protected function _findSource()
    {
        $path = $this->_manager->getPath();

        if ($path->isVirtual($this->_source)) {
            $path = $path->get($this->_source);

            $isStrictMode = $this->_manager->getParams()->get('strict_mode', false, 'bool');
            if ($isStrictMode && !$path) {
                throw new Exception("Asset file not found: {$this->_source}");
            }

            return $path;
        }

        if (Url::isAbsolute($this->_source)) {
            return $this->_source;
        }

        $fullPath = $path->get('root:' . $this->_source);

        return $fullPath;
    }