package main

import (
	"encoding/hex"
	"flag"
	"fmt"
	"io"
	"os"
	"sync"

	"github.com/zeebo/blake3"
)

var (
	help = flag.Bool("h", false, "Prints help information")
	length = flag.Int("l", 32,  "The number of output bytes, prior to hex encoding")
	par = flag.Int("p", 4, "The maximum concurrency")
)

func main() {
	flag.Parse()
	if *help || len(flag.Args()) == 0 || *par < 1 {
		flag.Usage()
		os.Exit(0)
	}
	q := make(chan struct{}, *par)
	wg := &sync.WaitGroup{}

	for _, name := range flag.Args() {
		q <- struct{}{}
		wg.Add(1)
		go func(name string) {
			buf := [65536]byte{}
			file, err := os.Open(name)
			if err != nil {
				panic(err)
			}
			hasher := blake3.NewSized(*length)
			for {
				n, err := file.Read(buf[:])
				hasher.Write(buf[:n])
				if err == io.EOF {
					break
				} else if err != nil {
					panic(err)
				}
			}
			file.Close()
			hash := hasher.Sum([]byte{})
			fmt.Print(hex.EncodeToString(hash))
			fmt.Print("  ")
			fmt.Println(name)
			<- q
			wg.Done()
		}(name)
	}
	wg.Wait()
}