// mmc -- Mattermost client
// Copyright (C) 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 Affero General Public License as
// published by the Free Software Foundation, either 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 Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package mmc

import (
	"io"
	"os"

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

func Lock(what string) (func(), error) {
	fd, err := os.OpenFile(
		what,
		os.O_WRONLY|os.O_TRUNC|os.O_CREATE,
		os.FileMode(0666),
	)
	dummy := func() {}
	if err != nil {
		return dummy, err
	}
	flock := unix.Flock_t{
		Type:   unix.F_WRLCK,
		Whence: io.SeekStart,
	}
	if err = unix.FcntlFlock(fd.Fd(), unix.F_SETLK, &flock); err != nil {
		fd.Close()
		return dummy, err
	}
	return func() {
		flock.Type = unix.F_UNLCK
		unix.FcntlFlock(fd.Fd(), unix.F_SETLK, &flock)
		fd.Close()
	}, nil
}