package client

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

// lockFile marks a mirror directory as being synchronized by one agent. Two
// agents on one directory would each think the other's writes were local
// saves and push them back, so the tray, `keeporg run` and a service unit
// started side by side must not all sync.
const lockFile = ".keeporg.lock"

// ErrMirrorBusy means another agent already holds the mirror directory.
var ErrMirrorBusy = errors.New("another keeporg agent is already synchronizing this directory")

// LockDir takes the mirror directory's lock for this process. The operating
// system releases it when the process exits, however it exits, so a crash
// never leaves a directory locked.
func LockDir(dir string) (unlock func(), err error) {
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return nil, err
	}
	path := filepath.Join(dir, lockFile)
	unlock, err = lockPath(path)
	if errors.Is(err, ErrMirrorBusy) {
		return nil, fmt.Errorf("%s: %w", dir, err)
	}
	return unlock, err
}