CssOptimizer.php

<?php

namespace Drupal\Core\Asset;

use Drupal\Component\Utility\Unicode;
use Drupal\Core\StreamWrapper\StreamWrapperManager;
use Drupal\Core\File\FileUrlGeneratorInterface;

/**
 * Optimizes a CSS asset.
 */
class CssOptimizer implements AssetOptimizerInterface {
    
    /**
     * The base path used by rewriteFileURI().
     *
     * @var string
     */
    public $rewriteFileURIBasePath;
    
    /**
     * The file URL generator.
     *
     * @var \Drupal\Core\File\FileUrlGeneratorInterface
     */
    protected $fileUrlGenerator;
    
    /**
     * Constructs a CssOptimizer.
     *
     * @param \Drupal\Core\File\FileUrlGeneratorInterface $file_url_generator
     *   The file URL generator.
     */
    public function __construct(FileUrlGeneratorInterface $file_url_generator) {
        $this->fileUrlGenerator = $file_url_generator;
    }
    
    /**
     * {@inheritdoc}
     */
    public function optimize(array $css_asset) {
        if ($css_asset['type'] != 'file') {
            throw new \Exception('Only file CSS assets can be optimized.');
        }
        if (!$css_asset['preprocess']) {
            throw new \Exception('Only file CSS assets with preprocessing enabled can be optimized.');
        }
        return $this->processFile($css_asset);
    }
    
    /**
     * Processes the contents of a CSS asset for cleanup.
     *
     * @param string $contents
     *   The contents of the CSS asset.
     *
     * @return string
     *   Contents of the CSS asset.
     */
    public function clean($contents) {
        // Remove multiple charset declarations for standards compliance (and fixing
        // Safari problems).
        $contents = preg_replace('/^@charset\\s+[\'"](\\S*?)\\b[\'"];/i', '', $contents);
        return $contents;
    }
    
    /**
     * Processes CSS file and adds base URLs to any relative resource paths.
     *
     * @param array $css_asset
     *   A CSS asset. The array should contain the `data` key where the value
     *   should be the path to the CSS file relative to the Drupal root. This is
     *   an example of the `data` key's value,
     *   "core/assets/vendor/normalize-css/normalize.css".
     *
     * @return string
     *   The asset's cleaned/optimized contents.
     */
    protected function processFile($css_asset) {
        $contents = $this->loadFile($css_asset['data'], TRUE);
        if ($css_asset['media'] !== 'print' && $css_asset['media'] !== 'all') {
            $contents = '@media ' . $css_asset['media'] . '{' . $contents . '}' . "\n";
        }
        $contents = $this->clean($contents);
        // Get the parent directory of this file, relative to the Drupal root.
        $css_base_path = substr($css_asset['data'], 0, strrpos($css_asset['data'], '/'));
        // Store base path.
        $this->rewriteFileURIBasePath = $css_base_path . '/';
        // Anchor all paths in the CSS with its base URL, ignoring external and absolute paths and paths starting with '#'.
        return preg_replace_callback('/url\\(\\s*[\'"]?(?![a-z]+:|\\/+|#|%23)([^\'")]+)[\'"]?\\s*\\)/i', [
            $this,
            'rewriteFileURI',
        ], $contents);
    }
    
    /**
     * Loads the stylesheet and resolves all @import commands.
     *
     * Loads a stylesheet and replaces @import commands with the contents of the
     * imported file. Use this instead of file_get_contents when processing
     * stylesheets.
     *
     * The returned contents are compressed removing white space and comments only
     * when CSS aggregation is enabled. This optimization will not apply for
     * color.module enabled themes with CSS aggregation turned off.
     *
     * Note: the only reason this method is public is so color.module can call it;
     * it is not on the AssetOptimizerInterface, so any future refactoring can
     * make it protected.
     *
     * @param $file
     *   Name of the stylesheet to be processed.
     * @param $optimize
     *   Defines if CSS contents should be compressed or not.
     * @param $reset_basepath
     *   Used internally to facilitate recursive resolution of @import commands.
     *
     * @return string
     *   Contents of the stylesheet, including any resolved @import commands.
     */
    public function loadFile($file, $optimize = NULL, $reset_basepath = TRUE) {
        // These statics are not cache variables, so we don't use drupal_static().
        static $_optimize, $basepath;
        if ($reset_basepath) {
            $basepath = '';
        }
        // Store the value of $optimize for preg_replace_callback with nested
        // @import loops.
        if (isset($optimize)) {
            $_optimize = $optimize;
        }
        // Stylesheets are relative one to each other. Start by adding a base path
        // prefix provided by the parent stylesheet (if necessary).
        if ($basepath && !StreamWrapperManager::getScheme($file)) {
            $file = $basepath . '/' . $file;
        }
        // Store the parent base path to restore it later.
        $parent_base_path = $basepath;
        // Set the current base path to process possible child imports.
        $basepath = dirname($file);
        // Load the CSS stylesheet. We suppress errors because themes may specify
        // stylesheets in their .info.yml file that don't exist in the theme's path,
        // but are merely there to disable certain module CSS files.
        $content = '';
        if ($contents = @file_get_contents($file)) {
            // If a BOM is found, convert the file to UTF-8, then use substr() to
            // remove the BOM from the result.
            if ($encoding = Unicode::encodingFromBOM($contents)) {
                $contents = mb_substr(Unicode::convertToUtf8($contents, $encoding), 1);
            }
            elseif (preg_match('/^@charset "([^"]+)";/', $contents, $matches)) {
                if ($matches[1] !== 'utf-8' && $matches[1] !== 'UTF-8') {
                    $contents = substr($contents, strlen($matches[0]));
                    $contents = Unicode::convertToUtf8($contents, $matches[1]);
                }
            }
            // Return the processed stylesheet.
            $content = $this->processCss($contents, $_optimize);
        }
        // Restore the parent base path as the file and its children are processed.
        $basepath = $parent_base_path;
        return $content;
    }
    
    /**
     * Loads stylesheets recursively and returns contents with corrected paths.
     *
     * This function is used for recursive loading of stylesheets and
     * returns the stylesheet content with all url() paths corrected.
     *
     * @param array $matches
     *   An array of matches by a preg_replace_callback() call that scans for
     *   @import-ed CSS files, except for external CSS files.
     *
     * @return string
     *   The contents of the CSS file at $matches[1], with corrected paths.
     *
     * @see \Drupal\Core\Asset\AssetOptimizerInterface::loadFile()
     */
    protected function loadNestedFile($matches) {
        $filename = $matches[1];
        // Load the imported stylesheet and replace @import commands in there as
        // well.
        $file = $this->loadFile($filename, NULL, FALSE);
        // Determine the file's directory.
        $directory = dirname($filename);
        // If the file is in the current directory, make sure '.' doesn't appear in
        // the url() path.
        $directory = $directory == '.' ? '' : $directory . '/';
        // Alter all internal asset paths. Leave external paths alone. We don't need
        // to normalize absolute paths here because that will be done later.
        return preg_replace('/url\\(\\s*([\'"]?)(?![a-z]+:|\\/+)([^\'")]+)([\'"]?)\\s*\\)/i', 'url(\\1' . $directory . '\\2\\3)', $file);
    }
    
    /**
     * Processes the contents of a stylesheet for aggregation.
     *
     * @param $contents
     *   The contents of the stylesheet.
     * @param $optimize
     *   (optional) Boolean whether CSS contents should be minified. Defaults to
     *   FALSE.
     *
     * @return string
     *   Contents of the stylesheet including the imported stylesheets.
     */
    protected function processCss($contents, $optimize = FALSE) {
        // Remove unwanted CSS code that cause issues.
        $contents = $this->clean($contents);
        if ($optimize) {
            // Perform some safe CSS optimizations.
            // Regexp to match comment blocks.
            $comment = '/\\*[^*]*\\*+(?:[^/*][^*]*\\*+)*/';
            // Regexp to match double quoted strings.
            $double_quot = '"[^"\\\\]*(?:\\\\.[^"\\\\]*)*"';
            // Regexp to match single quoted strings.
            $single_quot = "'[^'\\\\]*(?:\\\\.[^'\\\\]*)*'";
            // Strip all comment blocks, but keep double/single quoted strings.
            $contents = preg_replace("<({$double_quot}|{$single_quot})|{$comment}>Ss", "\$1", $contents);
            // Remove certain whitespace.
            // There are different conditions for removing leading and trailing
            // whitespace.
            // @see http://php.net/manual/regexp.reference.subpatterns.php
            $contents = preg_replace('<
        # Do not strip any space from within single or double quotes
          (' . $double_quot . '|' . $single_quot . ')
        # Strip leading and trailing whitespace.
        | \\s*([@{};,])\\s*
        # Strip only leading whitespace from:
        # - Closing parenthesis: Retain "@media (bar) and foo".
        | \\s+([\\)])
        # Strip only trailing whitespace from:
        # - Opening parenthesis: Retain "@media (bar) and foo".
        # - Colon: Retain :pseudo-selectors.
        | ([\\(:])\\s+
      >xSs', '$1$2$3$4', $contents);
            // End the file with a new line.
            $contents = trim($contents);
            $contents .= "\n";
        }
        // Replaces @import commands with the actual stylesheet content.
        // This happens recursively but omits external files and local files
        // with supports- or media-query qualifiers, as those are conditionally
        // loaded depending on the user agent.
        $contents = preg_replace_callback('/@import\\s*(?:url\\(\\s*)?[\'"]?(?![a-z]+:)(?!\\/\\/)([^\'"\\()]+)[\'"]?\\s*\\)?\\s*;/', [
            $this,
            'loadNestedFile',
        ], $contents);
        return $contents;
    }
    
    /**
     * Prefixes all paths within a CSS file for processFile().
     *
     * Note: the only reason this method is public is so color.module can call it;
     * it is not on the AssetOptimizerInterface, so any future refactoring can
     * make it protected.
     *
     * @param array $matches
     *   An array of matches by a preg_replace_callback() call that scans for
     *   url() references in CSS files, except for external or absolute ones.
     *
     * @return string
     *   The file path.
     */
    public function rewriteFileURI($matches) {
        // Prefix with base and remove '../' segments where possible.
        $path = $this->rewriteFileURIBasePath . $matches[1];
        $last = '';
        while ($path != $last) {
            $last = $path;
            $path = preg_replace('`(^|/)(?!\\.\\./)([^/]+)/\\.\\./`', '$1', $path);
        }
        return 'url(' . $this->fileUrlGenerator
            ->generateString($path) . ')';
    }

}