/*
godlighty -- highly-customizable HTTP, HTTP/2, HTTPS server
Copyright (C) 2021-2023 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package godlighty

import (
	"encoding/base64"
	"encoding/binary"
	"os"

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

func ctimeETag(fd *os.File) (string, error) {
	var stat unix.Stat_t
	err := unix.Fstat(int(fd.Fd()), &stat)
	if err != nil {
		return "", err
	}
	sec, nsec := stat.Ctim.Unix()
	buf := make([]byte, 8*2)
	binary.BigEndian.PutUint64(buf[:8], uint64(sec))
	binary.BigEndian.PutUint64(buf[8:], uint64(nsec))
	return `"` + base64.RawURLEncoding.EncodeToString(buf) + `"`, nil
}