.pipeline = this.pipeline
      if (cb) pipeTo.on('error', noop) // We already error handle this so supress crashes
      pipeTo.on('finish', this.pipeline.finished.bind(this.pipeline)) // TODO: just call finished from pipeTo itself
    } else {
      const onerror = this.pipeline.done.bind(this.pipeline, pipeTo)
      const onclose = this.pipeline.done.bind(this.pipeline, pipeTo, null) // onclose has a weird bool a