class FileCache

class FileCache implements FileCacheInterface {
    
    /**
     * Prefix that is used for cache entries.
     *
     * @var string
     */
    protected $prefix;
    
    /**
     * Static cache that contains already loaded cache entries.
     *
     * @var array
     */
    protected static $cached = [];
    
    /**
     * The collection identifier of this cache.
     *
     * @var string
     */
    protected $collection;
    
    /**
     * The cache backend backing this FileCache object.
     *
     * @var \Drupal\Component\FileCache\FileCacheBackendInterface
     */
    protected $cache;
    
    /**
     * Constructs a FileCache object.
     *
     * @param string $prefix
     *   The cache prefix.
     * @param string $collection
     *   A collection identifier to ensure that the same files could be cached for
     *   different purposes without clashing.
     * @param string|null $cache_backend_class
     *   (optional) The class that should be used as cache backend.
     * @param array $cache_backend_configuration
     *   (optional) The configuration for the backend class.
     */
    public function __construct($prefix, $collection, $cache_backend_class = NULL, array $cache_backend_configuration = []) {
        if (empty($prefix)) {
            throw new \InvalidArgumentException('Required prefix configuration is missing');
        }
        $this->prefix = $prefix;
        $this->collection = $collection;
        if (isset($cache_backend_class)) {
            $this->cache = new $cache_backend_class($cache_backend_configuration);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function get($filepath) {
        $filepaths = [
            $filepath,
        ];
        $cached = $this->getMultiple($filepaths);
        return $cached[$filepath] ?? NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMultiple(array $filepaths) {
        $file_data = [];
        $remaining_cids = [];
        // First load from the static cache what we can.
        foreach ($filepaths as $filepath) {
            if (!file_exists($filepath)) {
                continue;
            }
            $realpath = realpath($filepath);
            // If the file exists but realpath returns nothing, it is using a stream
            // wrapper, those are not supported.
            if (empty($realpath)) {
                continue;
            }
            $cid = $this->prefix . ':' . $this->collection . ':' . $realpath;
            if (isset(static::$cached[$cid]) && static::$cached[$cid]['mtime'] == filemtime($filepath)) {
                $file_data[$filepath] = static::$cached[$cid]['data'];
            }
            else {
                // Collect a list of cache IDs that we still need to fetch from cache
                // backend.
                $remaining_cids[$cid] = $filepath;
            }
        }
        // If there are any cache IDs left to fetch from the cache backend.
        if ($remaining_cids && $this->cache) {
            $cache_results = $this->cache
                ->fetch(array_keys($remaining_cids)) ?: [];
            foreach ($cache_results as $cid => $cached) {
                $filepath = $remaining_cids[$cid];
                if ($cached['mtime'] == filemtime($filepath)) {
                    $file_data[$cached['filepath']] = $cached['data'];
                    static::$cached[$cid] = $cached;
                }
            }
        }
        return $file_data;
    }
    
    /**
     * {@inheritdoc}
     */
    public function set($filepath, $data) {
        $realpath = realpath($filepath);
        $cached = [
            'mtime' => filemtime($filepath),
            'filepath' => $filepath,
            'data' => $data,
        ];
        $cid = $this->prefix . ':' . $this->collection . ':' . $realpath;
        static::$cached[$cid] = $cached;
        if ($this->cache) {
            $this->cache
                ->store($cid, $cached);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function delete($filepath) {
        $realpath = realpath($filepath);
        $cid = $this->prefix . ':' . $this->collection . ':' . $realpath;
        unset(static::$cached[$cid]);
        if ($this->cache) {
            $this->cache
                ->delete($cid);
        }
    }
    
    /**
     * Resets the static cache.
     *
     * @todo Replace this once https://www.drupal.org/node/2260187 is in.
     */
    public static function reset() {
        static::$cached = [];
    }

}