previousCommitMark := 0

		commitMark := nextMark()

		var commit Commit
		commit.Mark = nextMark()

		fmt.Println("commit refs/heads/master")
		fmt.Printf("mark :%d\n", commitMark)

		fmt.Println("committer", author, formatTime(c.Timestamp))

		commit.Committer = author
		commit.Timestamp = c.Timestamp

		fmt.Println("data", len(message))
		fmt.Println(message)
		if previousCommitMark != 0 {
			fmt.Printf("from :%d\n", previousCommitMark)

		commit.Message = message
		if err := commit.WriteTo(os.Stdout); err != nil {
			printErrorAndExit("Error writing commit:", err)

		fmt.Println()
		previousCommitMark = commitMark

package main
import (
	"fmt"
	"io"
	"time"
)
type Commit struct {
	Mark      int
	Committer string
	Timestamp time.Time
	Message   string
}
func (c Commit) WriteTo(w io.Writer) error {
	if _, err := fmt.Fprintln(w, "commit refs/heads/master"); err != nil {
		return err
	}
	if c.Mark != 0 {
		if _, err := fmt.Fprintf(w, "mark :%d\n", c.Mark); err != nil {
			return err
		}
	}
	if _, err := fmt.Fprintln(w, "committer", c.Committer, formatTime(c.Timestamp)); err != nil {
		return err
	}
	if _, err := fmt.Fprintln(w, "data", len(c.Message)); err != nil {
		return err
	}
	if _, err := fmt.Fprintln(w, c.Message); err != nil {
		return err
	}
	if _, err := fmt.Fprintln(w); err != nil {
		return err
	}
	return nil
}