'use strict';

var s3 = new (require('aws-sdk')).S3();
var gm = require('gm').subClass({ imageMagick: true });
var async = require('async');

var imageTypeRegExp = /(?:(jpg)e?|(png))$/;

var sizesConfigs = [
  { width: 800, destinationPath: 'large' },
  { width: 500, destinationPath: 'medium' },
  { width: 200, destinationPath: 'small' },
  { width: 45, destinationPath: 'thumbnail'}
];

exports.AwsHandler = function (event, context) {
  var s3Bucket = event.Records[0].s3.bucket.name;
  var s3Key = event.Records[0].s3.object.key;

  // Check if file has a supported image extension
  var imgExt = imageTypeRegExp.exec(s3Key);

  if (imgExt === null) {
    console.error('unable to infer the image type for key %s', s3Key);
    context.done(new Error('unable to infer the image type for key %s' + s3Key));
    return;
  }

  var imageType = imgExt[1] || imgExt[2];

  async.waterfall([
    function download(next) {
      s3.getObject({
        Bucket: s3Bucket,
        Key: s3Key
      }, next);
    },
    function transform(response, next) {
      async.map(sizesConfigs, function (sizeConfig, mapNext) {
        gm(response.Body, s3Key)
        .resize(sizeConfig.width)
        .toBuffer(imageType, function (err, buffer) {
          if (err) {
            mapNext(err);
            return;
          }

          s3.putObject({
            Bucket: s3Bucket,
            Key: 'dst/' + sizeConfig.destinationPath + '/' + s3Key,
            Body: buffer,
            ContentType: 'image/' + imageType
          }, mapNext)
        });
      }, next);
    }
  ], function (err) {
    if (err) {
      console.error('Error processing image, details %s', err.message);
      context.done(err);
    } else {
      context.done(null, 'Successfully resized images bucket: ' + s3Bucket + ' / key: ' + s3Key);
    }
  });
};