package main

import (
	"flag"
	"fmt"
	"github.com/rwcarlsen/goexif/exif"
	"log"
	"os"
	"path"
	"path/filepath"
	"strings"
)

func visit(pathname string, f os.FileInfo, err error) error {
	openedFile, err := os.Open(pathname)
	if err != nil {
		log.Fatal(err)
	}

	exifData, err := exif.Decode(openedFile)
	if err != nil {
		fmt.Printf("⨯ Unable to load file: %s", pathname)
		return nil
	}

	tm, _ := exifData.DateTime()

	newPathname := strings.ToLower(strings.Replace(pathname, f.Name(), fmt.Sprintf("%s%s", tm.Format("20060102030405"), path.Ext(pathname)), 1))

	os.Rename(pathname, newPathname)
	fmt.Printf("✓ Renaming to: %s\n", strings.Replace(pathname, f.Name(), newPathname, 1))

	return nil
}

func main() {
	flag.Parse()
	directory := flag.Arg(0)

	filepath.Walk(directory, visit)
}