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: order_strategy.go
    path of file: ./repos/dive/dive/filetree
    
    the code of the file until where you have to start completion: package filetree

import (
	"sort"
)

type SortOrder int

const (
	ByName = iota
	BySizeDesc

	NumSortOrderConventions
)

type OrderStrategy interface {
	orderKeys(files map[string]*FileNode) []string
}

func GetSortOrderStrategy(sortOrder SortOrder) OrderStrategy {
	switch sortOrder {
	case ByName:
		return orderB
    
func (orderBySizeDescStrategy) orderKeys(files map[string]*FileNode) []string {
	var keys []string
	for key := range files {
		keys = append(keys, key)
	}

	sort.Slice(keys, func(i, j int) bool {
		ki, kj := keys[i], keys[j]
		ni, nj := files[ki], files[kj]
		if ni.GetSize() == nj.GetSize() {
			return ki < kj
		}
		return ni.GetSize() > nj.GetSize()
	})

	return keys
}