// SaveDBFrom saves snapshot of the database from the given reader. It
// guarantees the save operation is atomic.
func (s *Snapshotter) SaveDBFrom(r io.Reader, id uint64) error {
	f, err := ioutil.TempFile(s.dir, "tmp")
	if err != nil {
		return err
	}
	var n int64
	n, err = io.Copy(f, r)
	if err == nil {
		err = fileutil.Fsync(f)
	}
	f.Close()
	if err != nil {
		os.Remove(f.Name())
		return err
	}
	fn := path.Join(s.dir, fmt.Sprintf("%016x.snap.db", id))
	if fileutil.Exist(fn) {
		os.Remove(f.Name())
		return nil
	}
	err = os.Rename(f.Name(), fn)
	if err != nil {
		os.Remove(f.Name())
		return err
	}

	plog.Infof("saved database snapshot to disk [total bytes: %d]", n)

	return nil
}

func snapshotSaveCommandFunc(cmd *cobra.Command, args []string) {
	if len(args) != 1 {
		err := fmt.Errorf("snapshot save expects one argument")
		ExitWithError(ExitBadArgs, err)
	}

	path := args[0]

	partpath := path + ".part"
	f, err := os.Create(partpath)
	defer f.Close()
	if err != nil {
		exiterr := fmt.Errorf("could not open %s (%v)", partpath, err)
		ExitWithError(ExitBadArgs, exiterr)
	}

	c := mustClientFromCmd(cmd)
	r, serr := c.Snapshot(context.TODO())
	if serr != nil {
		os.RemoveAll(partpath)
		ExitWithError(ExitInterrupted, serr)
	}
	if _, rerr := io.Copy(f, r); rerr != nil {
		os.RemoveAll(partpath)
		ExitWithError(ExitInterrupted, rerr)
	}

	fileutil.Fsync(f)

	if rerr := os.Rename(partpath, path); rerr != nil {
		exiterr := fmt.Errorf("could not rename %s to %s (%v)", partpath, path, rerr)
		ExitWithError(ExitIO, exiterr)
	}
	fmt.Printf("Snapshot saved at %s\n", path)
}

// WriteAndSyncFile behaves just like ioutil.WriteFile in the standard library,
// but calls Sync before closing the file. WriteAndSyncFile guarantees the data
// is synced if there is no error returned.
func WriteAndSyncFile(filename string, data []byte, perm os.FileMode) error {
	f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
	if err != nil {
		return err
	}
	n, err := f.Write(data)
	if err == nil && n < len(data) {
		err = io.ErrShortWrite
	}
	if err == nil {
		err = fileutil.Fsync(f)
	}
	if err1 := f.Close(); err == nil {
		err = err1
	}
	return err
}

// Create creates a WAL ready for appending records. The given metadata is
// recorded at the head of each WAL file, and can be retrieved with ReadAll.
func Create(dirpath string, metadata []byte) (*WAL, error) {
	if Exist(dirpath) {
		return nil, os.ErrExist
	}

	// keep temporary wal directory so WAL initialization appears atomic
	tmpdirpath := path.Clean(dirpath) + ".tmp"
	if fileutil.Exist(tmpdirpath) {
		if err := os.RemoveAll(tmpdirpath); err != nil {
			return nil, err
		}
	}
	if err := fileutil.CreateDirAll(tmpdirpath); err != nil {
		return nil, err
	}

	p := path.Join(tmpdirpath, walName(0, 0))
	f, err := fileutil.LockFile(p, os.O_WRONLY|os.O_CREATE, fileutil.PrivateFileMode)
	if err != nil {
		return nil, err
	}
	if _, err = f.Seek(0, os.SEEK_END); err != nil {
		return nil, err
	}
	if err = fileutil.Preallocate(f.File, SegmentSizeBytes, true); err != nil {
		return nil, err
	}

	w := &WAL{
		dir:      dirpath,
		metadata: metadata,
		encoder:  newEncoder(f, 0),
	}
	w.locks = append(w.locks, f)
	if err = w.saveCrc(0); err != nil {
		return nil, err
	}
	if err = w.encoder.encode(&walpb.Record{Type: metadataType, Data: metadata}); err != nil {
		return nil, err
	}
	if err = w.SaveSnapshot(walpb.Snapshot{}); err != nil {
		return nil, err
	}

	if w, err = w.renameWal(tmpdirpath); err != nil {
		return nil, err
	}

	// directory was renamed; sync parent dir to persist rename
	pdir, perr := fileutil.OpenDir(path.Dir(w.dir))
	if perr != nil {
		return nil, perr
	}
	if perr = fileutil.Fsync(pdir); perr != nil {
		return nil, perr
	}
	if perr = pdir.Close(); err != nil {
		return nil, perr
	}

	return w, nil
}

// cut closes current file written and creates a new one ready to append.
// cut first creates a temp wal file and writes necessary headers into it.
// Then cut atomically rename temp wal file to a wal file.
func (w *WAL) cut() error {
	// close old wal file; truncate to avoid wasting space if an early cut
	off, serr := w.tail().Seek(0, os.SEEK_CUR)
	if serr != nil {
		return serr
	}
	if err := w.tail().Truncate(off); err != nil {
		return err
	}
	if err := w.sync(); err != nil {
		return err
	}

	fpath := path.Join(w.dir, walName(w.seq()+1, w.enti+1))

	// create a temp wal file with name sequence + 1, or truncate the existing one
	newTail, err := w.fp.Open()
	if err != nil {
		return err
	}

	// update writer and save the previous crc
	w.locks = append(w.locks, newTail)
	prevCrc := w.encoder.crc.Sum32()
	w.encoder = newEncoder(w.tail(), prevCrc)
	if err = w.saveCrc(prevCrc); err != nil {
		return err
	}
	if err = w.encoder.encode(&walpb.Record{Type: metadataType, Data: w.metadata}); err != nil {
		return err
	}
	if err = w.saveState(&w.state); err != nil {
		return err
	}
	// atomically move temp wal file to wal file
	if err = w.sync(); err != nil {
		return err
	}

	off, err = w.tail().Seek(0, os.SEEK_CUR)
	if err != nil {
		return err
	}

	if err = os.Rename(newTail.Name(), fpath); err != nil {
		return err
	}
	if err = fileutil.Fsync(w.dirFile); err != nil {
		return err
	}

	newTail.Close()

	if newTail, err = fileutil.LockFile(fpath, os.O_WRONLY, fileutil.PrivateFileMode); err != nil {
		return err
	}
	if _, err = newTail.Seek(off, os.SEEK_SET); err != nil {
		return err
	}

	w.locks[len(w.locks)-1] = newTail

	prevCrc = w.encoder.crc.Sum32()
	w.encoder = newEncoder(w.tail(), prevCrc)

	plog.Infof("segmented wal file %v is created", fpath)
	return nil
}

// Repair tries to repair ErrUnexpectedEOF in the
// last wal file by truncating.
func Repair(dirpath string) bool {
	f, err := openLast(dirpath)
	if err != nil {
		return false
	}
	defer f.Close()

	rec := &walpb.Record{}
	decoder := newDecoder(f)
	for {
		lastOffset := decoder.lastOffset()
		err := decoder.decode(rec)
		switch err {
		case nil:
			// update crc of the decoder when necessary
			switch rec.Type {
			case crcType:
				crc := decoder.crc.Sum32()
				// current crc of decoder must match the crc of the record.
				// do no need to match 0 crc, since the decoder is a new one at this case.
				if crc != 0 && rec.Validate(crc) != nil {
					return false
				}
				decoder.updateCRC(rec.Crc)
			}
			continue
		case io.EOF:
			return true
		case io.ErrUnexpectedEOF:
			plog.Noticef("repairing %v", f.Name())
			bf, bferr := os.Create(f.Name() + ".broken")
			if bferr != nil {
				plog.Errorf("could not repair %v, failed to create backup file", f.Name())
				return false
			}
			defer bf.Close()

			if _, err = f.Seek(0, os.SEEK_SET); err != nil {
				plog.Errorf("could not repair %v, failed to read file", f.Name())
				return false
			}

			if _, err = io.Copy(bf, f); err != nil {
				plog.Errorf("could not repair %v, failed to copy file", f.Name())
				return false
			}

			if err = f.Truncate(int64(lastOffset)); err != nil {
				plog.Errorf("could not repair %v, failed to truncate file", f.Name())
				return false
			}
			if err = fileutil.Fsync(f.File); err != nil {
				plog.Errorf("could not repair %v, failed to sync file", f.Name())
				return false
			}
			return true
		default:
			plog.Errorf("could not repair error (%v)", err)
			return false
		}
	}
}