Agregate CSS into one file

I have noticed that even using “Aggregate and compress CSS files” (admin/config/development/performance) my theme is linking to a bunch of CSS files. Looking deeper, I have seen that every CSS belongs to a group (I couldn't find good documentation on this topic, though… maybe somebody could point me to the right documents to understand better about this topic…). Therefore, there is a CSS file per group.

But actually in the case I'm working on, I don't actually need all this… I can easily go with just one CSS file that combines all these different bits. But keeping the order of loading is important.

So I have created this function inside my theme's template.php:

function THEME_css_alter(&$css) { 

  // Sort CSS items, so that they appear in the correct order.
  // This is taken from drupal_get_css().
  uasort($css, 'drupal_sort_css_js');

  // The Print style sheets
  // I will populate this array with the print css (usually I have only one but just in case…)
  $print = array();

  // I will add some weight to the new $css array so every element keeps its position
  $weight = 0;

  foreach ($css as $name => $style) {

    // I leave untouched the conditional stylesheets
    // and put all the rest inside a 0 group
    if ($css[$name]['browsers']['!IE']) {
      $css[$name]['group'] = 0;
      $css[$name]['weight'] = ++$weight;
      $css[$name]['every_page'] = TRUE;
    }

    // I move all the print style sheets to a new array
    if ($css[$name]['media'] == 'print') {
      // remove and add to a new array
      $print[$name] = $css[$name];
      unset($css[$name]);
    }

  }
  
  // I merge the regular array and the print array
  $css = array_merge($css, $print);

}

Using this I obtain only one CSS file plus any print and conditional style sheets.

As this works for me, maybe is useful to others.