golang script to reverse gif picture

reverse-gif.go

package main

import (
	"image/gif"
	"log"
	"os"
	"path/filepath"
	"strings"
)

func main() {
	filename := os.Args[1]
	if filename == "" {
		return
	}
	path, err := filepath.Abs(filename)
	if err != nil {
		log.Fatal(err)
	}
	reader, err := os.Open(path)
	defer reader.Close()
	if err != nil {
		log.Fatal(err)
	}
	decoded, err := gif.DecodeAll(reader)
	if err != nil {
		log.Fatal(err)
	}
	data := decoded.Image
	for left, right := 0, len(data)-1; left < right; left, right = left+1, right-1 {
		data[left], data[right] = data[right], data[left]
	}

	dir, filename := filepath.Split(path)
	ext := filepath.Ext(filename)
	base := strings.TrimSuffix(filename, ext)

	filename = filepath.Join(dir, base + ".reverse" + ext)

	w, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY, 0664)
	defer w.Close()
	if err != nil {
		log.Fatal(err)
	}
	err = gif.EncodeAll(w, decoded)
	if err != nil {
		log.Fatal(err)
	}
}