//go:build !windows

package safeio

import (
	"os"
	"strings"

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

type unixParentHandles struct {
	descriptors []int
	parent      int
	target      string
}

func (parents *unixParentHandles) Close() {
	closeUnixDescriptors(parents.descriptors)
}

func openCanonicalUnixParent(path string) (*unixParentHandles, error) {
	if err := ValidateCanonicalPath(path); err != nil {
		return nil, ErrUnsafeFile
	}
	components := strings.Split(strings.TrimPrefix(path, string(os.PathSeparator)), string(os.PathSeparator))
	if len(components) == 0 || components[0] == "" {
		return nil, ErrUnsafeFile
	}
	directory, err := unix.Open(string(os.PathSeparator), unix.O_RDONLY|unix.O_CLOEXEC|unix.O_DIRECTORY, 0)
	if err != nil {
		return nil, ErrUnsafeFile
	}
	parents := &unixParentHandles{descriptors: []int{directory}, parent: directory, target: components[len(components)-1]}
	for _, component := range components[:len(components)-1] {
		next, err := unix.Openat(directory, component, unix.O_RDONLY|unix.O_CLOEXEC|unix.O_DIRECTORY|unix.O_NOFOLLOW, 0)
		if err != nil {
			parents.Close()
			return nil, ErrUnsafeFile
		}
		directory = next
		parents.descriptors = append(parents.descriptors, directory)
		parents.parent = directory
	}
	return parents, nil
}

func privateUnixDirectoryStat(stat *unix.Stat_t) bool {
	return stat != nil && stat.Mode&unix.S_IFMT == unix.S_IFDIR && stat.Uid == uint32(os.Geteuid()) &&
		stat.Mode&0o7777 == 0o700
}

func preflightPrivateDirectory(path string) (bool, error) {
	parents, err := openCanonicalUnixParent(path)
	if err != nil {
		return false, ErrUnsafeFile
	}
	defer parents.Close()
	descriptor, err := unix.Openat(parents.parent, parents.target, unix.O_RDONLY|unix.O_CLOEXEC|unix.O_DIRECTORY|unix.O_NOFOLLOW, 0)
	if err != nil {
		if err == unix.ENOENT {
			if unix.Faccessat(parents.parent, ".", unix.W_OK|unix.X_OK, unix.AT_EACCESS) != nil {
				return false, ErrUnsafeFile
			}
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	defer unix.Close(descriptor)
	var stat unix.Stat_t
	if unix.Fstat(descriptor, &stat) != nil || !privateUnixDirectoryStat(&stat) {
		return false, ErrUnsafeFile
	}
	return true, nil
}