// Package flock provides portable file locking. It is essentially ripped out
// from the code of github.com/syndtr/goleveldb. Strange enough that the
// standard library does not provide this functionality. Once this package has
// proven to work as expected, we should probably turn it into a separate
// general purpose package for humanity.
package flock

import (
	"os"
	"path/filepath"
)

// Releaser provides the Release method to release a file lock.
type Releaser interface {
	Release() error
}

// New locks the file with the provided name. If the file does not exist, it is
// created. The returned Releaser is used to release the lock. The returned
// boolean is true if the file to lock already existed. A non-nil error is
// returned if the locking has failed. Neither this function nor the returned
// Releaser is goroutine-safe.
func New(fileName string) (Releaser, bool, error) {
	if err := os.MkdirAll(filepath.Dir(fileName), 0755); err != nil {
		return nil, false, err
	}

	_, err := os.Stat(fileName)
	existed := err == nil

	lock, err := newLock(fileName)
	if err != nil {
		return nil, existed, err
	}

	return lock, existed, nil
}