//go:build !windows

package backup

import (
	"errors"

	"golang.org/x/sys/unix"
)

func restoreFreeBytes(target string) (uint64, error) {
	var statistics unix.Statfs_t
	if err := unix.Statfs(target, &statistics); err != nil {
		return 0, errors.New("restore filesystem capacity is unavailable")
	}
	blockSize := uint64(statistics.Bsize)
	available := uint64(statistics.Bavail)
	if blockSize != 0 && available > ^uint64(0)/blockSize {
		return 0, errors.New("restore filesystem capacity is invalid")
	}
	return blockSize * available, nil
}