package main

import (
	"encoding/hex"
	"flag"
	"fmt"
	"io"
	"os"
	"runtime"
	"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", runtime.NumCPU(), "The maximum concurrency")
)

func main() {
	flag.Parse()
	if *help || *par < 1 {
		flag.Usage()
		os.Exit(0)
	}
	sum := func(file io.ReadCloser) string {
		buf := [65536]byte{}
		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{})
		return hex.EncodeToString(hash)
	}

	if len(flag.Args()) == 0 {
		fmt.Println(sum(os.Stdin))
	} else {
		q := make(chan struct{}, *par)
		wg := &sync.WaitGroup{}

		for _, name := range flag.Args() {
			q <- struct{}{}
			wg.Add(1)
			go func(name string) {
				file, err := os.Open(name)
				if err != nil {
					panic(err)
				}
				fmt.Print(sum(file))
				fmt.Print("  ")
				fmt.Println(name)
				<- q
				wg.Done()
			}(name)
		}
		wg.Wait()
	}
}