package rootstate

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

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

func OpenAuthorityFile(path string) (*os.File, error) {
	if !filepath.IsAbs(path) || filepath.Clean(path) != path || path == "/" {
		return nil, os.ErrPermission
	}
	parent, err := os.Open("/")
	if err != nil {
		return nil, err
	}
	defer parent.Close()
	return openAuthorityFile(parent, strings.Split(strings.TrimPrefix(path, "/"), "/"), 0)
}

func openAuthorityFile(parent *os.File, parts []string, owner uint32) (*os.File, error) {
	if len(parts) == 0 {
		return nil, os.ErrPermission
	}
	fd, err := unix.FcntlInt(parent.Fd(), unix.F_DUPFD_CLOEXEC, 0)
	if err != nil {
		return nil, err
	}
	defer func() { unix.Close(fd) }()
	if err := trusted(fd, owner, unix.S_IFDIR); err != nil {
		return nil, err
	}
	for i, name := range parts {
		if !component(name) {
			return nil, os.ErrPermission
		}
		if i == len(parts)-1 {
			break
		}
		next, err := unix.Openat(fd, name, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
		if err != nil {
			return nil, err
		}
		unix.Close(fd)
		fd = next
		if err := trusted(fd, owner, unix.S_IFDIR); err != nil {
			return nil, err
		}
	}
	f, err := safefile.OpenFileAt(fd, parts[len(parts)-1], os.O_RDONLY, 0)
	if err != nil {
		return nil, err
	}
	if err := trusted(int(f.Fd()), owner, unix.S_IFREG); err != nil {
		f.Close()
		return nil, err
	}
	return f, nil
}