/*
 * This file is based on the original SES module for Nodemailer by dfellis
 * https://github.com/andris9/Nodemailer/blob/11fb3ef560b87e1c25e8bc15c2179df5647ea6f5/lib/engines/SES.js
 */

// NB! Amazon SES does not allow unicode filenames on attachments!

var http = require('http'),
    https = require('https'),
    crypto = require('crypto'),
    urllib = require("url");

// Expose to the world
module.exports = SESTransport;

/**
 * <p>Generates a Transport object for Amazon SES</p>
 *
 * <p>Possible options can be the following:</p>
 *
 * <ul>
 *     <li><b>AWSAccessKeyID</b> - AWS access key (required)</li>
 *     <li><b>AWSSecretKey</b> - AWS secret (required)</li>
 *     <li><b>ServiceUrl</b> - optional API endpoint URL (defaults to <code>"https://email.us-east-1.amazonaws.com"</code>)
 * </ul>
 *
 * @constructor
 * @param {Object} options Options object for the SES transport
 */
function SESTransport(options){
    this.options = options || {};

    //Set defaults if necessary
    this.options.ServiceUrl = this.options.ServiceUrl || "https://email.us-east-1.amazonaws.com";
}

/**
 * <p>Compiles a mailcomposer message and forwards it to handler that sends it.</p>
 *
 * @param {Object} emailMessage MailComposer object
 * @param {Function} callback Callback function to run when the sending is completed
 */
SESTransport.prototype.sendMail = function(emailMessage, callback) {

    // SES strips this header line by itself
    emailMessage.options.keepBcc = true;

    //Check if required config settings set
    if(!this.options.AWSAccessKeyID || !this.options.AWSSecretKey) {
        return callback(new Error("Missing AWS Credentials"));
    }

    this.generateMessage(emailMessage, (function(err, email){
        if(err){
            return typeof callback == "function" && callback(err);
        }
        this.handleMessage(email, callback);
    }).bind(this));
};

/**
 * <p>Compiles and sends the request to SES with e-mail data</p>
 *
 * @param {String} email Compiled raw e-mail as a string
 * @param {Function} callback Callback function to run once the message has been sent
 */
SESTransport.prototype.handleMessage = function(email, callback) {
    var request,
        date = new Date(),
        urlparts = urllib.parse(this.options.ServiceUrl),
        pairs = {
            'Action': 'SendRawEmail',
            'RawMessage.Data': (new Buffer(email, "utf-8")).toString('base64'),
            'Version': '2010-12-01',
            'Timestamp': this.ISODateString(date)
        };

    if (this.options.AWSSecurityToken) {
        pairs.SecurityToken = this.options.AWSSecurityToken;
    }

    var params = this.buildKeyValPairs(pairs),

        reqObj = {
            host: urlparts.hostname,
            path: urlparts.path || "/",
            method: "POST",
            headers: {
                'Content-Type': 'application/x-www-form-urlencoded',
                'Content-Length': params.length,
                'Date': date.toUTCString(),
                'X-Amzn-Authorization':
                    ['AWS3-HTTPS AWSAccessKeyID='+this.options.AWSAccessKeyID,
                    "Signature="+this.buildSignature(date.toUTCString(), this.options.AWSSecretKey),
                    "Algorithm=HmacSHA256"].join(",")
            }
        };

    //Execute the request on the correct protocol
    if(urlparts.protocol.substr() == "https:") {
        request = https.request(reqObj, this.responseHandler.bind(this, callback));
    } else {
        request = http.request(reqObj, this.responseHandler.bind(this, callback));
    }
    request.end(params);
};

/**
 * <p>Handles the response for the HTTP request to SES</p>
 *
 * @param {Function} callback Callback function to run on end (binded)
 * @param {Object} response HTTP Response object
 */
SESTransport.prototype.responseHandler = function(callback, response) {
    var body = "", match;
    response.setEncoding('utf8');

    //Re-assembles response data
    response.on('data', function(d) {
        body += d.toString();
    });

    //Performs error handling and executes callback, if it exists
    response.on('end', function(err) {
        if(err instanceof Error) {
            return typeof callback == "function" && callback(err, null);
        }
        if(response.statusCode != 200) {
            return typeof callback == "function" &&
                callback(new Error('Email failed: ' + response.statusCode + '\n' + body), {
                    message: body,
                    response: response
                });
        }
        match = (body || "").toString().match(/<MessageId\b[^>]*>([^<]+)<\/MessageId\b[^>]*>/i);
        return typeof callback == "function" && callback(null, {
            message: body,
            response: response,
            messageId: match && match[1] && match[1] + "@email.amazonses.com"
        });
    });
};

/**
 * <p>Compiles the messagecomposer object to a string.</p>
 *
 * <p>It really sucks but I don't know a good way to stream a POST request with
 * unknown legth, so the message needs to be fully composed as a string.</p>
 *
 * @param {Object} emailMessage MailComposer object
 * @param {Function} callback Callback function to run once the message has been compiled
 */

SESTransport.prototype.generateMessage = function(emailMessage, callback) {
    var email = "";

    emailMessage.on("data", function(chunk){
        email += (chunk || "").toString("utf-8");
    });

    emailMessage.on("end", function(chunk){
        email += (chunk || "").toString("utf-8");
        callback(null, email);
    });

    emailMessage.streamMessage();
};

/**
 * <p>Converts an object into a Array with "key=value" values</p>
 *
 * @param {Object} config Object with keys and values
 * @return {Array} Array of key-value pairs
 */
SESTransport.prototype.buildKeyValPairs = function(config){
    var keys = Object.keys(config).sort(),
        keyValPairs = [],
        key, i, len;

    for(i=0, len = keys.length; i < len; i++) {
        key = keys[i];
        if(key != "ServiceUrl") {
            keyValPairs.push((encodeURIComponent(key) + "=" + encodeURIComponent(config[key])));
        }
    }

    return keyValPairs.join("&");
};

/**
 * <p>Uses SHA-256 HMAC with AWS key on date string to generate a signature</p>
 *
 * @param {String} date ISO UTC date string
 * @param {String} AWSSecretKey ASW secret key
 */
SESTransport.prototype.buildSignature = function(date, AWSSecretKey) {
    var sha256 = crypto.createHmac('sha256', AWSSecretKey);
    sha256.update(date);
    return sha256.digest('base64');
};

/**
 * <p>Generates an UTC string in the format of YYY-MM-DDTHH:MM:SSZ</p>
 *
 * @param {Date} d Date object
 * @return {String} Date string
 */
SESTransport.prototype.ISODateString = function(d){
    return d.getUTCFullYear() +             '-' +
           this.strPad(d.getUTCMonth()+1) + '-' +
           this.strPad(d.getUTCDate()) +    'T' +
           this.strPad(d.getUTCHours()) +   ':' +
           this.strPad(d.getUTCMinutes()) + ':' +
           this.strPad(d.getUTCSeconds()) + 'Z';
};

/**
 * <p>Simple padding function. If the number is below 10, add a zero</p>
 *
 * @param {Number} n Number to pad with 0
 * @return {String} 0 padded number
 */
SESTransport.prototype.strPad = function(n){
    return n<10 ? '0'+n : n;
};

