package main

import "fmt"
import "crypto/sha256"
import "io"
import "log"
import "os"
import "path/filepath"
import "sync"

func sha256File(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()
	h := sha256.New()
	io.Copy(h, f)
	return fmt.Sprintf("SHA256 (%s) =  %x", path, h.Sum(nil)), nil
}

func runParallel(n uint, what func()) {
	var wg sync.WaitGroup
	for i := 0; i < int(n); i++ {
		wg.Add(1)
		what()
		wg.Done()
	}
	wg.Wait()
}

func main() {
	if len(os.Args) < 2 {
		log.Fatalln("Usage shadir file")
	}

	chan_hash, chan_path := make(chan string), make(chan string)

	go func() {
		runParallel(100, func() { // 100 routines hashing
			for path := range chan_path {
				if h, err := sha256File(path); err != nil {
					log.Print("Error "+path, err)
				} else {
					chan_hash <- h
				}
			}
		})
		close(chan_hash)
	}()

	go func() { // walk through files
		filepath.Walk(os.Args[1], func(path string, info os.FileInfo, err error) error {
			if err == nil && !info.IsDir() {
				chan_path <- path
			}
			return err
		})
		close(chan_path)
	}()

	for h := range chan_hash {
		fmt.Println(h)
	}
}