package main

import (
	"flag"
	"fmt"
	"log"
	"os"
	"regexp"
	"sync"
	"sync/atomic"
)

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

func main() {
	padSize := flag.Int("n", 5, "Pad size for new file names")
	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()
	nameFormat := fmt.Sprintf("%%0%dd", *padSize)

	originalExtensions := make(map[string]string)
	var mapMutex sync.RWMutex
	var wg sync.WaitGroup
	var mutex sync.Mutex
	extensionRegex := regexp.MustCompile(`\.[a-zA-Z0-9]+$`)
	var i int32

	if *recreate {
		log.Printf("Recreating all files first")
		for _, file := range flag.Args() {
			wg.Add(1)
			go func(file string) {
				defer wg.Done()
				res := extensionRegex.FindAllString(file, -1)
				if len(res) == 0 {
					log.Printf("No extension found for file %s", file)
					return
				}
				extension := res[0]
				bckpFile := file + ".bak"

				_, 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
			}

			mutex.Lock()
			atomic.AddInt32(&i, 1)
			newFile := fmt.Sprintf(nameFormat, i)
			mutex.Unlock()

			res := extensionRegex.FindAllString(file, -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
			}

			newFile = newFile + extension

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