//go:build !windows

package singleinstance

import (
	"fmt"
	"os"
	"path/filepath"
)

// Lock uses an exclusive lock file under the user config dir when available.
func Lock(appName string) (func(), error) {
	if appName == "" {
		appName = "Navis"
	}
	dir, err := os.UserConfigDir()
	if err != nil {
		return func() {}, nil
	}
	path := filepath.Join(dir, appName, "singleinstance.lock")
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return func() {}, nil
	}
	f, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR, 0o600)
	if err != nil {
		return func() {}, nil
	}
	if err := flockExclusive(f); err != nil {
		_ = f.Close()
		return nil, fmt.Errorf("%w", ErrAlreadyRunning)
	}
	return func() {
		_ = funlock(f)
		_ = f.Close()
	}, nil
}