golfing mass photo renamer

main.go

package main

import (
	"errors"
	"fmt"
	"github.com/rwcarlsen/goexif/exif"
	"io/fs"
	"log"
	"os"
	"path/filepath"
	"strconv"
	"strings"
)

func fileExt(filename string) string {
	ext := filepath.Ext(filename)
	return strings.ToLower(ext)
}

func generateFileName(fileName string) (string, error) {
	f, err := os.Open(fileName)
	if err != nil {
		return "", err
	}
	defer f.Close()
	x, err := exif.Decode(f)
	if err != nil {
		return "", err
	}

	t, err := x.DateTime()
	if err != nil {
		return "", err
	}

	buf := strings.Builder{}
	buf.WriteString(t.Format("2006-01-02_15:04:05"))
	imageUniqueID, err := x.Get("ImageUniqueID")
	if err == nil {
		idStr, err := imageUniqueID.StringVal()
		if err == nil {
			buf.WriteString("_")
			buf.WriteString(idStr)
		}
	} else {
		if stat, err := os.Stat(fileName); err == nil {
			buf.WriteString("_")
			buf.WriteString(strconv.FormatInt(stat.Size(), 10))
		}
	}
	buf.WriteString(fileExt(fileName))
	newFileName := buf.String()

	return filepath.Join(filepath.Dir(fileName), newFileName), nil
}

func walkFunc(path string, info fs.FileInfo, err0 error) error {
	if info.IsDir() {
		return nil
	}
	if fileExt(path) != ".jpg" {
		return nil
	}
	newFilePath, err := generateFileName(path)
	if err != nil {
		return nil
	}
	if _, err := os.Stat(newFilePath); errors.Is(err, os.ErrNotExist) {
		err = os.Rename(path, newFilePath)
		if err != nil {
			return nil
		}
		fmt.Printf("%s -> %s\n", path, newFilePath)
	}
	return nil
}

func main() {
	err := filepath.Walk(".", walkFunc)
	if err != nil {
		log.Fatal(err)
	}
}