package fileutil

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

type LockedFile struct {
	file *os.File
}

func WithLockedFile(path string, fn func() error) error {
	lock, err := acquireLock(path)
	if err != nil {
		return err
	}
	defer lock.Close()
	return fn()
}

func AtomicWriteFile(path string, data []byte, perm os.FileMode) error {
	dir := filepath.Dir(path)
	base := filepath.Base(path)
	tmp, err := os.CreateTemp(dir, base+".*.tmp")
	if err != nil {
		return fmt.Errorf("create tmp: %w", err)
	}
	tmpPath := tmp.Name()
	defer func() {
		_ = os.Remove(tmpPath)
	}()
	if err := tmp.Chmod(perm); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("chmod tmp: %w", err)
	}
	if _, err := tmp.Write(data); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("write tmp: %w", err)
	}
	if err := tmp.Sync(); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("sync tmp: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("close tmp: %w", err)
	}
	if err := os.Rename(tmpPath, path); err != nil {
		return fmt.Errorf("rename tmp: %w", err)
	}
	if err := syncDir(dir); err != nil {
		return err
	}
	return nil
}

func acquireLock(path string) (*LockedFile, error) {
	lockPath := path + ".lock"
	file, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0o600)
	if err != nil {
		return nil, fmt.Errorf("open lock: %w", err)
	}
	if err := syscall.Flock(int(file.Fd()), syscall.LOCK_EX); err != nil {
		_ = file.Close()
		return nil, fmt.Errorf("lock file: %w", err)
	}
	return &LockedFile{file: file}, nil
}

func (l *LockedFile) Close() error {
	if l == nil || l.file == nil {
		return nil
	}
	unlockErr := syscall.Flock(int(l.file.Fd()), syscall.LOCK_UN)
	closeErr := l.file.Close()
	if unlockErr != nil {
		return fmt.Errorf("unlock file: %w", unlockErr)
	}
	if closeErr != nil {
		return fmt.Errorf("close lock: %w", closeErr)
	}
	return nil
}

func syncDir(dir string) error {
	f, err := os.Open(dir)
	if err != nil {
		return fmt.Errorf("open dir: %w", err)
	}
	defer f.Close()
	if err := f.Sync(); err != nil {
		return fmt.Errorf("sync dir: %w", err)
	}
	return nil
}