package filelock

import (
	"errors"
	"fmt"
	"os"
	"path"
	"time"
)

var ErrLocked = errors.New("failed to get a lock in a timely manner")

type FileLock struct {
	lockPath string
}

func New(filepath string) *FileLock {
	dir, filename := path.Split(filepath)
	lockPath := path.Join(dir, fmt.Sprintf(".%s.lock", filename))
	return &FileLock{
		lockPath: lockPath,
	}
}

func (fl *FileLock) lockFileExists() bool {
	if _, err := os.Stat(fl.lockPath); errors.Is(err, os.ErrNotExist) {
		return false
	}
	return true
}

func (fl *FileLock) Lock(timeout time.Duration) error {
	start := time.Now().UTC()
	end := start.Add(timeout)

	for {
		if !fl.lockFileExists() {
			if _, err := os.Create(fl.lockPath); err != nil {
				return fmt.Errorf("failed to create lock: %w", err)
			}
			return nil
		}
		if time.Now().After(end) {
			return ErrLocked
		}
		time.Sleep(100 * time.Millisecond)
	}
}

func (fl *FileLock) Unlock() error {
	if err := os.Remove(fl.lockPath); err != nil {
		return fmt.Errorf("failed to remove lock: %w", err)
	}
	return nil
}