Extends the Leafo\ScssPhp\Server. Add source map. Part of Drupal 8 module.

CssServer.php

<?php
/**
 * Created by PhpStorm.
 * User: dima
 * Date: 11/12/16
 * Time: 11:58 AM
 */

namespace Drupal\bootstrap_sass_helper;

use Drupal\Core\Site\Settings;
use Leafo\ScssPhp\Compiler;
use Leafo\ScssPhp\Server ;
use Leafo\ScssPhp\Version;
use Symfony\Component\HttpFoundation\Response;

class CssServer extends Server {

  private $debug = FALSE;

  private $cacheFileSalt = '';

  private $displayErrors = FALSE;

  protected $inputName = '';

  const cacheDir = 'public://scss_cache';

  /**
   * @inheritdoc
   */
  protected function compile($in, $out) {
    $start   = microtime(true);

    $scss = new Compiler();
    $pi = pathinfo($in);
    $scss->addImportPath($pi['dirname'] . '/');

    if ($this->debug) {
      $scss->setLineNumberStyle(Compiler::LINE_COMMENTS);
    }

    $css = $scss->compile(file_get_contents($in), $in);

    $elapsed = round((microtime(true) - $start), 4);

    $v    = Version::VERSION;
    $t    = date('r');
    $css  = "/* compiled by scssphp $v on $t (${elapsed}s) */\n\n" . $css;
    $etag = md5($css);

    // Add debug source maps.
    if ($this->debug) {
      $cssDrupalPath = join('/',[static::cacheDir,  md5($this->cacheFileSalt . $in) . '.css']);
      $mapPath = file_create_url($cssDrupalPath);
      $css .= " /*# sourceMappingURL=". $mapPath .".map */";
      $css = preg_replace('#\\n[[:space:]]*\\n#',"\n", $css);
    }

    file_put_contents($out, $css);

    // Add debug source maps.
    if ($this->debug) {
      $this->generateMap($out);
    }


    file_put_contents(
      $this->metadataName($out),
      serialize([
        'etag'    => $etag,
        'imports' => $scss->getParsedFiles(),
        'vars'    => crc32(serialize($scss->getVariables())),
      ])
    );

    return [$css, $etag];
  }

  /**
   * Class constructor.
   *
   * CssServer constructor.
   * @param string $dir
   * @param null $scss
   * @param string $salt
   */
  function __construct($dir, $scss = NULL, $salt = '') {
    $cacheDir = $this->getCacheDir();
    $this->debug = Settings::get('bootstrap_sass_helper.debug', FALSE);
    $this->cacheFileSalt = $salt;

    parent::__construct($dir, $cacheDir, $scss);
  }


  /**
   * Serve the CSS.
   *
   * @param string $salt
   * Not used. Exist just to match the Just to match the parent class method.
   *
   * @return \Symfony\Component\HttpFoundation\Response
   */
  public function serve($salt = '') {
    $protocol = isset($_SERVER['SERVER_PROTOCOL'])
      ? $_SERVER['SERVER_PROTOCOL']
      : 'HTTP/1.0';
    $headers = [];
    $content = '';
    $code = 200;

    if ($input = $this->findInput()) {
      $output = $this->cacheName($this->cacheFileSalt . $input);
      $etag = $noneMatch = trim($this->getIfNoneMatchHeader(), '"');

      if ($this->needsCompile($output, $etag)) {
        try {
          list($css, $etag) = $this->compile($input, $output);

          $lastModified = gmdate('D, d M Y H:i:s', filemtime($output)) . ' GMT';

          $content = $css;
          $headers['Last-Modified'] = $lastModified;
          $headers['Content-type'] = 'text/css';
          $headers['ETag'] = $etag;

        }
        catch (\Exception $e) {
          if ($this->displayErrors) {
            $headers['Content-type'] = 'text/css';

            $content = $this->createErrorCSS($e);
          }
          else {
            $headers[$protocol] = '500 Internal Server Error';
            $headers['Content-type'] = 'text/plain';
            $code = 500;
            $content = 'Parse error: ' . $e->getMessage() . "\n";
          }
        }

        return new Response($content, $code, $headers);
      }

      $headers['X-SCSS-Cache'] = TRUE;
      $headers['Content-type'] = 'text/css';
      $headers['ETag'] = $etag;

      if ($etag === $noneMatch) {
        $headers[$protocol] = '304 Not Modified';
        $code = 304;

        return new Response($content, $code, $headers);
      }

      $modifiedSince = $this->getIfModifiedSinceHeader();
      $mtime = filemtime($output);

      if (strtotime($modifiedSince) === $mtime) {
        $headers[$protocol] = '304 Not Modified';
        $code = 304;

        return new Response($content, $code, $headers);
      }

      $lastModified  = gmdate('D, d M Y H:i:s', $mtime) . ' GMT';
      $headers['Last-Modified'] = $lastModified;

      $content = file_get_contents($output);

      return new Response($content, $code, $headers);
    }
    $headers[$protocol] = '404 Not Found';
    $headers['Content-type'] = 'text/plain';
    $code = 404;

    $v = Version::VERSION;
    $content = "/* INPUT NOT FOUND scss $v */\n";
    return new Response($content, $code, $headers);
  }

  /**
   * Generate source map.
   *
   * @param string $css
   * Path to cached css file.
   *
   * @return bool|string
   * Path to map or false if not able to generate.
   */
  public function generateMap($css) {

    $handle = fopen($css, 'r');

    $lNumber = 0;

    $compiled = file_get_contents($css);

    $sourceMapGenerator = \Kwf_SourceMaps_SourceMap::createEmptyMap($compiled);

    while (false !== ($line = fgets($handle))) {
      preg_match_all('#[[:space:]]*/\* line ([0-9]+), ([^[:space:]]+) \*/#', $line, $matches);

      $lNumber++;

      if (count($matches) < 3) {
        continue;
      }

      for ($i = 0; $i < count($matches[1]); $i++) {

        if (!isset($matches[2][$i])) {
          break;
        }

        $originalLine = $matches[1][$i];
        $originalFile = $matches[2][$i];

        // TODO set SCSS folder path relative to CSS folder
        $originalFile = preg_replace('#(.*/)?web/#', '/', $originalFile);

        $sourceMapGenerator->addMapping($lNumber, 0, $originalLine, 0, $originalFile);
      }

    }

    $map = $css . '.map';

    $sMap = $sourceMapGenerator->getMapContents();

    return (false === file_put_contents($map, $sMap)) ? false : $map;
  }

  public static function getCacheDir() {
    return drupal_realpath(static::cacheDir);
  }

  public function setInputName($name) {
    $this->inputName = $name;
  }

  private function getInputName() {
    return $this->inputName;
  }

  protected function inputName() {
    return $this->getInputName();
  }
}