text: var createTorrent = require('create-torrent')
  var debug = require('debug')('instant.io')
  var dragDrop = require('drag-drop')
  var path = require('path')
  var prettierBytes = require('prettier-bytes')
  var throttle = require('throttleit')
  var thunky = require('thunky')
  var uploadElement = require('upload-element')
  var WebTorrent = require('webtorrent')
  var xhr = require('xhr')
  
  var util = require('./util')
  
  global.WEBTORRENT_ANNOUNCE = createTorrent.announceList
    .map(function (arr) {
      return arr[0]
    })
    .filter(function (url) {
      return url.indexOf('wss://') === 0 || url.indexOf('ws://') === 0
    })
  
  if (!WebTorrent.WEBRTC_SUPPORT) {
    util.error('This browser is unsupported. Please use a browser with WebRTC support.')
  }
  
  var getClient = thunky(function (cb) {
    getRtcConfig('/rtcConfig', function (err, rtcConfig) {
      if (err && window.location.hostname === 'instant.io') {
        if (err) util.error(err)
        createClient(rtcConfig)
      } else if (err) {
        getRtcConfig('https://instant.io/rtcConfig', function (err, rtcConfig) {
          if (err) util.error(err)
          createClient(rtcConfig)
        })
      } else {
        createClient(rtcConfig)
      }
    })
  
    function createClient (rtcConfig) {
      var client = window.client = new WebTorrent({
        tracker: {
          rtcConfig: rtcConfig
        }
      })
      client.on('warning', util.warning)
      client.on('error', util.error)
      cb(null, client)
    }
  })
  
  // For performance, create the client immediately
  getClient(function () {})
  
  // Seed via upload input element
  var upload = document.querySelector('input[name=upload]')
  uploadElement(upload, function (err, files) {
    if (err) return util.error(err)
    files = files.map(function (file) { return file.file })
    onFiles(files)
  })
  
  // Seed via drag-and-drop
  dragDrop('body', onFiles)
  
  // Download via input element
  document.querySelector('form').addEventListener('submit', function (e) {
    e.preventDefault()
    downloadTorrent(document.querySelector('form input[name=torrentId]').value.trim())
  })
  
  // Download by URL hash
  onHashChange()
  window.addEventListener('hashchange', onHashChange)
  function onHashChange () {
    var hash = decodeURIComponent(window.location.hash.substring(1)).trim()
    if (hash !== '') downloadTorrent(hash)
  }
  
  // Register a protocol handler for "magnet:" (will prompt the user)
  navigator.registerProtocolHandler('magnet', window.location.origin + '#%s', 'Instant.io')
  
  function getRtcConfig (url, cb) {
    xhr(url, function (err, res) {
      if (err || res.statusCode !== 200) {
        cb(new Error('Could not get WebRTC config from server. Using default (without TURN).'))
      } else {
        var rtcConfig
        try {
          rtcConfig = JSON.parse(res.body)
        } catch (err) {
          return cb(new Error('Got invalid WebRTC config from server: ' + res.body))
        }
        debug('got rtc config: %o', rtcConfig)
        cb(null, rtcConfig)
      }
    })
  }
  
  function onFiles (files) {
    debug('got files:')
    files.forEach(function (file) {
      debug(' - %s (%s bytes)', file.name, file.size)
    })
  
    // .torrent file = start downloading the torrent
    files.filter(isTorrentFile).forEach(downloadTorrentFile)
  
    // everything else = seed these files
    seed(files.filter(isNotTorrentFile))
  }
  
  function isTorrentFile (file) {
    var extname = path.extname(file.name).toLowerCase()
    return extname === '.torrent'
  }
  
  function isNotTorrentFile (file) {
    return !isTorrentFile(file)
  }
  
  function downloadTorrent (torrentId) {
    util.log('Downloading torrent from ' + torrentId)
    getClient(function (err, client) {
      if (err) return util.error(err)
      client.add(torrentId, onTorrent)
    })
  }
  
  function downloadTorrentFile (file) {
    util.log('Downloading torrent from <strong>' + file.name + '</strong>')
    getClient(function (err, client) {
      if (err) return util.error(err)
      client.add(file, onTorrent)
    })
  }
  
  function seed (files) {
    if (files.length === 0) return
    util.log('Seeding ' + files.length + ' files')
  
    // Seed from WebTorrent
    getClient(function (err, client) {
      if (err) return util.error(err)
      client.seed(files, onTorrent)
    })
  }
  
  function onTorrent (torrent) {
    torrent.on('warning', util.warning)
    torrent.on('error', util.error)
  
    upload.value = upload.defaultValue // reset upload element
  
    var torrentFileName = path.basename(torrent.name, path.extname(torrent.name)) + '.torrent'
  
    util.log('"' + torrentFileName + '" contains ' + torrent.files.length + ' files:')
    torrent.files.forEach(function (file) {
      util.log('&nbsp;&nbsp;- ' + file.name + ' (' + prettierBytes(file.length) + ')')
    })
  
    util.log(
      'Torrent info hash: ' + torrent.infoHash + ' ' +
      '<a href="/#' + torrent.infoHash + '" onclick="prompt(\'Share this link with anyone you want to download this torrent:\', this.href);return false;">[Share link]</a> ' +
      '<a href="' + torrent.magnetURI + '" target="_blank">[Magnet URI]</a> ' +
      '<a href="' + torrent.torrentFileBlobURL + '" target="_blank" download="' + torrentFileName + '">[Download .torrent]</a>'
    )
  
    function updateSpeed () {
      var progress = (100 * torrent.progress).toFixed(1)
      util.updateSpeed(
        '<b>Peers:</b> ' + torrent.numPeers + ' ' +
        '<b>Progress:</b> ' + progress + '% ' +
        '<b>Download speed:</b> ' + prettierBytes(window.client.downloadSpeed) + '/s ' +
        '<b>Upload speed:</b> ' + prettierBytes(window.client.uploadSpeed) + '/s'
      )
    }
  
    torrent.on('download', throttle(updateSpeed, 250))
    torrent.on('upload', throttle(updateSpeed, 250))
    setInterval(updateSpeed, 5000)
    updateSpeed()
  
    torrent.files.forEach(function (file) {
      // append file
      file.appendTo(util.logElem, {
        maxBlobLength: 2 * 1000 * 1000 * 1000 // 2 GB
      }, function (err, elem) {
        if (err) return util.error(err)
      })
  
      // append download link
      file.getBlobURL(function (err, url) {
        if (err) return util.error(err)
  
        var a = document.createElement('a')
        a.target = '_blank'
        a.download = file.name
        a.href = url
        a.textContent = 'Download ' + file.name
        util.log(a)
      })
    })
  }
  