package main

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"runtime"
	"sync"
)

type Fdhashes struct {
	Path   string
	Hashes map[string]string
}

var hashes map[string]Fdhashes

var wg sync.WaitGroup
var mu sync.RWMutex

func main() {
	runtime.GOMAXPROCS(5)
	hashes = make(map[string]Fdhashes)
	flag.Parse()
	myFile := flag.Arg(0)
	file, err := os.Stat(myFile)
	if os.IsNotExist(err) {
		log.Fatalln("File does not exists:", myFile)
	}
	if file.IsDir() {
		log.Println("start with folder:", myFile)
		processFolder(myFile)
	} else {
		log.Printf("file %s has hash %s\n", myFile, getHash(myFile))
	}

	fmt.Println("waiting")
	wg.Wait()
	log.Println("done")
}

func getHash(fileStr string) string {
	f, err := os.Open(fileStr)
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()

	h := sha256.New()
	if _, err := io.Copy(h, f); err != nil {
		log.Fatal(err)
	}
	return hex.EncodeToString(h.Sum(nil))
}

func outputHash(fileStr string) {
	var hashFile Fdhashes
	doHash := true
	defer wg.Done()
	fmt.Print(".")
	dir, fileName := filepath.Split(fileStr)
	if fileName == ".fdhashes3" {
		return
	}
	mu.Lock()
	hashFile, ok := hashes[dir]
	if !ok {
		_, err := os.Stat(dir + ".fdhashes3")
		if os.IsNotExist(err) {
			hashFile = Fdhashes{Path: dir, Hashes: make(map[string]string)}
		} else {
			hashFile = loadHashfile(dir + ".fdhashes3")
		}
		hashes[dir] = hashFile
		saveHashfile(hashFile)
	}

	_, ok = hashFile.Hashes[fileName]
	doHash = !ok
	hashFile = hashes[dir]
	mu.Unlock()
	if doHash {
		hash := getHash(fileStr)
		mu.Lock()
		hashFile.Hashes[fileName] = hash
		saveHashfile(hashFile)
		mu.Unlock()
		log.Printf("file %s has hash %s\n", fileStr, hash)
	}
}

func processFolder(folder string) {
	err := filepath.Walk(folder, func(path string, info os.FileInfo, err error) error {
		if !info.IsDir() {
			wg.Add(1)
			go outputHash(path)
		}
		return nil
	})
	if err != nil {
		panic(err)
	}
}

func saveHashfile(hashFile Fdhashes) {
	b, err := json.Marshal(hashFile)
	if err != nil {
		fmt.Println(err)
		return
	}
	err = ioutil.WriteFile(hashFile.Path+".fdhashes3", b, 0644)
	if err != nil {
		panic(err)
	}
}

func loadHashfile(filename string) Fdhashes {
	file, err := ioutil.ReadFile(filename)
	if err != nil {
		panic(err)
	}
	data := Fdhashes{}
	err = json.Unmarshal([]byte(file), &data)
	if err != nil {
		panic(err)
	}
	return data
}