class LessFilter

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

class LessFilter implements FilterInterface {
  private $nodeBin;
  private $nodePaths;
  private $compress;

  /**
   * Constructor.
   *
   * @param string $nodeBin   The path to the node binary
   * @param array  $nodePaths An array of node paths
   */
  public function __construct($nodeBin = '/usr/bin/node', array $nodePaths = array()) {
    $this->nodeBin = $nodeBin;
    $this->nodePaths = $nodePaths;
  }
  public function setCompress($compress) {
    $this->compress = $compress;
  }
  public function filterLoad(AssetInterface $asset) {
    static $format = <<<'EOF'
var less = require('less');
var sys  = require(process.binding('natives').util ? 'util' : 'sys');

new(less.Parser)(%s).parse(%s, function(e, tree) {
    if (e) {
        less.writeError(e);
        process.exit(2);
    }

    try {
        sys.print(tree.toCSS(%s));
    } catch (e) {
        less.writeError(e);
        process.exit(3);
    }
});

EOF;
    $root = $asset
      ->getSourceRoot();
    $path = $asset
      ->getSourcePath();

    // parser options
    $parserOptions = array();
    if ($root && $path) {
      $parserOptions['paths'] = array(
        dirname($root . '/' . $path),
      );
      $parserOptions['filename'] = basename($path);
    }

    // tree options
    $treeOptions = array();
    if (null !== $this->compress) {
      $treeOptions['compress'] = $this->compress;
    }
    $pb = new ProcessBuilder();
    $pb
      ->inheritEnvironmentVariables();

    // node.js configuration
    if (0 < count($this->nodePaths)) {
      $pb
        ->setEnv('NODE_PATH', implode(':', $this->nodePaths));
    }
    $pb
      ->add($this->nodeBin)
      ->add($input = tempnam(sys_get_temp_dir(), 'assetic_less'));
    file_put_contents($input, sprintf($format, json_encode($parserOptions), json_encode($asset
      ->getContent()), json_encode($treeOptions)));
    $proc = $pb
      ->getProcess();
    $code = $proc
      ->run();
    unlink($input);
    if (0 < $code) {
      throw FilterException::fromProcess($proc)
        ->setInput($asset
        ->getContent());
    }
    $asset
      ->setContent($proc
      ->getOutput());
  }
  public function filterDump(AssetInterface $asset) {
  }

}