// Given a file containing sorted sha1 hashes in string form, this
// writes out a new file containing the same hashes in binary form.

package main

import (
	"bufio"
	"compress/bzip2"
	"encoding/hex"
	"flag"
	"io"
	"log"
	"os"

	"github.com/dustin/go-humanize"
)

var saw int64

func maybefatal(err error) {
	if err != nil {
		log.Fatalf("Dying with %v", err)
	}
}

func process(r *bufio.Reader, w io.Writer) {
	for {
		s, err := r.ReadString(byte('\n'))
		if err == io.EOF {
			log.Printf("Got an EOF")
			return
		}
		maybefatal(err)

		bytes, err := hex.DecodeString(s[:40])
		maybefatal(err)

		n, err := w.Write(bytes)
		maybefatal(err)
		if n != 20 {
			log.Fatalf("Expected to write 20 bytes, wrote %d", n)
		}

		saw += 1
	}
}

func main() {
	flag.Parse()

	infile := flag.Arg(0)
	outfile := flag.Arg(1)

	log.Printf("%s -> %s", infile, outfile)

	fin, err := os.Open(infile)
	maybefatal(err)
	defer fin.Close()
	b := bufio.NewReader(bzip2.NewReader(fin))

	fout, err := os.Create(outfile)
	maybefatal(err)
	defer fout.Close()

	process(b, fout)
	log.Printf("Wrote %s items", humanize.Comma(saw))
}