//go:build linux

package hostbox

import (
	"os"
	"path/filepath"
	"strings"

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

func CaptureInventoryIdentity(root, name string) (rootstate.FileIdentity, error) {
	if !filepath.IsAbs(root) || filepath.Clean(root) != root || !managedName(name) {
		return rootstate.FileIdentity{}, ErrTypedInventory
	}
	fd, err := unix.Openat2(unix.AT_FDCWD, root, &unix.OpenHow{Flags: unix.O_PATH | unix.O_DIRECTORY | unix.O_CLOEXEC, Resolve: unix.RESOLVE_NO_SYMLINKS})
	if err != nil {
		return rootstate.FileIdentity{}, err
	}
	defer unix.Close(fd)
	return inventoryIdentityAt(fd, name, false)
}

func inventoryIdentityAt(parent int, name string, symlink bool) (rootstate.FileIdentity, error) {
	flags := uint64(unix.O_PATH | unix.O_CLOEXEC)
	if symlink {
		flags |= unix.O_NOFOLLOW
	}
	fd, err := unix.Openat2(parent, name, &unix.OpenHow{Flags: flags, Resolve: unix.RESOLVE_BENEATH | unix.RESOLVE_NO_SYMLINKS})
	if err != nil {
		return rootstate.FileIdentity{}, err
	}
	f := os.NewFile(uintptr(fd), name)
	defer f.Close()
	var st unix.Stat_t
	if err := unix.Fstat(fd, &st); err != nil {
		return rootstate.FileIdentity{}, err
	}
	kind := st.Mode & unix.S_IFMT
	if kind != unix.S_IFDIR && kind != unix.S_IFREG && !(symlink && kind == unix.S_IFLNK) {
		return rootstate.FileIdentity{}, ErrTypedInventory
	}
	if kind == unix.S_IFREG && st.Nlink != 1 {
		return rootstate.FileIdentity{}, ErrTypedInventory
	}
	return rootstate.ObjectIdentity(f)
}

func VerifyInventoryIdentity(root string, e StopInventoryEntry) error {
	return VerifyInventoryIdentityForOwner(root, e, 0)
}

func VerifyInventoryIdentityForOwner(root string, e StopInventoryEntry, owner uint32) error {
	id, err := CaptureInventoryIdentity(root, e.RelativePath)
	if err != nil {
		return err
	}
	if e.Identity.Device != e.Device || e.Identity.Inode != e.Inode || e.Identity.Mode&unix.S_IFMT != e.Type || !sameInventoryIdentity(e.Identity, id) {
		return ErrChanged
	}
	if e.Identity.Boot != id.Boot {
		return checkedInventoryAncestryOwner(root, owner)
	}
	return nil
}

func checkedInventoryAncestry(root string) error {
	return checkedInventoryAncestryOwner(root, 0)
}

func checkedInventoryAncestryOwner(root string, owner uint32) error {
	if !filepath.IsAbs(root) || filepath.Clean(root) != root {
		return ErrTypedInventory
	}
	fd, err := unix.Open("/", unix.O_PATH|unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
	if err != nil {
		return err
	}
	defer func() { unix.Close(fd) }()
	parts := append([]string{""}, strings.Split(strings.TrimPrefix(root, "/"), "/")...)
	for index, part := range parts {
		if part != "" {
			next, err := unix.Openat(fd, part, unix.O_PATH|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
			if err != nil {
				return err
			}
			unix.Close(fd)
			fd = next
		}
		var st unix.Stat_t
		if err := unix.Fstat(fd, &st); err != nil {
			return err
		}
		allowedOwner := st.Uid == 0 || (index == len(parts)-1 && st.Uid == owner)
		if !allowedOwner || st.Mode&0022 != 0 {
			return os.ErrPermission
		}
	}
	return nil
}