//go:build linux

package host

import (
	"encoding/hex"
	"os"

	"github.com/carlosframework/platform/internal/hostbox"
	"golang.org/x/sys/unix"
)

// O_PATH pins the no-follow inode without opening a device or reading tenant
// bytes. Compare the descriptor and name around the handle lookup.
func servingParkPersistentArtifact(parent *os.File, expected servingParkFile) (servingParkPersistentFile, error) {
	var zero servingParkPersistentFile
	fd, err := unix.Openat(int(parent.Fd()), expected.Name, unix.O_PATH|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
	if err != nil {
		return zero, err
	}
	defer unix.Close(fd)
	var st unix.Statx_t
	if err = unix.Statx(fd, "", unix.AT_EMPTY_PATH|unix.AT_SYMLINK_NOFOLLOW, unix.STATX_BASIC_STATS|unix.STATX_MNT_ID, &st); err != nil {
		return zero, err
	}
	if !servingParkStatxMatches(expected, st) {
		return zero, hostbox.ErrChanged
	}
	var fs unix.Statfs_t
	if err = unix.Fstatfs(fd, &fs); err != nil {
		return zero, err
	}
	h, mount, err := unix.NameToHandleAt(fd, "", unix.AT_EMPTY_PATH)
	if err != nil {
		return zero, err
	}
	out := servingParkPersistentFile{Filesystem: fs.Fsid.Val, Type: h.Type(), Handle: hex.EncodeToString(h.Bytes()), Owner: st.Uid, Mode: uint32(st.Mode)}
	if !out.valid() || mount <= 0 || uint64(mount) != expected.Mount {
		return zero, hostbox.ErrChanged
	}
	var again unix.Statx_t
	if err = unix.Statx(int(parent.Fd()), expected.Name, unix.AT_SYMLINK_NOFOLLOW, unix.STATX_BASIC_STATS|unix.STATX_MNT_ID, &again); err != nil {
		return zero, err
	}
	if !servingParkStatxMatches(expected, again) || again.Uid != st.Uid || again.Mode != st.Mode {
		return zero, hostbox.ErrChanged
	}
	return out, nil
}

func servingParkStatxMatches(expected servingParkFile, st unix.Statx_t) bool {
	return expected.Present && st.Mask&unix.STATX_MNT_ID != 0 && st.Mode&unix.S_IFMT == unix.S_IFREG && st.Nlink == 1 && unix.Mkdev(st.Dev_major, st.Dev_minor) == expected.Device && st.Ino == expected.Inode && st.Mnt_id == expected.Mount && st.Blocks <= ^uint64(0)/512 && st.Blocks*512 == expected.Bytes
}