var async = require('async');
var AWS   = require('aws-sdk');
var gm    = require('gm').subClass({imageMagick: true});
var util  = require('util');

var MAX_WIDTH  = 100;
var MAX_HEIGTH = 100;

var s3 = new AWS.S3();

exports.handler = function(event, context, callback){
  console.log("Reading options from event:\n", util.inspect(event, {depth: 5}));
  var srcBucket = event.Records[0].s3.bucket.name;
  var srcKey    = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, " "));
  var dstBucket = process.env.TARGET_BUCKET;
  var dstKey    = "resized-" + srcKey;

  if(srcBucket == dstBucket){
    callback("Source and destination buckets are the same.");
    return;
  }

  var typeMatch = srcKey.match(/\.([^.]*)$/);
  if(!typeMatch){
    callback("Could not determine the image type.");
    return;
  }
  var imageType = typeMatch[1];
  if(imageType != "jpg" && imageType != "png"){
    callback("Unsupported image type: ${imageType}");
    return;
  }

  async.waterfall([
    function download(next){
      s3.getObject({
        Bucket: srcBucket,
        Key: srcKey
      },
      next);
    },
    function transform(response, next){
      gm(response.Body).size(function(err, size){
        var scalingFactor = Math.min(
          MAX_WIDTH / size.width,
          MAX_HEIGTH / size.height
        );
        var width = scalingFactor * size.width;
        var height = scalingFactor * size.height;

        this.resize(width, height).toBuffer(imageType, function(err, buffer){
            next(null, response.ContentType, buffer);
          }
        });
      });
    },
    function upload(contentType, data, next){
      s3.putObject({
        Bucket: dstBucket,
        Key: dstKey,
        Body: data,
        ContentType: contentType
      },
      next);
    }
  ], function(err){
    if(err){
      console.error(
        "Unable to resize " + srcBucket + "/" + srcKey +
        " and upload to " + dstBucket + "/" + dstKey +
        " due to an error:" + err
      );
    }else{
      console.log(
        "Successfully resized " +srcBucket + "/" + srcKey +
        " and uploaded to " + dstBucket + "/" + dstKey
      );
    }

    callback(null, "message");
  });
}