//go:build linux

package apply

import (
	"fmt"
	"path/filepath"
	"syscall"

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

// deviceOf is the device a path lives on; a variable so a test can name another file system. Below a home it is
// read through a descriptor opened without following a link (issue 1024).
var deviceOf = func(path string) (uint64, error) {
	var st unix.Stat_t
	if home := homeAbove(path); home != "" {
		fd, err := openDirUnder(home, path)
		if err != nil {
			return 0, err
		}
		defer unix.Close(fd)
		if err := unix.Fstat(fd, &st); err != nil {
			return 0, err
		}
		return uint64(st.Dev), nil
	}
	if err := unix.Stat(path, &st); err != nil {
		return 0, err
	}
	return uint64(st.Dev), nil
}

// renameUnder moves from to to, both below home, through descriptors of their parents opened without following a
// link, and never over something that is there: an account that owns the folders cannot point either at another
// place between the look and the move (issue 1024, novox/hq ADR 0266).
func renameUnder(home, from, to string) error {
	fromDir, err := openDirUnder(home, filepath.Dir(from))
	if err != nil {
		return err
	}
	defer unix.Close(fromDir)
	toDir, err := openDirUnder(home, filepath.Dir(to))
	if err != nil {
		return err
	}
	defer unix.Close(toDir)
	if err := unix.Renameat2(fromDir, filepath.Base(from), toDir, filepath.Base(to), unix.RENAME_NOREPLACE); err != nil {
		return fmt.Errorf("rename %s to %s: %w", from, to, err)
	}
	return nil
}

// ownerIDs is the user and group of a path, without following a link.
func ownerIDs(path string) (uid, gid int, ok bool) {
	var st syscall.Stat_t
	if err := syscall.Lstat(path, &st); err != nil {
		return 0, 0, false
	}
	return int(st.Uid), int(st.Gid), true
}