text: 'use strict'
  
  var assert = require('assert')
  var http = require('http')
  var https = require('https')
  var net = require('net')
  var util = require('util')
  var transport = require('spdy-transport')
  var debug = require('debug')('spdy:client')
  
  // Node.js 0.10 and 0.12 support
  Object.assign = process.versions.modules >= 46
    ? Object.assign // eslint-disable-next-line
    : util._extend
  
  var EventEmitter = require('events').EventEmitter
  
  var spdy = require('../spdy')
  
  var mode = /^v0\.8\./.test(process.version)
    ? 'rusty'
    : /^v0\.(9|10)\./.test(process.version)
      ? 'old'
      : /^v0\.12\./.test(process.version)
        ? 'normal'
        : 'modern'
  
  var proto = {}
  
  function instantiate (base) {
    function Agent (options) {
      this._init(base, options)
    }
    util.inherits(Agent, base)
  
    Agent.create = function create (options) {
      return new Agent(options)
    }
  
    Object.keys(proto).forEach(function (key) {
      Agent.prototype[key] = proto[key]
    })
  
    return Agent
  }
  
  proto._init = function _init (base, options) {
    base.call(this, options)
  
    var state = {}
    this._spdyState = state
  
    state.host = options.host
    state.options = options.spdy || {}
    state.secure = this instanceof https.Agent
    state.fallback = false
    state.createSocket = this._getCreateSocket()
    state.socket = null
    state.connection = null
  
    // No chunked encoding
    this.keepAlive = false
  
    var self = this
    this._connect(options, function (err, connection) {
      if (err) {
        return self.emit('error', err)
      }
  
      state.connection = connection
      self.emit('_connect')
    })
  }
  
  proto._getCreateSocket = function _getCreateSocket () {
    // Find super's `createSocket` method
    var createSocket
    var cons = this.constructor.super_
    do {
      createSocket = cons.prototype.createSocket
  
      if (cons.super_ === EventEmitter || !cons.super_) {
        break
      }
      cons = cons.super_
    } while (!createSocket)
    if (!createSocket) {
      createSocket = http.Agent.prototype.createSocket
    }
  
    assert(createSocket, '.createSocket() method not found')
  
    return createSocket
  }
  
  proto._connect = function _connect (options, callback) {
    var state = this._spdyState
  
    var protocols = state.options.protocols || [
      'h2',
      'spdy/3.1', 'spdy/3', 'spdy/2',
      'http/1.1', 'http/1.0'
    ]
  
    // TODO(indutny): reconnect automatically?
    var socket = this.createConnection(Object.assign({
      NPNProtocols: protocols,
      ALPNProtocols: protocols,
      servername: options.servername || options.host
    }, options))
    state.socket = socket
  
    socket.setNoDelay(true)
  
    function onError (err) {
      return callback(err)
    }
    socket.on('error', onError)
  
    socket.on(state.secure ? 'secureConnect' : 'connect', function () {
      socket.removeListener('error', onError)
  
      var protocol
      if (state.secure) {
        protocol = socket.npnProtocol ||
                   socket.alpnProtocol ||
                   state.options.protocol
      } else {
        protocol = state.options.protocol
      }
  
      // HTTP server - kill socket and switch to the fallback mode
      if (!protocol || protocol === 'http/1.1' || protocol === 'http/1.0') {
        debug('activating fallback')
        socket.destroy()
        state.fallback = true
        return
      }
  
      debug('connected protocol=%j', protocol)
      var connection = transport.connection.create(socket, Object.assign({
        protocol: /spdy/.test(protocol) ? 'spdy' : 'http2',
        isServer: false
      }, state.options.connection || {}))
  
      // Set version when we are certain
      if (protocol === 'h2') {
        connection.start(4)
      } else if (protocol === 'spdy/3.1') {
        connection.start(3.1)
      } else if (protocol === 'spdy/3') {
        connection.start(3)
      } else if (protocol === 'spdy/2') {
        connection.start(2)
      } else {
        socket.destroy()
        callback(new Error('Unexpected protocol: ' + protocol))
        return
      }
  
      if (state.options['x-forwarded-for'] !== undefined) {
        connection.sendXForwardedFor(state.options['x-forwarded-for'])
      }
  
      callback(null, connection)
    })
  }
  
  proto._createSocket = function _createSocket (req, options, callback) {
    var state = this._spdyState
    if (state.fallback) { return state.createSocket(req, options) }
  
    var handle = spdy.handle.create(null, null, state.socket)
  
    var socketOptions = {
      handle: handle,
      allowHalfOpen: true
    }
  
    var socket
    if (state.secure) {
      socket = new spdy.Socket(state.socket, socketOptions)
    } else {
      socket = new net.Socket(socketOptions)
    }
  
    handle.assignSocket(socket)
    handle.assignClientRequest(req)
  
    // Create stream only once `req.end()` is called
    var self = this
    handle.once('needStream', function () {
      if (state.connection === null) {
        self.once('_connect', function () {
          handle.setStream(self._createStream(req, handle))
        })
      } else {
        handle.setStream(self._createStream(req, handle))
      }
    })
  
    // Yes, it is in reverse
    req.on('response', function (res) {
      handle.assignRequest(res)
    })
    handle.assignResponse(req)
  
    // Handle PUSH
    req.addListener('newListener', spdy.request.onNewListener)
  
    // For v0.8
    socket.readable = true
    socket.writable = true
  
    if (callback) {
      return callback(null, socket)
    }
  
    return socket
  }
  
  if (mode === 'modern' || mode === 'normal') {
    proto.createSocket = proto._createSocket
  } else {
    proto.createSocket = function createSocket (name, host, port, addr, req) {
      var state = this._spdyState
      if (state.fallback) {
        return state.createSocket(name, host, port, addr, req)
      }
  
      return this._createSocket(req, {
        host: host,
        port: port
      })
    }
  }
  
  proto._createStream = function _createStream (req, handle) {
    var state = this._spdyState
  
    var self = this
    return state.connection.reserveStream({
      method: req.method,
      path: req.path,
      headers: req._headers,
      host: state.host
    }, function (err, stream) {
      if (err) {
        return self.emit('error', err)
      }
  
      stream.on('response', function (status, headers) {
        handle.emitResponse(status, headers)
      })
    })
  }
  
  // Public APIs
  
  proto.close = function close (callback) {
    var state = this._spdyState
  
    if (state.connection === null) {
      this.once('_connect', function () {
        this.close(callback)
      })
      return
    }
  
    state.connection.end(callback)
  }
  
  exports.Agent = instantiate(https.Agent)
  exports.PlainAgent = instantiate(http.Agent)
  
  exports.create = function create (base, options) {
    if (typeof base === 'object') {
      options = base
      base = null
    }
  
    if (base) {
      return instantiate(base).create(options)
    }
  
    if (options.spdy && options.spdy.plain) {
      return exports.PlainAgent.create(options)
    } else { return exports.Agent.create(options) }
  }
  