// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// The genbuilderkey binary generates a builder key or gomote user key
// from the build system's master key.
package main

import (
	"bytes"
	"crypto/hmac"
	"crypto/md5"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"strings"

	"cloud.google.com/go/compute/metadata"
)

func main() {
	flag.Parse()
	if flag.NArg() != 1 {
		log.Fatalf("expect one argument")
	}
	fmt.Println(key(flag.Arg(0)))
}

func key(principal string) string {
	h := hmac.New(md5.New, getMasterKey())
	io.WriteString(h, principal)
	return fmt.Sprintf("%x", h.Sum(nil))
}

func getMasterKey() []byte {
	v, err := metadata.ProjectAttributeValue("builder-master-key")
	if err == nil {
		return []byte(strings.TrimSpace(v))
	}
	key, err := ioutil.ReadFile(filepath.Join(os.Getenv("HOME"), "keys/gobuilder-master.key"))
	if err == nil {
		return bytes.TrimSpace(key)
	}
	log.Fatalf("no builder master key found")
	panic("not reachable")
}