var Net = require('net');
var util = require('util');
var Tls = require('tls');
var Timers = require('timers');
var EventEmitter = require('events').EventEmitter;
var Queue = require('denque');
var SqlString = require('sqlstring');
var LRU = require('lru-cache');

var PacketParser = require('./packet_parser.js');
var Packet = require('./packets/packet.js');
var Packets = require('./packets/index.js');
var Commands = require('./commands/index.js');
var ConnectionConfig = require('./connection_config.js');
var CharsetToEncoding = require('./constants/charset_encodings.js');
var Buffer = require('safe-buffer').Buffer;

var _connectionId = 0;
var noop = function() {};

function Connection(opts) {
  EventEmitter.call(this);
  this.config = opts.config;

  // TODO: fill defaults
  // if no params, connect to /var/lib/mysql/mysql.sock ( /tmp/mysql.sock on OSX )
  // if host is given, connect to host:3306

  // TODO: use `/usr/local/mysql/bin/mysql_config --socket` output? as default socketPath
  // if there is no host/port and no socketPath parameters?

  if (!opts.config.stream) {
    if (opts.config.socketPath) {
      this.stream = Net.connect(opts.config.socketPath);
    } else {
      this.stream = Net.connect(opts.config.port, opts.config.host);
    }
  } else {
    // if stream is a function, treat it as "stream agent / factory"
    if (typeof opts.config.stream == 'function') {
      this.stream = opts.config.stream(opts);
    } else {
      this.stream = opts.config.stream;
    }
  }
  this._internalId = _connectionId++;

  this._commands = new Queue();
  this._command = null;

  this._paused = false;
  this._paused_packets = new Queue();

  this._statements = LRU({
    max: this.config.maxPreparedStatements,
    dispose: function(key, statement) {
      statement.close();
    }
  });

  // TODO: make it lru cache
  // https://github.com/mercadolibre/node-simple-lru-cache
  // or https://github.com/rsms/js-lru
  // or https://github.com/monsur/jscache
  // or https://github.com/isaacs/node-lru-cache
  //
  // key is field.name + ':' + field.columnType + ':' field.flags + '/'
  this.textProtocolParsers = {};

  // TODO: not sure if cache should be separate (same key as with textProtocolParsers)
  // or part of prepared statements cache (key is sql query)
  this.binaryProtocolParsers = {};

  this.serverCapabilityFlags = 0;
  this.authorized = false;

  var connection = this;

  this.sequenceId = 0;
  this.compressedSequenceId = 0;

  this.threadId = null;
  this._handshakePacket = null;
  this._fatalError = null;
  this._protocolError = null;
  this._outOfOrderPackets = [];

  this.clientEncoding = CharsetToEncoding[this.config.charsetNumber];

  this.stream.on('error', connection._handleNetworkError.bind(this));

  // see https://gist.github.com/khoomeister/4985691#use-that-instead-of-bind
  this.packetParser = new PacketParser(function(p) {
    connection.handlePacket(p);
  });

  this.stream.on('data', function(data) {
    if (connection.connectTimeout) {
      Timers.clearTimeout(connection.connectTimeout);
      connection.connectTimeout = null;
    }
    connection.packetParser.execute(data);
  });

  this.stream.on('end', function() {
    // we need to set this flag everywhere where we want connection to close
    if (connection._closing) {
      return;
    }

    if (!connection._protocolError) {
      // no particular error message before disconnect
      connection._protocolError = new Error(
        'Connection lost: The server closed the connection.'
      );
      connection._protocolError.fatal = true;
      connection._protocolError.code = 'PROTOCOL_CONNECTION_LOST';
    }

    connection._notifyError(connection._protocolError);
  });
  var handshakeCommand;
  if (!this.config.isServer) {
    handshakeCommand = new Commands.ClientHandshake(this.config.clientFlags);
    handshakeCommand.on('end', function() {
      // this happens when handshake finishes early and first packet is error
      // and not server hello ( for example, 'Too many connactions' error)
      if (!handshakeCommand.handshake) {
        return;
      }
      connection._handshakePacket = handshakeCommand.handshake;
      connection.threadId = handshakeCommand.handshake.connectionId;
      connection.emit('connect', handshakeCommand.handshake);
    });
    handshakeCommand.on('error', function(err) {
      connection._closing = true;
      connection._notifyError(err);
    });
    this.addCommand(handshakeCommand);
  }

  // in case there was no initiall handshake but we need to read sting, assume it utf-8
  // most common example: "Too many connections" error ( packet is sent immediately on connection attempt, we don't know server encoding yet)
  // will be overwrittedn with actial encoding value as soon as server handshake packet is received
  this.serverEncoding = 'utf8';

  if (this.config.connectTimeout) {
    var timeoutHandler = this._handleTimeoutError.bind(this);
    this.connectTimeout = Timers.setTimeout(
      timeoutHandler,
      this.config.connectTimeout
    );
  }
}
util.inherits(Connection, EventEmitter);

Connection.prototype._addCommandClosedState = function(cmd) {
  var err = new Error(
    "Can't add new command when connection is in closed state"
  );
  err.fatal = true;
  if (cmd.onResult) {
    cmd.onResult(err);
  } else {
    this.emit('error', err);
  }
};

Connection.prototype._handleFatalError = function(err) {
  var connection = this;
  err.fatal = true;
  // stop receiving packets
  connection.stream.removeAllListeners('data');
  connection.addCommand = connection._addCommandClosedState;
  connection.write = function() {
    connection.emit('error', new Error("Can't write in closed state"));
  };
  connection._notifyError(err);
  connection._fatalError = err;
};

Connection.prototype._handleNetworkError = function(err) {
  this._handleFatalError(err);
};

Connection.prototype._handleTimeoutError = function() {
  if (this.connectTimeout) {
    Timers.clearTimeout(this.connectTimeout);
    this.connectTimeout = null;
  }

  this.stream.destroy && this.stream.destroy();

  var err = new Error('connect ETIMEDOUT');
  err.errorno = 'ETIMEDOUT';
  err.code = 'ETIMEDOUT';
  err.syscall = 'connect';

  this._handleNetworkError(err);
};

// notify all commands in the queue and bubble error as connection "error"
// called on stream error or unexpected termination
Connection.prototype._notifyError = function(err) {
  var connection = this;

  // prevent from emitting 'PROTOCOL_CONNECTION_LOST' after EPIPE or ECONNRESET
  if (connection._fatalError) {
    return;
  }

  var command;

  // if there is no active command, notify connection
  // if there are commands and all of them have callbacks, pass error via callback
  var bubbleErrorToConnection = !connection._command;
  if (connection._command && connection._command.onResult) {
    connection._command.onResult(err);
    connection._command = null;
  } else {
    // connection handshake is special because we allow it to be implicit
    // if error happened during handshake, but there are others commands in queue
    // then bubble error to other commands and not to connection
    if (
      !(connection._command &&
        connection._command.constructor == Commands.ClientHandshake &&
        connection._commands.length > 0)
    ) {
      bubbleErrorToConnection = true;
    }
  }
  while ((command = connection._commands.shift())) {
    if (command.onResult) {
      command.onResult(err);
    } else {
      bubbleErrorToConnection = true;
    }
  }
  // notify connection if some comands in the queue did not have callbacks
  // or if this is pool connection ( so it can be removed from pool )
  if (bubbleErrorToConnection || connection._pool) {
    connection.emit('error', err);
  }
};

Connection.prototype.write = function(buffer) {
  var connection = this;
  this.stream.write(buffer, function(err) {
    if (err) {
      connection._handleNetworkError(err);
    }
  });
};

// http://dev.mysql.com/doc/internals/en/sequence-id.html
//
// The sequence-id is incremented with each packet and may wrap around.
// It starts at 0 and is reset to 0 when a new command
// begins in the Command Phase.
// http://dev.mysql.com/doc/internals/en/example-several-mysql-packets.html

Connection.prototype._resetSequenceId = function() {
  this.sequenceId = 0;
  this.compressedSequenceId = 0;
};

Connection.prototype._bumpCompressedSequenceId = function(numPackets) {
  this.compressedSequenceId += numPackets;
  this.compressedSequenceId %= 256;
};

Connection.prototype._bumpSequenceId = function(numPackets) {
  this.sequenceId += numPackets;
  this.sequenceId %= 256;
};

Connection.prototype.writePacket = function(packet) {
  var MAX_PACKET_LENGTH = 16777215;
  var length = packet.length();
  var chunk, offset, header;

  if (length < MAX_PACKET_LENGTH) {
    packet.writeHeader(this.sequenceId);
    if (this.config.debug) {
      console.log(
        this._internalId +
          ' ' +
          this.connectionId +
          ' <== ' +
          this._command._commandName +
          '#' +
          this._command.stateName() +
          '(' +
          [this.sequenceId, packet._name, packet.length()].join(',') +
          ')'
      );
      console.log(
        this._internalId +
          ' ' +
          this.connectionId +
          ' <== ' +
          packet.buffer.toString('hex')
      );
    }
    this._bumpSequenceId(1);
    this.write(packet.buffer);
  } else {
    if (this.config.debug) {
      console.log(
        this._internalId +
          ' ' +
          this.connectionId +
          ' <== Writing large packet, raw content not written:'
      );
      console.log(
        this._internalId +
          ' ' +
          this.connectionId +
          ' <== ' +
          this._command._commandName +
          '#' +
          this._command.stateName() +
          '(' +
          [this.sequenceId, packet._name, packet.length()].join(',') +
          ')'
      );
    }
    for (offset = 4; offset < 4 + length; offset += MAX_PACKET_LENGTH) {
      chunk = packet.buffer.slice(offset, offset + MAX_PACKET_LENGTH);
      if (chunk.length === MAX_PACKET_LENGTH) {
        header = Buffer.from([0xff, 0xff, 0xff, this.sequenceId]);
      } else {
        header = Buffer.from([
          chunk.length & 0xff,
          (chunk.length >> 8) & 0xff,
          (chunk.length >> 16) & 0xff,
          this.sequenceId
        ]);
      }
      this._bumpSequenceId(1);
      this.write(header);
      this.write(chunk);
    }
  }
};

if (Tls.TLSSocket) {
  // 0.11+ environment
  Connection.prototype.startTLS = function _startTLS(onSecure) {
    if (this.config.debug) {
      console.log('Upgrading connection to TLS');
    }
    var connection = this;
    var stream = this.stream;
    var secureContext = Tls.createSecureContext({
      ca: this.config.ssl.ca,
      cert: this.config.ssl.cert,
      ciphers: this.config.ssl.ciphers,
      key: this.config.ssl.key,
      passphrase: this.config.ssl.passphrase
    });

    var rejectUnauthorized = this.config.ssl.rejectUnauthorized;
    var secureEstablished = false;
    var secureSocket = new Tls.TLSSocket(connection.stream, {
      rejectUnauthorized: rejectUnauthorized,
      requestCert: true,
      secureContext: secureContext,
      isServer: false
    });

    // error handler for secure socket
    secureSocket.on('_tlsError', function(err) {
      if (secureEstablished) {
        connection._handleNetworkError(err);
      } else {
        onSecure(err);
      }
    });

    secureSocket.on('secure', function() {
      secureEstablished = true;
      onSecure(rejectUnauthorized ? this.ssl.verifyError() : null);
    });
    secureSocket.on('data', function(data) {
      connection.packetParser.execute(data);
    });
    connection.write = function(buffer) {
      secureSocket.write(buffer);
    };
    // start TLS communications
    secureSocket._start();
  };
} else {
  Connection.prototype.startTLS = function _startTLS(onSecure) {
    if (this.config.debug) {
      console.log('Upgrading connection to TLS');
    }
    var connection = this;
    var crypto = require('crypto');
    var config = this.config;
    var stream = this.stream;
    var rejectUnauthorized = this.config.ssl.rejectUnauthorized;
    var credentials = crypto.createCredentials({
      key: config.ssl.key,
      cert: config.ssl.cert,
      passphrase: config.ssl.passphrase,
      ca: config.ssl.ca,
      ciphers: config.ssl.ciphers
    });
    var securePair = Tls.createSecurePair(
      credentials,
      false,
      true,
      rejectUnauthorized
    );

    if (stream.ondata) {
      stream.ondata = null;
    }
    stream.removeAllListeners('data');
    stream.pipe(securePair.encrypted);
    securePair.encrypted.pipe(stream);
    securePair.cleartext.on('data', function(data) {
      connection.packetParser.execute(data);
    });
    connection.write = function(buffer) {
      securePair.cleartext.write(buffer);
    };
    securePair.on('secure', function() {
      onSecure(rejectUnauthorized ? this.ssl.verifyError() : null);
    });
  };
}

Connection.prototype.pipe = function() {
  var connection = this;
  if (this.stream instanceof Net.Stream) {
    this.stream.ondata = function(data, start, end) {
      connection.packetParser.execute(data, start, end);
    };
  } else {
    this.stream.on('data', function(data) {
      connection.packetParser.execute(
        data.parent,
        data.offset,
        data.offset + data.length
      );
    });
  }
};

Connection.prototype.protocolError = function(message, code) {
  var err = new Error(message);
  err.fatal = true;
  err.code = code || 'PROTOCOL_ERROR';
  this.emit('error', err);
};

Connection.prototype.handlePacket = function(packet) {
  if (this._paused) {
    this._paused_packets.push(packet);
    return;
  }
  if (packet) {
    if (this.sequenceId !== packet.sequenceId) {
      console.error(
        'Warning: got packets out of order. Expected ' +
          this.sequenceId +
          ' but received ' +
          packet.sequenceId
      );
    }
    this._bumpSequenceId(packet.numPackets);
  }

  if (this.config.debug) {
    if (packet) {
      console.log(
        ' raw: ' +
          packet.buffer
            .slice(packet.offset, packet.offset + packet.length())
            .toString('hex')
      );
      console.trace();
      var commandName = this._command
        ? this._command._commandName
        : '(no command)';
      var stateName = this._command
        ? this._command.stateName()
        : '(no command)';
      console.log(
        this._internalId +
          ' ' +
          this.connectionId +
          ' ==> ' +
          commandName +
          '#' +
          stateName +
          '(' +
          [packet.sequenceId, packet.type(), packet.length()].join(',') +
          ')'
      );
    }
  }
  if (!this._command) {
    this.protocolError(
      'Unexpected packet while no commands in the queue',
      'PROTOCOL_UNEXPECTED_PACKET'
    );
    this.close();
    return;
  }

  var done = this._command.execute(packet, this);
  if (done) {
    this._command = this._commands.shift();
    if (this._command) {
      this.sequenceId = 0;
      this.compressedSequenceId = 0;
      this.handlePacket();
    }
  }
};

Connection.prototype.addCommand = function(cmd) {
  // this.compressedSequenceId = 0;
  // this.sequenceId = 0;

  if (this.config.debug) {
    console.log('Add command: ' + arguments.callee.caller.name);
    cmd._commandName = arguments.callee.caller.name;
  }
  if (!this._command) {
    this._command = cmd;
    this.handlePacket();
  } else {
    this._commands.push(cmd);
  }
  return cmd;
};

Connection.prototype.format = function(sql, values) {
  if (typeof this.config.queryFormat == 'function') {
    return this.config.queryFormat.call(
      this,
      sql,
      values,
      this.config.timezone
    );
  }
  var opts = {
    sql: sql,
    values: values
  };
  this._resolveNamedPlaceholders(opts);
  return SqlString.format(
    opts.sql,
    opts.values,
    this.config.stringifyObjects,
    this.config.timezone
  );
};

Connection.prototype.escape = function(value) {
  return SqlString.escape(value, false, this.config.timezone);
};

Connection.prototype.escapeId = function escapeId(value) {
  return SqlString.escapeId(value, false);
};

var convertNamedPlaceholders = null;
Connection.prototype._resolveNamedPlaceholders = function(options) {
  var unnamed;
  if (this.config.namedPlaceholders || options.namedPlaceholders) {
    if (convertNamedPlaceholders === null) {
      convertNamedPlaceholders = require('named-placeholders')();
    }
    unnamed = convertNamedPlaceholders(options.sql, options.values);
    options.sql = unnamed[0];
    options.values = unnamed[1];
  }
};

Connection.createQuery = function createQuery(sql, values, cb, config) {
  var options = {
    rowsAsArray: config.rowsAsArray
  };
  if (typeof sql === 'object') {
    // query(options, cb)
    options = sql;
    if (typeof values === 'function') {
      cb = values;
    } else if (values !== undefined) {
      options.values = values;
    }
  } else if (typeof values === 'function') {
    // query(sql, cb)
    cb = values;
    options.sql = sql;
    options.values = undefined;
  } else {
    // query(sql, values, cb)
    options.sql = sql;
    options.values = values;
  }
  return new Commands.Query(options, cb);
};

Connection.prototype.query = function query(sql, values, cb) {
  var cmdQuery;
  if (sql.constructor == Commands.Query) {
    cmdQuery = sql;
  } else {
    cmdQuery = Connection.createQuery(sql, values, cb, this.config);
  }
  this._resolveNamedPlaceholders(cmdQuery);
  var rawSql = this.format(cmdQuery.sql, cmdQuery.values || []);
  cmdQuery.sql = rawSql;
  return this.addCommand(cmdQuery);
};

Connection.prototype.pause = function pause() {
  this._paused = true;
  this.stream.pause();
};

Connection.prototype.resume = function resume() {
  var packet;
  this._paused = false;
  while ((packet = this._paused_packets.shift())) {
    this.handlePacket(packet);
    // don't resume if packet hander paused connection
    if (this._paused) {
      return;
    }
  }
  this.stream.resume();
};

Connection.prototype.keyFromFields = function keyFromFields(fields, options) {
  var res =
    typeof options.nestTables +
    '/' +
    options.nestTables +
    '/' +
    options.rowsAsArray +
    options.supportBigNumbers +
    '/' +
    options.bigNumberStrings +
    '/' +
    typeof options.typeCast;
  for (var i = 0; i < fields.length; ++i) {
    res +=
      '/' + fields[i].name + ':' + fields[i].columnType + ':' + fields[i].flags;
  }
  return res;
};

Connection.statementKey = function(options) {
  return (
    typeof options.nestTables +
    '/' +
    options.nestTables +
    '/' +
    options.rowsAsArray +
    options.sql
  );
};

// TODO: named placeholders support
Connection.prototype.prepare = function prepare(options, cb) {
  if (typeof options == 'string') {
    options = { sql: options };
  }
  return this.addCommand(new Commands.Prepare(options, cb));
};

Connection.prototype.unprepare = function unprepare(sql) {
  var options = {};
  if (typeof sql === 'object') {
    options = sql;
  } else {
    options.sql = sql;
  }
  var key = Connection.statementKey(options);
  var stmt = this._statements.get(key);
  if (stmt) {
    this._statements.del(key);
    stmt.close();
  }
  return stmt;
};

Connection.prototype.execute = function execute(sql, values, cb) {
  var options = {};
  if (typeof sql === 'object') {
    // execute(options, cb)
    options = sql;
    if (typeof values === 'function') {
      cb = values;
    } else {
      options.values = options.values || values;
    }
  } else if (typeof values === 'function') {
    // execute(sql, cb)
    cb = values;
    options.sql = sql;
    options.values = undefined;
  } else {
    // execute(sql, values, cb)
    options.sql = sql;
    options.values = values;
  }
  this._resolveNamedPlaceholders(options);

  var executeCommand = new Commands.Execute(options, cb);
  var prepareCommand = new Commands.Prepare(options, function(err, stmt) {
    if (err) {
      // skip execute command if prepare failed, we have main
      // combined callback here
      executeCommand.start = function() {
        return null;
      };

      if (cb) {
        cb(err);
      } else {
        executeCommand.emit('error', err);
      }
      executeCommand.emit('end');
      return;
    }

    executeCommand.statement = stmt;
  });

  this.addCommand(prepareCommand);
  this.addCommand(executeCommand);
  return executeCommand;
};

Connection.prototype.changeUser = function changeUser(options, callback) {
  if (!callback && typeof options === 'function') {
    callback = options;
    options = {};
  }

  var charsetNumber = options.charset
    ? ConnectionConfig.getCharsetNumber(options.charset)
    : this.config.charsetNumber;

  return this.addCommand(
    new Commands.ChangeUser(
      {
        user: options.user || this.config.user,
        password: options.password || this.config.password,
        passwordSha1: options.passwordSha1 || this.config.passwordSha1,
        database: options.database || this.config.database,
        timeout: options.timeout,
        charsetNumber: charsetNumber,
        currentConfig: this.config
      },
      function(err) {
        if (err) {
          err.fatal = true;
        }

        if (callback) {
          callback(err);
        }
      }
    )
  );
};

// transaction helpers
Connection.prototype.beginTransaction = function(cb) {
  return this.query('START TRANSACTION', cb);
};

Connection.prototype.commit = function(cb) {
  return this.query('COMMIT', cb);
};

Connection.prototype.rollback = function(cb) {
  return this.query('ROLLBACK', cb);
};

Connection.prototype.ping = function ping(cb) {
  return this.addCommand(new Commands.Ping(cb));
};

Connection.prototype._registerSlave = function registerSlave(opts, cb) {
  return this.addCommand(new Commands.RegisterSlave(opts, cb));
};

Connection.prototype._binlogDump = function binlogDump(opts, cb) {
  return this.addCommand(new Commands.BinlogDump(opts, cb));
};

// currently just alias to close
Connection.prototype.destroy = function() {
  this.close();
};

Connection.prototype.close = function() {
  if (this.connectTimeout) {
    Timers.clearTimeout(this.connectTimeout);
    this.connectTimeout = null;
  }
  this._closing = true;
  this.stream.end();
  var connection = this;
  connection.addCommand = connection._addCommandClosedState;
};

Connection.prototype.createBinlogStream = function(opts) {
  // TODO: create proper stream class
  // TODO: use through2
  var test = 1;
  var Readable = require('stream').Readable;
  var stream = new Readable({ objectMode: true });
  stream._read = function() {
    return {
      data: test++
    };
  };
  var connection = this;
  connection._registerSlave(opts, function(err) {
    var dumpCmd = connection._binlogDump(opts);
    dumpCmd.on('event', function(ev) {
      stream.push(ev);
    });
    dumpCmd.on('eof', function() {
      stream.push(null);
      // if non-blocking, then close stream to prevent errors
      if (opts.flags && opts.flags & 0x01) {
        connection.close();
      }
    });
    // TODO: pipe errors as well
  });
  return stream;
};

Connection.prototype.connect = function(cb) {
  if (!cb) {
    return;
  }
  var connectCalled = 0;

  function callbackOnce(isErrorHandler) {
    return function(param) {
      if (!connectCalled) {
        if (isErrorHandler) {
          cb(param);
        } else {
          cb(null, param);
        }
      }
      connectCalled = 1;
    };
  }
  this.once('error', callbackOnce(true));
  this.once('connect', callbackOnce(false));
};

// ===================================
// outgoing server connection methods
// ===================================

Connection.prototype.writeColumns = function(columns) {
  var connection = this;
  this.writePacket(Packets.ResultSetHeader.toPacket(columns.length));
  columns.forEach(function(column) {
    connection.writePacket(
      Packets.ColumnDefinition.toPacket(
        column,
        connection.serverConfig.encoding
      )
    );
  });
  this.writeEof();
};

// row is array of columns, not hash
Connection.prototype.writeTextRow = function(column) {
  this.writePacket(
    Packets.TextRow.toPacket(column, this.serverConfig.encoding)
  );
};

Connection.prototype.writeTextResult = function(rows, columns) {
  var connection = this;
  connection.writeColumns(columns);
  rows.forEach(function(row) {
    var arrayRow = new Array(columns.length);
    columns.forEach(function(column) {
      arrayRow.push(row[column.name]);
    });
    connection.writeTextRow(arrayRow);
  });
  connection.writeEof();
};

Connection.prototype.writeEof = function(warnings, statusFlags) {
  this.writePacket(Packets.EOF.toPacket(warnings, statusFlags));
};

Connection.prototype.writeOk = function(args) {
  if (!args) {
    args = { affectedRows: 0 };
  }
  this.writePacket(Packets.OK.toPacket(args, this.serverConfig.encoding));
};

Connection.prototype.writeError = function(args) {
  // if we want to send error before initial hello was sent, use default encoding
  var encoding = this.serverConfig ? this.serverConfig.encoding : 'cesu8';
  this.writePacket(Packets.Error.toPacket(args, encoding));
};

Connection.prototype.serverHandshake = function serverHandshake(args) {
  this.serverConfig = args;
  this.serverConfig.encoding =
    CharsetToEncoding[this.serverConfig.characterSet];
  return this.addCommand(new Commands.ServerHandshake(args));
};

// ===============================================================

Connection.prototype.end = function(callback) {
  var connection = this;

  if (this.config.isServer) {
    connection._closing = true;
    var quitCmd = new EventEmitter();
    setImmediate(function() {
      connection.stream.end();
      quitCmd.emit('end');
    });
    return quitCmd;
  }

  // trigger error if more commands enqueued after end command
  var quitCmd = this.addCommand(new Commands.Quit(callback));
  connection.addCommand = connection._addCommandClosedState;
  return quitCmd;
};

module.exports = Connection;