var AWS = require('aws-sdk');
var LineStream = require('byline').LineStream;
var parse = require('elb-log-parser');  // elb-log-parser  https://github.com/toshihirock/node-elb-log-parser
var path = require('path');
var stream = require('stream');
var indexTimestamp = new Date().toISOString().replace(/\-/g, '.').replace(/T.+/, '');

/* Globals */
var esDomain = {
    endpoint: 'elastic-search-domain-fs12fdwrdq2ahilw4zbrcocmmy.eu-west-1.es.amazonaws.com',
    region: 'eu-west-1',
    index: 'elblogs-' + indexTimestamp, // adds a timestamp to index. Example: elblogs-2016.03.31
    doctype: 'elb-access-logs'
};
var endpoint =  new AWS.Endpoint(esDomain.endpoint);
var s3 = new AWS.S3();
var totLogLines = 0;    // Total number of log lines in the file
var numDocsAdded = 0;   // Number of log lines added to ES so far

/*
 * The AWS credentials are picked up from the environment.
 * They belong to the IAM role assigned to the Lambda function.
 * Since the ES requests are signed using these credentials,
 * make sure to apply a policy that permits ES domain operations
 * to the role.
 */
var creds = new AWS.EnvironmentCredentials('AWS');

/*
 * Get the log file from the given S3 bucket and key.  Parse it and add
 * each log record to the ES domain.
 */
function s3LogsToES(bucket, key, context, lineStream, recordStream) {
    // Note: The Lambda function should be configured to filter for .log files
    // (as part of the Event Source "suffix" setting).

    var s3Stream = s3.getObject({Bucket: bucket, Key: key}).createReadStream();

    // Flow: S3 file stream -> Log Line stream -> Log Record stream -> ES
    s3Stream
      .pipe(lineStream)
      .pipe(recordStream)
      .on('data', function(parsedEntry) {
            postDocumentToES(parsedEntry, context);
      });

    s3Stream.on('error', function() {
        console.log(
            'Error getting object "' + key + '" from bucket "' + bucket + '".  ' +
            'Make sure they exist and your bucket is in the same region as this function.');
        context.fail();
    });
}

/*
 * Add the given document to the ES domain.
 * If all records are successfully added, indicate success to lambda
 * (using the "context" parameter).
 */
function postDocumentToES(doc, context) {
    var req = new AWS.HttpRequest(endpoint);

    req.method = 'POST';
    req.path = path.join('/', esDomain.index, esDomain.doctype);
    req.region = esDomain.region;
    req.body = doc;
    req.headers['presigned-expires'] = false;
    req.headers['Host'] = endpoint.host;

    // Sign the request (Sigv4)
    var signer = new AWS.Signers.V4(req, 'es');
    signer.addAuthorization(creds, new Date());

    // Post document to ES
    var send = new AWS.NodeHttpClient();
    send.handleRequest(req, null, function(httpResp) {
        var body = '';
        httpResp.on('data', function (chunk) {
            body += chunk;
        });
        httpResp.on('end', function (chunk) {
            numDocsAdded ++;
            if (numDocsAdded === totLogLines) {
                // Mark lambda success.  If not done so, it will be retried.
                console.log('All ' + numDocsAdded + ' log records added to ES.');
                context.succeed();
            }
        });
    }, function(err) {
        console.log('Error: ' + err);
        console.log(numDocsAdded + 'of ' + totLogLines + ' log records added to ES.');
        context.fail();
    });
}

/* Lambda "main": Execution starts here */
exports.handler = function(event, context) {
    console.log('Received event: ', JSON.stringify(event, null, 2));

    /* == Streams ==
    * To avoid loading an entire (typically large) log file into memory,
    * this is implemented as a pipeline of filters, streaming log data
    * from S3 to ES.
    * Flow: S3 file stream -> Log Line stream -> Log Record stream -> ES
    */
    var lineStream = new LineStream();
    // A stream of log records, from parsing each log line
    var recordStream = new stream.Transform({objectMode: true})
    recordStream._transform = function(line, encoding, done) {
        var logRecord = parse(line.toString());
        var serializedRecord = JSON.stringify(logRecord);
        this.push(serializedRecord);
        totLogLines ++;
        done();
    }

    event.Records.forEach(function(record) {
        var bucket = record.s3.bucket.name;
        var objKey = decodeURIComponent(record.s3.object.key.replace(/\+/g, ' '));
        s3LogsToES(bucket, objKey, context, lineStream, recordStream);
    });
}