var http = require('https');
var querystring = require('querystring');

// set the post request options
var reqOptions = {
    hostname: 'hooks.slack.com',
    port: 443,
    path: '/services/YOUR/SLACK/HOOK_HERE',
    method: 'POST'
};


/*
  Parse the SNS payload. This function assumes only one message
  notification is sent as part of the payload. The payload is
  broken up into key:value pairs and returned as an object.
*/
parse = function(payload) {
    parts = payload.Records[0].Sns.Message.split('\n');
    data = {};
    parts.forEach(function(part) {
        if(part.length < 1) {
            return;
        }
        key = part.split(':', 1)[0];
        value = part.split(key+': ').reverse()[0];
        data[key] = value;
    });
    return data;
};


/*
  Adds extra "attachment" data to display a customized message in Slack
  instead of a simple message. We're excluding 'Message' here beacuse
  we're using message as the main content of the Slack notification.
*/
makeSlackAttachmentFields = function(d) {
    var excludeKeys = ['RequestId', 'NotificationProcessId', 'Message'];
    var arr = [];
    Object.keys(d).forEach(function(k){
       if(excludeKeys.indexOf(k) != -1) {
           return;
       }
       arr.push({"title": k, "value": d[k], "short":false});
    });
    return arr;
};

/*
  Main Lambda handler
*/
exports.handler = function(event, context) {
    // Slack channel to notify
    var channel = "#awseb";
    
    // Parse event data from SNS
    var data = parse(event);
    
    // Create Slack attachment data
    var dataFields = makeSlackAttachmentFields(data);
    
    var postData = {
        // Set the Slack channel within the payload
        "channel": channel,
        
        // Name of the Slack "bot" (this can be anything, doesn't
        // have to be an existing user)
        "username": "awsbot",
        "attachments": [
            {
                "fallback": data.Message,
                "text": data.Message,
                "fields": dataFields
            }    
        ]
    };
    
    var payload = 'payload=' + querystring.escape(JSON.stringify(postData));

    // Create HTTP request
    var req = http.request(reqOptions, function(res){
        res.setEncoding("utf8");
        res.on('data', function(d) {
            console.log(d);
            // Wait for a response before calling succeed, otherwise
            // our Lambda function will exit too early
            context.succeed();
        });
    });
    req.on('error', function(err){
        console.log(err.message);
        // If we get an error, stop execution.
        context.fail(err.message);

    });
    
    // Set request headers
    req.setHeader('Content-Type', 'application/x-www-form-urlencoded');
    req.setHeader('Content-Length', payload.length);
    
    // Write the actual POST data
    req.write(payload);
    
    // Indicate no additional data will be written
    req.end();
};