package main

import (
	"flag"
	"fmt"
	"log"
	"os"
	"path"
	"regexp"
	"strings"
	"sync"
)

func init() {
	log.SetFlags(log.Lmicroseconds)
}

func main() {
	recreate := flag.Bool("f", false, "First rename all files to <name>.bak and then rename them to iter (to prevent conflicts of already existing files)")
	flag.Parse()

	originalExtensions := make(map[string]string)
	var mapMutex sync.RWMutex
	var wg sync.WaitGroup
	extensionRegex := regexp.MustCompile(`\.[a-zA-Z0-9]+$`)

	if *recreate {
		log.Printf("Recreating all files first")
		for _, file := range flag.Args() {
			wg.Add(1)
			go func(file string) {
				defer wg.Done()
				_, err := os.Stat(file)
				if os.IsNotExist(err) {
					log.Printf("File %s does not exist", file)
					return
				}

				res := extensionRegex.FindAllString(file, -1)
				if len(res) == 0 {
					log.Printf("No extension found for file %s", file)
					return
				}
				dir := path.Dir(file)
				extension := res[0]
				bckpFile := fmt.Sprintf("%s/%s.bak", dir, file)

				_, err = os.Stat(bckpFile)
				if !os.IsNotExist(err) {
					log.Printf("File %s already exists", bckpFile)
					return
				}

				log.Printf("%s -> %s", file, bckpFile)
				err = os.Rename(file, bckpFile)
				if err != nil {
					log.Printf("Error renaming file %s to %s: %s", file, bckpFile, err)
				}

				mapMutex.Lock()
				originalExtensions[bckpFile] = extension
				mapMutex.Unlock()
			}(file)
		}
	}

	wg.Wait()
	wg = sync.WaitGroup{}
	for _, file := range flag.Args() {
		wg.Add(1)
		go func(file string) {
			defer wg.Done()
			if *recreate {
				file = file + ".bak"
			}

			info, err := os.Stat(file)
			if os.IsNotExist(err) {
				log.Printf("File %s does not exist", file)
				return
			}

			if info.IsDir() {
				log.Printf("File %s is a directory", file)
				return
			}

			modtime := info.ModTime()
			modtimeString := modtime.Local().Format("2006-01-02T15-04-05")
			newFile := modtimeString

			bakless := strings.TrimRight(file, ".bak")
			res := extensionRegex.FindAllString(bakless, -1)
			if len(res) == 0 {
				log.Printf("No extension found for file %s", file)
				return
			}
			extension := res[0]

			mapMutex.RLock()
			prevExtension, ok := originalExtensions[file]
			mapMutex.RUnlock()
			if ok {
				extension = prevExtension
			}

			dir := path.Dir(file)
			newFile = fmt.Sprintf("%s/%s%s", dir, newFile, extension)
			newFile = path.Clean(newFile)
			newFile = strings.TrimRight(newFile, ".bak")

			_, err = os.Stat(newFile)
			if os.IsExist(err) {
				log.Printf("File %s already exists", newFile)
				return
			} else if !os.IsNotExist(err) {
				log.Printf("An unexpected error occurred: %v", err)
				return
			}

			log.Printf("%s -> %s", file, newFile)
			err = os.Rename(file, newFile)
			if err != nil {
				log.Printf("Error renaming file %s to %s: %s", file, newFile, err)
				return
			}
		}(file)
	}
	wg.Wait()
}