class AssetWriter

AssetWriterTest.php in drupal/core/vendor/kriswallsmith/assetic/tests/Assetic/Test/AssetWriterTest.php

class AssetWriter {
  private $dir;
  private $varValues;

  /**
   * Constructor.
   *
   * @param string $dir The base web directory
   */
  public function __construct($dir, array $varValues = array()) {
    foreach ($varValues as $var => $values) {
      foreach ($values as $value) {
        if (!is_string($value)) {
          throw new \InvalidArgumentException(sprintf('All variable values must be strings, but got %s for variable "%s".', json_encode($value), $var));
        }
      }
    }
    $this->dir = $dir;
    $this->varValues = $varValues;
  }
  public function writeManagerAssets(AssetManager $am) {
    foreach ($am
      ->getNames() as $name) {
      $this
        ->writeAsset($am
        ->get($name));
    }
  }
  public function writeAsset(AssetInterface $asset) {
    foreach ($this
      ->getCombinations($asset
      ->getVars()) as $combination) {
      $asset
        ->setValues($combination);
      static::write($this->dir . '/' . PathUtils::resolvePath($asset
        ->getTargetPath(), $asset
        ->getVars(), $asset
        ->getValues()), $asset
        ->dump());
    }
  }
  private function getCombinations(array $vars) {
    if (!$vars) {
      return array(
        array(),
      );
    }
    $combinations = array();
    $nbValues = array();
    foreach ($this->varValues as $var => $values) {
      if (!in_array($var, $vars, true)) {
        continue;
      }
      $nbValues[$var] = count($values);
    }
    for ($i = array_product($nbValues), $c = $i * 2; $i < $c; $i++) {
      $k = $i;
      $combination = array();
      foreach ($vars as $var) {
        $combination[$var] = $this->varValues[$var][$k % $nbValues[$var]];
        $k = intval($k / $nbValues[$var]);
      }
      $combinations[] = $combination;
    }
    return $combinations;
  }
  protected static function write($path, $contents) {
    if (!is_dir($dir = dirname($path)) && false === @mkdir($dir, 0777, true)) {
      throw new \RuntimeException('Unable to create directory ' . $dir);
    }
    if (false === @file_put_contents($path, $contents)) {
      throw new \RuntimeException('Unable to write file ' . $path);
    }
  }

}