// -*- Mode: Go; indent-tabs-mode: t -*-

/*
 * Copyright (C) 2015 Canonical Ltd
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

package asserts

import (
	"crypto"
	"encoding/base64"
	"fmt"
)

// EncodeDigest encodes a hash algorithm and a digest to be put in an assertion header.
func EncodeDigest(hash crypto.Hash, hashDigest []byte) (string, error) {
	algo := ""
	switch hash {
	case crypto.SHA512:
		algo = "sha512"
	default:
		return "", fmt.Errorf("unsupported hash")
	}
	if len(hashDigest) != hash.Size() {
		return "", fmt.Errorf("hash digest by %s should be %d bytes", algo, hash.Size())
	}
	return fmt.Sprintf("%s-%s", algo, base64.RawURLEncoding.EncodeToString(hashDigest)), nil
}
