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: rebase_todo.go
    path of file: ./repos/lazygit/pkg/utils
    
    the code of the file until where you have to start completion: package utils

import (
	"fmt"
	"os"
	"strings"

	"github.com/fsmiamoto/git-todo-parser/todo"
	"github.com/samber/lo"
)

type Todo struct {
	Sha    string
	Action todo.TodoCommand
}

// In order to change a TODO in git-rebase-todo, we need to specify th
    
func moveFixupCommitDown(todos []todo.Todo, originalSha string, fixupSha string) ([]todo.Todo, error) {
	isOriginal := func(t todo.Todo) bool {
		return t.Command == todo.Pick && equalShas(t.Commit, originalSha)
	}

	isFixup := func(t todo.Todo) bool {
		return t.Command == todo.Pick && equalShas(t.Commit, fixupSha)
	}

	originalShaCount := lo.CountBy(todos, isOriginal)
	if originalShaCount != 1 {
		return nil, fmt.Errorf("Expected exactly one original SHA, found %d", originalShaCount)
	}

	fixupShaCount := lo.CountBy(todos, isFixup)
	if fixupShaCount != 1 {
		return nil, fmt.Errorf("Expected exactly one fixup SHA, found %d", fixupShaCount)
	}

	_, fixupIndex, _ := lo.FindIndexOf(todos, isFixup)
	_, originalIndex, _ := lo.FindIndexOf(todos, isOriginal)

	newTodos := MoveElement(todos, fixupIndex, originalIndex+1)

	newTodos[originalIndex+1].Command = todo.Fixup

	return newTodos, nil
}