'use strict'
const MiniPass = require('minipass')
const EE = require('events').EventEmitter
const fs = require('fs')

let writev = fs.writev
/* istanbul ignore next */
if (!writev) {
  // This entire block can be removed if support for earlier than Node.js
  // 12.9.0 is not needed.
  const binding = process.binding('fs')
  const FSReqWrap = binding.FSReqWrap || binding.FSReqCallback

  writev = (fd, iovec, pos, cb) => {
    const done = (er, bw) => cb(er, bw, iovec)
    const req = new FSReqWrap()
    req.oncomplete = done
    binding.writeBuffers(fd, iovec, pos, req)
  }
}

const _autoClose = Symbol('_autoClose')
const _close = Symbol('_close')
const _ended = Symbol('_ended')
const _fd = Symbol('_fd')
const _finished = Symbol('_finished')
const _flags = Symbol('_flags')
const _flush = Symbol('_flush')
const _handleChunk = Symbol('_handleChunk')
const _makeBuf = Symbol('_makeBuf')
const _mode = Symbol('_mode')
const _needDrain = Symbol('_needDrain')
const _onerror = Symbol('_onerror')
const _onopen = Symbol('_onopen')
const _onread = Symbol('_onread')
const _onwrite = Symbol('_onwrite')
const _open = Symbol('_open')
const _path = Symbol('_path')
const _pos = Symbol('_pos')
const _queue = Symbol('_queue')
const _read = Symbol('_read')
const _readSize = Symbol('_readSize')
const _reading = Symbol('_reading')
const _remain = Symbol('_remain')
const _size = Symbol('_size')
const _write = Symbol('_write')
const _writing = Symbol('_writing')
const _defaultFlag = Symbol('_defaultFlag')

class ReadStream extends MiniPass {
  constructor (path, opt) {
    opt = opt || {}
    super(opt)

    this.writable = false

    if (typeof path !== 'string')
      throw new TypeError('path must be a string')

    this[_fd] = typeof opt.fd === 'number' ? opt.fd : null
    this[_path] = path
    this[_readSize] = opt.readSize || 16*1024*1024
    this[_reading] = false
    this[_size] = typeof opt.size === 'number' ? opt.size : Infinity
    this[_remain] = this[_size]
    this[_autoClose] = typeof opt.autoClose === 'boolean' ?
      opt.autoClose : true

    if (typeof this[_fd] === 'number')
      this[_read]()
    else
      this[_open]()
  }

  get fd () { return this[_fd] }
  get path () { return this[_path] }

  write () {
    throw new TypeError('this is a readable stream')
  }

  end () {
    throw new TypeError('this is a readable stream')
  }

  [_open] () {
    fs.open(this[_path], 'r', (er, fd) => this[_onopen](er, fd))
  }

  [_onopen] (er, fd) {
    if (er)
      this[_onerror](er)
    else {
      this[_fd] = fd
      this.emit('open', fd)
      this[_read]()
    }
  }

  [_makeBuf] () {
    return Buffer.allocUnsafe(Math.min(this[_readSize], this[_remain]))
  }

  [_read] () {
    if (!this[_reading]) {
      this[_reading] = true
      const buf = this[_makeBuf]()
      /* istanbul ignore if */
      if (buf.length === 0) return process.nextTick(() => this[_onread](null, 0, buf))
      fs.read(this[_fd], buf, 0, buf.length, null, (er, br, buf) =>
        this[_onread](er, br, buf))
    }
  }

  [_onread] (er, br, buf) {
    this[_reading] = false
    if (er)
      this[_onerror](er)
    else if (this[_handleChunk](br, buf))
      this[_read]()
  }

  [_close] () {
    if (this[_autoClose] && typeof this[_fd] === 'number') {
      fs.close(this[_fd], _ => this.emit('close'))
      this[_fd] = null
    }
  }

  [_onerror] (er) {
    this[_reading] = true
    this[_close]()
    this.emit('error', er)
  }

  [_handleChunk] (br, buf) {
    let ret = false
    // no effect if infinite
    this[_remain] -= br
    if (br > 0)
      ret = super.write(br < buf.length ? buf.slice(0, br) : buf)

    if (br === 0 || this[_remain] <= 0) {
      ret = false
      this[_close]()
      super.end()
    }

    return ret
  }

  emit (ev, data) {
    switch (ev) {
      case 'prefinish':
      case 'finish':
        break

      case 'drain':
        if (typeof this[_fd] === 'number')
          this[_read]()
        break

      default:
        return super.emit(ev, data)
    }
  }
}

class ReadStreamSync extends ReadStream {
  [_open] () {
    let threw = true
    try {
      this[_onopen](null, fs.openSync(this[_path], 'r'))
      threw = false
    } finally {
      if (threw)
        this[_close]()
    }
  }

  [_read] () {
    let threw = true
    try {
      if (!this[_reading]) {
        this[_reading] = true
        do {
          const buf = this[_makeBuf]()
          /* istanbul ignore next */
          const br = buf.length === 0 ? 0 : fs.readSync(this[_fd], buf, 0, buf.length, null)
          if (!this[_handleChunk](br, buf))
            break
        } while (true)
        this[_reading] = false
      }
      threw = false
    } finally {
      if (threw)
        this[_close]()
    }
  }

  [_close] () {
    if (this[_autoClose] && typeof this[_fd] === 'number') {
      try {
        fs.closeSync(this[_fd])
      } catch (er) {}
      this[_fd] = null
      this.emit('close')
    }
  }
}

class WriteStream extends EE {
  constructor (path, opt) {
    opt = opt || {}
    super(opt)
    this.readable = false
    this[_writing] = false
    this[_ended] = false
    this[_needDrain] = false
    this[_queue] = []
    this[_path] = path
    this[_fd] = typeof opt.fd === 'number' ? opt.fd : null
    this[_mode] = opt.mode === undefined ? 0o666 : opt.mode
    this[_pos] = typeof opt.start === 'number' ? opt.start : null
    this[_autoClose] = typeof opt.autoClose === 'boolean' ?
      opt.autoClose : true

    // truncating makes no sense when writing into the middle
    const defaultFlag = this[_pos] !== null ? 'r+' : 'w'
    this[_defaultFlag] = opt.flags === undefined
    this[_flags] = this[_defaultFlag] ? defaultFlag : opt.flags

    if (this[_fd] === null)
      this[_open]()
  }

  get fd () { return this[_fd] }
  get path () { return this[_path] }

  [_onerror] (er) {
    this[_close]()
    this[_writing] = true
    this.emit('error', er)
  }

  [_open] () {
    fs.open(this[_path], this[_flags], this[_mode],
      (er, fd) => this[_onopen](er, fd))
  }

  [_onopen] (er, fd) {
    if (this[_defaultFlag] &&
        this[_flags] === 'r+' &&
        er && er.code === 'ENOENT') {
      this[_flags] = 'w'
      this[_open]()
    } else if (er)
      this[_onerror](er)
    else {
      this[_fd] = fd
      this.emit('open', fd)
      this[_flush]()
    }
  }

  end (buf, enc) {
    if (buf)
      this.write(buf, enc)

    this[_ended] = true

    // synthetic after-write logic, where drain/finish live
    if (!this[_writing] && !this[_queue].length &&
        typeof this[_fd] === 'number')
      this[_onwrite](null, 0)
  }

  write (buf, enc) {
    if (typeof buf === 'string')
      buf = Buffer.from(buf, enc)

    if (this[_ended]) {
      this.emit('error', new Error('write() after end()'))
      return false
    }

    if (this[_fd] === null || this[_writing] || this[_queue].length) {
      this[_queue].push(buf)
      this[_needDrain] = true
      return false
    }

    this[_writing] = true
    this[_write](buf)
    return true
  }

  [_write] (buf) {
    fs.write(this[_fd], buf, 0, buf.length, this[_pos], (er, bw) =>
      this[_onwrite](er, bw))
  }

  [_onwrite] (er, bw) {
    if (er)
      this[_onerror](er)
    else {
      if (this[_pos] !== null)
        this[_pos] += bw
      if (this[_queue].length)
        this[_flush]()
      else {
        this[_writing] = false

        if (this[_ended] && !this[_finished]) {
          this[_finished] = true
          this[_close]()
          this.emit('finish')
        } else if (this[_needDrain]) {
          this[_needDrain] = false
          this.emit('drain')
        }
      }
    }
  }

  [_flush] () {
    if (this[_queue].length === 0) {
      if (this[_ended])
        this[_onwrite](null, 0)
    } else if (this[_queue].length === 1)
      this[_write](this[_queue].pop())
    else {
      const iovec = this[_queue]
      this[_queue] = []
      writev(this[_fd], iovec, this[_pos],
        (er, bw) => this[_onwrite](er, bw))
    }
  }

  [_close] () {
    if (this[_autoClose] && typeof this[_fd] === 'number') {
      fs.close(this[_fd], _ => this.emit('close'))
      this[_fd] = null
    }
  }
}

class WriteStreamSync extends WriteStream {
  [_open] () {
    let fd
    try {
      fd = fs.openSync(this[_path], this[_flags], this[_mode])
    } catch (er) {
      if (this[_defaultFlag] &&
          this[_flags] === 'r+' &&
          er && er.code === 'ENOENT') {
        this[_flags] = 'w'
        return this[_open]()
      } else
        throw er
    }
    this[_onopen](null, fd)
  }

  [_close] () {
    if (this[_autoClose] && typeof this[_fd] === 'number') {
      try {
        fs.closeSync(this[_fd])
      } catch (er) {}
      this[_fd] = null
      this.emit('close')
    }
  }

  [_write] (buf) {
    try {
      this[_onwrite](null,
        fs.writeSync(this[_fd], buf, 0, buf.length, this[_pos]))
    } catch (er) {
      this[_onwrite](er, 0)
    }
  }
}

exports.ReadStream = ReadStream
exports.ReadStreamSync = ReadStreamSync

exports.WriteStream = WriteStream
exports.WriteStreamSync = WriteStreamSync