protected function calculatePipelineHash(array $assets)
	{
		$salt = $this->pipeline;

		// Pipeline disabled. Do not salt hash
		if( ! $salt)
			return md5(implode($assets));

		// Custom salt
		if($salt !== 'auto')
			return md5(implode($assets) . $salt);

		// Automatic salt based on the last modification time of the assets
		$timestamps = array();
		foreach($assets as $asset)
		{
			if($this->isRemoteLink($asset))
				continue;

			$file = realpath($this->public_dir . DIRECTORY_SEPARATOR . $asset);
			if($file === false)
				continue;

			$timestamps[] = filemtime($file);
		}

		return md5(implode($assets) . implode($timestamps));
	}