/**
 * Module dependencies.
 */

var exec = require('child_process').exec;

var images = [
    'bowl.jpeg'
  , 'case.jpeg'
  , 'guitar.jpg'
];

function flags(options) {
  var keys = Object.keys(options);
  return keys.map(function(key){
    var val = options[key];
    return true === val
      ? '-' + key
      : '-' + key + ' ' + val;
  }).join(' ');
}

function convert(images, options, fn) {
  var ext = options.ext || '.png'
    , pending = images.length
    , done;
  delete options.ext;
  options = flags(options);
  images = images.map(function(image){
    var dest = image.replace(/\.(jpe?g|png|gif)$/, ext)
      , cmd = [
        'convert'
      , options
      , image
      , dest
      ].join(' ');
    exec(cmd, function(err, stdout, stderr){
        if (done) return;
        if (err) return done = true, fn(err);
        --pending || fn(null, images);
      });
    return dest;
  });
}

convert(images, { resize: '251x171', trim: true }, function(err, images){
  if (err) throw err;
  console.log(images);
  convert(images, { resize: '63x40', trim: true, ext: '.thumb.png' }, function(err, images){
    if (err) throw err;
    console.log(images);
  });
});