You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: spanner_cancel_backup_create.go
    path of file: ./repos/golang-samples/spanner/spanner_snippets/spanner
    
    the code of the file until where you have to start completion: // Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package spanner

// [START spanner_cancel_backup_create]

import (
	"context"
	"fmt"
	"io"
	"regexp"
	"time"

	longrunning "cloud.google.com/go/longrunning/autogen/longrunningpb"
	database "cloud.google.com/go/spanner/admin/database/apiv1"
	pbt "github.com/golang/protobuf/ptypes/timestamp"
	adminpb "google.golang.org/genproto/googleapis/spanner/admin/database/v1"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

func cancelBackup(ctx context.Context, w io.Writer, db, backupID string) error {
	matches := regexp.MustCompile("^(.+)/databases/(.+)$").FindStringSubmatch(db)
	if matches == nil || len(matches) != 3 {
		return fmt.Errorf("cancelBackup: invalid database id %q", db)
	}

	adminClient, err := database.NewDatabaseAdminClient(ctx)
	if err 
    
func cancelBackup(ctx context.Context, w io.Writer, db, backupID string) error {
	matches := regexp.MustCompile("^(.+)/databases/(.+)$").FindStringSubmatch(db)
	if matches == nil || len(matches) != 3 {
		return fmt.Errorf("cancelBackup: invalid database id %q", db)
	}

	adminClient, err := database.NewDatabaseAdminClient(ctx)
	if err != nil {
		return fmt.Errorf("cancelBackup.NewDatabaseAdminClient: %w", err)
	}
	defer adminClient.Close()

	expireTime := time.Now().AddDate(0, 0, 14)
	// Create a backup.
	req := adminpb.CreateBackupRequest{
		Parent:   matches[1],
		BackupId: backupID,
		Backup: &adminpb.Backup{
			Database:   db,
			ExpireTime: &pbt.Timestamp{Seconds: expireTime.Unix(), Nanos: int32(expireTime.Nanosecond())},
		},
	}
	op, err := adminClient.CreateBackup(ctx, &req)
	if err != nil {
		return fmt.Errorf("cancelBackup.CreateBackup: %w", err)
	}

	// Cancel backup creation.
	err = adminClient.LROClient.CancelOperation(ctx, &longrunning.CancelOperationRequest{Name: op.Name()})
	if err != nil {
		return fmt.Errorf("cancelBackup.CancelOperation: %w", err)
	}

	// Cancel operations are best effort so either it will complete or be
	// cancelled.
	backup, err := op.Wait(ctx)
	if err != nil {
		if waitStatus, ok := status.FromError(err); !ok || waitStatus.Code() != codes.Canceled {
			return fmt.Errorf("cancelBackup.Wait: %w", err)
		}
	} else {
		// Backup was completed before it could be cancelled so delete the
		// unwanted backup.
		err = adminClient.DeleteBackup(ctx, &adminpb.DeleteBackupRequest{Name: backup.Name})
		if err != nil {
			return fmt.Errorf("cancelBackup.DeleteBackup: %w", err)
		}
	}

	fmt.Fprintf(w, "Backup cancelled.\n")
	return nil
}