protected function copy( $files ) {
		$failures = [];

		foreach ( $files as $source => $destination ) {
			if ( file_exists( $destination ) ) {
				$failures[ $source ] = $destination;
				continue;
			}

			$directory = dirname( $destination );
			if ( ! file_exists( $directory ) ) {
				mkdir( $directory );
			}

			copy( $source, $destination );
		}

		return $failures;
	}