'use strict';

var packageInfo = require('../package.json');
var EventEmitter = require('events').EventEmitter;
var util = require('util');
var net = require('net');
var tls = require('tls');
var os = require('os');
var crypto = require('crypto');
var DataStream = require('./data-stream');
var PassThrough = require('stream').PassThrough;
var shared = require('nodemailer-shared');
var ntlm = require('httpntlm/ntlm');

module.exports = SMTPConnection;

/**
 * Generates a SMTP connection object
 *
 * Optional options object takes the following possible properties:
 *
 *  * **port** - is the port to connect to (defaults to 25 or 465)
 *  * **host** - is the hostname or IP address to connect to (defaults to 'localhost')
 *  * **secure** - use SSL
 *  * **ignoreTLS** - ignore server support for STARTTLS
 *  * **requireTLS** - forces the client to use STARTTLS
 *  * **name** - the name of the client server
 *  * **localAddress** - outbound address to bind to (see: http://nodejs.org/api/net.html#net_net_connect_options_connectionlistener)
 *  * **greetingTimeout** - Time to wait in ms until greeting message is received from the server (defaults to 10000)
 *  * **connectionTimeout** - how many milliseconds to wait for the connection to establish
 *  * **socketTimeout** - Time of inactivity until the connection is closed (defaults to 1 hour)
 *  * **lmtp** - if true, uses LMTP instead of SMTP protocol
 *  * **logger** - bunyan compatible logger interface
 *  * **debug** - if true pass SMTP traffic to the logger
 *  * **tls** - options for createCredentials
 *  * **socket** - existing socket to use instead of creating a new one (see: http://nodejs.org/api/net.html#net_class_net_socket)
 *  * **secured** - boolean indicates that the provided socket has already been upgraded to tls
 *
 * @constructor
 * @namespace SMTP Client module
 * @param {Object} [options] Option properties
 */
function SMTPConnection(options) {
    EventEmitter.call(this);

    this.id = crypto.randomBytes(8).toString('base64').replace(/\W/g, '');
    this.stage = 'init';

    this.options = options || {};

    this.secureConnection = !!this.options.secure;
    this.alreadySecured = !!this.options.secured;

    this.port = this.options.port || (this.secureConnection ? 465 : 25);
    this.host = this.options.host || 'localhost';

    if (typeof this.options.secure === 'undefined' && this.port === 465) {
        // if secure option is not set but port is 465, then default to secure
        this.secureConnection = true;
    }

    this.name = this.options.name || this._getHostname();

    this.logger = shared.getLogger(this.options);

    /**
     * Expose version nr, just for the reference
     * @type {String}
     */
    this.version = packageInfo.version;

    /**
     * If true, then the user is authenticated
     * @type {Boolean}
     */
    this.authenticated = false;

    /**
     * If set to true, this instance is no longer active
     * @private
     */
    this.destroyed = false;

    /**
     * Defines if the current connection is secure or not. If not,
     * STARTTLS can be used if available
     * @private
     */
    this.secure = !!this.secureConnection;

    /**
     * Store incomplete messages coming from the server
     * @private
     */
    this._remainder = '';

    /**
     * Unprocessed responses from the server
     * @type {Array}
     */
    this._responseQueue = [];

    /**
     * The socket connecting to the server
     * @publick
     */
    this._socket = false;

    /**
     * Lists supported auth mechanisms
     * @private
     */
    this._supportedAuth = [];

    /**
     * Lists supported extensions
     * @private
     */
    this._supportedExtensions = [];

    /**
     * Function to run if a data chunk comes from the server
     * @private
     */
    this._currentAction = false;

    /**
     * Timeout variable for waiting the greeting
     * @private
     */
    this._greetingTimeout = false;

    /**
     * Timeout variable for waiting the connection to start
     * @private
     */
    this._connectionTimeout = false;

    /**
     * If the socket is deemed already closed
     * @private
     */
    this._destroyed = false;

    /**
     * If the socket is already being closed
     * @private
     */
    this._closing = false;
}
util.inherits(SMTPConnection, EventEmitter);

/**
 * Creates a connection to a SMTP server and sets up connection
 * listener
 */
SMTPConnection.prototype.connect = function (connectCallback) {
    if (typeof connectCallback === 'function') {
        this.once('connect', function () {
            this.logger.debug('[%s] SMTP handshake finished', this.id);
            connectCallback();
        }.bind(this));
    }

    var opts = {
        port: this.port,
        host: this.host
    };

    if (this.options.localAddress) {
        opts.localAddress = this.options.localAddress;
    }

    if (this.options.connection) {
        // connection is already opened
        this._socket = this.options.connection;
        if (this.secureConnection && !this.alreadySecured) {
            setImmediate(this._upgradeConnection.bind(this, function (err) {
                if (err) {
                    this._onError(new Error('Error initiating TLS - ' + (err.message || err)), 'ETLS');
                    return;
                }
                this._onConnect();
            }.bind(this)));
        } else {
            setImmediate(this._onConnect.bind(this));
        }
    } else if (this.options.socket) {
        // socket object is set up but not yet connected
        this._socket = this.options.socket;
        try {
            this._socket.connect(this.port, this.host, this._onConnect.bind(this));
        } catch (E) {
            return setImmediate(this._onError.bind(this, E, 'ECONNECTION'));
        }
    } else if (this.secureConnection) {
        // connect using tls
        if (this.options.tls) {
            Object.keys(this.options.tls).forEach(function (key) {
                opts[key] = this.options.tls[key];
            }.bind(this));
        }
        try {
            this._socket = tls.connect(this.port, this.host, opts, this._onConnect.bind(this));
        } catch (E) {
            return setImmediate(this._onError.bind(this, E, 'ECONNECTION'));
        }
    } else {
        // connect using plaintext
        try {
            this._socket = net.connect(opts, this._onConnect.bind(this));
        } catch (E) {
            return setImmediate(this._onError.bind(this, E, 'ECONNECTION'));
        }
    }

    this._connectionTimeout = setTimeout(function () {
        this._onError('Connection timeout', 'ETIMEDOUT');
    }.bind(this), this.options.connectionTimeout || 60 * 1000);

    this._socket.on('error', this._onError.bind(this));
};

/**
 * Sends QUIT
 */
SMTPConnection.prototype.quit = function () {
    this._sendCommand('QUIT');
    this._currentAction = this.close;
};

/**
 * Closes the connection to the server
 */
SMTPConnection.prototype.close = function () {
    clearTimeout(this._connectionTimeout);
    clearTimeout(this._greetingTimeout);

    // allow to run this function only once
    if (this._closing) {
        return;
    }
    this._closing = true;

    var closeMethod = 'end';

    if (this.stage === 'init') {
        // Close the socket immediately when connection timed out
        closeMethod = 'destroy';
    }

    this.logger.debug('[%s] Closing connection to the server using "%s"', this.id, closeMethod);

    var socket = this._socket && this._socket.socket || this._socket;

    if (socket && !socket.destroyed) {
        try {
            this._socket[closeMethod]();
        } catch (E) {
            // just ignore
        }
    }

    this._destroy();
};

/**
 * Authenticate user
 */
SMTPConnection.prototype.login = function (authData, callback) {
    this._auth = authData || {};
    this._user = this._auth.xoauth2 && this._auth.xoauth2.options && this._auth.xoauth2.options.user || this._auth.user || '';

    var authMethod;
    if (this.options.authMethod) {
        authMethod = this.options.authMethod.toUpperCase().trim();
    } else if (this._auth.xoauth2 && this._supportedAuth.indexOf('XOAUTH2') >= 0) {
        authMethod = 'XOAUTH2';
    } else if (this._auth.domain && this._supportedAuth.indexOf('NTLM') >= 0) {
        authMethod = 'NTLM';
    } else {
        // use first supported
        authMethod = (this._supportedAuth[0] || 'PLAIN').toUpperCase().trim();
    }

    switch (authMethod) {
        case 'XOAUTH2':
            this._handleXOauth2Token(false, callback);
            return;
        case 'LOGIN':
            this._currentAction = function (str) {
                this._actionAUTH_LOGIN_USER(str, callback);
            }.bind(this);
            this._sendCommand('AUTH LOGIN');
            return;
        case 'PLAIN':
            this._currentAction = function (str) {
                this._actionAUTHComplete(str, callback);
            }.bind(this);
            this._sendCommand('AUTH PLAIN ' + new Buffer(
                //this._auth.user+'\u0000'+
                '\u0000' + // skip authorization identity as it causes problems with some servers
                this._auth.user + '\u0000' +
                this._auth.pass, 'utf-8').toString('base64'));
            return;
        case 'CRAM-MD5':
            this._currentAction = function (str) {
                this._actionAUTH_CRAM_MD5(str, callback);
            }.bind(this);
            this._sendCommand('AUTH CRAM-MD5');
            return;
        case 'NTLM':
            this._currentAction = function (str) {
                this._actionAUTH_NTLM_TYPE1(str, callback);
            }.bind(this);
            this._sendCommand('AUTH ' + ntlm.createType1Message({
                domain: this._auth.domain || '',
                workstation: this._auth.workstation || ''
            }));
            return;
    }

    return callback(this._formatError('Unknown authentication method "' + authMethod + '"', 'EAUTH'));
};

/**
 * Sends a message
 *
 * @param {Object} envelope Envelope object, {from: addr, to: [addr]}
 * @param {Object} message String, Buffer or a Stream
 * @param {Function} callback Callback to return once sending is completed
 */
SMTPConnection.prototype.send = function (envelope, message, done) {
    if (!message) {
        return done(this._formatError('Empty message', 'EMESSAGE'));
    }

    // ensure that callback is only called once
    var returned = false;
    var callback = function () {
        if (returned) {
            return;
        }
        returned = true;

        done.apply(null, Array.prototype.slice.call(arguments));
    };

    if (typeof message.on === 'function') {
        message.on('error', function (err) {
            return callback(this._formatError(err, 'ESTREAM'));
        }.bind(this));
    }

    this._setEnvelope(envelope, function (err, info) {
        if (err) {
            return callback(err);
        }
        var stream = this._createSendStream(function (err, str) {
            if (err) {
                return callback(err);
            }
            info.response = str;
            return callback(null, info);
        });
        if (typeof message.pipe === 'function') {
            message.pipe(stream);
        } else {
            stream.write(message);
            stream.end();
        }

    }.bind(this));
};

/**
 * Connection listener that is run when the connection to
 * the server is opened
 *
 * @event
 */
SMTPConnection.prototype._onConnect = function () {
    clearTimeout(this._connectionTimeout);

    this.logger.info('[%s] %s established to %s:%s', this.id, this.secure ? 'Secure connection' : 'Connection', this._socket.remoteAddress, this._socket.remotePort);

    if (this._destroyed) {
        // Connection was established after we already had canceled it
        this.close();
        return;
    }

    this.stage = 'connected';

    // clear existing listeners for the socket
    this._socket.removeAllListeners('data');
    this._socket.removeAllListeners('timeout');
    this._socket.removeAllListeners('close');
    this._socket.removeAllListeners('end');

    this._socket.on('data', this._onData.bind(this));
    this._socket.once('close', this._onClose.bind(this));
    this._socket.once('end', this._onEnd.bind(this));

    this._socket.setTimeout(this.options.socketTimeout || (10 * 60 * 1000)); // 10 min.
    this._socket.on('timeout', this._onTimeout.bind(this));

    this._greetingTimeout = setTimeout(function () {
        // if still waiting for greeting, give up
        if (this._socket && !this._destroyed && this._currentAction === this._actionGreeting) {
            this._onError('Greeting never received', 'ETIMEDOUT');
        }
    }.bind(this), this.options.greetingTimeout || 10000);

    this._currentAction = this._actionGreeting;

    // we have a 'data' listener set up so resume socket if it was paused
    this._socket.resume();
};

/**
 * 'data' listener for data coming from the server
 *
 * @event
 * @param {Buffer} chunk Data chunk coming from the server
 */
SMTPConnection.prototype._onData = function (chunk) {
    if (this._destroyed || !chunk || !chunk.length) {
        return;
    }

    var data = (chunk || '').toString('binary');
    var lines = (this._remainder + data).split(/\r?\n/);
    var lastline;

    this._remainder = lines.pop();

    for (var i = 0, len = lines.length; i < len; i++) {
        if (this._responseQueue.length) {
            lastline = this._responseQueue[this._responseQueue.length - 1];
            if (/^\d+\-/.test(lastline.split('\n').pop())) {
                this._responseQueue[this._responseQueue.length - 1] += '\n' + lines[i];
                continue;
            }
        }
        this._responseQueue.push(lines[i]);
    }

    this._processResponse();
};

/**
 * 'error' listener for the socket
 *
 * @event
 * @param {Error} err Error object
 * @param {String} type Error name
 */
SMTPConnection.prototype._onError = function (err, type, data) {
    clearTimeout(this._connectionTimeout);
    clearTimeout(this._greetingTimeout);

    if (this._destroyed) {
        // just ignore, already closed
        // this might happen when a socket is canceled because of reached timeout
        // but the socket timeout error itself receives only after
        return;
    }

    err = this._formatError(err, type, data);

    this.logger.error('[%s] %s', this.id, err.message);

    this.emit('error', err);
    this.close();
};

SMTPConnection.prototype._formatError = function (message, type, response) {
    var err;

    if (/Error\]$/i.test(Object.prototype.toString.call(message))) {
        err = message;
    } else {
        err = new Error(message);
    }

    if (type && type !== 'Error') {
        err.code = type;
    }

    if (response) {
        err.response = response;
        err.message += ': ' + response;
    }

    var responseCode = typeof response === 'string' && Number((response.match(/^\d+/) || [])[0]) || false;
    if (responseCode) {
        err.responseCode = responseCode;
    }

    return err;
};

/**
 * 'close' listener for the socket
 *
 * @event
 */
SMTPConnection.prototype._onClose = function () {
    this.logger.info('[%s] Connection closed', this.id);

    if ([this._actionGreeting, this.close].indexOf(this._currentAction) < 0 && !this._destroyed) {
        return this._onError(new Error('Connection closed unexpectedly'), 'ECONNECTION');
    }

    this._destroy();
};

/**
 * 'end' listener for the socket
 *
 * @event
 */
SMTPConnection.prototype._onEnd = function () {
    this._destroy();
};

/**
 * 'timeout' listener for the socket
 *
 * @event
 */
SMTPConnection.prototype._onTimeout = function () {
    return this._onError(new Error('Timeout'), 'ETIMEDOUT');
};

/**
 * Destroys the client, emits 'end'
 */
SMTPConnection.prototype._destroy = function () {
    if (this._destroyed) {
        return;
    }
    this._destroyed = true;
    this.emit('end');
};

/**
 * Upgrades the connection to TLS
 *
 * @param {Function} callback Callback function to run when the connection
 *        has been secured
 */
SMTPConnection.prototype._upgradeConnection = function (callback) {
    // do not remove all listeners or it breaks node v0.10 as there's
    // apparently a 'finish' event set that would be cleared as well

    // we can safely keep 'error', 'end', 'close' etc. events
    this._socket.removeAllListeners('data'); // incoming data is going to be gibberish from this point onwards
    this._socket.removeAllListeners('timeout'); // timeout will be re-set for the new socket object

    var socketPlain = this._socket;
    var opts = {
        socket: this._socket,
        host: this.host
    };

    Object.keys(this.options.tls || {}).forEach(function (key) {
        opts[key] = this.options.tls[key];
    }.bind(this));

    this._socket = tls.connect(opts, function () {
        this.secure = true;
        this._socket.on('data', this._onData.bind(this));

        socketPlain.removeAllListeners('close');
        socketPlain.removeAllListeners('end');

        return callback(null, true);
    }.bind(this));

    this._socket.on('error', this._onError.bind(this));
    this._socket.once('close', this._onClose.bind(this));
    this._socket.once('end', this._onEnd.bind(this));

    this._socket.setTimeout(this.options.socketTimeout || (10 * 60 * 1000)); // 10 min.
    this._socket.on('timeout', this._onTimeout.bind(this));

    // resume in case the socket was paused
    socketPlain.resume();
};

/**
 * Processes queued responses from the server
 *
 * @param {Boolean} force If true, ignores _processing flag
 */
SMTPConnection.prototype._processResponse = function () {
    if (!this._responseQueue.length) {
        return false;
    }

    var str = (this._responseQueue.shift() || '').toString();

    if (/^\d+\-/.test(str.split('\n').pop())) {
        // keep waiting for the final part of multiline response
        return;
    }

    if (this.options.debug) {
        this.logger.debug('[%s] S: %s', this.id, str.replace(/\r?\n$/, ''));
    }

    if (!str.trim()) { // skip unexpected empty lines
        setImmediate(this._processResponse.bind(this, true));
    }

    var action = this._currentAction;
    this._currentAction = null;

    if (typeof action === 'function') {
        action.call(this, str);
        setImmediate(this._processResponse.bind(this, true));
    } else {
        return this._onError(new Error('Unexpected Response'), 'EPROTOCOL', str);
    }
};

/**
 * Send a command to the server, append \r\n
 *
 * @param {String} str String to be sent to the server
 */
SMTPConnection.prototype._sendCommand = function (str) {
    if (this._destroyed) {
        // Connection already closed, can't send any more data
        return;
    }

    if (this._socket.destroyed) {
        return this.close();
    }

    if (this.options.debug) {
        this.logger.debug('[%s] C: %s', this.id, (str || '').toString().replace(/\r?\n$/, ''));
    }

    this._socket.write(new Buffer(str + '\r\n', 'utf-8'));
};

/**
 * Initiates a new message by submitting envelope data, starting with
 * MAIL FROM: command
 *
 * @param {Object} envelope Envelope object in the form of
 *        {from:'...', to:['...']}
 *        or
 *        {from:{address:'...',name:'...'}, to:[address:'...',name:'...']}
 */
SMTPConnection.prototype._setEnvelope = function (envelope, callback) {
    var args = [];
    var useSmtpUtf8 = false;

    this._envelope = envelope || {};
    this._envelope.from = (this._envelope.from && this._envelope.from.address || this._envelope.from || '').toString().trim();

    this._envelope.to = [].concat(this._envelope.to || []).map(function (to) {
        return (to && to.address || to || '').toString().trim();
    });

    if (!this._envelope.to.length) {
        return callback(this._formatError('No recipients defined', 'EENVELOPE'));
    }

    if (this._envelope.from && /[\r\n<>]/.test(this._envelope.from)) {
        return callback(this._formatError('Invalid sender ' + JSON.stringify(this._envelope.from), 'EENVELOPE'));
    }

    // check if the sender address uses only ASCII characters,
    // otherwise require usage of SMTPUTF8 extension
    if (/[\x80-\uFFFF]/.test(this._envelope.from)) {
        useSmtpUtf8 = true;
    }

    for (var i = 0, len = this._envelope.to.length; i < len; i++) {
        if (!this._envelope.to[i] || /[\r\n<>]/.test(this._envelope.to[i])) {
            return callback(this._formatError('Invalid recipient ' + JSON.stringify(this._envelope.to[i]), 'EENVELOPE'));
        }

        // check if the recipients addresses use only ASCII characters,
        // otherwise require usage of SMTPUTF8 extension
        if (/[\x80-\uFFFF]/.test(this._envelope.to[i])) {
            useSmtpUtf8 = true;
        }
    }

    // clone the recipients array for latter manipulation
    this._envelope.rcptQueue = JSON.parse(JSON.stringify(this._envelope.to || []));
    this._envelope.rejected = [];
    this._envelope.accepted = [];

    this._currentAction = function (str) {
        this._actionMAIL(str, callback);
    }.bind(this);

    // If the server supports SMTPUTF8 and the envelope includes an internationalized
    // email address then append SMTPUTF8 keyword to the MAIL FROM command
    if (useSmtpUtf8 && this._supportedExtensions.indexOf('SMTPUTF8') >= 0) {
        args.push('SMTPUTF8');
    }

    this._sendCommand('MAIL FROM:<' + (this._envelope.from) + '>' + (args.length ? ' ' + args.join(' ') : ''));
};

SMTPConnection.prototype._createSendStream = function (callback) {
    var dataStream = new DataStream();
    var logStream;

    this._currentAction = function (str) {
        this._actionStream(str, callback);
    }.bind(this);

    dataStream.pipe(this._socket, {
        end: false
    });

    if (this.options.debug) {
        logStream = new PassThrough();
        logStream.on('readable', function () {
            var chunk;
            while ((chunk = logStream.read())) {
                this.logger.debug('[%s] C: %s', this.id, chunk.toString('binary').replace(/\r?\n$/, ''));
            }
        }.bind(this));
        dataStream.pipe(logStream);
    }

    dataStream.once('end', function () {
        this.logger.info('[%s] C: <%s bytes encoded mime message (source size %s bytes)>', this.id, dataStream.outByteCount, dataStream.inByteCount);
    }.bind(this));

    return dataStream;
};

/** ACTIONS **/

/**
 * Will be run after the connection is created and the server sends
 * a greeting. If the incoming message starts with 220 initiate
 * SMTP session by sending EHLO command
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionGreeting = function (str) {
    clearTimeout(this._greetingTimeout);

    if (str.substr(0, 3) !== '220') {
        this._onError(new Error('Invalid greeting from server:\n' + str), 'EPROTOCOL', str);
        return;
    }

    if (this.options.lmtp) {
        this._currentAction = this._actionLHLO;
        this._sendCommand('LHLO ' + this.name);
    } else {
        this._currentAction = this._actionEHLO;
        this._sendCommand('EHLO ' + this.name);
    }
};

/**
 * Handles server response for LHLO command. If it yielded in
 * error, emit 'error', otherwise treat this as an EHLO response
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionLHLO = function (str) {
    if (str.charAt(0) !== '2') {
        this._onError(new Error('Invalid response for LHLO:\n' + str), 'EPROTOCOL', str);
        return;
    }

    this._actionEHLO(str);
};

/**
 * Handles server response for EHLO command. If it yielded in
 * error, try HELO instead, otherwise initiate TLS negotiation
 * if STARTTLS is supported by the server or move into the
 * authentication phase.
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionEHLO = function (str) {
    if (str.substr(0, 3) === '421') {
        this._onError(new Error('Server terminates connection:\n' + str), 'ECONNECTION', str);
        return;
    }

    if (str.charAt(0) !== '2') {
        if (this.options.requireTLS) {
            this._onError(new Error('EHLO failed but HELO does not support required STARTTLS:\n' + str), 'ECONNECTION', str);
            return;
        }

        // Try HELO instead
        this._currentAction = this._actionHELO;
        this._sendCommand('HELO ' + this.name);
        return;
    }

    // Detect if the server supports STARTTLS
    if (!this.secure && !this.options.ignoreTLS && (/[ \-]STARTTLS\b/mi.test(str) || this.options.requireTLS)) {
        this._sendCommand('STARTTLS');
        this._currentAction = this._actionSTARTTLS;
        return;
    }

    // Detect if the server supports SMTPUTF8
    if (/[ \-]SMTPUTF8\b/mi.test(str)) {
        this._supportedExtensions.push('SMTPUTF8');
    }

    // Detect if the server supports PLAIN auth
    if (str.match(/AUTH(?:(\s+|=)[^\n]*\s+|\s+|=)PLAIN/i)) {
        this._supportedAuth.push('PLAIN');
    }

    // Detect if the server supports LOGIN auth
    if (str.match(/AUTH(?:(\s+|=)[^\n]*\s+|\s+|=)LOGIN/i)) {
        this._supportedAuth.push('LOGIN');
    }

    // Detect if the server supports CRAM-MD5 auth
    if (str.match(/AUTH(?:(\s+|=)[^\n]*\s+|\s+|=)CRAM-MD5/i)) {
        this._supportedAuth.push('CRAM-MD5');
    }

    // Detect if the server supports XOAUTH2 auth
    if (str.match(/AUTH(?:(\s+|=)[^\n]*\s+|\s+|=)XOAUTH2/i)) {
        this._supportedAuth.push('XOAUTH2');
    }

    this.emit('connect');
};

/**
 * Handles server response for HELO command. If it yielded in
 * error, emit 'error', otherwise move into the authentication phase.
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionHELO = function (str) {
    if (str.charAt(0) !== '2') {
        this._onError(new Error('Invalid response for EHLO/HELO:\n' + str), 'EPROTOCOL', str);
        return;
    }

    this.emit('connect');
};

/**
 * Handles server response for STARTTLS command. If there's an error
 * try HELO instead, otherwise initiate TLS upgrade. If the upgrade
 * succeedes restart the EHLO
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionSTARTTLS = function (str) {
    if (str.charAt(0) !== '2') {
        this._onError(new Error('Error upgrading connection with STARTTLS'), 'ETLS', str);
        return;
    }

    this._upgradeConnection(function (err, secured) {
        if (err) {
            this._onError(new Error('Error initiating TLS - ' + (err.message || err)), 'ETLS');
            return;
        }

        this.logger.info('[%s] Connection upgraded with STARTTLS', this.id);

        if (secured) {
            // restart session
            this._currentAction = this._actionEHLO;
            this._sendCommand('EHLO ' + this.name);
        } else {
            this.emit('connect');
        }
    }.bind(this));
};

/**
 * Handle the response for AUTH LOGIN command. We are expecting
 * '334 VXNlcm5hbWU6' (base64 for 'Username:'). Data to be sent as
 * response needs to be base64 encoded username.
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionAUTH_LOGIN_USER = function (str, callback) {
    if (str !== '334 VXNlcm5hbWU6') {
        callback(this._formatError('Invalid login sequence while waiting for "334 VXNlcm5hbWU6"', 'EAUTH', str));
        return;
    }

    this._currentAction = function (str) {
        this._actionAUTH_LOGIN_PASS(str, callback);
    }.bind(this);

    this._sendCommand(new Buffer(this._auth.user + '', 'utf-8').toString('base64'));
};

/**
 * Handle the response for AUTH NTLM, which should be a
 * '334 <challenge string>'. See http://davenport.sourceforge.net/ntlm.html
 * We already sent the Type1 message, the challenge is a Type2 message, we
 * need to respond with a Type3 message.
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionAUTH_NTLM_TYPE1 = function (str, callback) {
    var challengeMatch = str.match(/^334\s+(.+)$/);
    var challengeString = '';

    if (!challengeMatch) {
        return callback(this._formatError('Invalid login sequence while waiting for server challenge string', 'EAUTH', str));
    } else {
        challengeString = challengeMatch[1];
    }

    if (!/^NTLM/i.test(challengeString)) {
        challengeString = 'NTLM ' + challengeString;
    }

    var type2Message = ntlm.parseType2Message(challengeString, callback);
    if (!type2Message) {
        return;
    }

    var type3Message = ntlm.createType3Message(type2Message, {
        domain: this._auth.domain || '',
        workstation: this._auth.workstation || '',
        username: this._auth.user,
        password: this._auth.pass
    });

    type3Message = type3Message.substring(5); // remove the "NTLM " prefix

    this._currentAction = function (str) {
        this._actionAUTH_NTLM_TYPE3(str, callback);
    }.bind(this);

    this._sendCommand(type3Message);
};

/**
 * Handle the response for AUTH CRAM-MD5 command. We are expecting
 * '334 <challenge string>'. Data to be sent as response needs to be
 * base64 decoded challenge string, MD5 hashed using the password as
 * a HMAC key, prefixed by the username and a space, and finally all
 * base64 encoded again.
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionAUTH_CRAM_MD5 = function (str, callback) {
    var challengeMatch = str.match(/^334\s+(.+)$/);
    var challengeString = '';

    if (!challengeMatch) {
        return callback(this._formatError('Invalid login sequence while waiting for server challenge string', 'EAUTH', str));
    } else {
        challengeString = challengeMatch[1];
    }

    // Decode from base64
    var base64decoded = new Buffer(challengeString, 'base64').toString('ascii'),
        hmac_md5 = crypto.createHmac('md5', this._auth.pass);

    hmac_md5.update(base64decoded);

    var hex_hmac = hmac_md5.digest('hex'),
        prepended = this._auth.user + ' ' + hex_hmac;

    this._currentAction = function (str) {
        this._actionAUTH_CRAM_MD5_PASS(str, callback);
    }.bind(this);


    this._sendCommand(new Buffer(prepended).toString('base64'));
};

/**
 * Handles the response to CRAM-MD5 authentication, if there's no error,
 * the user can be considered logged in. Start waiting for a message to send
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionAUTH_CRAM_MD5_PASS = function (str, callback) {
    if (!str.match(/^235\s+/)) {
        return callback(this._formatError('Invalid login sequence while waiting for "235"', 'EAUTH', str));
    }

    this.logger.info('[%s] User %s authenticated', this.id, JSON.stringify(this._user));
    this.authenticated = true;
    callback(null, true);
};

/**
 * Handles the TYPE3 response for NTLM authentication, if there's no error,
 * the user can be considered logged in. Start waiting for a message to send
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionAUTH_NTLM_TYPE3 = function (str, callback) {
    if (!str.match(/^235\s+/)) {
        return callback(this._formatError('Invalid login sequence while waiting for "235"', 'EAUTH', str));
    }

    this.logger.info('[%s] User %s authenticated', this.id, JSON.stringify(this._user));
    this.authenticated = true;
    callback(null, true);
};

/**
 * Handle the response for AUTH LOGIN command. We are expecting
 * '334 UGFzc3dvcmQ6' (base64 for 'Password:'). Data to be sent as
 * response needs to be base64 encoded password.
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionAUTH_LOGIN_PASS = function (str, callback) {
    if (str !== '334 UGFzc3dvcmQ6') {
        return callback(this._formatError('Invalid login sequence while waiting for "334 UGFzc3dvcmQ6"', 'EAUTH', str));
    }

    this._currentAction = function (str) {
        this._actionAUTHComplete(str, callback);
    }.bind(this);

    this._sendCommand(new Buffer(this._auth.pass + '', 'utf-8').toString('base64'));
};

/**
 * Handles the response for authentication, if there's no error,
 * the user can be considered logged in. Start waiting for a message to send
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionAUTHComplete = function (str, isRetry, callback) {
    if (!callback && typeof isRetry === 'function') {
        callback = isRetry;
        isRetry = undefined;
    }

    if (str.substr(0, 3) === '334') {
        this._currentAction = function (str) {
            if (isRetry || !this._auth.xoauth2 || typeof this._auth.xoauth2 !== 'object') {
                this._actionAUTHComplete(str, true, callback);
            } else {
                setTimeout(this._handleXOauth2Token.bind(this, true, callback), Math.random() * 4000 + 1000);
            }
        }.bind(this);
        this._sendCommand('');
        return;
    }

    if (str.charAt(0) !== '2') {
        this.logger.info('[%s] User %s failed to authenticate', this.id, JSON.stringify(this._user));
        return callback(this._formatError('Invalid login', 'EAUTH', str));
    }

    this.logger.info('[%s] User %s authenticated', this.id, JSON.stringify(this._user));
    this.authenticated = true;
    callback(null, true);
};

/**
 * Handle response for a MAIL FROM: command
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionMAIL = function (str, callback) {
    if (Number(str.charAt(0)) !== 2) {
        return callback(this._formatError('Mail command failed', 'EENVELOPE', str));
    }

    if (!this._envelope.rcptQueue.length) {
        return callback(this._formatError('Can\'t send mail - no recipients defined', 'EENVELOPE'));
    } else {
        this._envelope.curRecipient = this._envelope.rcptQueue.shift();
        this._currentAction = function (str) {
            this._actionRCPT(str, callback);
        }.bind(this);
        this._sendCommand('RCPT TO:<' + this._envelope.curRecipient + '>');
    }
};

/**
 * Handle response for a RCPT TO: command
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionRCPT = function (str, callback) {
    if (Number(str.charAt(0)) !== 2) {
        // this is a soft error
        this._envelope.rejected.push(this._envelope.curRecipient);
    } else {
        this._envelope.accepted.push(this._envelope.curRecipient);
    }

    if (!this._envelope.rcptQueue.length) {
        if (this._envelope.rejected.length < this._envelope.to.length) {
            this._currentAction = function (str) {
                this._actionDATA(str, callback);
            }.bind(this);
            this._sendCommand('DATA');
        } else {
            return callback(this._formatError('Can\'t send mail - all recipients were rejected', 'EENVELOPE', str));
        }
    } else {
        this._envelope.curRecipient = this._envelope.rcptQueue.shift();
        this._currentAction = function (str) {
            this._actionRCPT(str, callback);
        }.bind(this);
        this._sendCommand('RCPT TO:<' + this._envelope.curRecipient + '>');
    }
};

/**
 * Handle response for a DATA command
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionDATA = function (str, callback) {
    // response should be 354 but according to this issue https://github.com/eleith/emailjs/issues/24
    // some servers might use 250 instead, so lets check for 2 or 3 as the first digit
    if ([2, 3].indexOf(Number(str.charAt(0))) < 0) {
        return callback(this._formatError('Data command failed', 'EENVELOPE', str));
    }

    callback(null, {
        accepted: this._envelope.accepted,
        rejected: this._envelope.rejected
    });
};

/**
 * Handle response for a DATA stream
 *
 * @param {String} str Message from the server
 */
SMTPConnection.prototype._actionStream = function (str, callback) {
    if (Number(str.charAt(0)) !== 2) {
        // Message failed
        return callback(this._formatError('Message failed', 'EMESSAGE', str));
    } else {
        // Message sent succesfully
        return callback(null, str);
    }
};

SMTPConnection.prototype._handleXOauth2Token = function (isRetry, callback) {
    this._currentAction = function (str) {
        this._actionAUTHComplete(str, isRetry, callback);
    }.bind(this);

    if (this._auth.xoauth2 && typeof this._auth.xoauth2 === 'object') {
        this._auth.xoauth2[isRetry ? 'generateToken' : 'getToken'](function (err, token) {
            if (err) {
                this.logger.info('[%s] User %s failed to authenticate', this.id, JSON.stringify(this._user));
                return callback(this._formatError(err, 'EAUTH'));
            }
            this._sendCommand('AUTH XOAUTH2 ' + token);
        }.bind(this));
    } else {
        this._sendCommand('AUTH XOAUTH2 ' + this._buildXOAuth2Token(this._auth.user, this._auth.xoauth2));
    }
};

/**
 * Builds a login token for XOAUTH2 authentication command
 *
 * @param {String} user E-mail address of the user
 * @param {String} token Valid access token for the user
 * @return {String} Base64 formatted login token
 */
SMTPConnection.prototype._buildXOAuth2Token = function (user, token) {
    var authData = [
        'user=' + (user || ''),
        'auth=Bearer ' + token,
        '',
        ''
    ];
    return new Buffer(authData.join('\x01')).toString('base64');
};

SMTPConnection.prototype._getHostname = function () {
    // defaul hostname is machine hostname or [IP]
    var defaultHostname = os.hostname() || '';

    // ignore if not FQDN
    if (defaultHostname.indexOf('.') < 0) {
        defaultHostname = '[127.0.0.1]';
    }

    // IP should be enclosed in []
    if (defaultHostname.match(/^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/)) {
        defaultHostname = '[' + defaultHostname + ']';
    }

    return defaultHostname;
};
