//go:build linux

package birddeploy

import (
	"context"
	"errors"
	"os"
	"time"

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

func lockTarget(ctx context.Context, path string) (*os.File, error) {
	f, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR, 0o600)
	if err != nil {
		return nil, err
	}
	for {
		err = unix.Flock(int(f.Fd()), unix.LOCK_EX|unix.LOCK_NB)
		if err == nil {
			return f, nil
		}
		if !errors.Is(err, unix.EWOULDBLOCK) && !errors.Is(err, unix.EAGAIN) {
			_ = f.Close()
			return nil, err
		}
		select {
		case <-ctx.Done():
			_ = f.Close()
			return nil, ctx.Err()
		case <-time.After(25 * time.Millisecond):
		}
	}
}