import EventEmitter from 'events'
import { Readable } from 'streamx'
import { chunkStoreRead } from 'chunk-store-iterator'
import mime from 'mime/lite.js'
import FileIterator from './file-iterator.js'

export default class File extends EventEmitter {
  constructor (torrent, file) {
    super()

    this._torrent = torrent
    this._destroyed = false
    this._fileStreams = new Set()
    this._iterators = new Set()

    this.name = file.name
    this.path = file.path
    this.length = file.length
    this.size = file.length
    this.type = mime.getType(this.name) || 'application/octet-stream'
    this.offset = file.offset

    this.done = false

    const start = file.offset
    const end = start + file.length - 1

    this._startPiece = start / this._torrent.pieceLength | 0
    this._endPiece = end / this._torrent.pieceLength | 0

    if (this.length === 0) {
      this.done = true
      this.emit('done')
    }

    this._client = torrent.client
  }

  get downloaded () {
    if (this._destroyed || !this._torrent.bitfield) return 0

    const { pieces, bitfield, pieceLength, lastPieceLength } = this._torrent
    const { _startPiece: start, _endPiece: end } = this

    const getPieceLength = (pieceIndex) => (
      pieceIndex === pieces.length - 1 ? lastPieceLength : pieceLength
    )

    const getPieceDownloaded = (pieceIndex) => {
      const len = pieceIndex === pieces.length - 1 ? lastPieceLength : pieceLength
      if (bitfield.get(pieceIndex)) {
        // verified data
        return len
      } else {
        // "in progress" data
        return len - pieces[pieceIndex].missing
      }
    }

    let downloaded = 0
    for (let index = start; index <= end; index += 1) {
      const pieceDownloaded = getPieceDownloaded(index)
      downloaded += pieceDownloaded

      if (index === start) {
        // First piece may have an offset, e.g. irrelevant bytes from the end of
        // the previous file
        const irrelevantFirstPieceBytes = this.offset % pieceLength
        downloaded -= Math.min(irrelevantFirstPieceBytes, pieceDownloaded)
      }

      if (index === end) {
        // Last piece may have an offset, e.g. irrelevant bytes from the start
        // of the next file
        const irrelevantLastPieceBytes = getPieceLength(end) - (this.offset + this.length) % pieceLength
        downloaded -= Math.min(irrelevantLastPieceBytes, pieceDownloaded)
      }
    }

    return downloaded
  }

  get progress () {
    return this.length ? this.downloaded / this.length : 0
  }

  select (priority) {
    if (this.length === 0) return
    this._torrent.select(this._startPiece, this._endPiece, priority)
  }

  deselect () {
    if (this.length === 0) return
    this._torrent.deselect(this._startPiece, this._endPiece)
  }

  [Symbol.asyncIterator] (opts = {}) {
    if (this.length === 0) return (async function * empty () {})()

    const { start = 0 } = opts ?? {}
    const end = (opts?.end && opts.end < this.length)
      ? opts.end
      : this.length - 1

    if (this.done) {
      return chunkStoreRead(this._torrent.store, { offset: start + this.offset, length: end - start + 1 })
    }

    const iterator = new FileIterator(this, { start, end })
    this._iterators.add(iterator)
    iterator.once('return', () => {
      this._iterators.delete(iterator)
    })

    return iterator
  }

  createReadStream (opts) {
    const iterator = this[Symbol.asyncIterator](opts)
    const fileStream = Readable.from(iterator)

    this._fileStreams.add(fileStream)
    fileStream.once('close', () => {
      this._fileStreams.delete(fileStream)
    })

    return fileStream
  }

  async arrayBuffer (opts) {
    const data = new Uint8Array(this.length)
    let offset = 0
    for await (const chunk of this[Symbol.asyncIterator](opts)) {
      data.set(chunk, offset)
      offset += chunk.length
    }
    return data.buffer
  }

  async blob (opts) {
    return new Blob([await this.arrayBuffer(opts)], { type: this.type })
  }

  stream (opts) {
    let iterator
    return new ReadableStream({
      start: () => {
        iterator = this[Symbol.asyncIterator](opts)
      },
      async pull (controller) {
        const { value, done } = await iterator.next()
        if (done) {
          controller.close()
        } else {
          controller.enqueue(value)
        }
      },
      cancel () {
        iterator.return()
      }
    })
  }

  get streamURL () {
    if (!this._client._server) throw new Error('No server created')
    return `${this._client._server.pathname}/${this._torrent.infoHash}/${this.path}`
  }

  streamTo (elem) {
    elem.src = this.streamURL
    return elem
  }

  includes (piece) {
    return this._startPiece <= piece && this._endPiece >= piece
  }

  _destroy () {
    this._destroyed = true
    this._torrent = null

    for (const fileStream of this._fileStreams) {
      fileStream.destroy()
    }
    this._fileStreams.clear()
    for (const iterator of this._iterators) {
      iterator.destroy()
    }
    this._iterators.clear()
  }
}