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: change_superblock.go
    path of file: ./repos/seaweedfs/unmaintained/change_superblock
    
    the code of the file until where you have to start completion: package main

import (
	"flag"
	"fmt"
	"os"
	"path"
	"strconv"

	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/storage/backend"
	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
)

var (
	fixVolumePath       = flag.String("dir", "/tmp", "data directory to store files")
	fixVolumeCollection = flag.String("collection", "", "the volume collection name")
	fixVolumeId         = flag.Int("volumeId", -1, "a volume id. The volume should already exist in the dir. The volume index file should not exist.")
	targetReplica       = flag.String("replication", "", "If just empty, only print out current replication setting.")
	targetTTL           = flag.String("ttl", "", "If just empty, only print out current ttl setting.")
)

/*
This is to change replication factor in .dat file header. Need to shut down the volume servers
that has those volumes.

1. fix the .d
    
func main() {
	flag.Parse()
	fileName := strconv.Itoa(*fixVolumeId)
	if *fixVolumeCollection != "" {
		fileName = *fixVolumeCollection + "_" + fileName
	}
	datFile, err := os.OpenFile(path.Join(*fixVolumePath, fileName+".dat"), os.O_RDWR, 0644)
	if err != nil {
		glog.Fatalf("Open Volume Data File [ERROR]: %v", err)
	}
	datBackend := backend.NewDiskFile(datFile)
	defer datBackend.Close()

	superBlock, err := super_block.ReadSuperBlock(datBackend)

	if err != nil {
		glog.Fatalf("cannot parse existing super block: %v", err)
	}

	fmt.Printf("Current Volume Replication: %s\n", superBlock.ReplicaPlacement)
	fmt.Printf("Current Volume TTL: %s\n", superBlock.Ttl.String())

	hasChange := false

	if *targetReplica != "" {
		replica, err := super_block.NewReplicaPlacementFromString(*targetReplica)

		if err != nil {
			glog.Fatalf("cannot parse target replica %s: %v", *targetReplica, err)
		}

		fmt.Printf("Changing replication to: %s\n", replica)

		superBlock.ReplicaPlacement = replica
		hasChange = true
	}

	if *targetTTL != "" {
		ttl, err := needle.ReadTTL(*targetTTL)

		if err != nil {
			glog.Fatalf("cannot parse target ttl %s: %v", *targetTTL, err)
		}

		fmt.Printf("Changing ttl to: %s\n", ttl)

		superBlock.Ttl = ttl
		hasChange = true
	}

	if hasChange {

		header := superBlock.Bytes()

		if n, e := datBackend.WriteAt(header, 0); n == 0 || e != nil {
			glog.Fatalf("cannot write super block: %v", e)
		}

		fmt.Println("Change Applied.")
	}

}